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| <?xml version="1.0" encoding="UTF-8"?><!DOCTYPE article PUBLIC "-//NLM//DTD JATS (Z39.96) Journal Archiving and Interchange DTD v1.1d1 20130915//EN" "JATS-archivearticle1.dtd"><article article-type="research-article" dtd-version="1.1d1" xmlns:xlink="http://www.w3.org/1999/xlink"><front><journal-meta><journal-id journal-id-type="nlm-ta">elife</journal-id><journal-id journal-id-type="hwp">eLife</journal-id><journal-id journal-id-type="publisher-id">eLife</journal-id><journal-title-group><journal-title>eLife</journal-title></journal-title-group><issn publication-format="electronic">2050-084X</issn><publisher><publisher-name>eLife Sciences Publications, Ltd</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="publisher-id">01888</article-id><article-id pub-id-type="doi">10.7554/eLife.01888</article-id><article-categories><subj-group subj-group-type="display-channel"><subject>Research article</subject></subj-group><subj-group subj-group-type="heading"><subject>Cell biology</subject></subj-group><subj-group subj-group-type="heading"><subject>Immunology</subject></subj-group></article-categories><title-group><article-title>Epidermal barrier defects link atopic dermatitis with altered skin cancer susceptibility</article-title></title-group><contrib-group><contrib contrib-type="author" equal-contrib="yes" id="author-9196"><name><surname>Cipolat</surname><given-names>Sara</given-names></name><xref ref-type="aff" rid="aff1"/><xref ref-type="aff" rid="aff2"/><xref ref-type="fn" rid="equal-contrib">†</xref><xref ref-type="other" rid="par-1"/><xref ref-type="other" rid="par-2"/><xref ref-type="other" rid="par-3"/><xref ref-type="other" rid="par-4"/><xref ref-type="fn" rid="con1"/><xref ref-type="fn" rid="conf2"/></contrib><contrib contrib-type="author" equal-contrib="yes" id="author-9197"><name><surname>Hoste</surname><given-names>Esther</given-names></name><xref ref-type="aff" rid="aff1"/><xref ref-type="aff" rid="aff2"/><xref ref-type="fn" rid="equal-contrib">†</xref><xref ref-type="other" rid="par-1"/><xref ref-type="other" rid="par-2"/><xref ref-type="other" rid="par-3"/><xref ref-type="other" rid="par-4"/><xref ref-type="fn" rid="con2"/><xref ref-type="fn" rid="conf2"/></contrib><contrib contrib-type="author" id="author-9198"><name><surname>Natsuga</surname><given-names>Ken</given-names></name><xref ref-type="aff" rid="aff2"/><xref ref-type="aff" rid="aff3"/><xref ref-type="other" rid="par-1"/><xref ref-type="other" rid="par-2"/><xref ref-type="other" rid="par-3"/><xref ref-type="other" rid="par-4"/><xref ref-type="fn" rid="con3"/><xref ref-type="fn" rid="conf2"/></contrib><contrib contrib-type="author" id="author-9199"><name><surname>Quist</surname><given-names>Sven R</given-names></name><xref ref-type="aff" rid="aff2"/><xref ref-type="aff" rid="aff4"/><xref ref-type="other" rid="par-1"/><xref ref-type="other" rid="par-2"/><xref ref-type="other" rid="par-3"/><xref ref-type="other" rid="par-4"/><xref ref-type="fn" rid="con4"/><xref ref-type="fn" rid="conf2"/></contrib><contrib contrib-type="author" corresp="yes" id="author-1031"><name><surname>Watt</surname><given-names>Fiona M</given-names></name><xref ref-type="aff" rid="aff1"/><xref ref-type="corresp" rid="cor1">*</xref><xref ref-type="other" rid="par-1"/><xref ref-type="other" rid="par-2"/><xref ref-type="other" rid="par-3"/><xref ref-type="other" rid="par-4"/><xref ref-type="fn" rid="con5"/><xref ref-type="fn" rid="conf1"/></contrib><aff id="aff1"><institution content-type="dept">Centre for Stem Cells and Regenerative Medicine</institution>, <institution>King's College London</institution>, <addr-line><named-content content-type="city">London</named-content></addr-line>, <country>United Kingdom</country></aff><aff id="aff2"><institution>Cancer Research UK Cambridge Research Institute</institution>, <addr-line><named-content content-type="city">Cambridge</named-content></addr-line>, <country>United Kingdom</country></aff><aff id="aff3"><institution content-type="dept">Department of Dermatology</institution>, <institution>Hokkaido University</institution>, <addr-line><named-content content-type="city">Sapporo</named-content></addr-line>, <country>Japan</country></aff><aff id="aff4"><institution content-type="dept">Department of Dermatology and Venereology</institution>, <institution>Otto von Guericke University Magdeburg</institution>, <addr-line><named-content content-type="city">Magdeburg</named-content></addr-line>, <country>Germany</country></aff></contrib-group><contrib-group content-type="section"><contrib contrib-type="editor"><name><surname>Fuchs</surname><given-names>Elaine</given-names></name><role>Reviewing editor</role><aff><institution>Rockefeller University</institution>, <country>United States</country></aff></contrib></contrib-group><author-notes><corresp id="cor1"><label>*</label>For correspondence: <email>fiona.watt@kcl.ac.uk</email></corresp><fn fn-type="con" id="equal-contrib"><label>†</label><p>These authors contributed equally to this work</p></fn></author-notes><pub-date date-type="pub" publication-format="electronic"><day>06</day><month>05</month><year>2014</year></pub-date><pub-date pub-type="collection"><year>2014</year></pub-date><volume>3</volume><elocation-id>e01888</elocation-id><history><date date-type="received"><day>14</day><month>11</month><year>2013</year></date><date date-type="accepted"><day>03</day><month>04</month><year>2014</year></date></history><permissions><copyright-statement>© 2014, Cipolat et al</copyright-statement><copyright-year>2014</copyright-year><copyright-holder>Cipolat et al</copyright-holder><license xlink:href="http://creativecommons.org/licenses/by/3.0/"><license-p>This article is distributed under the terms of the <ext-link ext-link-type="uri" xlink:href="http://creativecommons.org/licenses/by/3.0/">Creative Commons Attribution License</ext-link>, which permits unrestricted use and redistribution provided that the original author and source are credited.</license-p></license></permissions><self-uri content-type="pdf" xlink:href="elife01888.pdf"/><abstract><object-id pub-id-type="doi">10.7554/eLife.01888.001</object-id><p>Atopic dermatitis can result from loss of structural proteins in the outermost epidermal layers, leading to a defective epidermal barrier. To test whether this influences tumour formation, we chemically induced tumours in EPI−/− mice, which lack three barrier proteins—Envoplakin, Periplakin, and Involucrin. EPI−/− mice were highly resistant to developing benign tumours when treated with 7,12-dimethylbenz(a)anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA). The DMBA response was normal, but EPI−/− skin exhibited an exaggerated atopic response to TPA, characterised by abnormal epidermal differentiation, a complex immune infiltrate and elevated serum thymic stromal lymphopoietin (TSLP). The exacerbated TPA response could be normalised by blocking TSLP or the immunoreceptor NKG2D but not CD4+ T cells. We conclude that atopy is protective against skin cancer in our experimental model and that the mechanism involves keratinocytes communicating with cells of the immune system via signalling elements that normally protect against environmental assaults.</p><p><bold>DOI:</bold> <ext-link ext-link-type="doi" xlink:href="10.7554/eLife.01888.001">http://dx.doi.org/10.7554/eLife.01888.001</ext-link></p></abstract><abstract abstract-type="executive-summary"><object-id pub-id-type="doi">10.7554/eLife.01888.002</object-id><title>eLife digest</title><p>Skin cancer is a common and growing problem—according to the World Health Organization, skin cancers account for one in every three cancers diagnosed world wide. There is some evidence from epidemiological studies that patients with certain allergies might be protected against cancer and, in particular, that the allergic skin condition atopic dermatitis is associated with reduced levels of various skin cancers. However, it is difficult to know if this reduction is due to the atopic dermatitis itself or to the drugs used to treat this allergy.</p><p>Genetically engineered mice that are lacking three proteins that are involved in the formation of the cornified envelope—the protective layer that replaces the normal plasma membrane in the cells of the outermost skin layers—can be used to study atopic dermatitis. These ‘triple knockout mice’ have a defective epidermal barrier and altered levels of immune T-cells in the skin.</p><p>Now Cipolat et al. have investigated whether defects in the epidermal barrier protect against skin cancer. Knockout mice and wild-type mice were treated with two chemicals: DMBA, which causes mutations in a gene called <italic>HRas</italic>, and TPA, which promotes the formation of tumours from cells that contain <italic>HRas</italic> mutations. After about 16 weeks almost all of the wild-type mice had at least one benign tumour, whereas half of the knockout mice had no tumours. Overall, the average number of benign tumours per mouse was six times higher in the wild-type mice. This shows that the mutations that cause the epidermal barrier defects in knockout mice also protect them against the tumours caused by the combined effects of DMBA and TPA.</p><p>Cipolat et al. then compared how the mice responded to DMBA or TPA alone. The knockout mice and the wild-type mice responded to DMBA in the same way; however, the knockout mice showed an exaggerated response to TPA, including a strong inflammatory reaction. This response comprised the production of higher levels of various proteins that are involved in communications between skin cells and the immune system. Cipolat et al. propose that the immune reaction caused by this exaggerated response could help to prevent tumour formation by eliminating tumour-forming cells in the skin.</p><p><bold>DOI:</bold> <ext-link ext-link-type="doi" xlink:href="10.7554/eLife.01888.002">http://dx.doi.org/10.7554/eLife.01888.002</ext-link></p></abstract><kwd-group kwd-group-type="author-keywords"><title>Author keywords</title><kwd>skin</kwd><kwd>eczema</kwd><kwd>cancer</kwd></kwd-group><kwd-group kwd-group-type="research-organism"><title>Research organism</title><kwd>Mouse</kwd></kwd-group><funding-group><award-group id="par-1"><funding-source><institution-wrap><institution-id institution-id-type="FundRef">http://dx.doi.org/10.13039/501100000265</institution-id><institution>Medical Research Council</institution></institution-wrap></funding-source><principal-award-recipient><name><surname>Cipolat</surname><given-names>Sara</given-names></name><name><surname>Hoste</surname><given-names>Esther</given-names></name><name><surname>Natsuga</surname><given-names>Ken</given-names></name><name><surname>Quist</surname><given-names>Sven R</given-names></name><name><surname>Watt</surname><given-names>Fiona M</given-names></name></principal-award-recipient></award-group><award-group id="par-2"><funding-source><institution-wrap><institution-id institution-id-type="FundRef">http://dx.doi.org/10.13039/100004440</institution-id><institution>Wellcome Trust</institution></institution-wrap></funding-source><principal-award-recipient><name><surname>Cipolat</surname><given-names>Sara</given-names></name><name><surname>Hoste</surname><given-names>Esther</given-names></name><name><surname>Natsuga</surname><given-names>Ken</given-names></name><name><surname>Quist</surname><given-names>Sven R</given-names></name><name><surname>Watt</surname><given-names>Fiona M</given-names></name></principal-award-recipient></award-group><award-group id="par-3"><funding-source><institution-wrap><institution>European Union</institution></institution-wrap></funding-source><principal-award-recipient><name><surname>Cipolat</surname><given-names>Sara</given-names></name><name><surname>Hoste</surname><given-names>Esther</given-names></name><name><surname>Natsuga</surname><given-names>Ken</given-names></name><name><surname>Quist</surname><given-names>Sven R</given-names></name><name><surname>Watt</surname><given-names>Fiona M</given-names></name></principal-award-recipient></award-group><award-group id="par-4"><funding-source><institution-wrap><institution-id institution-id-type="FundRef">http://dx.doi.org/10.13039/501100000289</institution-id><institution>Cancer Research UK</institution></institution-wrap></funding-source><principal-award-recipient><name><surname>Cipolat</surname><given-names>Sara</given-names></name><name><surname>Hoste</surname><given-names>Esther</given-names></name><name><surname>Natsuga</surname><given-names>Ken</given-names></name><name><surname>Quist</surname><given-names>Sven R</given-names></name><name><surname>Watt</surname><given-names>Fiona M</given-names></name></principal-award-recipient></award-group><funding-statement>The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.</funding-statement></funding-group><custom-meta-group><custom-meta><meta-name>elife-xml-version</meta-name><meta-value>2</meta-value></custom-meta><custom-meta specific-use="meta-only"><meta-name>Author impact statement</meta-name><meta-value>A mouse model of atopic dermatitis provides mechanistic evidence for an association between allergic disease and skin cancer.</meta-value></custom-meta></custom-meta-group></article-meta></front><body><sec id="s1" sec-type="intro"><title>Introduction</title><p>There is an ongoing debate as to whether allergic disease is a risk factor for cancer or whether it is protective, with recent studies indicating that the relationship is complex and site specific (<xref ref-type="bibr" rid="bib6">Arana et al., 2010</xref>; <xref ref-type="bibr" rid="bib57">Wedgeworth et al., 2011</xref>; <xref ref-type="bibr" rid="bib24">Hwang et al., 2012</xref>). Several epidemiological studies have suggested that atopic dermatitis (AD; eczema), hives, allergies to animal fur, and certain food ingredients are inversely associated with cancers of tissues that provide an interface with the external environment, such as the skin (<xref ref-type="bibr" rid="bib26">Jensen-Jarolim et al., 2008</xref>; <xref ref-type="bibr" rid="bib50">Sherman et al., 2008</xref>). In a recent large-scale analysis, the risk of nonmelanoma skin cancer was reduced in patients who had both allergic rhinitis and asthma (<xref ref-type="bibr" rid="bib24">Hwang et al., 2012</xref>).</p><p>It is challenging to draw firm conclusions from the epidemiological data, in part because of the relapsing and remitting nature of AD and the potential cancer modulatory effects of treatments that are used to manage AD. Therefore, we sought to examine the link between AD and cancer susceptibility using a mouse model of AD in which the primary defect is in the epidermal barrier that is normally protective against pathogens. The skin barrier is formed by terminally differentiated keratinocytes in the outermost layers of the epidermis, known as the cornified layers or stratum corneum. In cornified keratinocytes, the plasma membrane is replaced with a layer of highly insoluble, transglutaminase cross-linked proteins with covalently attached lipids, known as the cornified envelope (<xref ref-type="bibr" rid="bib9">Candi et al., 2005</xref>). Involucrin, envoplakin, and periplakin are the first proteins to be cross-linked by transglutaminase-1 and create the protein scaffold for the attachment of lipids on which the cornified envelope assembles (<xref ref-type="bibr" rid="bib44">Rice and Green, 1977</xref>; <xref ref-type="bibr" rid="bib51">Simon and Green, 1984</xref>; <xref ref-type="bibr" rid="bib46">Ruhrberg et al., 1996</xref>, <xref ref-type="bibr" rid="bib45">1997</xref>).</p><p>Mice triply deficient in <italic>envoplakin</italic>, <italic>periplakin,</italic> and <italic>involucrin</italic> (EPI−/− mice) have a defective epidermal barrier and exhibit a reduction in epidermal γδTCR<sup>+</sup> CD3<sup>+</sup> cells (dendritic epidermal T cells; DETCs) and infiltration of CD4<sup>+</sup> T cells into the dermis (<xref ref-type="bibr" rid="bib49">Sevilla et al., 2007</xref>). In contrast, the individual and double knockouts for <italic>envoplakin</italic>, <italic>periplakin,</italic> and <italic>involucrin</italic> do not have observable barrier defects or an altered immune infiltrate (<xref ref-type="bibr" rid="bib49">Sevilla et al., 2007</xref>). The skin barrier phenotype of EPI−/− mice shares similarity with the <italic>flaky tail</italic> mouse, which has nonsense mutations in the keratin filament associated protein filaggrin and the transmembrane protein Tmem79, which is a component of lamellar granules (<xref ref-type="bibr" rid="bib16">Fallon et al., 2009</xref>; <xref ref-type="bibr" rid="bib47">Sasaki et al., 2013</xref>; <xref ref-type="bibr" rid="bib48">Saunders et al., 2013</xref>), the latter resulting in defective stratum corneum formation. Filaggrin mutations in humans are linked to ichthyosis vulgaris (dry, flaky skin) and increased risk of AD (<xref ref-type="bibr" rid="bib39">Palmer et al., 2006</xref>, <xref ref-type="bibr" rid="bib40">2007</xref>; <xref ref-type="bibr" rid="bib8">Brown and McLean, 2012</xref>), while Tmem79 mutations are found in some patients with AD (<xref ref-type="bibr" rid="bib48">Saunders et al., 2013</xref>).</p><p>To test the potential association between a defective skin barrier, AD and cancer, we have subjected EPI−/− mice to the classic two-stage chemical carcinogenesis protocol (<xref ref-type="bibr" rid="bib43">Perez-Losada and Balmain, 2003</xref>). A single exposure to the polycyclic aromatic hydrocarbon 7,12-dimethylbenz(a)anthracene (DMBA) induces oncogenic mutations in HRas (initiation). Repeated applications of the promoting agent 12-O-tetradecanoylphorbol-13-acetate (TPA) (promotion) allow initiated, mutagenized cells to clonally expand and form benign tumours called papillomas, some of which progress to malignant squamous cell carcinomas (SCCs) (<xref ref-type="bibr" rid="bib1">Abel et al., 2009</xref>). While most human skin SCCs are associated with UV, rather than chemical, carcinogenesis, 10% do have Ras gene mutations (<xref ref-type="bibr" rid="bib33">Lopez-Pajares et al., 2013</xref>), and DMBA/TPA carcinogenesis has contributed substantially to our understanding of the steps of tumour development in human skin (<xref ref-type="bibr" rid="bib22">Hirst and Balmain, 2004</xref>).</p></sec><sec id="s2" sec-type="results"><title>Results</title><sec id="s2-1"><title>EPI −/− mice are resistant to chemical carcinogenesis</title><p>To determine whether lack of <italic>Evpl, Ppl</italic> and <italic>Ivl</italic> influences sensitivity to tumour formation, we compared DMBA/TPA skin carcinogenesis (<xref ref-type="bibr" rid="bib1">Abel et al., 2009</xref>) in mice lacking all three genes (EPI−/−) and wild-type (WT) mice on the same genetic background. Since EPI−/− mice were on a mixed Sv129 and C57Bl/6 background, F2 crosses between WT Sv129 and C57Bl/6J mice were used to generate the WT controls for all experiments. The data from one experiment are presented in <xref ref-type="fig" rid="fig1">Figure 1</xref>. A second, independent, carcinogenesis experiment gave similar results (data not shown). Mice that received DMBA or TPA alone did not develop tumours.<fig id="fig1" position="float"><object-id pub-id-type="doi">10.7554/eLife.01888.003</object-id><label>Figure 1.</label><caption><title>Chemical carcinogenesis in EPI−/− and WT mice.</title><p>(<bold>A</bold>) Average number of papillomas per mouse. (<bold>B</bold>) % mice with one or more papilloma. (<bold>C</bold>) Average number of SCCs per mouse. (<bold>D</bold>) % mice with one or more SCC. (<bold>A</bold> and <bold>C</bold>) Data are means ± SEM. (<bold>E</bold>) Back skin, papillomas (pap) and SCCs from WT mice were immunostained for Envoplakin, Periplakin, or Involucrin (red) and DAPI (blue). Dotted line indicates basement membrane. Scale bars: 100 μm.</p><p><bold>DOI:</bold> <ext-link ext-link-type="doi" xlink:href="10.7554/eLife.01888.003">http://dx.doi.org/10.7554/eLife.01888.003</ext-link></p></caption><graphic xlink:href="elife01888f001"/></fig></p><p>The first papillomas emerged in both groups 5–6 weeks after the start of TPA promotion, and the maximum number of papillomas was reached by 15–16 weeks (<xref ref-type="fig" rid="fig1">Figure 1A</xref>). The average number of papillomas per mouse was approximately sixfold lower in EPI−/− than WT mice (<xref ref-type="fig" rid="fig1">Figure 1A</xref>; week 15, p=0.0007; week 57, p=0.0001). The incidence of papilloma formation was also lower in EPI−/− mice (<xref ref-type="fig" rid="fig1">Figure 1B</xref>). Over 95% of WT mice had at least one papilloma 14 weeks after the start of promotion, whereas 50% of EPI−/− mice were tumour-free at the end of the experiment (p=0.0063). Thus combined deletion of <italic>envoplakin</italic>, <italic>periplakin,</italic> and <italic>involucrin</italic> decreased epidermal susceptibility to chemically induced benign tumours.</p><p>As expected from the genetic background of the mice (<xref ref-type="bibr" rid="bib60">Woodworth et al., 2004</xref>), only a small subset of papillomas progressed to invasive squamous cell carcinomas (SCCs) (<xref ref-type="fig" rid="fig1">Figure 1C</xref>). There was no difference in SCC burden or incidence between EPI−/− and WT mice (<xref ref-type="fig" rid="fig1">Figure 1C,D</xref>). However, since EPI−/− mice had fewer papillomas, the SCC conversion frequency was higher than in WT mice. We observed a downregulation of envoplakin, periplakin, and involucrin in WT papillomas and SCCs (<xref ref-type="fig" rid="fig1">Figure 1E</xref>), leading us to speculate that the increased risk of SCC conversion in EPI−/− papillomas may be linked to the lack of two desmosomal proteins (<xref ref-type="bibr" rid="bib54">Thiery and Chopin, 1999</xref>). No metastases were observed in any mice (data not shown).</p></sec><sec id="s2-2"><title>DMBA responsiveness is unaffected in EPI−/− mice</title><p>To determine whether the resistance of EPI−/− mice to papilloma formation was due to a reduced DMBA response, we examined responses to a single topical application of carcinogen. Skin was analysed 24 hr after one application of DMBA in 4 mice per genotype.</p><p>DMBA binds to the aryl hydrocarbon receptor (AhR), leading to upregulation of the cytochrome P-450 enzymes Cyp1a1 and Cyp1b1, which convert DMBA into the active metabolite that causes <italic>HRas</italic> mutations (<xref ref-type="bibr" rid="bib17">Gao et al., 2005</xref>). There were no differences in expression of AhR, the AhR repressor (AhRR), Cyp1a1 and Cyp1b1 between WT and EPI−/− epidermis, either in the steady state or after application of DMBA (<xref ref-type="fig" rid="fig2">Figure 2A</xref>). Langerhans cells resident in the epidermis metabolise DMBA to the active form and as a result DMBA/TPA treated Langerhans cell-deficient mice do not develop papillomas (<xref ref-type="bibr" rid="bib35">Modi et al., 2012</xref>). However, EPI−/− and WT epidermis contained similar numbers of CD207<sup>+</sup> Langerhans cells (<xref ref-type="fig" rid="fig2">Figure 2B</xref>). We conclude that DMBA was activated to a similar extent whether or not the epidermal cornified envelope was defective.<fig id="fig2" position="float"><object-id pub-id-type="doi">10.7554/eLife.01888.004</object-id><label>Figure 2.</label><caption><title>Response of EPI−/− and WT mice to DMBA.</title><p>(<bold>A</bold>) Q-PCR of enzymes responsible for DMBA uptake and metabolic activation. (<bold>B</bold>) Number of CD207<sup>+</sup> Langerhans cells per mm<sup>2</sup> ear epidermis. (<bold>C</bold>–<bold>E</bold>) Number of epidermal cells that scored positive for γH2AX (<bold>C</bold>), PH3 (<bold>D</bold>) or active caspase-3 (<bold>E</bold>) per cm. 7-cm skin was analysed per marker. (<bold>F</bold>) Q-PCR of anti- and pro-apoptotic genes. (<bold>A</bold>–<bold>F</bold>) Data in all histograms are means ± SEM of at least three mice per genotype. (<bold>G</bold>) Hras codon 61 mutations in 4 SCCs per genotype were quantified by Q-PCR of genomic DNA.</p><p><bold>DOI:</bold> <ext-link ext-link-type="doi" xlink:href="10.7554/eLife.01888.004">http://dx.doi.org/10.7554/eLife.01888.004</ext-link></p></caption><graphic xlink:href="elife01888f002"/></fig></p><p>We next analysed epidermal protective responses to carcinogen-induced DNA damage (DNA repair and induction of apoptosis). Phosphorylated Histone H2A variant H2AX (γH2AX) is recruited to sites of dsDNA damage and subsequent breaks, and is upregulated on DMBA treatment. The proportion of epidermal cells that expressed γH2AX was similar in EPI−/− and WT epidermis, whether or not the skin had been treated with DMBA (<xref ref-type="fig" rid="fig2">Figure 2C</xref>). The proliferative response of keratinocytes to DMBA was comparable in both genotypes, as assessed by the proportion of phospho-Histone 3 (PH3) positive cells (<xref ref-type="fig" rid="fig2">Figure 2D</xref>). Furthermore, topical application of DMBA resulted in a similar apoptotic response, as detected by cleaved caspase-3-positive cells and quantitation of mRNA levels for a panel of apoptotic and anti-apoptotic genes (<xref ref-type="fig" rid="fig2">Figure 2E,F</xref>).</p><p>Levels of the DMBA ‘signature’ <italic>Hras</italic> (codon 61) mutation (<xref ref-type="bibr" rid="bib35">Modi et al., 2012</xref>) were the same in mRNA extracted from SCCs of WT or EPI−/− mice (<xref ref-type="fig" rid="fig2">Figure 2G</xref>). We did not detect mutations in exons 4, 5, 8 and 9 of <italic>p53</italic> in WT or EPI−/− tumours (data not shown).</p><p>We conclude that differences in DMBA uptake and activation or activity did not account for the resistance of EPI−/− mice to chemical carcinogenesis.</p></sec><sec id="s2-3"><title>EPI−/− mice exhibit an exacerbated keratinocyte response to TPA</title><p>Since WT and EPI−/− mice did not differ in DMBA responsiveness, we next investigated whether their response to the promotion phase of the two-stage carcinogenesis protocol was aberrant. Mice received three topical applications of TPA (or vehicle control), which corresponds to 1 week of promotion, and skin was collected 48 hr after the last treatment.</p><p>EPI−/− mice exhibited an exacerbated response to TPA (<xref ref-type="fig" rid="fig3">Figure 3A</xref>). Their skin was reddened, dry and scaly, whereas that of WT mice was not (data not shown). Histological analysis revealed increased hyperkeratosis (thickened stratum corneum) and parakeratosis (retention of nuclei in cornified cells) (<xref ref-type="fig" rid="fig3">Figure 3B,C</xref>), consistent with defective desquamation (<xref ref-type="bibr" rid="bib49">Sevilla et al., 2007</xref>). Widening of intercellular spaces in the epidermal basal layer (spongiosis) was extensive in EPI−/− but not WT skin (<xref ref-type="fig" rid="fig3">Figure 3A</xref>). Epidermal thickness, measured as the distance from the basal to the upper granular layer, was greater in EPI−/− mice treated with TPA or DMBA/TPA than in WT mice, and this correlated with a greater number of suprabasal layers (<xref ref-type="fig" rid="fig3">Figure 3A,D</xref>). The numbers of keratinocytes with dsDNA breaks and active caspase-3 were similar in EPI−/− and WT epidermis (<xref ref-type="fig" rid="fig3">Figure 3F,G</xref>).<fig id="fig3" position="float"><object-id pub-id-type="doi">10.7554/eLife.01888.005</object-id><label>Figure 3.</label><caption><title>Keratinocyte responses to TPA treatment.</title><p>(<bold>A</bold>) H&E stained skin sections of mice treated three times with acetone or TPA. Asterisk: neutrophil containing pustule; white arrow: spongiosis; black arrow: parakeratosis. % hyperkeratotic (<bold>B</bold>) and parakeratotic (<bold>C</bold>) stratum corneum (8 cm skin analysed per condition). (<bold>D</bold>) Epidermal thickness in μm (8 cm skin analysed per condition). (<bold>E</bold>–<bold>G</bold>) Number of epidermal cells positively labeled for PH3 (<bold>E</bold>), γH2AX (<bold>F</bold>) and active caspase-3 (<bold>G</bold>) per cm skin (7 cm skin analysed per condition). (<bold>H</bold>) Number of BrdU positive cells in basal and uppermost two granular layers per cm epidermis of mice treated three times with TPA and injected with BrdU 24 hr before harvesting. Data from all graphs represent means ± SEM from at least four mice per genotype. Scale bar: 100 μm.</p><p><bold>DOI:</bold> <ext-link ext-link-type="doi" xlink:href="10.7554/eLife.01888.005">http://dx.doi.org/10.7554/eLife.01888.005</ext-link></p></caption><graphic xlink:href="elife01888f003"/></fig></p><p>The number of mitotically active basal cells, measured by PhosphoHistone3 staining, was similar in TPA-treated EPI−/− and WT epidermis, whether or not the skin was pre-treated with DMBA (<xref ref-type="fig" rid="fig3">Figure 3E</xref>). To examine whether the transit time through the suprabasal layers was altered, mice were injected with BrdU 24hr prior to sacrifice and the position of labelled cells was quantified. The numbers of BrdU positive cells in the basal layer and outermost granular layers of EPI−/− and WT epidermis were not significantly different (<xref ref-type="fig" rid="fig3">Figure 3H</xref>). Since EPI−/− epidermis contained more suprabasal layers, the transit time of keratinocytes through the epidermis was faster in EPI−/− than WT epidermis. These observations are consistent with a model whereby precocious differentiation can act as a tumour suppressive mechanism in skin (<xref ref-type="bibr" rid="bib19">Guinea-Viniegra et al., 2012</xref>).</p><p>We conclude that, in contrast to the DMBA response, the response of epidermal keratinocytes to TPA was markedly different in EPI−/− and WT mice.</p></sec><sec id="s2-4"><title>EPI−/− mice exhibit an exacerbated inflammatory response to TPA</title><p>Because inflammation is a crucial factor in skin tumour development (<xref ref-type="bibr" rid="bib27">Johansson et al., 2008</xref>; <xref ref-type="bibr" rid="bib62">Zamarron and Chen, 2011</xref>) and EPI−/− skin has an abnormal number of DETCs and CD4<sup>+</sup>CD3<sup>+</sup> lymphocytes (<xref ref-type="bibr" rid="bib49">Sevilla et al., 2007</xref>), we examined whether the inflammatory response to short term TPA treatment was altered in skin with a defective epidermal barrier. Consistent with our previous observations (<xref ref-type="bibr" rid="bib49">Sevilla et al., 2007</xref>), vehicle-treated EPI−/− skin had a reduced number of epidermal γδTCR<sup>+</sup>CD3<sup>+</sup> lymphocytes (DETCs) (<xref ref-type="fig" rid="fig4">Figure 4A</xref>) and EPI−/− γδ T cells exhibited a more rounded morphology, indicative of activation (<xref ref-type="fig" rid="fig4">Figure 4I</xref>; <xref ref-type="bibr" rid="bib52">Strid et al., 2008</xref>). On TPA treatment, the number of DETCs in both EPI−/− and WT epidermis decreased (<xref ref-type="fig" rid="fig4">Figure 4A</xref>). In contrast, TPA treatment stimulated recruitment of CD4<sup>+</sup>CD3<sup>+</sup> lymphocytes into the skin of EPI−/− mice to a greater extent than in WT mice (<xref ref-type="fig" rid="fig4">Figure 4B,J</xref>). On TPA treatment, CD4+ T cells infiltrated EPI−/− but not WT epidermis (<xref ref-type="fig" rid="fig4">Figure 4J</xref>). Infiltration of granulocytes of the neutrophil family (Cd11b<sup>+</sup>LY6G<sup>+</sup>) is a typical sign of chronic skin inflammation, where they accumulate in pustules (<xref ref-type="fig" rid="fig4">Figure 4D,E</xref>). The number of pustules was significantly higher in TPA-treated EPI−/− compared with WT skin (<xref ref-type="fig" rid="fig4">Figure 4E</xref>).<fig id="fig4" position="float"><object-id pub-id-type="doi">10.7554/eLife.01888.006</object-id><label>Figure 4.</label><caption><title>Immune cell responses to TPA treatment.</title><p>(<bold>A</bold>–<bold>C</bold> and <bold>E</bold>–<bold>H</bold>) Quantitation of specific T lymphocyte populations (<bold>A</bold>–<bold>C</bold>), pustules (<bold>E</bold>), mast cells (<bold>F</bold>), eosinophils (<bold>G</bold>), and macrophages (<bold>H</bold>) per mm epidermis or mm<sup>2</sup> dermis. Data in all histograms are means ± SEM of at least three mice per genotype. <bold>(D</bold>, <bold>I</bold>, <bold>J)</bold> Skin sections of mice treated three times with acetone (<bold>I</bold>) or TPA (<bold>D</bold> and <bold>J</bold>) and labelled for CD11b (green, <bold>D</bold>), Ly6G (red, <bold>D</bold>), CD3 (red <bold>I</bold>, green <bold>J</bold>), γδTCR (green <bold>I</bold>) or CD4 (red, <bold>J</bold>) with DAPI nuclear counterstain (blue). White asterisk: neutrophil pustule. Insets in <bold>I</bold> and <bold>J</bold> are higher magnification views of boxed areas. Scale bars: 100 μm.</p><p><bold>DOI:</bold> <ext-link ext-link-type="doi" xlink:href="10.7554/eLife.01888.006">http://dx.doi.org/10.7554/eLife.01888.006</ext-link></p></caption><graphic xlink:href="elife01888f004"/></fig></p><p>TPA treated EPI−/− skin showed a pronounced infiltration of dermal mast cells and eosinophils (<xref ref-type="fig" rid="fig4">Figure 4F,G</xref>), but not macrophages (F4/80<sup>+</sup>Cd11b<sup>+</sup> cells) (<xref ref-type="fig" rid="fig4">Figure 4H</xref>). Similar differences in immune cell recruitment in EPI−/− and WT skin were observed when mice were treated with DMBA prior to TPA (data not shown).</p><p>Pustule formation and dermal infiltration of mast cells, eosinophils and CD4<sup>+</sup> T cells are hallmarks of the acute phase of atopic dermatitis in humans. Thus the response of EPI−/− skin to TPA resembled the acute phase of the human disease and involved recruitment of multiple leukocyte subsets.</p></sec><sec id="s2-5"><title>EPI−/− keratinocytes express elevated levels of cytokines and chemokines and an exacerbated lymphoid stress surveillance response</title><p>Keratinocytes communicate with different immune cell populations by production of an array of cytokines and chemokines, collectively known as the ‘epimmunome’ (<xref ref-type="bibr" rid="bib53">Swamy et al., 2010</xref>). Tissue damage triggers upregulation of keratinocyte ‘stress-associated’ genes such as Rae-1 (<xref ref-type="bibr" rid="bib18">Gasser et al., 2005</xref>) and H60 (<xref ref-type="bibr" rid="bib58">Whang et al., 2009</xref>). These stress antigens engage the immunoreceptor NKG2D expressed by cells of the innate (NK cells and DETC) and adaptive (activated CD8<sup>+</sup> T cells, NKT cells) immune system, triggering a lymphoid stress-surveillance response (<xref ref-type="bibr" rid="bib20">Hayday, 2009</xref>).</p><p>To investigate how a defective epidermal barrier could lead to an enhanced inflammatory response to TPA, we compared cytokine and chemokine expression in epidermis and dermis of WT and EPI−/− mice. We examined markers of innate, type 1 (cellular), type 2 (humoral) and type 17 (anti-microbial) immunity. In EPI−/− epidermis treated with acetone, transcripts related to innate immunity (in particular RAGE, S100A8, S100A9 and IL-1β) were higher than in WT, and these differences were maintained when transcript levels were upregulated by TPA treatment (<xref ref-type="fig" rid="fig5">Figure 5A</xref>). Type 1 cytokine transcripts were expressed at similar levels in WT and EPI−/− epidermis and dermis and were not upregulated to the same extent as other types of cytokines by TPA (<xref ref-type="fig" rid="fig5">Figure 5A</xref>). There was a striking upregulation of type 2 cytokines, including IL-4, IL-6, IL-13, IL-33 and thymic stromal lymphopoietin (TSLP), in epidermis and dermis of EPI−/− TPA-treated mice; this was not observed to a similar extent in WT skin. Type 17 transcripts were upregulated by TPA in epidermis of both genotypes, but were higher in EPI−/− epidermis (<xref ref-type="fig" rid="fig5">Figure 5A</xref>). Increased transcript levels of a number of chemokines, in particular Cxcl-5 and GM-CSF, were found in TPA treated EPI−/− vs WT skin, in agreement with the increased dermal infiltration of neutrophils and eosinophils. We conclude that the immune response to TPA in EPI−/− skin correlated with expression of pro-inflammatory genes with a type 2/type 17 profile.<fig id="fig5" position="float"><object-id pub-id-type="doi">10.7554/eLife.01888.007</object-id><label>Figure 5.</label><caption><title>Stress signals, cytokine, and chemokine production in EPI−/− and WT skin.</title><p>(<bold>A</bold>) Heatmap of mRNA levels relative to GAPDH from epidermis and dermis. Each value represents the mean of data obtained from four mice. (<bold>B</bold> and <bold>C</bold>) Serum levels of IgE (<bold>B</bold>) and TSLP (<bold>C</bold>) determined by ELISA. (<bold>D</bold>–<bold>F</bold>) Q-PCR of indicated mRNAs in epidermis. All histograms represent mean ± SEM (N = 5 untreated, N = 7 acetone, N = 4 DMBA, N = 10 TPA treated mice per genotype).</p><p><bold>DOI:</bold> <ext-link ext-link-type="doi" xlink:href="10.7554/eLife.01888.007">http://dx.doi.org/10.7554/eLife.01888.007</ext-link></p></caption><graphic xlink:href="elife01888f005"/></fig></p><p>Consistent with the type 2 response (<xref ref-type="fig" rid="fig5">Figure 5A</xref>) and mast cell influx (<xref ref-type="fig" rid="fig4">Figure 4F</xref>), serum IgE levels were 3.4-fold higher in EPI−/− than WT mice (<xref ref-type="fig" rid="fig5">Figure 5B</xref>). There was also a higher level of TSLP in EPI−/− serum (<xref ref-type="fig" rid="fig5">Figure 5C</xref>). TSLP is mainly produced by keratinocytes and is associated with increased resistance to skin carcinogenesis (<xref ref-type="bibr" rid="bib30">Kuramoto et al., 2002</xref>; <xref ref-type="bibr" rid="bib2">Aberg et al., 2008</xref>; <xref ref-type="bibr" rid="bib10">Demehri et al., 2008</xref>, <xref ref-type="bibr" rid="bib11">2012</xref>; <xref ref-type="bibr" rid="bib13">Di Piazza et al., 2012</xref>). TSLP levels are elevated when Notch signalling in skin is impaired (<xref ref-type="bibr" rid="bib10">Demehri et al., 2008</xref>; <xref ref-type="bibr" rid="bib15">Dumortier et al., 2010</xref>). However, EPI−/− and WT epidermis expressed comparable levels of Notch1, 2 and 3, Notch ligand Jag1 and Notch target genes Hey-1, Hes-1 and Hes-5, with or without TPA treatment (<xref ref-type="fig" rid="fig5">Figure 5D</xref>). Thus, upregulation of TSLP is associated with barrier defects rather than being a direct consequence of altered Notch signalling (<xref ref-type="bibr" rid="bib10">Demehri et al., 2008</xref>; <xref ref-type="bibr" rid="bib15">Dumortier et al., 2010</xref>).</p><p>These results suggested that lymphoid stress-surveillance of tissue damage could underlie the exacerbated inflammatory response to TPA exposure in EPI−/− mice. We therefore measured expression of the keratinocyte ‘stress-associated’ genes Rae-1 and H60 (<xref ref-type="fig" rid="fig5">Figure 5E,F</xref>). Rae-1 and H60 levels were significantly higher in EPI−/− than WT epidermis under steady-state conditions. Both were strongly upregulated 24 hr after DMBA treatment, H60 to a greater extent in EPI−/− mice. The effects of TPA treatment on Rae-1 and H60 expression were less pronounced. We conclude that the defective barrier of EPI−/− mice results in elevated expression of keratinocyte stress-associated genes that could prime them for an exacerbated atopic response to TPA.</p></sec><sec id="s2-6"><title>The TPA response of EPI−/− skin depends on an immune infiltrate, but is not specific for neutrophils or CD4+ T cells</title><p>To investigate the mechanism by which TPA provoked an exacerbated atopic response in EPI−/− epidermis, we used several different inhibitory strategies. Treatment with the anti-inflammatory drug dexamethasone (DXM) markedly reduced epidermal thickening and dermal cellularity (<xref ref-type="fig" rid="fig6">Figure 6A,B</xref>). DXM also prevented the selective increase in spleen size observed in TPA-treated EPI−/− mice (<xref ref-type="fig" rid="fig6">Figure 6F</xref>).<fig id="fig6" position="float"><object-id pub-id-type="doi">10.7554/eLife.01888.008</object-id><label>Figure 6.</label><caption><title>Blocking strategies to revert the atopic response to TPA treatment.</title><p>(<bold>A</bold>–<bold>E</bold>) H&E stained skin sections of WT and EPI−/− mice painted with TPA and injected with IgG (<bold>A</bold>), Dexamethasone (<bold>B</bold>), α-CD4 antibody (<bold>C</bold>), α-Ly6G antibody (<bold>D</bold>) or α-IL4 (<bold>E</bold>). Scale bars: 100 μm. (<bold>F</bold>) Spleen mass of mice treated with acetone, TPA or TPA + Dexamethasone as % of body weight. Data are means ± SEM from 12 (acetone, TPA) or 3 (TPA + DXM) mice per genotype. (<bold>G</bold>) Numbers of granulocytes per μl blood in TPA treated mice injected with IgG or α-Ly6G antibody. (<bold>H</bold>) Quantification of serum levels of IL-4 in EPI−/− mice treated with IL-4 or control antibodies. (<bold>I</bold> and <bold>J</bold>) Effects of anti-IL-4 on epidermal thickness (μm) (8 cm skin analysed per condition) (<bold>I</bold>) and dermal CD4 + T cells (<bold>J</bold>).</p><p><bold>DOI:</bold> <ext-link ext-link-type="doi" xlink:href="10.7554/eLife.01888.008">http://dx.doi.org/10.7554/eLife.01888.008</ext-link></p></caption><graphic xlink:href="elife01888f006"/></fig></p><p>Since tumour resistance of Notch deficient skin is attributable mainly to CD4+ T cells (<xref ref-type="bibr" rid="bib11">Demehri et al., 2012</xref>), we examined the effect of intraperitoneal injections of blocking CD4 antibodies. In vivo CD4 depletion was confirmed by quantifying CD4<sup>+</sup> cells in the spleen (data not shown). Specific CD4 targeting resulted in augmented skin hyperplasia and dermal inflammation in TPA-treated WT mice, but had no effect on EPI−/− skin (<xref ref-type="fig" rid="fig6">Figure 6C</xref>). The immunosuppressive role of CD4<sup>+</sup> cells in WT skin may be attributable to the regulatory subset of CD4<sup>+</sup> cells (CD4<sup>+</sup>CD25<sup>+</sup>Foxp3<sup>+</sup>) (<xref ref-type="bibr" rid="bib55">Teige et al., 2009</xref>).</p><p>There was a marked increase in neutrophil infiltration in EPI−/− TPA-treated skin compared to WT (<xref ref-type="fig" rid="fig4">Figure 4D,E</xref>). However, when circulating neutrophils were depleted by anti-LY6G injection (<xref ref-type="fig" rid="fig6">Figure 6G</xref>), there was no effect on epidermal hyperplasia and dermal inflammation (<xref ref-type="fig" rid="fig6">Figure 6D</xref>). We also targeted IL-4 to evaluate whether inhibition of a generalised type 2 immune response could normalize the effects of TPA in EPI−/− skin (<xref ref-type="fig" rid="fig6">Figure 6E</xref>). We confirmed a decrease in IL-4 serum levels by ELISA (<xref ref-type="fig" rid="fig6">Figure 6H</xref>). Inhibition of IL-4 reduced the number of CD4+ cells in the dermis (<xref ref-type="fig" rid="fig6">Figure 6J</xref>), as expected, but had no effect on epidermal thickness (<xref ref-type="fig" rid="fig6">Figure 6I</xref>) nor on the number of mast cells, eosinophils or epidermal γδ T cells (data not shown).</p><p>Taken together, these observations indicate that the exacerbated TPA response in EPI−/− skin involves multiple immune cell types and cannot be normalized by inhibiting one specific leukocyte subset.</p></sec><sec id="s2-7"><title>TSLP and NKG2D inhibition suppress the exacerbated TPA response of EPI−/− mice</title><p>To analyse the role of the Rae-1/NKG2D/TSLP axis in the exacerbated atopic response of EPI−/− skin to TPA, we interfered with the epidermal lymphoid stress surveillance response by in vivo antibody blockade of TSLP or NKG2D (<xref ref-type="fig" rid="fig7">Figure 7A</xref>). We confirmed effective inhibition of TSLP by ELISA (<xref ref-type="fig" rid="fig7">Figure 7B</xref>).<fig id="fig7" position="float"><object-id pub-id-type="doi">10.7554/eLife.01888.009</object-id><label>Figure 7.</label><caption><title>TSLP and NKG2D inhibition reduce epidermal responses to TPA.</title><p>(<bold>A</bold>) H&E stained sections of skin from TPA-treated mice injected with IgG, anti-TSLP, or anti-NKG2D antibodies. (<bold>B</bold>) Quantification of serum levels of TSLP in WT and EPI−/− mice treated with TSLP or control antibodies. (<bold>C</bold> and <bold>D</bold>) Quantification of PH3<sup>+</sup> cells (<bold>C</bold>) and epidermal thickness (μm) (<bold>D</bold>). (<bold>E</bold> and <bold>F</bold>) Number of BrdU positive cells in basal (<bold>E</bold>) and uppermost two granular (<bold>F</bold>) epidermal layers in mice treated with TPA and the indicated antibodies. (<bold>G</bold> and <bold>H</bold>) % hyperkeratotic (<bold>G</bold>) and parakeratotic (<bold>H</bold>) stratum corneum. (<bold>C</bold>–<bold>D</bold> and <bold>E</bold>–<bold>F</bold>) 7-cm skin analysed per condition.</p><p><bold>DOI:</bold> <ext-link ext-link-type="doi" xlink:href="10.7554/eLife.01888.009">http://dx.doi.org/10.7554/eLife.01888.009</ext-link></p></caption><graphic xlink:href="elife01888f007"/></fig></p><p>Neutralization of TSLP completely abrogated the atopic dermatitis phenotype in TPA treated EPI−/− mice (<xref ref-type="fig" rid="fig7">Figure 7A</xref>). Anti-NKG2D also reduced the atopic phenotype, albeit to a lesser extent (<xref ref-type="fig" rid="fig7 fig8">Figures 7A and 8</xref>). TPA-induced epidermal thickening was significantly reduced in TSLP or NKG2D suppressive conditions, without any differential effect on the number of PH3+ basal layer cells (<xref ref-type="fig" rid="fig7">Figure 7A,C, D</xref>). TSLP treatment reduced the transit time of BrdU + cells from the basal to the outermost granular layers since although the epidermis was thinner the proportion of labelled granular cells was unaffected (<xref ref-type="fig" rid="fig7">Figure 7E,F</xref>). There was a slight reduction in hyperkeratosis, and parakeratosis was clearly decreased (<xref ref-type="fig" rid="fig7">Figure 7G,H</xref>). Targeting the Rae-1/NKG2D/TSLP axis also reduced the number of dermal CD4<sup>+</sup>CD3<sup>+</sup> lymphocytes, mast cells, eosinophils, and epidermal pustules in EPI−/− mice (<xref ref-type="fig" rid="fig8">Figure 8A–D</xref>). Furthermore, under TSLP suppressive conditions the number of epidermal DETCs was increased in EPI−/− skin (<xref ref-type="fig" rid="fig8">Figure 8E</xref>). Macrophage numbers were unaffected by TSLP or NKG2D blockade (data not shown).<fig id="fig8" position="float"><object-id pub-id-type="doi">10.7554/eLife.01888.010</object-id><label>Figure 8.</label><caption><title>Effects of TSLP and NKG2D inhibition and quantitation of cytokine levels in SCCs.</title><p>(<bold>A</bold>–<bold>E</bold>) CD4<sup>+</sup> T cells (<bold>A</bold>), mast cells (<bold>B</bold>), eosinophils (<bold>C</bold>), pustules (<bold>D</bold>), and γδ T cells (<bold>E</bold>) per mm epidermis or mm<sup>2</sup> dermis. Data are means ± SEM from at least three mice per genotype. (<bold>F</bold> and <bold>G</bold>) Serum (<bold>F</bold>) and whole skin (<bold>G</bold>) protein levels of the cytokines indicated. Data are means ± SEM from 6 IgG and 3 α-TSLP-treated mice. (<bold>H</bold> and <bold>I</bold>) Q-PCR of mRNAs indicated in SCCs. Data are means ± SEM of 4 SCCs per genotype. (<bold>J</bold>) Serum levels of TSLP in EPI−/− mice bearing papillomas smaller than 2 mm<sup>2</sup> or at least one papilloma larger than 2 mm<sup>2</sup>. Data are means ± SEM of at least three mice per group.</p><p><bold>DOI:</bold> <ext-link ext-link-type="doi" xlink:href="10.7554/eLife.01888.010">http://dx.doi.org/10.7554/eLife.01888.010</ext-link></p></caption><graphic xlink:href="elife01888f008"/></fig></p><p>To examine whether the anti-inflammatory effects of blocking TSLP were mediated by down-regulating epidermal expression of inflammatory mediators (<xref ref-type="fig" rid="fig5">Figure 5A</xref>), we measured expression of representative type 1 and type 2 cytokines. TPA treatment induced a marked and significant release of type 2 cytokines (IL-4, IL-6) in the skin and serum of EPI−/− mice, and this was diminished by systemic administration of anti-TSLP antibodies (<xref ref-type="fig" rid="fig8">Figure 8F,G</xref>). In contrast, there was no effect on the type 1 cytokines, TNFα and IFNγ. Thus, the inflammation-suppressive effects of systemic TSLP inhibition were mediated at the level of both local and systemic suppression of inflammatory mediator production.</p><p>EPI−/− SCCs expressed higher TSLP levels than WT SCC (<xref ref-type="fig" rid="fig8">Figure 8I</xref>), whereas there were no significant differences in IL-4 and IL-17 (<xref ref-type="fig" rid="fig8">Figure 8H</xref>). In addition, EPI−/− mice bearing papillomas larger than 2 mm<sup>2</sup> had higher levels of systemic TSLP than EPI−/− mice with smaller papillomas (<xref ref-type="fig" rid="fig8">Figure 8J</xref>). This indicates that when tumours do arise in an atopic environment, TSLP may have a tumour growth-promoting role. This is in contrast to the reported ability of TSLP to shrink tumours in Notch-deficient skin (<xref ref-type="bibr" rid="bib11">Demehri et al., 2012</xref>), but in agreement with the potent tumorigenic effect of TSLP in breast and pancreatic cancers (<xref ref-type="bibr" rid="bib12">De Monte et al., 2011</xref>; <xref ref-type="bibr" rid="bib42">Pedroza-Gonzalez et al., 2011</xref>).</p><p>We conclude that targeting the Rae1/NKG2D/TSLP axis reverts the atopic phenotype observed in EPI−/− mice upon TPA treatment by interfering with the crosstalk between keratinocytes and immune cells.</p></sec></sec><sec id="s3" sec-type="discussion"><title>Discussion</title><p>Mice deficient in <italic>Evpl, Ppl</italic> and <italic>Ivl</italic> exhibited a striking resistance to benign tumour formation. This was not due to a difference in DMBA-induced initiation, indicating that the tumour-protective effect was not mediated by cell-autonomous changes associated with acquisition of oncogenic mutations. Rather, short-term TPA treatment exacerbated atopic dermatitis in EPI−/− mice, resulting in a phenotype that shared key hallmarks of the acute phase of the disease in humans (<xref ref-type="bibr" rid="bib7">Bieber, 2010</xref>) (<xref ref-type="fig" rid="fig9">Figure 9</xref>). These hallmarks included epidermal acanthosis, spongiosis, hyperkeratosis, and parakeratosis, systemic type 2 cell expansion with a dramatic accumulation of CD4<sup>+</sup> T cells, neutrophils, eosinophils and dermal mast cells, and elevation of serum IgE and TSLP levels.<fig id="fig9" position="float"><object-id pub-id-type="doi">10.7554/eLife.01888.011</object-id><label>Figure 9.</label><caption><title>Model of the role of an epidermal barrier defect in tumour protection.</title><p>EPI−/− mice lack three cornified envelope proteins, resulting in a defective epidermal barrier. Topical application of DMBA induces H-Ras mutations, as in wild-type mice. Topical TPA treatment elicits an exaggerated atopic response, characterized by altered keratinocyte differentiation and an enhanced inflammatory response. Epidermal production of TSLP and activation of the ligand-NKG2D pathway on immune cells are proposed to contribute to tumour protection.</p><p><bold>DOI:</bold> <ext-link ext-link-type="doi" xlink:href="10.7554/eLife.01888.011">http://dx.doi.org/10.7554/eLife.01888.011</ext-link></p></caption><graphic xlink:href="elife01888f009"/></fig></p><p>The enhanced thickening of TPA-treated EPI−/− epidermis reflected an increase in the number of suprabasal, differentiated cell layers and defective desquamation. Proliferation in the basal layer was similar to wild type, but the transit time of cells through the epidermis was faster. These changes in differentiation have previously been shown to be tumour-suppressive in oncogene-driven skin carcinogenesis (<xref ref-type="bibr" rid="bib19">Guinea-Viniegra et al., 2012</xref>), consistent with our observation that EPI−/− mice are resistant to developing papillomas. Upon TPA treatment EPI−/− defective keratinocytes released high levels of chemokines and type 2-type 17 cytokines, including TSLP. This correlated with recruitment of innate immune cells, including mast cells, granulocytes (both neutrophils and eosinophils) and adaptive immune cells, such as CD4<sup>+</sup> T cells, which could potentially play a role in immuno-editing of nascent papillomas.</p><p>Defective epidermal differentiation in concert with activation of innate and adaptive immune responses is known to create the first line of defence against physical, chemical, and toxic assaults in the skin (<xref ref-type="bibr" rid="bib34a">Milstone, 2004</xref>; <xref ref-type="bibr" rid="bib50">Sherman et al., 2008</xref>). Key players in the crosstalk between keratinocytes and leukocytes are DETCs, since they orchestrate the inflammatory response to pathogen-derived and environmental signals (<xref ref-type="bibr" rid="bib29">King et al., 1999</xref>; <xref ref-type="bibr" rid="bib36">Moore et al., 2000</xref>). DETCs are already in an activated state in untreated EPI−/− epidermis, as demonstrated by their round shape and reduced number (<xref ref-type="bibr" rid="bib49">Sevilla et al., 2007</xref>). This is most likely a consequence of increased expression of keratinocyte stress signals (Rae-1 and H60), which would be responsible for establishing the observed Th2 immune-surveillance response. We propose that this pre-activated, ‘alarmed’ condition enables EPI−/− skin to react more promptly and strongly to TPA treatment than WT skin. In contrast to EPI−/− mice, in mice that overexpress activin βA in the epidermis downregulation of DETCs only occurs after DMBA/TPA treatment and is linked to increased skin carcinogenesis (<xref ref-type="bibr" rid="bib5">Antsiferova et al., 2011</xref>). The exaggerated TPA response in EPI−/− mice resulted in increased numbers of CD4+ T cells, neutrophils, mast cells, and eosinophils, and many of these leukocyte populations have been shown to be able to exert tumour protective effects, which could potentially bypass the function of γδ T cells.</p><p>Targeting the Rae-1/NKG2D/TSLP axis, by blocking TSLP or NKG2D, suppressed the crosstalk between keratinocytes and immune cells and abrogated the atopic phenotype of TPA-treated EPI−/− skin, as seen by normalisation of epidermal differentiation and inflammation. In mice, epidermal overexpression of TSLP results in an atopic dermatitis phenotype characterized by epidermal hyperproliferation, acanthosis, spongiosis, and hyperkeratosis, as well as mast cell infiltration in the dermis (<xref ref-type="bibr" rid="bib61">Yoo et al., 2005</xref>). In humans, TSLP is implicated in the pathogenesis of both atopic dermatitis and asthma (<xref ref-type="bibr" rid="bib31">Leonard, 2002</xref>; <xref ref-type="bibr" rid="bib4">Al-Shami et al., 2005</xref>; <xref ref-type="bibr" rid="bib63">Zhou et al., 2005</xref>; <xref ref-type="bibr" rid="bib23">Huston and Liu, 2006</xref>; <xref ref-type="bibr" rid="bib32">Liu, 2006</xref>). TSLP has potent anti-tumour activity in skin carcinogenesis (<xref ref-type="bibr" rid="bib11">Demehri et al., 2012</xref>; <xref ref-type="bibr" rid="bib13">Di Piazza et al., 2012</xref>). Consistent with this, TPA-treated EPI−/− skin produced higher levels of TSLP than WT skin, and was protected from chemically induced papilloma formation.</p><p>NKG2D ligands have been shown to be upregulated in many inflammatory lesions and can act as an axis of immunoregulation (<xref ref-type="bibr" rid="bib52">Strid et al., 2008</xref>). Our findings demonstrate that the proposed role for Rae-1 and NKG2D in establishment of the lymphoid stress-surveillance response and consequent atopic phenotype also applies to the situation in which there is a defective epidermal barrier.</p><p>Although two-stage chemical skin carcinogenesis has been used extensively to elucidate the role of individual components of the immune system (specific cell types, cytokines and signalling molecules), ours is the first mouse model to link the lack of structural proteins and consequent defective epidermal barrier to cancer susceptibility. Epidemiological studies of the association between allergic disease and cancer risk have given conflicting results, in part because of the difficulty of factoring in immune suppressive treatments for the disease and in part because the association can be positive or negative according to cancer type (<xref ref-type="bibr" rid="bib6">Arana et al., 2010</xref>; <xref ref-type="bibr" rid="bib56">Van Hemelrijck et al., 2010</xref>; <xref ref-type="bibr" rid="bib59">Wiemels et al., 2011</xref>; <xref ref-type="bibr" rid="bib25">Jensen et al., 2012</xref>; <xref ref-type="bibr" rid="bib28">Kaae et al., 2013</xref>). Our study provides a mechanistic framework for further analysis of the link between atopic dermatitis and cancer incidence.</p></sec><sec id="s4" sec-type="materials|methods"><title>Materials and methods</title><sec id="s4-1"><title>EPI−/− and control mice</title><p>Mice deficient for <italic>envoplakin, periplakin,</italic> and <italic>involucrin</italic> (EPI−/−) were generated as previously described (<xref ref-type="bibr" rid="bib49">Sevilla et al., 2007</xref>) by interbreeding single knockout mice for <italic>envoplakin</italic> (<xref ref-type="bibr" rid="bib34">Maatta et al., 2001</xref>), <italic>involucrin</italic> (<xref ref-type="bibr" rid="bib14">Djian et al., 2000</xref>), and <italic>periplakin</italic> (<xref ref-type="bibr" rid="bib3">Aho et al., 2004</xref>). Single knockout mice were generated and maintained on a variety of genetic backgrounds and as a result there was a potential contribution of Sv129, C57BL/6, BALB/c and nu/nu to EPI−/− animals. Since DMBA/TPA sensitivity is affected by genetic background (<xref ref-type="bibr" rid="bib21">Hennings et al., 1993</xref>; <xref ref-type="bibr" rid="bib60">Woodworth et al., 2004</xref>), DNA of 4 EPI−/− mice (each from a different breeding pair) was subjected to genome scanning by the Jackson Laboratory (Bar Harbor, ME, USA). Single nucleotide polymorphisms (SNPs) were used to determine the relative contributions of different genetic backgrounds. EPI−/− mice were primarily Sv129 (40.98%, ±1.52) and C57Bl/6 (51.39%, ±1.62), with a small contribution of BALB/c (4.7%, ±1.24). The nu/nu mutation was not detected. Based on these results, the F2 generation of crosses between Sv129 and C57Bl/6J mice was used as the WT control (51.82%, ±3.35 Sv129; 49.92%, ±1.98 C57Bl/6) for all experiments.</p></sec><sec id="s4-2"><title>Two stage carcinogenesis</title><p>Chemical carcinogenesis experiments were performed as previously described (<xref ref-type="bibr" rid="bib1">Abel et al., 2009</xref>). All experiments were carried out under the terms of a UK Government Home Office project licence, with local ethical approval. The back skin of 7-week-old female mice was shaved with electric clippers. 3 days later animals that did not show signs of hair regrowth received a topical application of 100 nmol (25 μg) DMBA (Sigma–Aldrich) in 200 μl acetone, followed by three times weekly applications of 6 nmol (3.7 μg) of TPA (Sigma-Aldrich, Dorset, UK) in 200 μl acetone for 15 weeks. As controls, mice (5–10 animals/group) were subjected to the same protocol, but substituting DMBA or TPA with acetone. Papillomas and SCCs were recorded once a week for up to 57 weeks after the start of promotion. Recordings were made by an observer who was ‘blinded’ to the experimental groups. 1 hr before culling, mice were injected intraperitoneally with 50 mg/kg bodyweight 5-bromo-2'-deoxyuridine BrdU (Sigma-Aldrich). In some experiments, age and gender matched mice received 1 application of DMBA and/or 3 applications of TPA on alternating days. Skin was harvested 24 hr after DMBA painting or 48 hr after the last TPA treatment.</p></sec><sec id="s4-3"><title>Tissue processing, immunohistochemistry and immunofluorescence labelling</title><p>For paraffin sections, tissue was fixed in 10% neutral buffered formalin for 24 hr and embedded in paraffin after dehydration. For frozen sections, tissue was submerged in OCT embedding matrix (Raymond A Lamb, UK) and frozen on dry ice. 4–6 μm (paraffin or frozen) sections were prepared and collected onto glass slides.</p><p>Quantitation of the proportion of the epidermis with a parakeratotic or hyperkeratotic stratum corneum was performed on hematoxylin-eosin stained paraffin sections. A minimum epidermal length of 7 cm was analysed from ≥4 mice per condition. Parakeratosis was defined as retention of nuclei in the cornified layers. Hyperkeratosis was defined as abnormal thickening of the stratum corneum relative to wild type, untreated stratum corneum.</p><p>BrdU, PH3, and Caspase-3 were detected in formalin-fixed paraffin-embedded sections. Sections were dewaxed and rehydrated on an automated Leica ST5020, then treated for antigen-retrieval and incubated with primary antibody at the indicated dilution. Secondary antibodies were diluted 1:250 and probed using the Bond Intense R Detection kit (Leica Microsystems; Wetzlar, Germany). Sections were scanned and analysed using the Ariol SL-50 system (Applied Imaging Corp., San Jose).</p><p>Prior to immunofluorescence staining, frozen sections were air-dried for 10 min at room temperature and fixed in 4% PFA/PBS pH 7.4 for 10 min. Sections were blocked with 2% BSA, 0.02% fish skin gelatin, and 10% goat serum for 1 hr in PBS at room temperature. Sections were incubated in unconjugated or fluorochrome-conjugated primary antibody and DAPI overnight at 4<bold>°</bold>C, washed in PBS and then mounted using DAKO mounting reagent (DAKO). AlexaFluor 488- or 633-conjugated goat anti-rabbit or anti-mouse IgG (Invitrogen) were diluted 1:1000 and used for detection of unconjugated primary antibodies. The following species-specific antibodies conjugated with Alexafluor 488 or 555 or 647 were used at a dilution of 1:100: anti-CD3 (clone 17.A2; BDPharmingen), anti-CD4 (clone RM4-5; eBioscience), anti-CD8α (clone 53-6.7; BioLegend), anti-γδ TCR (clone GL3; BDPharmingen), anti-F4/80 (clone BM8; eBioscience), anti-Ly6G (clone 1A8; BDPharmingen), anti-CD207 (clone eBioRMUL.2; eBioscience) and anti-CD11b (clone M1/70; eBioscience). In-house produced antibodies against periplakin, envoplakin and involucrin were also used (<xref ref-type="bibr" rid="bib46">Ruhrberg et al., 1996</xref>, <xref ref-type="bibr" rid="bib45">1997</xref>; <xref ref-type="bibr" rid="bib49">Sevilla et al., 2007</xref>). The following species-specific unconjugated antibodies were used at the dilutions stated: anti-PH3 (Upstate rabbit polyclonal, catalogue number 06-570, 1:500), anti-BrdU (Abcam sheep polyclonal, ab1893, 1:500), anti-caspase-3 (Cell Signaling rabbit monoclonal, catalogue number 9664, 1:100) and anti-γH2AX (05-636; 1;10; Millipore0). Mast cells were detected with toluidine blue, and eosinophils were detected by Congo red staining.</p><p>Hematoxylin and eosin–stained sections of skin and tumours were graded in a blinded manner by two experts in mouse skin pathology, as described previously (<xref ref-type="bibr" rid="bib38">Owens and Watt, 2001</xref>). When quantifying the number of cells that were positive for a particular marker, at least 6 fields per treated skin or tumour section were analysed.</p></sec><sec id="s4-4"><title>Quantitative RT-PCR</title><p>RNA was extracted from whole skin, tumours or epidermis that had been scraped from skin following heat treatment for 60 s at 56°C in PBS +10 mM EDTA or from cultured keratinocytes using the RNeasy mini kit (Qiagen, UK). RNA was quantified using a ND-100 NanoDrop spectrophotometer (NanoDrop Technologies). cDNA was prepared using a Superscript III First-Strand Synthesis Supermix for qRT-PCR kit (Invitrogen) according to the manufacturers' instructions.</p><p>Quantitative RT-PCR was carried out using designed primers and fast SYBR Green or Taqman probes with Taqman Fast Universal PCR Master Mix (Applied Biosystems) and run on an ABI Prism 7900HT Sequence detection system (Applied Biosystems). The RT-PCR was run for 40 cycles and specificity of the reactions was determined by subsequent melting curve analysis. Quantitation was based on ΔCt calculations using the SDS analysis software and all samples were compared against mouse GAPDH as a house keeping control. Matrix visualization was performed using the online Matrix2PNG tool (<xref ref-type="bibr" rid="bib41">Pavlidis and Noble, 2003</xref>). Primers and TaqMan probes are listed in <xref ref-type="supplementary-material" rid="SD1-data">Supplementary file 1</xref>.</p></sec><sec id="s4-5"><title>TP53 sequencing and mutant specific HRas qPCR</title><p>Genomic DNA was isolated from SCCs using the NucleoSpin kit (Macherey–Nagel) as per the manufacturer's protocol. PCR amplification of <italic>HRas</italic> and <italic>p53</italic> exons of interest was performed on 100 ng of DNA using primers described previously (<xref ref-type="bibr" rid="bib37">Niemann et al., 2007</xref>). PCR products were purified and sequenced. To quantify the number of DMBA-induced codon-61 <italic>Hras</italic> CAA->CTA mutations, mutant-specific primers were used as previously described (<xref ref-type="bibr" rid="bib35">Modi et al., 2012</xref>). Obtained Ct values were normalised against genomic GAPDH (gGAPDH).</p></sec><sec id="s4-6"><title>Peripheral blood collection, white blood cell analysis, and plasma preparation</title><p>Mice were anesthetized with Isoflurane (Anaesthesia, UK) and then blood for differential white blood cell counts was collected by cardiac puncture in the presence of EDTA (1.75 mg of EDTA dihydrate solution per ml of blood) to prevent coagulation. For plasma protein analysis, blood was allowed to clot at room temperature for at least 1 hr. After centrifugation at 14,000 rpm for 15 min at 4°C the serum was collected, aliquoted, and kept at −80°C until analysis.</p></sec><sec id="s4-7"><title>Measurement of cytokine production in whole skin and serum</title><p>Whole skin lysates and serum were collected, snap-frozen in liquid nitrogen and kept at −80°C prior to analysis. The Cytometric Bead Array Cytokine Flex Kit (BD) was used following the manufacturer's instructions. Samples were run on a LSR-II flow cytometer and the data were analysed with BD Cytometric Bead Array software. Cytokine production was determined as picograms per ml serum or mg of whole skin lysate.</p></sec><sec id="s4-8"><title>Quantification of ear epidermal Langerhans cells</title><p>Epidermal sheets were prepared from mouse ears that had been split into dorsal and ventral sides and floated dermal side down for 2 hr at 37°C in 20 mM EDTA. Epidermal sheets were gently lifted from the dermis, washed in PBS and fixed in cold acetone for 20 min at −20°C. After washing in PBS, epidermal sheets were incubated for 1 hr at room temperature with 2% (g/vol) BSA in PBS and stained overnight at 4°C with CD207 Alexa 647 conjugated antibody (eBioscience, clone eBioRMUL.2) and DAPI. After extensive washing, epidermal sheets were mounted on slides with DAKO mounting medium and visualized by confocal microscopy.</p></sec><sec id="s4-9"><title>In vivo injection of dexamethasone and inhibitory antibodies</title><p>Functional grade purified antibodies against CD4 (16-0042, clone RM4-5 and clone GK1.5, rat IgG2bK; eBioscience), TSLP (MAB555, clone 152614; R&D System, 16-5491, clone eBio28F12; eBioscience ), NKG2D (catalogue number BE0111; BioXCell), LY6G (clone 1A8; BioXCell), IL-4 (catalogue number BE0045; BioXCell), and appropriate isotype controls (BioXCell Rat IgG2a, catalogue number BE0089 for TSLP and Ly6G; Rat IgG2b, catalogue number BE0090 for CD4; hamster IgG catalogue number BE0091 for NKG2D; Rat IgG1, catalogue number BE0088 for IL-4) were injected intraperitoneally at a dose of 0.1 mg/mouse. Dexamethasone 21-phosphate disodium salt (DXM) (D1159; Sigma) was injected at 10 mg/kg mouse body weight, the same volume of PBS being injected in control mice.</p></sec><sec id="s4-10"><title>Serum ELISAs</title><p>TSLP (Quantikine mouse TSLP kit, R&D Systems), IL-4 (ELISA IL-4 Ready-set-go, eBiosciences), and IgE (Bethyl Laboratory) immunoassays were performed on mouse serum according to the manufacturer's instructions.</p></sec><sec id="s4-11"><title>Whole skin lysates</title><p>Whole skin protein lysates were prepared by mechanical lysis using ceramic beads (Precellys) in NP-40 buffer (50 mM Tris–HCl, 150 mM NaCl, 1% NP-40, pH<bold>.</bold>7.4) with complete protease inhibitor cocktail (Roche, Burgess Hill, UK). Tissue was homogenized twice at 1600 rpm for 50 s, then centrifuged for 20 min 200 µl aliquots were snap frozen and kept at −80C.</p></sec><sec id="s4-12"><title>Statistics</title><p>Statistical analyses were performed using GraphPad Prism (GraphPad Software). The statistical significance of differences between most experimental groups was determined with a two-tailed Student's t-test for unpaired data or Fisher's exact test. For analysis of differences between WT and EPI−/− mouse tumour burden Mann Whitney testing was performed. For analysis of differences between WT and EPI−/− mouse tumour incidence a test of difference in proportions was used. p-values are indicated with: * 0.01<p<0.05, ** 0.01<p<0.001, *** 0.0001<p<0.001, ****p<0.0001.</p></sec></sec></body><back><ack id="ack"><title>Acknowledgements</title><p>This work was supported by a FEBS postdoctoral fellowship to SC, a JSPS fellowship to KN, a SRS fellowship to SQ, and funds to FMW from Cancer Research UK, the Wellcome Trust, MRC and the EU FP7 programme (HEALING). We thank Rachida Nachat and Lisa Sevilla for their input and core facilities of the CRUK Cambridge Research Institute for superb technical assistance.</p></ack><sec sec-type="additional-information"><title>Additional information</title><fn-group content-type="competing-interest"><title>Competing interests</title><fn fn-type="conflict" id="conf1"><p>FMW: Deputy Editor, <italic>eLife</italic>.</p></fn><fn fn-type="conflict" id="conf2"><p>The other authors declare that no competing interests exist.</p></fn></fn-group><fn-group content-type="author-contribution"><title>Author contributions</title><fn fn-type="con" id="con1"><p>SC, Conception and design, Acquisition of data, Analysis and interpretation of data, Drafting or revising the article</p></fn><fn fn-type="con" id="con2"><p>EH, Conception and design, Acquisition of data, Analysis and interpretation of data, Drafting or revising the article</p></fn><fn fn-type="con" id="con3"><p>KN, Conception and design, Acquisition of data, Analysis and interpretation of data</p></fn><fn fn-type="con" id="con4"><p>SRQ, Acquisition of data, Analysis and interpretation of data</p></fn><fn fn-type="con" id="con5"><p>FMW, Conception and design, Analysis and interpretation of data, Drafting or revising the article</p></fn></fn-group><fn-group content-type="ethics-information"><title>Ethics</title><fn fn-type="other"><p>Animal experimentation: All experiments were carried out under the terms of a UK Government Home Office project licence (PPL 80/2378), with local ethical approval from King's College London and the University of Cambridge.</p></fn></fn-group></sec><sec sec-type="supplementary-material"><title>Additional files</title><supplementary-material id="SD1-data"><object-id pub-id-type="doi">10.7554/eLife.01888.012</object-id><label>Supplementary file 1.</label><caption><p>Primers and TaqMan probes used.</p><p><bold>DOI:</bold> <ext-link ext-link-type="doi" 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pub-id-type="doi">10.7554/eLife.01888.013</article-id><title-group><article-title>Decision letter</article-title></title-group><contrib-group content-type="section"><contrib contrib-type="editor"><name><surname>Fuchs</surname><given-names>Elaine</given-names></name><role>Reviewing editor</role><aff><institution>Rockefeller University</institution>, <country>United States</country></aff></contrib></contrib-group></front-stub><body><boxed-text><p>eLife posts the editorial decision letter and author response on a selection of the published articles (subject to the approval of the authors). An edited version of the letter sent to the authors after peer review is shown, indicating the substantive concerns or comments; minor concerns are not usually shown. Reviewers have the opportunity to discuss the decision before the letter is sent (see <ext-link ext-link-type="uri" xlink:href="http://elifesciences.org/review-process">review process</ext-link>). Similarly, the author response typically shows only responses to the major concerns raised by the reviewers.</p></boxed-text><p>Thank you for sending your work entitled “Epidermal barrier defects link atopic dermatitis with altered skin cancer susceptibility” for consideration at <italic>eLife</italic>. Your article has been favorably evaluated by a Senior editor, a Reviewing editor, and 3 reviewers, one of whom, Valerie Horsley, has agreed to reveal her identity.</p><p>As you can see, the reviewers' comments are favorable on the whole although there are some issues that will need to be addressed satisfactorily before proceeding with publication in <italic>eLife</italic>. The Reviewing editor and the other reviewers discussed their comments before we reached this decision, and the Reviewing editor has assembled the following comments to help you prepare a revised submission.</p><p>The reviewers contrasted your manuscript and its findings with that of the Kopan Cancer Cell paper (2012), both of which explore the relationship of skin barrier and tumor initiation and invoke TSLP. There was general agreement that the Kopan paper was more novel at the time and the reviewers were somewhat split regarding whether the current paper sufficiently extends mechanistic aspects regarding the link between skin barrier and tumorigenesis to a level appropriate for <italic>eLife</italic>. The reviewers did agree that the link between barrier and tumorigenesis is more clearly established in the Watt paper, since the Notch loss of function model in the Kopan paper could alter non-barrier mechanisms to control tumor formation. They also concur that most of the data presented are convincing. However, they also feel that in addition to the provided blocking antibodies experiment, more mechanistic insights are needed to make this into a clear case for <italic>eLife</italic>. Specifically, the most important question becomes how TSLP is acting, since Kopan's lab has implicated TSLP in the tumor formation following barrier issues. Kopan has suggested that TSLP acts on T cells (Dehmehri et al 2012) and a recent paper by Diana Baustista shows nicely that TSLP signals in neurons in the skin (Wilson et al Cell 2013). If the authors can establish whether TSLP acts directly on inflammatory or other cell populations to control tumor formation, this would represent the kind of mechanistic advance requisite for <italic>eLife</italic>. The other comments listed, while extensive, will be relatively straightforward, but this is the only major experimental issue that the authors should address.</p><p>The reviewers felt that the link clinically between atopic dermatitis and skin cancer is weak, and here, some of this can be handled textually, by making the paper crisper in its focus and making fewer sweeping statements. In addition, there are some specific comments, which will strengthen the paper, including substantiating the mechanism, and which are lengthy but seem relatively straightforward to address.</p><p><italic>Experimental issues/interpretations</italic> <italic>of the data:</italic></p><p>1) While EPI-/- mice have defects in skin tumor initiation, it is possible that these genes also play a role in tumor progression. Are Envoplakin, Periplakin or Involucrin expressed in WT skin papillomas or SCCs? If so, they may play additional roles once the skin tumor is already formed.</p><p>2) The authors nicely show that the mutagenic effect of DMBA is unaffected by the EPI mutations. The pro-inflammatory effect of TPA, however, is strongly exaggerated in EPI-/- mice. This is likely because barrier defect in these mice makes them more susceptible to the toxic effect of TPA. The authors note that there is increased expression of some inflammatory genes, genes involved in lymphoid stress immune-surveillance (e.g., RAE1) and barrier defense (e.g., TSLP). Blocking TSLP and NKG2D (receptor for RAE1) significantly reduce the inflammatory response. However, another group found that a reduction in DETC number resulted in increased skin tumorigenesis (Antisferova, Nature Communications, 2011). Although EPI-/- mice also have fewer DETCs, they develop fewer tumors. Could the overall increase in immune activation in EPI-/- mice render DETC function dispensable? Some comments on this difference would be helpful.</p><p>3) Are there any differences in the presence of alpha/beta T cells in EPI-/- epidermis?</p><p>4) The authors use antibodies against cytokines to suppress cytokine signaling during TPA treatment which many of these cytokines (in particular TSLP) have been implicated before. An extension of this mechanistic angle should implicate which cell types are responsible for the suppression of tumorigenesis. How these signals act in the immune cells etc.</p><p>5) A model might help this manuscript to better depict mechanistic findings of this manuscript. As presented the paper appears to be a set of fairly standard experiments with histology and RT-PCR.</p><p>6) The study reports two sets of findings: first, that EPI mice are protected from DMBA/TPA induced skin papillomas; second, that EPI mice have exaggerated inflammatory response to TPA. It is not clear whether the two are related and whether (and how) the latter explains the former. Normally, this would be tested using either mice deficient in the suspected components (TSLP, NKG2D), or by blocking these proteins with antibodies. The reviewers agreed that neither approach can be reasonably used here because the mice are already triple knockouts and because the treatment with antibodies for several months is not practical.</p><p>The results overall fit with the emerging idea (and epidemiological data) that allergic defenses may confer protection against environmental carcinogenes. One possible interpretation of the results is that structural barrier defect caused y EPI mutations results in compensatory immune-mediated barrier defense that confers protection. The mouse model can be very useful to examine the mechanisms of protective effects of immune stress surveillance response.</p><p><italic>Textual issues/interpretations</italic> <italic>of the data:</italic></p><p>1) The authors may want to consult with an immunologist regarding their terminology and the choice of genes used as indicators of different types of immune responses. For example, IL-12p40 is not a Th17 marker and IL-6 is not a Th2 marker. These cytokines are made by myeloid cells and affect multiple responses; they are not produced by T cells.</p><p>2) In addition, the article could benefit from some heavy editing. For example, the authors present as a fact that there is a causal relationship between barrier impairment, structural proteins, and atopic dermatitis. But the authors should use greater precision. In humans, mutations in FLG (a structural protein) are linked to ichthyosis vulgaris and associated with atopic dermatitis and atopic disorders, such as asthma and allergic rhinitis. But the authors state causality, when genetically correlation has been defined. Mouse models of FLG-/- display some features of AD, but not allergic airway inflammation (asthma model). Moreover these findings are more in question now that the animal model (flaky tail) has been shown to be a compound mutation of FLG and Tmem79.</p><p>There is true controversy that cancer is associated with atopy. Some references to support this model are Hwang CY (2012) Int J Cancer and Wedgeworth E (2011) Br JDerm but many dermatologists feel that the connection is more tenuous and may be driven by severe atopics being treated with heavy immunosuppressants, which have been associated with increased risk of malignancies. UV light therapy is also a potential treatment that would underlie an increase risk of skin cancer. These are confounding issues for patient data.</p><p>3) The extent to which DMBA/TPA treatment is a model for human skin cancer needs to be better addressed in the manuscript as most human SCC do not have H-ras mutations. These issues are mentioned, but typically toward the end of arguments, and need to be addressed before a more simplistic interpretation is depicted as the truth.</p><p>4) Authors should read through and edit the entire manuscript. There are lots of circuitous arguments, typographical errors, and information provided in the wrong sections.</p><p><italic>Methods/statistics/clarifications</italic>:</p><p>1) How was the function of the antibody blockade of TSLP or NKG2D measured? What percent neutralization was achieved?</p><p>2) How was RNA normalized for the acanthosis observed in EPI-/- skin? Basically, if RNA levels are higher, does this reflect an upregulation of the gene or simply that there are more suprabasal cells in the skin? Was RT-PCR deltaCt normalized to B2u or some other ubiquitous gene?</p><p>3) In <xref ref-type="fig" rid="fig3">Figures 3B and 3C</xref>, how is the percent of hyperkeratotic and parakeratotic epidermis quantified?</p><p>4) Are wt animals +/+;+/+;+/+ or compound heterozygotes. Nu/nu is not a genetic background but rather exists on multiple genetic backgrounds. This is confusing in the Methods section.</p><p>5) How representative are the 4 EPI-/- mice of genetic variation?</p></body></sub-article><sub-article article-type="reply" id="SA2"><front-stub><article-id pub-id-type="doi">10.7554/eLife.01888.014</article-id><title-group><article-title>Author response</article-title></title-group></front-stub><body><p><italic>The reviewers contrasted your manuscript and its findings with that of the Kopan Cancer Cell paper (2012), both of which explore the relationship of skin barrier and tumor initiation and invoke TSLP. There was general agreement that the Kopan paper was more novel at the time and the reviewers were somewhat split regarding whether the current paper sufficiently extends mechanistic aspects regarding the link between skin barrier and tumorigenesis to a level appropriate for eLife. The reviewers did agree that the link between barrier and tumorigenesis is more clearly established in the Watt paper, since the Notch loss of function model in the Kopan paper could alter non-barrier mechanisms to control tumor formation. They also concur that most of the data presented are convincing. However, they also feel that in addition to the provided blocking antibodies experiment, more mechanistic insights are needed to make this into a clear case for eLife. Specifically, the most important question becomes how TSLP is acting, since Kopan's lab has implicated TSLP in the tumor formation following barrier issues. Kopan has suggested that TSLP acts on T cells (Dehmehri et al 2012) and a recent paper by Diana Baustista shows nicely that TSLP signals in neurons in the skin (Wilson et al Cell 2013). If the authors can establish whether TSLP acts directly on inflammatory or other cell populations to control tumor formation, this would represent the kind of mechanistic advance requisite for</italic> eLife.</p><p>As the reviewers point out, our model is distinct from the Kopan model in that tumour resistance is directly attributable to loss of epidermal barrier proteins, rather than to disturbed barrier function as a consequence of deleting Notch receptors.</p><p>Kopan and co-workers attributed the anti-tumorigenic action of TSLP in Notch deficient skin mainly to CD4+ T cells. We now demonstrate that injection of CD4 blocking antibodies does not abrogate the atopic phenotype of TPA treated EPI-/- mice (new <xref ref-type="fig" rid="fig6">Figure 6C</xref>). There is no difference in the abundance of CD8+ cells between TPA treated EPI-/- and WT skin, but there is a marked increase in neutrophil infiltration. We therefore depleted neutrophils with anti-LY6G antibody, and now show no reduction in hyperplasia and dermal inflammation (new <xref ref-type="fig" rid="fig6">Figure 6D</xref>). Nevertheless, treatment with the broad-spectrum anti-inflammatory drug dexamethasone (DXM) markedly reduces the TPA response in EPI-/- skin (new <xref ref-type="fig" rid="fig6">Figure 6B</xref>). We conclude that, in contrast to the Kopan model, multiple immune cell types contribute to the tumour resistance of the EPI-/- model.</p><p>One of the novel features of our study, again distinct from the Kopan model, is the demonstration that an intrinsic barrier defect results in activation of the Rae-1/NKG2D/TSLP axis. This provokes a lymphoid stress-surveillance response, which underlies the atopic phenotype in TPA treated EPI-/- mice, since there is reduced dermal infiltration of specific immune cell populations and a reduced keratinocyte response when TSLP or NKG2D is blocked (<xref ref-type="fig" rid="fig7">Figure 7</xref>; <xref ref-type="fig" rid="fig8">Figure 8A-E</xref>).</p><p>Kopan and collaborators show that when mice are treated with calcipotriol, a potent TSLP inducer, tumors shrink over time. In contrast, an interesting feature of our model is that when papillomas do arise in EPI-/- mice they have a higher frequency of malignant conversion to SCCs than WT papillomas (<xref ref-type="fig" rid="fig1">Figure 1</xref>). We have now compared cytokine levels in WT and EPI-/- SCCs (new <xref ref-type="fig" rid="fig8">Figure 8H, I</xref>). There was no difference in the expression of IL-4 (a type-2 cytokine) or IL-17 (a type-17 cytokine) (<xref ref-type="fig" rid="fig8">Figure 8H</xref>). However, EPI-/- SCCs expressed higher TSLP levels (<xref ref-type="fig" rid="fig8">Figure 8I</xref>) and EPI-/- mice bearing papillomas larger than 2mm<sup>2</sup> had higher levels of systemic TSLP than EPI-/- mice with smaller papillomas (<xref ref-type="fig" rid="fig8">Figure 8J</xref>). Our data again highlight the difference between our model and that of Kopan, and corroborate reports that TSLP is a potent growth-promoting cytokine in breast and pancreatic cancers (<xref ref-type="bibr" rid="bib12">De Monte et al., 2011</xref>; <xref ref-type="bibr" rid="bib42">Pedroza-Gonzalez et al., 2011</xref>, now cited).</p><p><italic>The reviewers felt that the link clinically between atopic dermatitis and skin cancer is weak, and here, some of this can be handled textually, by making the paper crisper in its focus and making fewer sweeping statements</italic>.</p><p>We agree and we have revised the text accordingly.</p><p>Experimental issues/interpretations of the data:</p><p><italic>1) While EPI-/- mice have defects in skin tumor initiation, it is possible that these genes also play a role in tumor progression. Are Envoplakin, Periplakin or Involucrin expressed in WT skin papillomas or SCCs? If so, they may play additional roles once the skin tumor is already formed</italic>.</p><p>We have included immunostaining for envoplakin, periplakin and involucrin in WT skin, papillomas and SCCs (new <xref ref-type="fig" rid="fig1">Figure 1E</xref>), and show downregulation of all three proteins in tumours, which is most pronounced in SCCs. We agree that this could play a role in tumour progression as envoplakin and periplakin are desmosome-associated genes, and we now comment on this in the text.</p><p><italic>2) The authors nicely show that the mutagenic effect of DMBA is unaffected by the EPI mutations. The pro-inflammatory effect of TPA, however, is strongly exaggerated in EPI-/- mice. This is likely because barrier defect in these mice makes them more susceptible to the toxic effect of TPA. The authors note that there is increased expression of some inflammatory genes, genes involved in lymphoid stress immune-surveillance (e.g., RAE1) and barrier defense (e.g., TSLP). Blocking TSLP and NKG2D (receptor for RAE1) significantly reduce the inflammatory response. However, another group found that a reduction in DETC number resulted in increased skin tumorigenesis (Antisferova, Nature Communications, 2011). Although EPI-/- mice also have fewer DETCs, they develop fewer tumors. Could the overall increase in immune activation in EPI-/- mice render DETC function dispensable? Some comments on this difference would be helpful</italic>.</p><p>We have now included images of γδ T cells (DETCs) in acetone treated EPI-/- and WT mice to show that in EPI-/- epidermis there are fewer γδ T cells (as we reported previously) and those that remain are in an activated state, as demonstrated by their rounded shape (new <xref ref-type="fig" rid="fig4">Figure 4I</xref>). It has previously been reported that upon activation γδ T cells acquire a round shape before leaving the epidermis (Strid et al., Nature Immunology 2008; cited). K14-activin βA expressing mice (Antisferova et al., now cited) differ from EPI-/- mice, because downregulation of DETCs only occurs after DMBA/TPA treatment. The exaggerated TPA response in EPI-/- mice resulted in increased numbers of CD4+ T cells, neutrophils, mast cells and eosinophils, and many of these leukocyte populations have been shown to be able to exert tumor protective effects, which could potentially bypass the function of γδ T cells.</p><p><italic>3) Are there any differences in the presence</italic> <italic>of alpha/beta T cells in EPI-/- epidermis?</italic></p><p>We have now included immunostaining for CD4+ T cells in TPA treated WT and EPI-/- skin, showing that CD4+ T cells are not present in WT epidermis, but do infiltrate EPI-/- epidermis (new <xref ref-type="fig" rid="fig4">Figure 4J</xref>). In contrast, CD8+ T cells infiltrate the skin of untreated and TPA treated WT and EPI-/- mice to the same extent.</p><p><italic>4) The authors use antibodies against cytokines to suppress cytokine signaling during TPA treatment which many of these cytokines (in particular TSLP) have been implicated before. An extension of this mechanistic angle should implicate which cell types are responsible for the suppression of tumorigenesis. How these signals act in the immune cells etc</italic>.</p><p>As described in the opening response, we have now included additional antibody targeting strategies (new <xref ref-type="fig" rid="fig6">Figure 6C, D</xref>). One of the novel aspects of our work is that NKG2D has not been implicated before in linking atopic disease with skin tumorigenesis. Our studies show that blocking TSLP and NKG2D can normalize the exaggerated atopic response of keratinocytes and multiple leukocyte types in TPA treated EPI-/- skin, indicating that these targeting strategies affect a plethora of different cell types.</p><p><italic>5) A model might help this manuscript to better depict mechanistic findings of this manuscript. As presented the paper appears to be a set of fairly standard experiments with histology and RT-PCR</italic>.</p><p>We have now included a model summarizing our findings (new <xref ref-type="fig" rid="fig9">Figure 9</xref>).</p><p><italic>6) The study reports two sets of findings: first, that EPI mice are protected from DMBA/TPA induced skin papillomas; second, that EPI mice have exaggerated inflammatory response to TPA. It is not clear whether the two are related and whether (and how) the latter explains the former. Normally, this would be tested using either mice deficient in the suspected components (TSLP, NKG2D), or by blocking these proteins with antibodies. The reviewers agreed that neither approach can be reasonably used here because the mice are already triple knockouts and because the treatment with antibodies for several months is not practical</italic>.</p><p>Given that mice overexpressing TSLP in keratinocytes are protected from DMBA/TPA induced skin tumorigenesis (<xref ref-type="bibr" rid="bib11">Demehri et al., 2012</xref>), our data linking the exacerbated TPA response to upregulation of TSLP provides a strong link between our two sets of findings. We believe that this is clarified in the revised version of the manuscript and by inclusion of the model in <xref ref-type="fig" rid="fig9">Figure 9</xref>. Our results are of considerable interest because they provide experimental support for the emerging epidemiological data that allergic defenses can confer protection against environmental carcinogens in some contexts.</p><p>Textual issues/interpretations of the data:</p><p><italic>1) The authors may want to consult with an immunologist regarding their terminology and the choice of genes used as indicators of different types of immune responses. For example, IL-12p40 is not a Th17 marker and IL-6 is not a Th2 marker. These cytokines are made by myeloid cells and affect multiple responses; they are not produced by T cells</italic>.</p><p>We have now changed the terminology to type-1, type-2, and type-17 responses (<xref ref-type="fig" rid="fig5">Figure 5A</xref>).</p><p><italic>2) In addition, the article could benefit from some heavy editing. For example, the authors present as a fact that there is a causal relationship between barrier impairment, structural proteins, and atopic dermatitis. But the authors should use greater precision. In humans, mutations in FLG (a structural protein) are linked to ichthyosis vulgaris and associated with atopic dermatitis and atopic disorders, such as asthma and allergic rhinitis. But the authors state causality, when genetically correlation has been defined. Mouse models of FLG-/- display some features of AD, but not allergic airway inflammation (asthma model). Moreover these findings are more in question now that the animal model (flaky tail) has been shown to be a compound mutation of FLG and Tmem79</italic>.</p><p>We have revised the text to address these points.</p><p><italic>There is true controversy that cancer is associated with atopy. Some references to support this model are Hwang CY (2012) Int J Cancer and Wedgeworth E (2011) Br JDerm but many dermatologists feel that the connection is more tenuous and may be driven by severe atopics being treated with heavy immunosuppressants, which have been associated with increased risk of malignancies. UV light therapy is also a potential treatment that would underlie an increase risk of skin cancer. These are confounding issues for patient data</italic>.</p><p>We have revised the text and included these references.</p><p><italic>3) The extent to which DMBA/TPA treatment is a model for human skin cancer needs to be better addressed in the manuscript as most human SCC do not have H-ras mutations. These issues are mentioned, but typically toward the end of arguments, and need to be addressed before a more simplistic interpretation is depicted as the truth</italic>.</p><p>We have now revised the Introduction to address this point and cited reviews by Lopez-Pajares et al. and Hirst and Balmain.</p><p><italic>4) Authors should read through and edit the entire manuscript. There are lots of circuitous arguments, typographical errors, and information provided in the wrong sections</italic>.</p><p>We have subjected the text to extensive editing to address this criticism.</p><p>Methods/statistics/clarifications:</p><p><italic>1) How was the function of the antibody blockade of TSLP or NKG2D measured? What percent neutralization</italic> <italic>was achieved?</italic></p><p>We demonstrate potent blockade of TSLP and IL-4 by ELISA (see <xref ref-type="fig" rid="fig6 fig7">Figure 6I and 7B</xref>). We show reduced spleen mass as a readout for efficacy of Dexamethasone (new <xref ref-type="fig" rid="fig6">Figure 6F</xref>) and show that anti-LY6G reduces both the number of neutrophils in circulation and the number of neutrophil containing skin pustules (new <xref ref-type="fig" rid="fig6">Figure 6G, H</xref>). There is no straightforward method to confirm functional inhibition of NKG2D as this receptor has multiple downstream targets that are shared with other pathways. Nevertheless, we conclude that NKG2D function was at least partially blocked, because of the statistically significant differences in immune cell infiltration and epidermal thickness (<xref ref-type="fig" rid="fig7 fig8">Figure 7D and 8A-E</xref>).</p><p><italic>2) How was RNA normalized for the acanthosis observed in EPI-/- skin? Basically, if RNA levels are higher, does this reflect an upregulation of the gene or simply that there are more suprabasal cells in the skin? Was RT-PCR deltaCt normalized</italic> <italic>to B2u or some other ubiquitous gene?</italic></p><p>All normalizations were performed relative to GAPDH. We can exclude the possibility that QPCR data reveal differences in acanthosis rather than specific gene effects, as gene expression levels of Notch pathway genes, H60 and Rae-1 were similar in TPA treated (acanthotic) and vehicle treated EPI-/- epidermis (<xref ref-type="fig" rid="fig5">Figure 5D-F</xref>).</p><p><italic>3) In</italic> <xref ref-type="fig" rid="fig3"><italic>Figures 3B and 3C</italic></xref><italic>, how is the percent of hyperkeratotic</italic> <italic>and parakeratotic epidermis quantified?</italic></p><p>We quantified hyperkeratosis by measuring the length of epidermis that had marked thickening of the cornified layers relative to untreated WT epidermis. Parakeratotic regions were apparent from the persistence of nuclei in the cornified layers, which are normally anuclear. Parakeratotic regions were quantified by measuring the length of epidermis that was covered by parakeratotic plaques. We now explain this more clearly in the text.</p><p><italic>4) Are wt animals +/+;+/+;+/+ or compound heterozygotes. Nu/nu is not a genetic background but rather exists on multiple genetic backgrounds. This is confusing in the Methods section</italic>.</p><p>We apologize for the confusion in the description of the genetic background of EPI-/- mice in the Methods section. WT animals used in this study were +/+:+/+;+/+. We checked for the presence of the Nu/Nu mutation on the BALBc background and all mice analyzed were negative. We have now made this section clearer.</p><p><italic>5) How representative are the</italic> <italic>4 EPI-/- mice of genetic variation?</italic></p><p>To address this we performed SNP analysis on EPI-/- and WT mice to determine the relative contributions of the different genetic backgrounds. This showed that EPI-/- mice were primarily Sv129 (40.98%, ± 1.52) and C57Bl/6 (51.39%, ± 1.62). We therefore used F2 crosses between Sv129 and C57Bl/6 mice as the WT control (51.82%, ± 3.35 Sv129; 49.92%, ± 1.98 C57Bl/6) for all experiments, as now explained in the text. The 4 EPI-/- mice analyzed came from 4 separate breeding pairs that were used to generate the mice for the DMBA/TPA carcinogenesis experiments.</p></body></sub-article></article> |