title: Epidermal α6β4 integrin stimulates the influx of immunosuppressive cells during skin tumor promotion.
abstract: BACKGROUND
  Induction of α6β4 integrin in the differentiated epidermal cell layers in skin is a hallmark of human cutaneous squamous cell carcinoma (SCC) pathogenesis and stimulates chemically induced SCC formation in Invα6β4 transgenic mice, which exhibit persistent expression of α6β4 in the suprabasal epidermal layers. However, the molecular basis for the support of SCC development by suprabasal α6β4 is not fully understood.
  
  
  OBJECTIVE
  We examined the relevance for suprabasal α6β4 expression in the epidermis for the recruitment of immunosuppressive leukocytes during the early stages of tumor promotion.
  
  
  METHODS
  In this study, we made use of the Invα6β4 transgenic mouse model, which exhibits expression of α6β4 integrin in the suprabasal layers of the epidermis driven by the involucrin promoter. First, we examined protein lysates from Invα6β4 transgenic skin using a pro-inflammatory cytokine array panel. Next, we immunofluorescence labeling of murine skin sections was employed to immunophenotype tumor promoter-treated Invα6β4 transgenic skin. Finally, a macrophage colony stimulating factor (M-CSF) neutralizing antibody strategy was administered to resolve Invα6β4 transgenic skin inflammation.
  
  
  RESULTS
  Employing the Invα6β4 transgenic mouse model, we show that suprabasal α6β4 integrin expression selectively alters the profile of secreted pro-inflammatory molecules by epidermal cells, in particular CXCL5 and M-CSF, in response to acute tumor promoter treatment. The induction of CXCL5 and M-CSF in Invα6β4 transgenic epidermis was shortly followed by an exacerbated influx of CD200R(+) myeloid-derived suppressor cells (MDSCs), which co-expressed the M-CSF receptor, and FoxP3(+) Treg cells compared to wild-type mice. As a result, the levels of activated CD4(+) T lymphocytes were dramatically diminished in Invα6β4 transgenic compared to wild-type skin, whereas similar levels of lymphocyte activation were observed in the peripheral blood. Finally, 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced CD200R(+) infiltrative cells and epidermal proliferation were suppressed in Invα6β4 mice treated with M-CSF neutralizing antibodies.
  
  
  CONCLUSIONS
  We conclude that aberrant expression of α6β4 integrin in post-mitotic epidermal keratinocytes stimulates a pro-tumorigenic skin microenvironment by augmenting the influx of immunosuppressive granular cells during tumor promotion.
authors.affiliation: Department of Dermatology, Columbia University, College of Physicians and Surgeons, New York, NY 10032, USA.
authors.forename: Samar W
authors.initials: SW
authors.lastname: Maalouf
authors.forename: Surein
authors.initials: S
authors.lastname: Theivakumar
authors.forename: David M
authors.initials: DM
authors.lastname: Owens
mesh_terms: D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism; D002273:Carcinogens / Q000633:toxicity; D002294:Carcinoma, Squamous Cell / Q000209:etiology / Q000276:immunology* / Q000473:pathology; D054365:Chemokine CXCL5 / Q000378:metabolism; D004817:Epidermis / Q000276:immunology* / Q000473:pathology; D015870:Gene Expression; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D039161:Integrin alpha6beta4 / Q000235:genetics / Q000276:immunology*; D015603:Keratinocytes / Q000276:immunology / Q000473:pathology; D008213:Lymphocyte Activation; D016173:Macrophage Colony-Stimulating Factor / Q000037:antagonists & inhibitors / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D022423:Myeloid Cells / Q000276:immunology / Q000473:pathology; D064446:Orexin Receptors; D011956:Receptors, Cell Surface / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000276:immunology; D012878:Skin Neoplasms / Q000209:etiology / Q000276:immunology* / Q000473:pathology; D013601:T-Lymphocytes / Q000276:immunology; D050378:T-Lymphocytes, Regulatory / Q000276:immunology / Q000473:pathology; D013755:Tetradecanoylphorbol Acetate / Q000633:toxicity; D059016:Tumor Microenvironment / Q000276:immunology
chemical_list: D000954:Antigens, Surface; D002273:Carcinogens; C501103:Cd200r1 protein, mouse; D054365:Chemokine CXCL5; C094739:Cxcl5 protein, mouse; D018836:Inflammation Mediators; D039161:Integrin alpha6beta4; D064446:Orexin Receptors; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; D016173:Macrophage Colony-Stimulating Factor; D013755:Tetradecanoylphorbol Acetate