RESUMO
BACKGROUND: Induction of α6ß4 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 Invα6ß4 transgenic mice, which exhibit persistent expression of α6ß4 in the suprabasal epidermal layers. However, the molecular basis for the support of SCC development by suprabasal α6ß4 is not fully understood. OBJECTIVE: We examined the relevance for suprabasal α6ß4 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 Invα6ß4 transgenic mouse model, which exhibits expression of α6ß4 integrin in the suprabasal layers of the epidermis driven by the involucrin promoter. First, we examined protein lysates from Invα6ß4 transgenic skin using a pro-inflammatory cytokine array panel. Next, we immunofluorescence labeling of murine skin sections was employed to immunophenotype tumor promoter-treated Invα6ß4 transgenic skin. Finally, a macrophage colony stimulating factor (M-CSF) neutralizing antibody strategy was administered to resolve Invα6ß4 transgenic skin inflammation. RESULTS: Employing the Invα6ß4 transgenic mouse model, we show that suprabasal α6ß4 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 Invα6ß4 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 Invα6ß4 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 Invα6ß4 mice treated with M-CSF neutralizing antibodies. CONCLUSIONS: We conclude that aberrant expression of α6ß4 integrin in post-mitotic epidermal keratinocytes stimulates a pro-tumorigenic skin microenvironment by augmenting the influx of immunosuppressive granular cells during tumor promotion.
