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 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 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, 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.

Mammalian skin cell biology: At the interface between laboratory and clinic

“…Suprabasal epidermal expression of a6b4 integrin is a feature of human skin squamous cell carcinomas and increases susceptibility to chemically induced tumor formation in mice. Suprabasal a6b4 integrin expression stimulates secretion of pro-inflammatory molecules such as CXCL5 and M-CSF and stimulates a protumorigenic skin microenvironment by augmenting the influx of immunosuppressive granular cells during tumor promotion (46).…”

Increased Expression of Integrin α6β4 in the Basement Membrane Zone Lining the Sebaceous Glands in Hidradenitis Suppurativa

“…Finally, increased expression of α6β4 may also contribute to the development of squamous cell carcinoma (SCC), which is a well-known complication of HS (12,13). In fact, mice with aberrant α6β4 expression showed a greater infiltration of immunosuppressive cells during tumour promotion, a phenomenon that may contribute to the susceptibility of SCC formation (13).…”

The Promise of Genomics and the Development of Targeted Therapies for Cutaneous Squamous Cell Carcinoma

“…Adhesion molecules including integrins and cadherins mediate changes in cell-matrix and cell-cell interactions, respectively and are important in cSCC tumour cell migration, invasion and metastasis. Integrins link matrix proteins to the cytoskeleton in focal adhesions and changes in expression, mutation and loca-cSCC genomics lization impact on SCC development (99). Loss of kindlin-1, which binds to and activates integrin b6 subunits in hair follicle stem cells, induces skin tumours though both TGFß and wnt-b-catenin mediated mechanisms (100).…”