The epidermis is the site of the first and second most common cancers in the U.S., basal cell carcinoma and squamous cell carcinoma (SCC). Human tumor samples and mouse models of SCC induction show a correlation between upregulation of basement membrane proteins and tumor progression. The medical relevance of murine studies of SCC, however, is limited by major differences between mouse and human skin and by greater ease of transformation of murine tissues. While the importance of cell-matrix interactions in tumor initiation and growth is well-appreciated, no studies have yet addressed the need for specific stromal elements and their cellular receptors in this process. Their our lab's recent evidence that integrin and its ligand laminin 5 are required for SCC development implies that hemidesmosome-mediated adhesion may potentiate tumorigenesis. The overall goal of this proposal is to determine the role of specific epidermal matrix components in promoting human epidermal tumor formation. First, the roles of Type XVII collagen (BP180, BPAG2) and Type VII collagen, which interact with integrin alpha6beta4 and laminin 5, will be examined. Primary keratinocytes deficient in collagen XVII and collagen VII from patients with the inherited skin disease epidermolysis bullosa (EB) will be used to assess the tumor formation potential of deficient cells as compared to cells with restored protein expression. Corrected and uncorrected cells will be transduced with Ras and other retrovectors and assayed for their ability to support subcutaneous tumor growth. Additional studies will assess the effect of laminin 5 ablation on the continued growth of epidermal tumors. Laminin 5 blocking antibodies will be tested for their ability to inhibit growth of established Ras-induced tumors. Furthermore, a genetic approach will be used in which Cre recombinase inducibly removes retrovirally restored laminin 5 eDNA from EB cells within a growing Ras-induced epidermal tumor. These studies provide an initial evaluation of matrix components involved in the establishment and growth of tumors. Subsequent explorations that include delineation of specific functional domains within the matrix proteins found to enhance tumor growth may provide potential targets for therapeutic interference with SCC progression. At the end of the funding period, they hope to have defined the functional importance of epidermal matrix components in invasive human epidermal neoplasia.
