545 Shedding of collagen XVII accelerates tumor growth and invasion in skin carcinogenesis

Collagen XVII (ColXVII) is an important epithelial anchorage molecule in the skin that is highly upregulated in several epithelial cancers during dysplasia-to-cancer transformation. Since ColXVII ectodomain is proteolytically released from the cell surface, we employed ectodomain selective antibodies to visualize ColXVII shedding in human squamous cell carcinomas (SCCs). ColXVII ectodomain was mainly located at the invasive front of SCCs, suggesting important functions in tumor progression. To investigate the role of ColXVII expression and shedding in skin carcinogenesis, we knocked down ColXVII in SCC-cell lines (Kd) using a viral shRNA approach. Loss of ColXVII in these cells resulted in dramatically decreased clonal growth capacity and invasiveness in vitro, as well as significantly reduced growth of SCC-25 xenografts in immunodeficient mice. Re-expression of wild-type full-length ColXVII in Kd cells fully restored matrix independent cell growth and matrigel invasion, while re-expression of a non-sheddable ColXVII mutant did not, indicating that both processes are modulated by ColXVII shedding. Moreover, specific blockage of shedding by monoclonal ColXVII antibodies repressed matrix-independent growth and invasion of SCC cells in organotypic co-cultures. Besides releasing an ectodomain, ColXVII shedding also generates a membrane-anchored endodomain. To explore their functions in cancer growth and invasion we either introduced the ectodomain (Ecto) or the endodomain (Endo) in Kd cells via retroviral transduction. Our data suggest that both domains have distinct functions during tumor progression: Endo selectively promotes clonal growth capacity, while Ecto mainly supports invasiveness. These results indicate that ColXVII shedding promotes proliferation and motility in SCCs. Thus, selective inhibition of ColXVII shedding may offer a therapeutic strategy to delay carcinoma progression.