UV radiation promotes melanoma dissemination mediated by the sequential reaction axis of cathepsins-TGF-beta 1-FAP-alpha

Background: Ultraviolet radiation (UVR) is the major risk factor for development of malignant melanoma. Fibroblast activation protein (FAP)-alpha is a serine protease expressed on the surface of activated fibroblasts, promoting tumour invasion through extracellular matrix (ECM) degradation. The signalling mechanism behind the upregulation of FAP-alpha is not yet completely revealed. Methods: Expression of FAP-alpha was analysed after UVR exposure in in vitro co-culture systems, gene expression arrays and artificial skin constructs. Cell migration and invasion was studied in relation to cathepsin activity and secretion of transforming growth factor (TGF)-beta 1. Results: Fibroblast activation protein-a expression was induced by UVR in melanocytes of human skin. The FAP-alpha expression was regulated by UVR-induced release of TGF-beta 1 and cathepsin inhibitors prevented such secretion. In melanoma cell culture models and in a xenograft tumour model of zebrafish embryos, FAP-alpha mediated ECM degradation and facilitated tumour cell dissemination. Conclusions: Our results provide evidence for a sequential reaction axis from UVR via cathepsins, TGF-beta 1 and FAP-alpha expression, promoting cancer cell dissemination and melanoma metastatic spread.Funding Agencies|Swedish Research Council; Welander-Finsen Foundation; Ostgotaregionens Cancer Foundation; Swedish Cancer Society; County Council of Ostergotland; Olle Engkvist Foundation