NOTCH1 gene amplification promotes expansion of Cancer Associated Fibroblast populations in human skin. NOTCH1 gene amplification promotes expansion of Cancer Associated Fibroblast populations in human skin

Cancer associated fibroblasts (CAFs) represent a key component of the tumor microenvironment. Possible genomic alterations in these cells remain a point of contention. The skin is constantly exposed to clastogenic insults, such as UVA light that can target directly the stromal compartment, therefore representing a relevant model to study. Here we report that CAFs from skin Squamous Cell Carcinoma (SCC) lesions display chromosomal alterations, with heterogeneous levels of NOTCH1 gene amplification that also occur, to a lesser extent, in dermal fibroblasts of apparently unaffected skin. The fraction of the latter cells harboring NOTCH1 gene amplification is expanded by chronic UVA exposure, which induces a DNA damage response (DDR) to which CAFs are resistant. The selective advantage conferred by NOTCH1 gene amplification and over-expression can be explained by NOTCH1 ability to block DDR-mediated growth arrest through competitive suppression of ATM-FOXO3a association and downstream signaling cascade. These findings are of translational significance as, in an orthotopic model of skin SCC, genetic or pharmacological inhibition of NOTCH1 activity suppresses cancer / stromal cells expansion. Thus, NOTCH1 amplification and increased expression contribute to CAFs evolution and are an attractive target for preventing cancer / stromal cell expansion. Overall design: Three independent CAF strains, at the 2nd passage after tumor dissociation, were analyzed by Comparative Genomic Hybridization (CGH).