Effect of ultraviolet light, methyl methanesulfonate and ionizing radiation on the genotoxic response and apoptosis of mouse fibroblasts lacking c-Fos, p53 or both

c-Fos and p53 are DNA damage-inducible proteins that are involved in gene r egulation, cell cycle checkpoint control and cell proliferation following e xposure to genotoxic agents. To investigate comparatively the role of c-Fos and p53 in the maintenance of genomic stability and the induction of apopt osis, we generated mouse fibroblast cell lines from knockout mice deficient for either c-fos (fos-/-) or p53 (p53-/-) or for both gene products (fosp5 3-/-), The sensitivity of these established cell lines was compared with th e corresponding wild-type cells as to the cytotoxic, clastogenic and apopto sis-inducing effects of ultraviolet (UV-C) light and methyl methanesulfonat e (MMS). Additionally, we analysed the frequency of apoptosis of the cell l ines after treatment with ionizing radiation (IR), We observed c-fos-/-, p5 3-/- and fosp53-/- cells to be more sensitive than wild-type cells with res pect to cell death, as measured in a cytotoxicity (MTT) assay. Regarding ap optosis, all deficient cell lines displayed hypersensitivity to UV-C light, MMS and IR, With chromosomal aberrations as the endpoint, the sensitivity of the double-knockout cells was between wild-type and single-knockouts. Th e results indicate that both c-Fos and p53 play an important role in protec ting fibroblasts against a broad range of genotoxic agents. The results als o show that, in fibroblasts, apoptosis induced by UV-C light, MMS and IR do es not require p53 and that, in this cell type, p53 rather protects against DNA damage-induced apoptotic cell death.