SUPERNATANT MEDIUM FROM UV-IRRADIATED CELLS INFLUENCES THE CYTOTOXICITY AND MUTAGENICITY OF V79 CELLS

It is known that UV light induces the secretion of some proteins into the extracellular medium. We have carried out experiments to study how the supernatant medium from UV-irradiated cells affects the cytotoxic ity and mutagenicity of V79 cells exposed to different damaging agents . So we exposed exponentially growing cells to 20 J/m(2) of UV light a nd then harvested the supernatant medium after 22 h. This supernatant medium was then used to treat a fresh batch of cells for 2 h. After th e treatment with this supernatant medium the cells were subsequently e xposed to UV light, gamma-rays, hydrogen peroxide or MNNG. We found th at exposure to this medium had a protective effect on the survival lev els for UV light, gamma-rays and hydrogen peroxide while MNNG-induced killing remained unaffected. With UV light and gamma-rays we found tha t mutation induction at all doses was increased. Cycloheximide could i nhibit this protection and the increase in mutation frequencies was al so suppressed. The results indicated a protective role for the UV-indu ced factor(s). They were probably involved directly or they triggered repair process(es) that were related to oxidative stress.