CHARACTERIZATION OF A MAMMALIAN-CELL LINE THAT EXHIBITS SPONTANEOUS AND ULTRAVIOLET LIGHT-INDUCED HYPERMUTABILITY WHILE RETAINING RESISTANCE TO CELL-KILLING BY ULTRAVIOLET-LIGHT

Chronic exposure of V79 cells to 80 daily doses of 150 J/M(2), 290-330 -nm ultraviolet light (UVB) produced a mixed cell population that was found to be generally more resistant to cell killing by both UVB and U VC (254 nm) than the wild-type cells. Several subclones from this popu lation were studied for their survival and mutation responses and then one was chosen for further characterization based on this data. The s tudies carried out on this subclone, designated N806, show that its sp ontaneous HPRT mutation rate is approximately 10 times higher than tha t of wild-type V79 cells and it is almost three times more mutable tha n the wild-type cells when both are induced by UVB or UVC. The mutatio n responses of N806 and MI2G cells to 50-kVp X-rays are different, but the N806 cells do not appear to be hypermutable as they are with UV. N806 cells are also moderately more resistant to the cytotoxic effects of UV radiation but are more sensitive than MI2G cells when exposed t o X-rays. Assays to measure the removal of cyclobutane pyrimidine dime rs (CPDs) and the incision step of nucleotide exciscion repair have re vealed no detectable difference in the repair capacities of N806 and p arental V79 cells. These results suggest that chronic, protracted UV i rradiation may be able to induce a 'mutator phenotype' in a subpopulat ion of the progenitor cells.