TRANSGENIC GPT(-LINES DIFFER IN THEIR MUTAGENIC RESPONSE TO CLASTOGENS() V79 CELL)

Several gpt(+) transgenic cell lines were derived from hprt(-) V79 cel ls to study mutagenesis mechanisms in mammalian eels. The G12 cell lin e was previously shown to be hypermutable by X-rays and UV at the gpt locus compared to the endogenous hprt gene of the parental V79 cells ( Klein and Rossman, 1990), and is now shown to be highly mutable by the clastogenic anti-tumor agent bleomycin sulfate. A second transgenic c ell line G10, which has a different gpt insertion site, was studied in comparison with G12. Both G12 and G10 cell lines carry the stable gpt locus at a single integration site in the Chinese hamster genome, and neither spontaneously deletes the integrated gpt sequence at a high f requency. Although spontaneous mutation to 6-thioguanine resistance in G10 cells is 3-4 times higher than in G12 cells, the cell lines diffe r to a much greater extent when mutated by clastogens. In comparison t o G12 cells, the gpt locus in G10 cells is up to 13 times more sensiti ve to bleomycin mutagenesis and 5 times more responsive to X-ray mutag enesis. In contrast, there is much less difference in UV-induced mutag enesis and no differences in mutagenesis induced by alkylating agents such as N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). The dose-dependen t decrease in survival of the transgenic cells is the same for all mut agens tested, and does not differ from that of V79 cells. Neither tran sgenic cell line is generally hypermutable, since mutagenesis at an en dogenous gene, Na+K+/ATPase, is similar to that of the parental V79 ce ll line. Although both cell lines can be induced to delete the transge ne following clastogen exposure, deletions are not the only recovered mutations, and the cell lines can also be used to study mutations with in the PCR recoverable gpt gene. The utility of these transgenic cells to investigate genome position effects related to mammalian mutagenes is mechanisms is discussed.