Studies on DNA polymerases involved in repair (unscheduled) DNA synthesis in cultured human cells treated with carcinogens, such as MNNG and 4NQO

DNA polymerases involved in carcinogen-induced repair (unscheduled) DNA synthesis in HeLa and HEp-2 cells were studied by using selective inhibitors (aphidicolin, 2', 3'-dideoxythymidine-5'-triphosphate and N-ethylmaleimide) for DNA polymerases. DNA synthesis was analyzed biochemically and autoradiographically in intact cells and in permeable cells. To measure repair DNA synthesis with minimum interference of replicative DNA synthesis, carcinogens were used at the concentration inducing maximum repair DNA synthesis with each drug and also repair DNA synthesis was measured in the presence of 10 mM hydroxyurea which preferentially inhibits replicative DNA synthesis. The maximum induction of repair DNA synthesis in HeLa cells in the present assay conditions was obtained at 100-200 μg/ml (0.68-1.4 mM) of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), 10-50 μM of 4-nitroquinoline-1-oxide (4NQO), 0.5-1 mM of methyl methanesulfonate and approximately 1mM of N-methyl-N-nitrosourea (MNU). Carcinogen-induced repair DNA synthesis was partially inhibited by a polymerase α-specific inhibitor, aphidicolin. The aphidicolin-resistant unscheduled DNA synthesis in permeable cells was sensitive to 2', 3'-dideoxythymidine-5'-triphosphate which preferentially inhibits DNA polymerases β and γ. The present results indicated that both aphidicolin-sensitive and -insensitive DNA polymerases, e.g. α-DNA polymerase and a non-α-DNA polymerase (possibly DNA polymerase β) were involved in repair DNA synthesis induced by these carcinogens in human cells. The participation of α- and non-α-DNA polymerases in repair DNA synthesis was suggested to differ depending on cell types and carcinogens used for the induction of repair DNA synthesis.