PHORBOL ESTER ABROGATES UP-REGULATION OF DNA-POLYMERASE-BETA BY DNA-ALKYLATING AGENTS IN CHINESE-HAMSTER OVARY CELLS

Mammalian DNA polymerase beta (beta-pol), a DNA repair polymerase, is known to be constitutively expressed in cultured cells, but treatment of cells with the DNA-alkylating agents MNNG or methyl methanesulfonat e has been shown to up-regulate beta-pol mRNA level. To further charac terize this response, we prepared a panel of monoclonal antibodies and used one of them to quantify beta-pol in whole cell extracts by immun oblotting. We found that treatment of Chinese hamster ovary cells with either DNA-alkylating agent up-regulated the beta-pol protein level 5 -10-fold. This induction appeared to be secondary to DNA alkylation, a s induction was not observed with a genetically altered cell line over expressing the DNA repair enzyme O-6-methylguanine-methyltransferase W e also found that 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment of wild type Chinese hamster ovary cells increased expression of beta -pol protein (similar to 10-fold). Any interrelationship between this TPA response and the DNA-alkylation response was studied by treatment with combinations of MNNG and TPA. The beta-pol up-regulation observed with MNNG treatment was abrogated by TPA, and conversely the up-regul ation observed with TPA treatment was abrogated by MNNG.