Abstract

The DNA alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) upregulates the level of the base excision DNA repair enzyme DNA polymerase β (β-pol) in several mammalian cell types. Previous studies suggested that β-pol expression is upregulated via a transcriptional mechanism that requires: the specific cAMP response element (CRE) in the β-pol core promoter; a phosphorylated form of CREbinding protein-1 (CREB-1); and cellular protein kinase A activity. A large family of CRE-binding proteins, i.e., the ATF/CREB factors, has been identified in various cell types. This study further examines the role of CREbinding proteins in regulating β-pol expression through study of Chinese hamster ovary (CHO) cells. In CHO cell nuclear extract, CREB-1 and ATF-1 are the predominant CRE-binding protein family members recognizing the CRE in the β-pol core promoter. The concentration of CREB-1 increases strongly in CHO cells after exposure to MNNG. In contrast, the level of ATF-1 does not change after MNNG treatment. Recombinant expression of CREB-1 in CHO cells is sufficient to increase expression of the endogenous β-pol gene, even in the absence of MNNG exposure. These results indicate that β-pol gene expression in CHO cells can be upregulated by CREB-1 and that the activation of β-pol gene expression in response to DNA alkylating agent exposure involves a strong increase in the level of CREB-1.