Abstract LB-151: REV1 has critical roles in base excision repair intermediate-mediated transversion mutations but not for O6-methylguanine-initiated mutations in vertebrate cells.

Abstract

Abstract Isogenic chicken DT40 cells deficient in various DNA repair pathways are a great tool for understanding the DNA damage response and mutagenesis caused by genotoxic agents by a comparison of mutants and parental DT40 cells. We recently found that ~55% of PIGO mutations are located at A:T sites with a high frequency of A to T transversion mutations in DT40 cells exposed to methyl methanesulfonate (MMS). These results suggest that A to T transversion mutations found in MMS exposure-derived PIGO mutant cells are due to base excision repair intermediates, such as abasic sites and single strand breaks originated from N3-methyladenine. It has been reported that DNA repair protein REV1 acts as not only as a deoxycytidine transferase across abasic sites but also as a scaffold protein to coordinate translesion DNA synthesis (TLS) polymerase switching. To address effects of REV1 on MMS-induced PIGO mutations in DT40 cells, we exposed REV1 knockout DT40 cells to low-dose MMS. REV1 knockout DT40 cells showed hyper-sensitivity in cell survival after MMS treatment with no increase in PIG-O mutations. These results indicate that PIG-O mutations in DT40 cells exposed to MMS are caused through REV1-dependent, but REV1 deoxycytidyl transferase-independent, TLS. In contrast to MMS, REV1 and parental DT40 cells showed similar toxicity and mutagenicity caused by a combination of low-dose N-methyl-N-nitrosourea and O6-benzylguanine. These results suggest that base excision repair intermediates appear to initiate REV1-dependent TLS, whereas, O6-methylguanine could be by-passed by replicative polymerases, such as polymerase delta complexes, with an associated increase in G to A transition mutations. Citation Format: Jun Nakamura, Xu Tian, James Swenberg. REV1 has critical roles in base excision repair intermediate-mediated transversion mutations but not for O6-methylguanine-initiated mutations in vertebrate cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-151. doi:10.1158/1538-7445.AM2013-LB-151