Interferon Regulatory Factor 1 Transactivates Expression of Human DNA Polymerase η in Response to Carcinogen N-Methyl-N′-nitro-N-nitrosoguanidine

DNA polymerase eta (Pol eta) implements translesion DNA synthesis but has low fidelity in replication. We have previously shown that Pol eta plays an important role in the genesis of non-targeted mutations at undamaged DNA sites in cells exposed to the carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Here, we report that MNNG-induced Pol eta expression in an interferon regulatory factor 1 (IRF1)-dependent manner in human cells. Mutagenesis analysis showed that four critical residues (Arg-82, Cys-83, Asn-86, and Ser-87) located in the IRF family conserved DNA binding domain-helix alpha 3 were involved in DNA binding and POLH transactivation by IRF1. Furthermore, Pol eta up-regulation induced by IRF1 was responsible for the increase of mutation frequency in a SupF shuttle plasmid replicated in the MNNG-exposed cells. Interestingly, IRF1 was acetylated by the histone acetyltransferase CBP in these cells. Lys -> Arg substitution revealed that Lys-78 of helix alpha 3 was the major acetylation site, and the IRF1-K78R mutation partially inhibited DNA binding and its transcriptional activity. Thus, we propose that IRF1 activation is responsible for MNNG-induced Pol eta up-regulation, which contributes to mutagenesis and ultimately carcinogenesis in cells.