Mutator phenotype of mammalian cells due to deficiency of NEIL1 DNA glycosylase, an oxidized base-specific repair enzyme

Abstract

The recently characterized NEIL1 and NEIL2 are distinct from the previously characterized mammalian DNA glycosylases (OGG1 and NTH1) involved in repair of oxidized bases because of the NEILs' preference for excising base lesions from single-stranded DNA present in bubble and fork structures. OGG1 and NTH1 are active only with duplex DNA. This raises the possibility that NEILs function in the repair of base lesions during DNA replication and/or transcription. S-phasespecific activation of only NEIL1 suggests its preferential involvement in repair during DNA replication. Here we show that antisense oligonucleotides specific for human or Chinese hamster NEIL1 decreased in vivo NEIL1 levels by 70-80%, concomitant with increased oxidative damage in the genome. Moreover, NEIL1 downregulation enhanced spontaneous mutation in the HPRT locus by about 3-fold in both Chinese hamster V79 and human bronchial A549 cell lines. The mutant frequency was further enhanced (7-to 8-fold) under oxidative stress. The majority of both spontaneous and induced mutations occurred at A•T base pairs, indicating that oxidized A and/or T are NEIL1's preferred in vivo substrates. NEIL1 thus plays a distinct and important role in repairing endogenous and induced mutagenic oxidized bases, and hence in maintaining the functional integrity of mammalian genomes.

Neil2-null Mice Accumulate Oxidized DNA Bases in the Transcriptionally Active Sequences of the Genome and Are Susceptible to Innate Inflammation

“…We also identified a polymorphic variant of NEIL2 that occurs more frequently in human lung cancer patients than in normal individuals (19). Furthermore, depletion of NEIL2 caused a significant increase in the spontaneous mutation frequency in the HPRT gene of the V79 Chinese hamster lung cell line (20). All these studies collectively indicate that NEIL2 plays an important role in maintaining genomic integrity and preventing DNA mutagenesis in mammalian cells.…”

Specific Inhibition of NEIL-initiated Repair of Oxidized Base Damage in Human Genome by Copper and Iron

“…The higher metal concentration required to cause a similar level of inhibition in cell versus in vitro may be due to metal absorption efficiency of the cells as well as their sequestering by cellular proteins. We showed earlier that NEIL1 down-regulation in mammalian cells results in elevated oxidative damage in the genome and increased spontaneous mutations (72). Further, NEILs play a vital role in repair of oxidized bases in brain cells (27).…”

Oxidative DNA damage in disease—Insights gained from base excision repair glycosylase‐deficient mouse models

“…In human studies, inactivating mutations of NEIL1 have been associated with gastric cancers [Shinmura et al, 2004]. Furthermore, cell culture studies have indicated that knock down of Neil1 renders cells more sensitive to oxidative stress, such as that induced by glucose oxidase or gamma irradiation [Rosenquist et al, 2003;Maiti et al, 2008]. NEIL1-deficient mice, although initially expected to display a promutagenic phenotype, have not been found to be significantly prone to spontaneous tumor formation, although lung adenomas and hepatocellular carcinomas have been documented in about 10-20% of aged animals [Chan et al, 2009].…”