Polk mutant mice have a spontaneous mutator phenotype

Abstract

Mice defective in the Polk gene (which encodes DNA polymerase kappa) are viable and do not manifest obvious phenotypes. The present studies document a spontaneous mutator phenotype in Polk−/− mice. The initial indication of enhanced spontaneous mutations in these mice came from the serendipitous observation of a postulated founder mutation that manifested in multiple disease states among a cohort of mice comprising all three possible Polk genotypes. Polk−/− and isogenic wild type controls carrying a reporter transgene (the λ-phage cII gene) were used for subsequent quantitative and qualitative studies on mutagenesis in various tissues. We observed significantly increased mutation frequencies in the kidney, liver, and lung of Polk−/− mice, but not in the spleen or testis. G:C base pairs dominated the mutation spectra of the kidney, liver, and lung. These results are consistent with the notion that Polκ is required for accurate translesion DNA synthesis past naturally occurring polycyclic guanine adducts, possibly generated by cholesterol and/or its metabolites.

In vivo evidence that DNA polymerase kappa is responsible for error-free bypass across DNA cross-links induced by mitomycin C

“…An increase in spontaneous mutations in Polk KO mice at 9 months and 12 months of age has been reported [34,35]. Base substitutions of G:C to T:A or G:C to C:G in liver and kidney, and G:C to A:T in lung are probably increased by intrinsic bulky DNA adducts.…”

“…In addition to TLS, Polk is reported to be involved in nucleotide excision repair [30], replication checkpoint [31], repair of single-strand breaks in DNA [32], and microsatellite stability [33]. Knockout (KO) mice of Polk are viable and exhibit more frequent spontaneous mutations in liver, lung, and kidney in aged mice [34,35]. However, it is still unclear which of the DNA lesions Polk protects cells from in vivo (the whole body system) and what roles it plays in preventing cancer induced by environmental stresses.…”

Variants of mouse DNA polymerase κ reveal a mechanism of efficient and accurate translesion synthesis past a benzo[ a ]pyrene dG adduct

“…In agreement with in vitro analyses, Polκ-deficient mouse embryonic fibroblasts (MEFs) and embryo stem cells are sensitive to killing by BP and exhibit increased BPDEinduced mutagenesis (11)(12)(13)(14). E. coli DinB can also correctly incorporate dCMP opposite some N 2 -dG adducts, including N 2 -furfuryl-dG (15) and N 2 -(1-carboxyethyl)-2′-dG (16) with greater catalytic proficiency than opposite normal dG.…”

“…It was previously shown that Polκ-deficient MEFs are abnormally sensitive to UV radiation (38,39) and BPDE treatments (13,14), and complementation with GFP-Polκ can rescue cellular hypersensitivity. We thus determined whether Polκ-deficient MEFs complemented with WT, PGM1, or PGM2 GFP fusion proteins showed altered sensitivity to BPDE treatment.…”

Mouse models of DNA polymerases

“…Burr et al measured spontaneous mutation rates at two expanded simple tandem repeat (ESTR) loci and reported that the spontaneous mutation rate of Polk 2/2 mice (129Sv*C57BL/6*BALB/c background) was higher than the wild-type Polk 1/1 mice. Stancel et al used the lambda-phage cII mutagenesis assay to determine that Polk 2/2 mice had elevated spontaneous mutagenesis in the kidney, liver, and lung [Stancel et al, 2009]. No defects in somatic hypermutation were reported in Pol j-null mice [Shimizu et al, 2003].…”