Functional Analysis of Cancer-Associated DNA Polymerase ε Variants in Saccharomyces cerevisiae.

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Functional Analysis of Cancer-Associated DNA Polymerase ε Variants in Saccharomyces cerevisiae.

G3 (Bethesda). 2018 Jan 19;:

Authors: Barbari SR, Kane DP, Moore EA, Shcherbakova PV

Abstract
DNA replication fidelity relies on base selectivity of the replicative DNA polymerases, exonucleolytic proofreading, and post-replicative DNA mismatch repair (MMR). Ultramutated human cancers without MMR defects carry alterations in the exonuclease domain of DNA polymerase ε (Polε). They have been hypothesized to result from defective proofreading. However, modeling in yeast of the most common variant, Polε-P286R, produced an unexpectedly strong mutator effect that exceeded the effect of proofreading deficiency by two orders of magnitude and indicated the involvement of other infidelity factors. The in vivo consequences of many additional Polε mutations reported in cancers remain poorly understood. Here we genetically characterized 13 cancer-associated Polε variants in the yeast system. Only variants directly altering the DNA binding cleft in the exonuclease domain elevated mutation rate. Among these, frequently recurring variants were stronger mutators than rare variants, in agreement with the idea that mutator phenotype plays a causative role in tumorigenesis. In nearly all cases, the mutator effects exceeded those of an exonuclease-null allele, suggesting that mechanisms distinct from loss of proofreading may drive the genome instability in most ultramutated tumors. All mutator alleles were semidominant, supporting the view that heterozygosity for the polymerase mutations is sufficient for tumor development. In contrast to the DNA binding cleft alterations, peripherally located variants, including a highly recurrent V411L, did not significantly elevate mutagenesis. Finally, the analysis of Polε variants found in MMR-deficient tumors suggested that the majority cause no mutator phenotype alone but some can synergize with MMR deficiency to increase mutation rate.

PMID: 29352080 [PubMed - as supplied by publisher]

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