Title: A cancer-associated DNA polymerase delta variant modeled in yeast causes a catastrophic increase in genomic instability.
Authors: Daee, Danielle L; Mertz, Tony M; Shcherbakova, Polina V
Published In Proc Natl Acad Sci U S A, (2010 Jan 5)
Abstract: Accurate DNA synthesis by the replicative DNA polymerases alpha, delta, and epsilon is critical for genome stability in eukaryotes. In humans, over 20 SNPs were reported that result in amino-acid changes in Poldelta or Polepsilon. In addition, Poldelta variants were found in colon-cancer cell lines and in sporadic colorectal carcinomas. Using the yeast-model system, we examined the functional consequences of two cancer-associated Poldelta mutations and four polymorphisms affecting well-conserved regions of Poldelta or Polepsilon. We show that the R696W substitution in Poldelta (analog of the R689W change in the human cancer-cell line DLD-1) is lethal in haploid and homozygous diploid yeast. The cell death results from a catastrophic increase in spontaneous mutagenesis attributed to low-fidelity DNA synthesis by Poldelta-R696W. Heterozygotes survive, and the mutation rate depends on the relative expression level of wild-type versus mutant alleles. Based on these observations, we propose that the mutation rate in heterozygous human cells could be regulated by transient changes in gene expression leading to a temporary excess of Poldelta-R689W. The similarities between the mutational spectra of the yeast strains producing Poldelta-R696W and DLD-1 cells suggest that the altered Poldelta could be responsible for a significant proportion of spontaneous mutations in this cancer cell line. These results suggest that the highly error-prone Poldelta-R689W could contribute to cancer initiation and/or progression in humans.
PubMed ID: 19966286
MeSH Terms: Amino Acid Sequence; DNA Damage; DNA Polymerase III/genetics; DNA Polymerase III/metabolism*; Genomic Instability*; Humans; Isoenzymes/genetics; Isoenzymes/metabolism*; Molecular Sequence Data; Mutation; Neoplasms*/enzymology; Neoplasms*/genetics; Polymorphism, Genetic; Saccharomyces cerevisiae*/enzymology; Saccharomyces cerevisiae*/genetics