title: A cancer-associated DNA polymerase delta variant modeled in yeast causes a catastrophic increase in genomic instability.
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.
authors: Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68118, USA.
authors: Danielle L
authors: DL
authors: Daee
authors: Tony M
authors: TM
authors: Mertz
authors: Polina V
authors: PV
authors: Shcherbakova
mesh_terms: D000595:Amino Acid Sequence; D004249:DNA Damage; D004258:DNA Polymerase III / Q000235:genetics / Q000378:metabolism*; D042822:Genomic Instability; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D009369:Neoplasms / Q000201:enzymology / Q000235:genetics; D011110:Polymorphism, Genetic; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics
chemical_list: D007527:Isoenzymes; D004258:DNA Polymerase III