Genomic Instability Promoted by Overexpression of Mismatch Repair Factors in Yeast: A Model for Understanding Cancer Progression

• Published in: Genetics (Austin) Vol. 209; no. 2; pp. 439 - 456
• Main Authors: Chakraborty, Ujani, Dinh, Timothy A, Alani, Eric
• Format: Journal Article
• Language: English
• Published: United States Genetics Society of America 01.06.2018
• Subjects: Baking yeast; Cancer; Cell Cycle; Copy number; Deoxyribonucleic acid; DNA; DNA biosynthesis; DNA damage; DNA helicase; DNA methylation; DNA Mismatch Repair; DNA polymerase; DNA Replication; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; DNA-directed DNA polymerase; Gene expression; Gene Expression Regulation, Neoplastic; Gene sequencing; Genes; Genetic recombination; Genetics; Genomes; Genomic Instability; Heterozygosity; Humans; Investigations; Metastases; Mismatch repair; MMR protein; MSH2 protein; MSH6 protein; Mutation; MutS Homolog 2 Protein - genetics; MutS Homolog 2 Protein - metabolism; MutS Homolog 3 Protein - genetics; MutS Homolog 3 Protein - metabolism; Nucleotide sequence; Phenotypes; Proliferating cell nuclear antigen; Proliferating Cell Nuclear Antigen - metabolism; Prostate cancer; Protein Binding; Proteins; Recombination; RecQ Helicases - genetics; RecQ Helicases - metabolism; Repair; Replication; Saccharomyces cerevisiae; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Sequestering; Stability; Tumors; Up-Regulation; Yeast; PCNA; Msh2-Msh6 and Msh6 overexpression; Sgs1; heteroduplex rejection; DNA mismatch repair
• ISSN: 1943-2631; 0016-6731; 1943-2631
• DOI: 10.1534/genetics.118.300923

Mismatch repair (MMR) proteins act in spellchecker roles to excise misincorporation errors that occur during DNA replication. Curiously, large-scale analyses of a variety of cancers showed that increased expression of MMR proteins often correlated with tumor aggressiveness, metastasis, and early recurrence. To better understand these observations, we used The Cancer Genome Atlas and Gene Expression across Normal and Tumor tissue databases to analyze MMR protein expression in cancers. We found that the MMR genes and are overexpressed more frequently than , and that and are often cooverexpressed as a result of copy number amplifications of these genes. These observations encouraged us to test the effects of upregulating MMR protein levels in baker's yeast, where we can sensitively monitor genome instability phenotypes associated with cancer initiation and progression. Msh6 overexpression (two- to fourfold) almost completely disrupted mechanisms that prevent recombination between divergent DNA sequences by interacting with the DNA polymerase processivity clamp PCNA and by sequestering the Sgs1 helicase. Importantly, cooverexpression of Msh2 and Msh6 (∼eightfold) conferred, in a PCNA interaction-dependent manner, several genome instability phenotypes including increased mutation rate, increased sensitivity to the DNA replication inhibitor HU and the DNA-damaging agents MMS and 4-nitroquinoline N-oxide, and elevated loss-of-heterozygosity. Msh2 and Msh6 cooverexpression also altered the cell cycle distribution of exponentially growing cells, resulting in an increased fraction of unbudded cells, consistent with a larger percentage of cells in G1. These novel observations suggested that overexpression of MSH factors affected the integrity of the DNA replication fork, causing genome instability phenotypes that could be important for promoting cancer progression.