title: The predicted truncation from a cancer-associated variant of the MSH2 initiation codon alters activity of the MSH2-MSH6 mismatch repair complex.
abstract: Lynch syndrome (LS) is caused by germline mutations in DNA mismatch repair (MMR) genes. MMR recognizes and repairs DNA mismatches and small insertion/deletion loops. Carriers of MMR gene variants have a high risk of developing colorectal, endometrial, ovarian, and other extracolonic carcinomas. We report on an ovarian cancer patient who carries a germline MSH2 c.1A>C variant which alters the translation initiation codon. Mutations affecting the MSH2 start codon have been described previously for LS-related malignancies. However, the patients often lack a clear family history indicative of LS and their tumors often fail to display microsatellite instability, a hallmark feature of LS. Therefore, the pathogenicity of start codon variants remains undefined. Loss of the MSH2 start codon has been predicted to result in a truncated protein translated from a downstream in-frame AUG that would lack the first 25 amino acids. We therefore purified recombinant MSH2(NΔ25)-MSH6 and MSH2(NΔ25)-MSH3 to examine their DNA lesion recognition and adenosine nucleotide processing functions in vitro. We found that the MSH2(NΔ25) mutant confers distinct biochemical defects on MSH2-MSH6, but does not have a significant effect on MSH2-MSH3. We confirmed that expression of the MSH2 c.1A>C cDNA results in the production of multiple protein products in human cells that may include the truncated and full-length forms of MSH2. An in vivo MMR assay revealed a slight reduction in MMR efficiency in these cells. These data suggest that mutation of the MSH2 initiation codon, while not a strong, high-risk disease allele, may have a moderate impact on disease phenotype.
authors.affiliation: Neag Comprehensive Cancer Center and Center for Molecular Medicine, University of Connecticut Health Center, Farmington, Connecticut 06030-3101, USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Cyr
authors.forename: Graham D
authors.initials: GD
authors.lastname: Brown
authors.forename: Jennifer
authors.initials: J
authors.lastname: Stroop
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Heinen
mesh_terms: D000595:Amino Acid Sequence; D020137:Base Pair Mismatch; D001483:Base Sequence; D018387:Codon, Initiator / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005192:Family Health; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism; D051718:MutS Homolog 2 Protein / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D010051:Ovarian Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D010375:Pedigree; D011485:Protein Binding; D017434:Protein Structure, Tertiary
chemical_list: D018387:Codon, Initiator; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; D046912:Multiprotein Complexes; C497172:MSH2 protein, human; D051718:MutS Homolog 2 Protein