title: Assessing how reduced expression levels of the mismatch repair genes MLH1, MSH2, and MSH6 affect repair efficiency.
abstract: Lynch syndrome (LS), the most common familial colon cancer, is associated with mismatch repair (MMR) malfunction. As mutation carriers inherit one normal and one defected MMR gene allele, cancer risk can be considered as limited amount of normal MMR gene product. How reductions in different MMR gene expressions affect MMR capability is, however, not known. The in vitro MMR assay is a method for the pathogenicity assessment of MMR gene variants causing functional or expressional defects and thus also suitable to evaluate the effects of reduced expression of normal mRNA. Here, the assay was applied to quantify repair efficiencies of human cells retaining varying expression levels (25%/50%/75%) of the main LS susceptibility genes MLH1, MSH2, or MSH6. Compared with the shRNA knockdown control, already a 50% reduction in mRNA levels could be detected as decreased MMR function although without statistical significance in MLH1. In MSH2 and MLH1, total loss of MMR was achieved with 25% expression, whereas in MSH6 and MSH2, the repair capability decreased significantly already with 75% expression. Our results provide a preliminary indication of relative expressions required for wild-type function and suggest that the in vitro MMR assay could be used to recognize expression levels indicative of LS.
authors.affiliation: Department of Biosciences, Division of Genetics, University of Helsinki, Helsinki, Finland.
authors.forename: Minttu
authors.initials: M
authors.lastname: Kansikas
authors.forename: Mariann
authors.initials: M
authors.lastname: Kasela
authors.forename: Jukka
authors.initials: J
authors.lastname: Kantelinen
authors.forename: Minna
authors.initials: M
authors.lastname: Nyström
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D002460:Cell Line; D053843:DNA Mismatch Repair / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D015536:Down-Regulation; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D006801:Humans; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein / Q000235:genetics*; D009687:Nuclear Proteins / Q000235:genetics*; D034622:RNA Interference
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; C501486:MLH1 protein, human; D009687:Nuclear Proteins; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein
keywords: Lynch syndrome; MLH1; MSH2; MSH6; in vitro MMR assay; knockdown cells; mRNA expression; mismatch repair