title: Human mismatch repair protein hMutLα is required to repair short slipped-DNAs of trinucleotide repeats.
abstract: Mismatch repair (MMR) is required for proper maintenance of the genome by protecting against mutations. The mismatch repair system has also been implicated as a driver of certain mutations, including disease-associated trinucleotide repeat instability. We recently revealed a requirement of hMutSβ in the repair of short slip-outs containing a single CTG repeat unit (1). The involvement of other MMR proteins in short trinucleotide repeat slip-out repair is unknown. Here we show that hMutLα is required for the highly efficient in vitro repair of single CTG repeat slip-outs, to the same degree as hMutSβ. HEK293T cell extracts, deficient in hMLH1, are unable to process single-repeat slip-outs, but are functional when complemented with hMutLα. The MMR-deficient hMLH1 mutant, T117M, which has a point mutation proximal to the ATP-binding domain, is defective in slip-out repair, further supporting a requirement for hMLH1 in the processing of short slip-outs and possibly the involvement of hMHL1 ATPase activity. Extracts of hPMS2-deficient HEC-1-A cells, which express hMLH1, hMLH3, and hPMS1, are only functional when complemented with hMutLα, indicating that neither hMutLβ nor hMutLγ is sufficient to repair short slip-outs. The resolution of clustered short slip-outs, which are poorly repaired, was partially dependent upon a functional hMutLα. The joint involvement of hMutSβ and hMutLα suggests that repeat instability may be the result of aberrant outcomes of repair attempts.
authors.affiliation: Department of Genetics and Genome Biology, The Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Gagan B
authors.initials: GB
authors.lastname: Panigrahi
authors.forename: Meghan M
authors.initials: MM
authors.lastname: Slean
authors.forename: Jodie P
authors.initials: JP
authors.lastname: Simard
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Pearson
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D004260:DNA Repair / Q000502:physiology*; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D000070957:MutL Protein Homolog 1; D000070956:MutL Proteins; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D018911:Trinucleotide Repeats / Q000502:physiology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C501486:MLH1 protein, human; C500929:MutLalpha protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; C088996:PMS1 protein, human; D000070957:MutL Protein Homolog 1; D000070956:MutL Proteins; D045643:DNA Repair Enzymes