Human mismatch repair protein hMutLα is required to repair short slipped-DNAs of trinucleotide repeats

J Biol Chem. 2012 Dec 7;287(50):41844-50. doi: 10.1074/jbc.M112.420398. Epub 2012 Oct 18.

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism
  • DNA Repair / physiology*
  • DNA Repair Enzymes / genetics
  • DNA Repair Enzymes / metabolism*
  • HEK293 Cells
  • Humans
  • MutL Protein Homolog 1
  • MutL Proteins
  • Neoplasm Proteins / genetics
  • Neoplasm Proteins / metabolism
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism
  • Point Mutation
  • Protein Structure, Tertiary
  • Trinucleotide Repeats / physiology*

Substances

  • Adaptor Proteins, Signal Transducing
  • MLH1 protein, human
  • MutLalpha protein, human
  • Neoplasm Proteins
  • Nuclear Proteins
  • PMS1 protein, human
  • MutL Protein Homolog 1
  • MutL Proteins
  • DNA Repair Enzymes