Functional characterization of MLH1 missense variants identified in Lynch syndrome patients.

Germline mutations in the human DNA mismatch repair (MMR) genes MSH2 and MLH1 are associated with the inherited cancer disorder Lynch syndrome (LS), also known as hereditary nonpolyposis colorectal cancer or HNPCC. A proportion of MSH2 and MLH1 mutations found in suspected LS patients give rise to single amino acid substitutions. The functional consequences in regard to pathogenicity of many of these variants are unclear.

Characterization of a highly conserved binding site of Mlh1 required for exonuclease I-dependent mismatch repair.

Mlh1 is an essential factor of mismatch repair (MMR) and meiotic recombination. It interacts through its C-terminal region with MutL homologs and proteins involved in DNA repair and replication. In this study, we identified the site of yeast Mlh1 critical for the interaction with Exo1, Ntg2, and Sgs1 proteins, designated as site S2 by reference to the Mlh1/Pms1 heterodimerization site S1.

Nuclear localization of human DNA mismatch repair protein exonuclease 1 (hEXO1).

Human exonuclease 1 (hEXO1) is implicated in DNA mismatch repair (MMR) and mutations in hEXO1 may be associated with hereditary nonpolyposis colorectal cancer (HNPCC). Since the subcellular localization of MMR proteins is essential for proper MMR function, we characterized possible nuclear localization signals (NLSs) in hEXO1. Using fluorescent fusion proteins, we show that the sequence 418KRPR421, which exhibit strong homology to other monopartite NLS sequences, is responsible for correct nuclear localization of hEXO1.

Cadmium inhibits human DNA mismatch repair in vivo.

The heavy metal cadmium (Cd) is a human carcinogen that inhibits DNA repair activities. We show that DNA mismatch repair (MMR)-mediated cell cycle arrest after alkylation damage is suppressed by exposure to Cd and that this effect is reversed by preincubation with excess of zinc (Zn). We show that Cd-mediated inactivation of MMR activity is not caused by disruption of complex formation between the MMR proteins hEXO1-hMutS alpha and hEXO1-hMutL alpha nor does Cd inhibit 5'-exonuclease activity of hEXO1 in vitro.