Functional analysis of HNPCC-related missense mutations in MSH2

Area of Science:

• Genetics and Molecular Biology
• Cancer Research
• DNA Repair Mechanisms

Background:

• Hereditary nonpolyposis colorectal cancer (HNPCC) is linked to germline mutations in DNA mismatch repair (MMR) genes, primarily MSH2 and MLH1.
• While many HNPCC mutations cause loss-of-function through truncations, the impact of missense mutations on MMR protein function remains largely unknown.
• Understanding these missense mutations is crucial for diagnosing and managing HNPCC risk.

Purpose of the Study:

• To investigate the functional consequences of seven MSH2 missense mutations identified in HNPCC families.
• To assess the impact of these mutations on MSH2 protein activity, DNA mismatch binding, protein interactions, and cellular localization.
• To correlate observed biochemical defects with HNPCC pathogenesis.

Main Methods:

• Functional assays were performed on seven MSH2 missense mutant proteins.
• Equivalent missense mutations were introduced into Escherichia coli MutS to analyze phenotypes in a prokaryotic system.
• Assessed mismatch binding, in vivo interaction with MSH6 and EXO1, nuclear localization, and ATP-dependent mismatch release.

Main Results:

• MSH2-P622L and MSH2-C697F mutants exhibited defects in mismatch binding, interaction with MSH6/EXO1, and nuclear localization.
• The MSH2-G674R mutation, in the ATP-binding region, conferred resistance to ATP-dependent mismatch release.
• Mutations D167H and H639R showed reduced mismatch binding; an E. coli MutS mutant equivalent to MSH2-A834T was repair deficient.
• All tested MSH2 mutants, except MSH2-A305T, displayed defects in at least one critical DNA repair function.

Conclusions:

• All seven MSH2 missense mutations investigated, except MSH2-A305T, confer significant functional defects.
• These defects include impaired mismatch binding, altered ATP-dependent mismatch release, disrupted protein-protein interactions, and abnormal subcellular localization.
• The findings elucidate the molecular basis for MSH2 dysfunction in HNPCC and highlight the importance of evaluating missense mutations in MMR genes.