The interaction of the human MutL homologues in hereditary nonpolyposis colon cancer

Germline mutations in two human mismatch repair (MMR) genes, hMSH2 and hMLH 1, appear to account for approximately 70% of the common cancer susceptibil ity syndrome hereditary nonpolyposis colorectal cancer (HNPCC). Although th e hMLH1 protein has been found to copurify with another MMR protein hPMS2 a s a heterodimer, their function in MMR is unknown. In this study, we have i dentified the physical interaction regions of both hMLH1 with hPMS2. We the n examined the effects of hMLH1 missense alterations found in HNPCC kindred s for their interaction with hPMS2. Four of these missense alterations (L57 4P, K616 Delta, R659P, and A681T) displayed >95% reduction in binding to hP MS2. Two additional missense alterations (K618A and K618T) displayed a >85% reduction in binding to hPMS2, whereas three missense alterations (S44F, V 506A, and E578G) displayed 25-65% reduction in binding to hPMS2. Interestin gly, two HNPCC missense alterations (Q542L and L582V) contained within the consensus interaction region displayed no effect on interaction with hPMS2, suggesting that they may affect other functions of hMLH1. These data confi rm that functional deficiencies in the interaction of hMLH1 with hPMS2 are associated with HNPCC as well as suggest that other unknown functional alte ration of the human MutL homologues may lead to tumorigenesis in HNPCC kind reds.