hMutSβ, a heterodimer of hMSH2 and hMSH3, binds to insertion/deletion loops in DNA

Abstract

In human cells, mismatch recognition is mediated by a heterodimeric complex, hMutSalpha, comprised of two members of the MutS homolog (MSH) family of proteins, hMSH2 and GTBP [1,2]. Correspondingly, tumour-derived cell lines defective in hMSH2 and GTBP have a mutator phenotype [3,4], and extracts prepared from these cells lack mismatch-binding activity [1]. However, although hMSH2 mutant cell lines showed considerable microsatellite instability in tracts of mononucleotide and dinucleotide repeats [4,5], only mononucleotide repeats were somewhat unstable in GTBP mutants [4,6]. These findings, together with data showing that extracts of cells lacking GTBP are partially proficient in the repair of two-nucleotide loops [2], suggested that loop repair can be GTBP-independent. We show here that hMSH2 can also heterodimerize with a third human MSH family member, hMSH3, and that this complex, hMutSbeta, binds loops of one to four extrahelical bases. Our data further suggest that hMSH3 and GTBP are redundant in loop repair, and help explain why only mutations in hMSH2, and not in GTBP or hMSH3, segregate with hereditary non-polyposis colorectal cancer (HNPCC) [7].

Genetic progression in microsatellite instability high (MSI-H) colon cancers correlates with clinico-pathological parameters: A study of theTGRβRII,BAX,hMSH3,hMSH6,IGFIIR andBLM genes

“…Instead, we found that aneuploidy was significantly correlated with hMSH3 frameshifts. Although a larger series of MSI aneuploid tumors must be analyzed before reaching a definitive conclusions on this point, these results suggest a possible role for hMSH3 in the maintenance of both microsatellite (Palombo et al, 1996) and chromosomal stability.…”

Identification of hMutLβ, a Heterodimer of hMLH1 and hPMS1

“…1), while hPMS1 and hPMS2 were found mostly in the insoluble fraction (data not shown). We argued that this could be due to incorrect folding of the PMS proteins in the absence of their cognate partner, similar to the case of the MutS homologues (13). The Sf9 cultures were therefore co-infected with all the possible combinations of the three baculovirus constructs.…”

“…This hypothesis was substantiated when germline mutations in the hMSH2 and hMLH1 genes, which encode the human homologues of the Escherichia coli MMR proteins MutS and MutL, were identified in HNPCC families (6 -9). Because mutations in these two genes accounted initially for only about one half of the HNPCC kindreds (10,11), and because biochemical (12)(13)(14)(15) and genetic evidence (1, 16 -18) demonstrated that both hMSH2 and hMLH1 proteins interact with other polypeptides in vivo, an intensive search was instigated for other genes that might function in MMR. To date, six MutS homologues (hMSH1-6) and several MutL homologues (hMLH1, hPMS1, and hPMS2, as well as a cluster of PMS-like (pseudo)genes on chromosome 7) have been identified in the human genome (19).…”

“…Mismatch recognition, the initial step of the repair process, is mediated principally by a heterodimer of hMSH2 and hMSH6. This abundant complex binds both base/ base mismatches and small insertion/deletion loops (IDLs) (13) and is thus involved in the correction of misinsertions, as well as of primer/template slippage errors. However, the latter lesions are addressed also by a second heterodimer, formed by hMSH2 and hMSH3.…”

DNA Polymerase δ Is Required for Human Mismatch Repair in Vitro

“…MutS␣ (a heterodimer of MSH2 and MSH6) and MutL␣ (a heterodimer of MLH1 and PMS2) were isolated by virtue of their ability to restore strand-specific mismatch correction to nuclear extracts of repair-deficient tumor cell lines (16,18,30). In addition to its subunit function in MutS␣, MSH2 forms a molecular complex with the MutS homolog MSH3 (31,32). This MutS␤ complex binds to insertion/deletion mismatches and presumably plays a role in their processing.…”