Hereditary nonpolyposis colorectal cancer (HNPCC), sometimes referred to as Lynch syndrome, is inherited in an autosomal dominant fashion, where inheritance of only one copy of a mutated mismatch repair gene is enough to cause disease phenotype. Mutations in the MSH2 gene account for 40% of genetic alterations associated with this disease and is the leading cause, together with MLH1 mutations. Mutations associated with HNPCC are broadly distributed in all domains of MSH2, and hypothetical functions of these mutations based on the crystal structure of the MutSα include protein-protein interactions, stability, allosteric regulation, MSH2-MSH6 interface, and DNA binding. Mutations in MSH2 and other mismatch repair genes cause mutations to build up over a person's life that otherwise would have been fixed when the mutation was made.
The viability of MMR genes including MSH2 can be tracked via microsatellite instability, a biomarker test that analyzes short sequence repeats which are very difficult for cells to replicate without a functioning mismatch repair system. Because these sequences vary in the population, the actual number of copies of short sequence repeats does not matter, just that the number the patient does have is consistent from tissue to tissue and over time. This phenomena occurs because these sequences are prone to mistakes by the DNA replication complex, which then need to be fixed by the mismatch repair genes. If these are not working, over time either duplications or deletions of these sequences will occur, leading to different numbers of repeats in the same patient.
71% of HNPCC patients show microsatellite instability. Detection methods for microsatellite instability include polymerase chain reaction (PCR) and immunohistochemical (IHC) methods, polymerase chain checking the DNA and immunohistochemical surveying mismatch repair protein levels. "Currently, there are evidences that universal testing for MSI starting with either IHC or PCR-based MSI testing is cost effective, sensitive, specific and is generally widely accepted."
Role in mismatch repair
In eukaryotes from yeast to humans, MSH2 dimerizes with MSH6 to form the MutSα complex, which is involved in base mismatch repair and short insertion/deletion loops. MSH2 heterodimerization stabilizes MSH6, which is not stable because of its N-terminal disordered domain. Conversely, MSH2 does not have a nuclear localization sequence (NLS), so it is believed that MSH2 and MSH6 dimerize in the cytoplasm and then are imported into the nucleus together. In the MutSα dimer, MSH6 interacts with the DNA for mismatch recognition while MSH2 provides the stability that MSH6 requires. MSH2 can be imported into the nucleus without dimerizing to MSH6, in this case, MSH2 is probably dimerized to MSH3 to form MutSβ. MSH2 has two interacting domains with MSH6 in the MutSα heterodimer, a DNA interacting domain, and an ATPase domain.
The MutSα dimer scans double stranded DNA in the nucleus, looking for mismatched bases. When the complex finds one, it repairs the mutation in an ATP dependent manner. The MSH2 domain of MutSα prefers ADP to ATP, with the MSH6 domain preferring the opposite. Studies have indicated that MutSα only scans DNA with the MSH2 domain harboring ADP, while the MSH6 domain can contain either ADP or ATP. MutSα then associates with MLH1 to repair the damaged DNA.
MutSβ is formed when MSH2 complexes with MSH3 instead of MSH6. This dimer repairs longer insertion/deletion loops than MutSα. Because of the nature of the mutations that this complex repairs, this is probably the state of MSH2 that causes the microsatellite instability phenotype. Large DNA insertions and deletions intrinsically bend the DNA double helix. The MSH2/MSH3 dimer can recognize this topology and initiate repair. The mechanism by which it recognizes mutations is different as well, because it separates the two DNA strands, which MutSα does not.
^Mellon I, Rajpal DK, Koi M, Boland CR, Champe GN (April 1996). "Transcription-coupled repair deficiency and mutations in human mismatch repair genes". Science272 (5261): 557–60. doi:10.1126/science.272.5261.557. PMID8614807.
^de Wind N, Dekker M, Berns A, Radman M, te Riele H (July 1995). "Inactivation of the mouse Msh2 gene results in mismatch repair deficiency, methylation tolerance, hyperrecombination, and predisposition to cancer". Cell82 (2): 321–30. doi:10.1016/0092-8674(95)90319-4. PMID7628020.
^Pitsikas P, Lee D, Rainbow AJ (May 2007). "Reduced host cell reactivation of oxidative DNA damage in human cells deficient in the mismatch repair gene hMSH2". Mutagenesis22 (3): 235–43. doi:10.1093/mutage/gem008. PMID17351251.
^Bonis PA, Trikalinos TA, Chung M, Chew P, Ip S, DeVine DA, Lau J (May 2007). "Hereditary nonpolyposis colorectal cancer: diagnostic strategies and their implications". Evid Rep Technol Assess (Full Rep) (150): 1–180. PMID17764220.
^Drummond JT, Li GM, Longley MJ, Modrich P (June 1995). "Isolation of an hMSH2-p160 heterodimer that restores DNA mismatch repair to tumor cells". Science268 (5219): 1909–12. doi:10.1126/science.7604264. PMID7604264.
^Christmann M, Kaina B (November 2000). "Nuclear translocation of mismatch repair proteins MSH2 and MSH6 as a response of cells to alkylating agents". J. Biol. Chem.275 (46): 36256–62. doi:10.1074/jbc.M005377200. PMID10954713.
^Edelbrock MA, Kaliyaperumal S, Williams KJ (February 2013). "Structural, molecular and cellular functions of MSH2 and MSH6 during DNA mismatch repair, damage signaling and other noncanonical activities". Mutat. Res. 743-744: 53–66. doi:10.1016/j.mrfmmm.2012.12.008. PMID23391514.
^Qiu R, DeRocco VC, Harris C, Sharma A, Hingorani MM, Erie DA, Weninger KR (May 2012). "Large conformational changes in MutS during DNA scanning, mismatch recognition and repair signalling". EMBO J.31 (11): 2528–40. doi:10.1038/emboj.2012.95. PMID22505031.
^Wang Q, Zhang H, Guerrette S, Chen J, Mazurek A, Wilson T, Slupianek A, Skorski T, Fishel R, Greene MI (August 2001). "Adenosine nucleotide modulates the physical interaction between hMSH2 and BRCA1". Oncogene20 (34): 4640–9. doi:10.1038/sj.onc.1204625. PMID11498787.
^Brown KD, Rathi A, Kamath R, Beardsley DI, Zhan Q, Mannino JL, Baskaran R (January 2003). "The mismatch repair system is required for S-phase checkpoint activation". Nat. Genet.33 (1): 80–4. doi:10.1038/ng1052. PMID12447371.
^Rasmussen LJ, Rasmussen M, Lee B, Rasmussen AK, Wilson DM, Nielsen FC, Bisgaard HC (June 2000). "Identification of factors interacting with hMSH2 in the fetal liver utilizing the yeast two-hybrid system. In vivo interaction through the C-terminal domains of hEXO1 and hMSH2 and comparative expression analysis". Mutat. Res.460 (1): 41–52. doi:10.1016/S0921-8777(00)00012-4. PMID10856833.
^Schmutte C, Marinescu RC, Sadoff MM, Guerrette S, Overhauser J, Fishel R (October 1998). "Human exonuclease I interacts with the mismatch repair protein hMSH2". Cancer Res.58 (20): 4537–42. PMID9788596.
^Schmutte C, Sadoff MM, Shim KS, Acharya S, Fishel R (August 2001). "The interaction of DNA mismatch repair proteins with human exonuclease I". J. Biol. Chem.276 (35): 33011–8. doi:10.1074/jbc.M102670200. PMID11427529.
^Mac Partlin M, Homer E, Robinson H, McCormick CJ, Crouch DH, Durant ST, Matheson EC, Hall AG, Gillespie DA, Brown R (February 2003). "Interactions of the DNA mismatch repair proteins MLH1 and MSH2 with c-MYC and MAX". Oncogene22 (6): 819–25. doi:10.1038/sj.onc.1206252. PMID12584560.
^ abBocker T, Barusevicius A, Snowden T, Rasio D, Guerrette S, Robbins D, Schmidt C, Burczak J, Croce CM, Copeland T, Kovatich AJ, Fishel R (February 1999). "hMSH5: a human MutS homologue that forms a novel heterodimer with hMSH4 and is expressed during spermatogenesis". Cancer Res.59 (4): 816–22. PMID10029069.
^Scherer SJ, Welter C, Zang KD, Dooley S (April 1996). "Specific in vitro binding of p53 to the promoter region of the human mismatch repair gene hMSH2". Biochem. Biophys. Res. Commun.221 (3): 722–8. doi:10.1006/bbrc.1996.0663. PMID8630028.
Warusavitarne J, Schnitzler M (2007). "The role of chemotherapy in microsatellite unstable (MSI-H) colorectal cancer.". International journal of colorectal disease22 (7): 739–48. doi:10.1007/s00384-006-0228-0. PMID17109103.
Wei Q, Xu X, Cheng L, et al. (1995). "Simultaneous amplification of four DNA repair genes and beta-actin in human lymphocytes by multiplex reverse transcriptase-PCR.". Cancer Res.55 (21): 5025–9. PMID7585546.
Wilson TM, Ewel A, Duguid JR, et al. (1995). "Differential cellular expression of the human MSH2 repair enzyme in small and large intestine.". Cancer Res.55 (22): 5146–50. PMID7585562.
Drummond JT, Li GM, Longley MJ, Modrich P (1995). "Isolation of an hMSH2-p160 heterodimer that restores DNA mismatch repair to tumor cells.". Science268 (5219): 1909–12. doi:10.1126/science.7604264. PMID7604264.
Kolodner RD, Hall NR, Lipford J, et al. (1995). "Structure of the human MSH2 locus and analysis of two Muir-Torre kindreds for msh2 mutations.". Genomics24 (3): 516–26. doi:10.1006/geno.1994.1661. PMID7713503.
Mary JL, Bishop T, Kolodner R, et al. (1995). "Mutational analysis of the hMSH2 gene reveals a three base pair deletion in a family predisposed to colorectal cancer development.". Hum. Mol. Genet.3 (11): 2067–9. PMID7874129.
Fishel R, Ewel A, Lescoe MK (1994). "Purified human MSH2 protein binds to DNA containing mismatched nucleotides.". Cancer Res.54 (21): 5539–42. PMID7923193.
Fishel R, Ewel A, Lee S, et al. (1994). "Binding of mismatched microsatellite DNA sequences by the human MSH2 protein.". Science266 (5189): 1403–5. doi:10.1126/science.7973733. PMID7973733.
Liu B, Parsons RE, Hamilton SR, et al. (1994). "hMSH2 mutations in hereditary nonpolyposis colorectal cancer kindreds.". Cancer Res.54 (17): 4590–4. PMID8062247.
Fishel R, Lescoe MK, Rao MR, et al. (1994). "The human mutator gene homolog MSH2 and its association with hereditary nonpolyposis colon cancer.". Cell75 (5): 1027–38. doi:10.1016/0092-8674(93)90546-3. PMID8252616.