title: MSH3 mismatch repair protein regulates sensitivity to cytotoxic drugs and a histone deacetylase inhibitor in human colon carcinoma cells.
abstract: BACKGROUND
  MSH3 is a DNA mismatch repair (MMR) gene that undergoes frequent somatic mutation in colorectal cancers (CRCs) with MMR deficiency. MSH3, together with MSH2, forms the MutSβ heteroduplex that interacts with interstrand cross-links induced by drugs such as cisplatin. To date, the impact of MSH3 on chemosensitivity is unknown.
  
  
  METHODS
  We utilized isogenic HCT116 (MLH1-/MSH3-) cells where MLH1 is restored by transfer of chromosome 3 (HCT116+ch3) and also MSH3 by chromosome 5 (HCT116+3+5). We generated HCT116+3+5, SW480 (MLH1+/MSH3+) and SW48 (MLH1-/MSH3+) cells with shRNA knockdown of MSH3. Cells were treated with 5-fluorouracil (5-FU), SN-38, oxaliplatin, or the histone deacetylase (HDAC) inhibitor PCI-24781 and cell viability, clonogenic survival, DNA damage and apoptosis were analyzed.
  
  
  RESULTS
  MSH3-deficient vs proficient CRC cells showed increased sensitivity to the irinotecan metabolite SN-38 and to oxaliplatin, but not 5-FU, as shown in assays for apoptosis and clonogenic survival. In contrast, suppression of MLH1 attenuated the cytotoxic effect of 5-FU, but did not alter sensitivity to SN-38 or oxaliplatin. The impact of MSH3 knockdown on chemosensitivity to SN-38 and oxaliplatin was maintained independent of MLH1 status. In MSH3-deficient vs proficient cells, SN-38 and oxaliplatin induced higher levels of phosphorylated histone H2AX and Chk2, and similar results were found in MLH1-proficient SW480 cells. MSH3-deficient vs proficient cells showed increased 53BP1 nuclear foci after irradiation, suggesting that MSH3 can regulate DNA double strand break (DSB) repair. We then utilized PCI-24781 that interferes with homologous recombination (HR) indicated by a reduction in Rad51 expression. The addition of PCI-24781 to oxaliplatin enhanced cytotoxicity to a greater extent compared to either drug alone.
  
  
  CONCLUSIONS
  MSH3 status can regulate the DNA damage response and extent of apoptosis induced by chemotherapy. The ability of MSH3 to regulate chemosensitivity was independent of MLH1 status. PCI-24781-mediated impairment of HR enhanced oxaliplatin sensitivity, suggesting that reduced DSB repair capacity may be contributory.
authors.affiliation: Mayo Clinic and Mayo Cancer Center, Rochester, Minnesota, United States of America.
authors.forename: Jae Myung
authors.initials: JM
authors.lastname: Park
authors.forename: Shengbing
authors.initials: S
authors.lastname: Huang
authors.forename: David
authors.initials: D
authors.lastname: Tougeron
authors.forename: Frank A
authors.initials: FA
authors.lastname: Sinicrope
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use*; D001572:Benzofurans / Q000494:pharmacology; D002166:Camptothecin / Q000031:analogs & derivatives / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000473:pathology*; D004249:DNA Damage; D053843:DNA Mismatch Repair / Q000187:drug effects*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004354:Drug Screening Assays, Antitumor; D005455:Fluorescent Antibody Technique; D005472:Fluorouracil / Q000494:pharmacology; D055785:Gene Knockdown Techniques; D045325:HCT116 Cells; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D000077146:Irinotecan; D000070957:MutL Protein Homolog 1; D000074081:MutS Homolog 3 Protein; D009687:Nuclear Proteins / Q000378:metabolism; D009944:Organoplatinum Compounds / Q000494:pharmacology; D000077150:Oxaliplatin; D051135:Rad51 Recombinase / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000970:Antineoplastic Agents; D001572:Benzofurans; D004268:DNA-Binding Proteins; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; C501486:MLH1 protein, human; C078444:MSH3 protein, human; D000074081:MutS Homolog 3 Protein; D009687:Nuclear Proteins; D009944:Organoplatinum Compounds; D000077150:Oxaliplatin; D000077146:Irinotecan; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D000070957:MutL Protein Homolog 1; C512352:abexinostat; D005472:Fluorouracil; D002166:Camptothecin