title: Both hMutSα and hMutSß DNA mismatch repair complexes participate in 5-fluorouracil cytotoxicity.
abstract: BACKGROUND
  Patients with advanced microsatellite unstable colorectal cancers do not show a survival benefit from 5-fluorouracil (5-FU)-based chemotherapy. We and others have shown that the DNA mismatch repair (MMR) complex hMutSα binds 5-FU incorporated into DNA. Although hMutSß is known to interact with interstrand crosslinks (ICLs) induced by drugs such as cisplatin and psoralen, it has not been demonstrated to interact with 5-FU incorporated into DNA. Our aim was to examine if hMutSß plays a role in 5-FU recognition.
  
  
  METHODS
  We compared the normalized growth of 5-FU treated cells containing either or both mismatch repair complexes using MTT and clonogenic assays. We utilized oligonucleotides containing 5-FU and purified baculovirus-synthesized hMutSα and hMutSß in electromobility shift assays (EMSA) and further analyzed binding using surface plasmon resonance.
  
  
  RESULTS
  MTT and clonogenic assays after 5-FU treatment demonstrated the most cytotoxicity in cells with both hMutSα and hMutSß, intermediate cytotoxicity in cells with hMutSα alone, and the least cytotoxicity in cells with hMutSß alone, hMutSß binds 5-FU-modified DNA, but its relative binding is less than the binding of 5-FU-modified DNA by hMutSα.
  
  
  CONCLUSIONS
  Cytotoxicity induced by 5-FU is dependent on intact DNA MMR, with relative cell death correlating directly with hMutSα and/or hMutSß 5-FU binding ability (hMutSα>hMutSß). The MMR complexes provide a hierarchical chemosensitivity for 5-FU cell death, and may have implications for treatment of patients with certain MMR-deficient tumors.
authors.affiliation: Division of Gastroenterology, Department of Medicine, University of California San Diego, La Jolla, California, United States of America.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Tajima
authors.forename: Moriya
authors.initials: M
authors.lastname: Iwaizumi
authors.forename: Stephanie
authors.initials: S
authors.lastname: Tseng-Rogenski
authors.forename: Betty L
authors.initials: BL
authors.lastname: Cabrera
authors.forename: John M
authors.initials: JM
authors.lastname: Carethers
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D016367:Baculoviridae / Q000235:genetics; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000188:drug therapy; D003432:Cross-Linking Reagents / Q000494:pharmacology; D053843:DNA Mismatch Repair; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology; D005472:Fluorouracil / Q000494:pharmacology*; D006801:Humans; D018895:Microsatellite Repeats / Q000235:genetics*; D009841:Oligonucleotides / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry; D020349:Surface Plasmon Resonance; D013778:Tetrazolium Salts / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D016896:Treatment Outcome
chemical_list: D000964:Antimetabolites, Antineoplastic; D000970:Antineoplastic Agents; D003432:Cross-Linking Reagents; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; D009841:Oligonucleotides; D011994:Recombinant Proteins; D013778:Tetrazolium Salts; D013844:Thiazoles; C022616:thiazolyl blue; D005472:Fluorouracil