title: Acidic tumor microenvironment downregulates hMLH1 but does not diminish 5-fluorouracil chemosensitivity.
abstract: Human DNA mismatch repair (MMR) recognizes and binds 5-fluorouracil (5FU) incorporated into DNA and triggers a MMR-dependent cell death. Absence of MMR in a patient's colorectal tumor abrogates 5FU's beneficial effects on survival. Changes in the tumor microenvironment like low extracellular pH (pHe) may diminish DNA repair, increasing genomic instability. Here, we explored if low pHe modifies MMR recognition of 5FU, as 5FU can exist in ionized and non-ionized forms depending on pH. We demonstrate that MMR-proficient cells at low pHe show downregulation of hMLH1, whereas expression of TDG and MBD4, known DNA glycosylases for base excision repair (BER) that can remove 5FU from DNA, were unchanged. We show in vitro that 5FU within DNA pairs with adenine (A) at high and low pH (in absence of MMR and BER). Surprisingly, 5FdU:G was repaired to C:G in hMLH1-deficient cells cultured at both low and normal pHe, similar to MMR-proficient cells. Moreover, both hMSH6 and hMSH3, components of hMutSα and hMutSβ, respectively, bound 5FU within DNA (hMSH6>hMSH3) but is influenced by hMLH1. We conclude that an acidic tumor microenvironment triggers downregulation of hMLH1, potentially removing the execution component of MMR for 5FU cytotoxicity, whereas other mechanisms remain stable to implement overall 5FU sensitivity.
authors: Division of Gastroenterology, Department of Internal Medicine, University of Michigan, Ann Arbor, MI, United States.
authors: Moriya
authors: M
authors: Iwaizumi
authors: Stephanie
authors: S
authors: Tseng-Rogenski
authors: John M
authors: JM
authors: Carethers
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000096:biosynthesis* / Q000172:deficiency / Q000235:genetics; D000225:Adenine / Q000737:chemistry; D000230:Adenocarcinoma / Q000235:genetics / Q000473:pathology*; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D020029:Base Pairing; D045744:Cell Line, Tumor / Q000187:drug effects / Q000378:metabolism; D015179:Colorectal Neoplasms / Q000235:genetics / Q000473:pathology*; D053843:DNA Mismatch Repair; D004260:DNA Repair; D004273:DNA, Neoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D005467:Floxuridine / Q000378:metabolism; D005472:Fluorouracil / Q000494:pharmacology*; D006147:Guanine / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein / Q000378:metabolism; D000074081:MutS Homolog 3 Protein; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000172:deficiency / Q000235:genetics; D009687:Nuclear Proteins / Q000096:biosynthesis* / Q000172:deficiency / Q000235:genetics; D009690:Nucleic Acid Conformation; D059016:Tumor Microenvironment
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000964:Antimetabolites, Antineoplastic; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; C501486:MLH1 protein, human; C078444:MSH3 protein, human; D000074081:MutS Homolog 3 Protein; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D005467:Floxuridine; D006147:Guanine; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D000225:Adenine; D005472:Fluorouracil
references: Nat Rev Cancer. 2011 Aug 11;11(9):671-7
references: 21833026
references: J Clin Oncol. 2010 Jul 10;28(20):3219-26
references: 20498393
references: Cancer Biol Ther. 2011 Oct 15;12(8):756-64
references: 21814034
references: PLoS Biol. 2009 Apr 28;7(4):e91
references: 19402749
references: Gastroenterology. 2004 Feb;126(2):394-401
references: 14762775
references: Proc Natl Acad Sci U S A. 1980 Dec;77(12):7380-4
references: 6261253
references: Mol Cell Biol. 2004 Oct;24(19):8504-18
references: 15367671
references: Trends Biochem Sci. 1999 Feb;24(2):68-72
references: 10098401
references: Science. 1956 Feb 24;123(3191):309-14
references: 13298683
references: Proc Natl Acad Sci U S A. 1996 Jun 25;93(13):6443-7
references: 8692834
references: Cancer Res. 2000 Aug 15;60(16):4372-6
references: 10969780
references: J Biol Chem. 1998 Jul 31;273(31):19895-901
references: 9677427
references: Curr Biol. 1996 Sep 1;6(9):1185-7
references: 8805366
references: Cancer Res. 2004 Jan 15;64(2):517-22
references: 14744764
references: Gastroenterology. 2004 Dec;127(6):1678-84
references: 15578504
references: J Biol Chem. 2011 Apr 8;286(14):12157-65
references: 21285347
references: J Physiol. 2007 Dec 1;585(Pt 2):351-60
references: 17916606
references: Cancer Res. 2001 Nov 1;61(21):7934-42
references: 11691815
references: Mol Biol Cell. 2005 Mar;16(3):1513-26
references: 15647386
references: Gastroenterology. 1999 Jul;117(1):123-31
references: 10381918
references: J Clin Oncol. 1998 Jan;16(1):301-8
references: 9440757
references: J Biol Chem. 1988 Oct 15;263(29):14794-801
references: 3170564
references: Cell. 1980 Nov;22(1 Pt 1):309-17
references: 6253083
references: Genetics. 1998 Apr;148(4):1637-46
references: 9560383
references: J Biol Chem. 1996 Mar 29;271(13):7285-8
references: 8631743
references: J Clin Oncol. 1989 Oct;7(10):1447-56
references: 2778478
references: Cancer Cell. 2004 Aug;6(2):139-50
references: 15324697
references: Proc Natl Acad Sci U S A. 2003 Dec 23;100(26):15387-92
references: 14657349
references: Nucleic Acids Res. 2003 May 1;31(9):2261-71
references: 12711670
references: Nat Genet. 1999 Nov;23(3):359-62
references: 10545954
references: Nat Rev Clin Oncol. 2010 Apr;7(4):197-208
references: 20177404
references: Mol Cell. 2005 Mar 18;17(6):793-803
references: 15780936
references: J Biol Chem. 1998 Nov 27;273(48):32049-54
references: 9822679
references: Ann Intern Med. 1995 Mar 1;122(5):321-6
references: 7847642
references: Gastroenterology. 2000 Feb;118(2 Suppl 1):S115-28
references: 10868902
references: PLoS One. 2011;6(12):e28117
references: 22164234
references: J Biol Chem. 1999 Sep 17;274(38):26668-82
references: 10480869
references: N Engl J Med. 1990 Feb 8;322(6):352-8
references: 2300087
references: J Biol Chem. 2005 Feb 18;280(7):5516-26
references: 15611052
references: Mol Cell Biol. 2003 May;23(9):3265-73
references: 12697826
references: N Engl J Med. 2003 Jul 17;349(3):247-57
references: 12867608
references: J Magn Reson Imaging. 2002 Oct;16(4):430-50
references: 12353258
references: J Natl Cancer Inst. 2007 Oct 3;99(19):1441-54
references: 17895480
references: Mutat Res. 2005 Jan 6;569(1-2):75-85
references: 15603753
references: Eur J Cancer. 2009 Feb;45(3):365-73
references: 18722765
references: Semin Radiat Oncol. 2004 Jul;14(3):198-206
references: 15254862
references: Cancer Res. 1989 Aug 15;49(16):4373-84
references: 2545340
references: Gastroenterology. 2007 Dec;133(6):1858-68
references: 18054558
references: Br J Pharmacol. 2009 Oct;158(3):679-92
references: 19775280
references: J Med Chem. 1980 Feb;23(2):103-11
references: 6987403
references: Cancer Res. 2009 Sep 15;69(18):7285-93
references: 19723658
references: Oncogene. 2003 Oct 16;22(46):7130-6
references: 14562041
references: J Biol Chem. 2000 Oct 20;275(42):32422-9
references: 10930409
references: Proc Natl Acad Sci U S A. 1996 Nov 26;93(24):13629-34
references: 8942985
references: FASEB J. 2010 Oct;24(10):3903-15
references: 20547664
references: Nucleic Acids Res. 2009 Jul;37(13):4420-9
references: 19468048
references: Nat Med. 1997 Feb;3(2):177-82
references: 9018236
references: Nature. 2008 Jun 12;453(7197):940-3
references: 18509335