title: Decreased expression of the DNA mismatch repair gene Mlh1 under hypoxic stress in mammalian cells.
abstract: The hypoxic tumor microenvironment has been shown to contribute to genetic instability. As one possible mechanism for this effect, we report that expression of the DNA mismatch repair (MMR) gene Mlh1 is specifically reduced in mammalian cells under hypoxia, whereas expression of other MMR genes, including Msh2, Msh6, and Pms2, is not altered at the mRNA level. However, levels of the PMS2 protein are reduced, consistent with destabilization of PMS2 in the absence of its heterodimer partner, MLH1. The hypoxia-induced reduction in Mlh1 mRNA was prevented by the histone deacetylase inhibitor trichostatin A, suggesting that hypoxia causes decreased Mlh1 transcription via histone deacetylation. In addition, treatment of cells with the iron chelator desferrioxamine also reduced MLH1 and PMS2 levels, in keeping with low oxygen tension being the stress signal that provokes the altered MMR gene expression. Functional MMR deficiency under hypoxia was detected as induced instability of a (CA)(29) dinucleotide repeat and by increased mutagenesis in a chromosomal reporter gene. These results identify a potential new pathway of genetic instability in cancer: hypoxia-induced reduction in the expression of key MMR proteins. In addition, this stress-induced genetic instability may represent a conceptual parallel to the pathway of stationary-phase mutagenesis seen in bacteria.
authors.affiliation: Departments of Therapeutic Radiology. Genetics. Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-8040, USA.
authors.forename: Valia T
authors.initials: VT
authors.lastname: Mihaylova
authors.forename: Ranjit S
authors.initials: RS
authors.lastname: Bindra
authors.forename: Jianling
authors.initials: J
authors.lastname: Yuan
authors.forename: Denise
authors.initials: D
authors.lastname: Campisi
authors.forename: Latha
authors.initials: L
authors.lastname: Narayanan
authors.forename: Ryan
authors.initials: R
authors.lastname: Jensen
authors.forename: Frank
authors.initials: F
authors.lastname: Giordano
authors.forename: Randall S
authors.initials: RS
authors.lastname: Johnson
authors.forename: Sara
authors.initials: S
authors.lastname: Rockwell
authors.forename: Peter M
authors.initials: PM
authors.lastname: Glazer
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D020137:Base Pair Mismatch; D002352:Carrier Proteins; D015687:Cell Hypoxia / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D004260:DNA Repair / Q000235:genetics*; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D003676:Deferoxamine / Q000494:pharmacology; D018900:Dinucleotide Repeats; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D017930:Genes, Reporter; D006367:HeLa Cells / Q000166:cytology; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007502:Iron Chelating Agents / Q000494:pharmacology; D008745:Methylation; D051379:Mice; D008822:Mice, Transgenic; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D009363:Neoplasm Proteins / Q000235:genetics* / Q000378:metabolism*; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D014157:Transcription Factors / Q000187:drug effects / Q000235:genetics; D001616:beta-Galactosidase / Q000235:genetics
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; C094443:G-T mismatch-binding protein; C497442:HIF1A protein, human; D006877:Hydroxamic Acids; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007502:Iron Chelating Agents; C501486:MLH1 protein, human; C501485:Mlh1 protein, mouse; C102997:Msh6 protein, mouse; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; C012589:trichostatin A; D001616:beta-Galactosidase; D000251:Adenosine Triphosphatases; C094934:PMS2 protein, human; C499533:Pms2 protein, mouse; C497172:MSH2 protein, human; D000070976:Mismatch Repair Endonuclease PMS2; C497173:Msh2 protein, mouse; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D045643:DNA Repair Enzymes; D003676:Deferoxamine