Cadmium inhibits the functions of eukaryotic MutS complexes.
Exposure of yeast cells to low concentrations of cadmium results in elevated mutation rates due to loss of mismatch repair (MMR), and cadmium inhibits MMR activity in extracts of human cells. Here we show that cadmium inhibits both Msh2-Msh6- and Msh2-Msh3-dependent human MMR activity in vitro. This inhibition, which occurs at a step or steps preceding repair DNA synthesis, is observed for repair directed by either a 3' or a 5' nick. In an attempt to identify the protein target(s) of cadmium inhibition, we show that cadmium inhibition of MMR is not reversed by addition of zinc to the repair reaction, suggesting that the target is not a zinc metalloprotein. We then show that cadmium inhibits ATP hydrolysis by yeast Msh2-Msh6 but has no effect on ATPase hydrolysis by yeast Mlh1-Pms1. Steady state kinetic analysis with wild type Msh2-Msh6, and with heterodimers containing subunit-specific Glu to Ala replacements inferred to inactivate the ATPase activity of either Msh2 or Msh6, suggest that cadmium inhibits ATP hydrolysis by Msh6 but not Msh2. Cadmium also reduces DNA binding by Msh2-Msh6 and more so for mismatched than matched duplexes. These data indicate that eukaryotic Msh2-Msh3 and Msh2-Msh6 complexes are targets for inhibition of MMR by cadmium, a human lung carcinogen that is ubiquitous in the environment.
Clark
Alan B
AB
Laboratory of Molecular Genetics, NIEHS, Research Triangle Park, North Carolina 27709, USA.
Kunkel
Thomas A
TA
D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors; D000255:Adenosine Triphosphate / Q000378:metabolism; D020137:Base Pair Mismatch; D002104:Cadmium / Q000494:pharmacology*; D019256:Cadmium Chloride / Q000494:pharmacology; D002413:Cations, Divalent; D004247:DNA / Q000378:metabolism; D004260:DNA Repair / Q000187:drug effects*; D004261:DNA Replication / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D005057:Eukaryotic Cells; D005656:Fungal Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D051718:MutS Homolog 2 Protein; D000074081:MutS Homolog 3 Protein; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D015032:Zinc / Q000494:pharmacology
D002413:Cations, Divalent; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C094443:G-T mismatch-binding protein; C078444:MSH3 protein, human; C098790:MSH6 protein, S cerevisiae; D000074081:MutS Homolog 3 Protein; D011518:Proto-Oncogene Proteins; D029701:Saccharomyces cerevisiae Proteins; D002104:Cadmium; D000255:Adenosine Triphosphate; D004247:DNA; D000251:Adenosine Triphosphatases; C489751:MSH2 protein, S cerevisiae; C497172:MSH2 protein, human; D051718:MutS Homolog 2 Protein; D015032:Zinc; D019256:Cadmium Chloride