title: Mismatch repair proteins are activators of toxic responses to chromium-DNA damage.
abstract: Chromium(VI) is a toxic and carcinogenic metal that causes the formation of DNA phosphate-based adducts. Cr-DNA adducts are genotoxic in human cells, although they do not block replication in vitro. Here, we report that induction of cytotoxicity in Cr(VI)-treated human colon cells and mouse embryonic fibroblasts requires the presence of all major mismatch repair (MMR) proteins. Cr-DNA adducts lost their ability to block replication of Cr-modified plasmids in human colon cells lacking MLH1 protein. The presence of functional mismatch repair caused induction of p53-independent apoptosis associated with activation of caspases 2 and 7. Processing of Cr-DNA damage by mismatch repair resulted in the extensive formation of gamma-H2AX foci in G(2) phase, indicating generation of double-stranded breaks as secondary toxic lesions. Induction of gamma-H2AX foci was observed at 6 to 12 h postexposure, which was followed by activation of apoptosis in the absence of significant G(2) arrest. Our results demonstrate that mismatch repair system triggers toxic responses to Cr-DNA backbone modifications through stress mechanisms that are significantly different from those for other forms of DNA damage. Selection for Cr(VI) resistant, MMR-deficient cells may explain the very high frequency of lung cancers with microsatellite instability among chromate workers.
authors.affiliation: Pathology and Laboratory Medicine, Brown University, 70 Ship St., Box G-E507, Providence, RI 02912, USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Peterson-Roth
authors.forename: Mindy
authors.initials: M
authors.lastname: Reynolds
authors.forename: George
authors.initials: G
authors.lastname: Quievryn
authors.forename: Anatoly
authors.initials: A
authors.lastname: Zhitkovich
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017209:Apoptosis; D020137:Base Pair Mismatch / Q000235:genetics / Q000502:physiology*; D002352:Carrier Proteins; D053143:Caspase 2; D053179:Caspase 7; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D002857:Chromium / Q000633:toxicity*; D003106:Colon / Q000166:cytology / Q000187:drug effects; D018736:DNA Adducts / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair / Q000235:genetics / Q000502:physiology; D004261:DNA Replication / Q000235:genetics / Q000502:physiology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D005347:Fibroblasts / Q000187:drug effects; D016195:G2 Phase / Q000502:physiology; D006657:Histones / Q000032:analysis / Q000378:metabolism; D006801:Humans; D051379:Mice; D000070957:MutL Protein Homolog 1; D009363:Neoplasm Proteins / Q000235:genetics / Q000502:physiology*; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism / Q000502:physiology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018736:DNA Adducts; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; C468783:H2AX protein, human; D006657:Histones; C501486:MLH1 protein, human; C501485:Mlh1 protein, mouse; C102997:Msh6 protein, mouse; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D016159:Tumor Suppressor Protein p53; D002857:Chromium; C505520:CASP7 protein, human; C505524:Casp7 protein, mouse; D053143:Caspase 2; D053179:Caspase 7; D020169:Caspases; D000070957:MutL Protein Homolog 1