title: DNA mismatch repair as an effector for promoting phorbol ester-induced apoptotic DNA damage and cell killing: implications in tumor promotion.
abstract: Phorbol ester was known to activate protein kinase C (PKC) and exert numerous cellular effects, including proliferation, apoptosis, and oncogenic transformation. How phorbol ester stimulates both apoptosis and tumor promotion is not clear. Here DNA mismatch repair (MMR)-proficient human colon cancer cells (DLD-1+Ch2; hMSH6+) treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) undergo rapid cell death, which is significantly abolished by staurosporine (PKC inhibitor) or antioxidant, compared with the paired MMR-deficient (DLD-1; hMSH6-) cells. Induction of reactive oxygen species (ROS) by TPA is shown to be one of downstream effectors required, but not sufficient, for cell killing as it is also observed in DLD-1 cells. Strikingly, DLD-1+Ch2 cells selected for resistance to TPA are found to lose the expression of hMSH6. Treatment of TPA-resistant DLD-1+Ch2 cells with 5-aza-2'-deoxycytidine, not only restores hMSH6 expression but also resensitizes TPA-resistant cells to TPA, suggesting that expression of hMSH6 is transcriptionally silenced by cytosine methylation confirmed directly by bisulfite sequencing. Knockdown hMSH6 or hPMS2 with siRNA in DLD-1+Ch2 cells resulted in more resistant to TPA-induced cell killing, further suggesting that MMR proteins involve in TPA or ROS-induced cell killing. Results suggest that deficiency in MMR could promote tumorigenesis by inhibiting apoptotic responses to ROS-mediated DNA damages as ROS are continuously produced as a byproduct of normal metabolism.
authors.affiliation: Institute of Cancer Research, National Health Research Institutes, Taipei, Taiwan, Republic of China. linct@nhri.org.tw
authors.forename: Ching-Tai
authors.initials: CT
authors.lastname: Lin
authors.forename: Wei-Hsin
authors.initials: WH
authors.lastname: Lin
authors.forename: Kuan-Der
authors.initials: KD
authors.lastname: Lee
authors.forename: Pay-Yu
authors.initials: PY
authors.lastname: Tzeng
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D020137:Base Pair Mismatch / Q000235:genetics; D045744:Cell Line, Tumor; D018899:CpG Islands; D004247:DNA / Q000235:genetics*; D004249:DNA Damage; D004260:DNA Repair / Q000187:drug effects*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D000077209:Decitabine; D006801:Humans; D008745:Methylation / Q000187:drug effects; D009369:Neoplasms / Q000235:genetics* / Q000473:pathology*; D010703:Phorbol Esters / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; D010703:Phorbol Esters; D047428:Protein Kinase Inhibitors; D017382:Reactive Oxygen Species; D000077209:Decitabine; D004247:DNA; D011493:Protein Kinase C; D001374:Azacitidine