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-11Ch2; hMSH6 1 ) 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 2 ) 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-11Ch2 cells selected for resistance to TPA are found to lose the expression of hMSH6. Treatment of TPA-resistant DLD-11Ch2 cells with 5-aza-2 0 -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-11Ch2 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. ' 2006 Wiley-Liss, Inc.

Potentiation of reactive oxygen species is a marker for synergistic cytotoxicity of MS-275 and 5-azacytidine in leukemic cells

“…Together with previous data demonstrating that N-acetyl-cysteine (NAC), a general oxidant, blocks DNA fragmentation by MS-275 in leukemia cells (20), this finding suggests that the intracellular oxidative environment may dictate sensitivity to HDACi containing regimens. NAC's action as an antioxidant is thought to be due to heightened GSH levels, so our data is consistent with the notion that high intracellular GSH may be a determinant of HDACi sensitivity.…”

“…In addition, given data from several groups indicating that MS-275 as a single agent or combined with other anti-tumor agents generates reactive oxygen species (ROS) in certain tumor cell lines (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32), the potentiation of ROS with the combined exposure was studied. Our findings show that the production of ROS in AML and ALL cells is an indicator for the synergistic, cytotoxic effects of MS-275 and 5-azacytidine.…”

Induction of Prdx1 and Prdx6 in Liver Cells by Serum and TPA

“…Although the mechanism by which it elicits these two effects is unclear, the requirement of ROS in TPA-induced toxicity has been demonstrated (Lin et al, 2006). Induction of Prdx1 by TPA in H2.35 cells is not surprising given a prior study reporting Prdx1 induction by TPA in rat liver tissue macrophages and monocytic cells through a PKC/Ras/p38MAPK pathway (Hess et al, 2003).…”

Evaluation of anticancer activity of Cordia dichotoma leaves against a human prostate carcinoma cell line, PC3

“…Deficient DNA repair or DNA damage by it is reported to have a prognostic or etiological role in cancer, the disease which is one of the leading causes of death 2, 3. Chemotherapy is an important choice for the cancer management clinically apart from the utilities of irradiation and surgical operations.…”