MLH1 expression sensitises ovarian cancer cells to cell death mediated by XIAP inhibition.

BACKGROUND: The X-linked inhibitor of apoptosis protein (XIAP), an endogenous apoptosis suppressor, can determine the level of caspase accumulation and the resultant response to apoptosis-inducing agents such as cisplatin in epithelial ovarian cancer (EOC). In addition, the mismatch repair protein, hMLH1, has been linked to DNA damage-induced apoptosis by cisplatin by both p53-dependent and -independent mechanisms. METHODS: In this study, hMLH1 expression was correlated with clinical response to platinum drugs and survival in advanced stage (III-IV) EOC patients. We then investigated whether MLH1 loss was a determinant in anti-apoptosis response to cisplatin mediated by XIAP in isogenic and established EOC cell lines with differential p53 status. RESULTS: The percentage of cells undergoing cisplatin-induced cell killing was higher in MLH1-proficient cells than in MLH1-defective cells. In addition, the presence of wild-type hMLH1 or hMLH1 re-expression significantly increased sensitivity to 6-thioguanine, a MMR-dependent agent. Cell-death response to 6-thioguanine and cisplatin was associated with significant proteolysis of MLH1, with XIAP destabilisation and increased caspase-3 activity. The siRNA-mediated inhibition of XIAP increased MLH1 proteolysis and cell death in MLH1-proficient cells but not in MLH1-defective cells. CONCLUSION: These data suggest that XIAP inhibitors may prove to be an effective means of sensitising EOC to MLH1-dependent apoptosis.

Duke Scholars

Author Zhiqing Huang Obstetrics and Gynecology, Reproductive Sciences

Author Herbert Kim Lyerly Surgery, Surgical Sciences

Author Andrew Berchuck Obstetrics and Gynecology, Gynecologic Oncology

Author Susan Kay Murphy Obstetrics and Gynecology, Reproductive Sciences

Author Gayathri R. Devi Surgery, Surgical Sciences