Background: Identification of platinum resistance is key to improving ovarian cancer treatment and patient outcomes. Although DNA excision repair proteins function to remove platinum-induced crosslinks, conflicting data raises doubt as to the utility of these proteins as biomarkers for platinum sensitivity and survival. The present differential proteomics investigation of platinum-sensitive and resistant epithelial ovarian cancer cells was undertaken to identify novel biochemical mechanisms of platinum resistance lines. Methods: Human epithelial ovarian cancer cell lines A2780 (cisplatin-sensitive), A2780cis (cisplatin-resistant), and SKOV3 (cisplatin-resistant) were cultured. Cell lysates were trypsin-digested and analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Differential protein abundances were quantified and protein associations were analyzed by Ingenuity Pathway Analysis. Western blot and real-time (rt) PCR were used for validation. The roles of select candidates in conferring cisplatin resistance were determined through silencing with small interfering (si) RNA. Results: Mre11, a protein that recognizes DNA damage and recruits BRCA1 and other proteins for homologous recombination repair, was significantly increased in platinum-resistant cells. This increased expression level of Mre11 in resistant cells was verified by rtPCR and western blot. Suppression of Mre11 protein expression in A2780cis and SKOV3 cells utilizing RNA interference resulted in sensitization of these cell lines to cisplatin. Since the promotor for Mre11 contains a consensus sequence for the tumor suppressors p63/p73, we hypothesized that p63/p73 may act to induce Mre11 expression in a cisplatin-dependent manner. Suppression of p63 or p73 with siRNA resulted in decreased Mre11 expression and sensitization of A2780cis cells to cisplatin. Conclusions: Homologous recombination repair as mediated by the Mre11 pathway represents a previously unrecognized mechanism in conferring platinum resistance in epithelial ovarian cancer cells in a p63/p73-dependent manner.
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