PLATFORM SESSION 5: GROWTH FACTOR ACTION AND SIGNALING MECHANISMS
Chair: Christenson, Lane1, 1
Co-chair: Jones, Jenny1, 1
4:30 PM-6:30 PM
(36) POSSIBLE ROLE OF AKT IN X-LINKED INHIBITOR OF APOPTOSIS PROTEIN (XIAP)-MEDIATED CHEMORESISTANCE IN HUMAN OVARIAN CANCER CELLS.
Leung, Brendan3,4, Tsang, Benjamin1,2,4, 3 Dept of Biochemistry, Microbiology & Immunology, Ottawa, CA4 Ottawa Health Research Institute, Ottawa, CA1 Department of Obstetrics & Gynaecology, Ottawa, CA2 Cellular & Molecular Medicine, Ottawa, CA
ABSTRACT- The over-expression of cell survival factors has been suggested as a determinant in chemoresistance in ovarian cancer. We have previously shown that cisplatin decreases Xiap content and induce apoptosis in chemosensitive but not resistant cells, supporting the contention that chemoresistance may in part be due to the inability of the chemotherapeutic agents to down-regulate Xiap and to induce apoptosis. In addition, over-expression of constitutively active PI3-kinase or Akt in chemosensitive cells prevents apoptosis induced by chemotherapeutic agents. While Xiap up-regulation in chemosensitive cells increases Phospho-Akt (activated) content, whether Xiap-mediated chemoresistance is in part a consequence of the Xiap-induced Akt activation, is not known. In the current study, we have investigated the role of Akt in Xiap-mediated chemoresistance, using cisplatin sensitive (OV2008) and resistant (C13) ovarian cancer cells infected with adenoviral Xiap sense or antisense cDNA, LacZ (as control) and/or dominant negative Akt (Akt-DN; triple A mutant, dead kinase) and in the presence or absence of cisplatin (0-20M). Changes in cisplatin-sensitivity were assessed in terms of apoptosis, as determined by Hoescht staining. While cisplatin (10M) induced apoptosis in chemosensitive cells, and over-expression of Xiap attenuated this response, infection of chemoresistant cells with Xiap-antisense (MOI=10-40) sensitized the cells to the cytotoxic effect of cisplatin, confirming the importance of Xiap in the control of chemosensitivity. Moreover, over-expression of Akt-DN in chemosensitive cells infected with Xiap-sense (MOI=5) attenuated the chemoresistance conferred by Xiap expression in a viral load-dependent manner (MOI=0-40) and resulted in a shift of the cisplatin concentration-apoptosis response curve to the left. These findings suggest that Xiap-induced chemoresistance in ovarian cancer is mediated in part by Akt activation (Supported by CIHR).
KEY WORDS: Ovary, Apoptosis, Cell Survival Genes, Akt