Abstract 251: Role of ß-catenin in prostate cancer cell apoptosis

Introduction: Evasion of apoptosis is a hallmark of cancer cells, and apoptotic signaling pathways are attractive targets for cancer therapy. TNF-related apoptosis inducing ligand (TRAIL) has gained much importance recently due to its ability to preferentially induce apoptosis in transformed cells and not in normal cells. Since many tumor cells develop TRAIL resistance, developing combinatorial treatment strategies to enhance TRAIL sensitivity is a major challenge of current cancer research. The reasons behind TRAIL resistance are multiple, and might be linked with aberrant activation of various oncogenic pathways. s-catenin is a well established oncogene being overexpressed in various cancers and might be involved in TRAIL resistance. Normally, it functions as a component of both the adherens junction complex and the Wnt/wingless signaling pathway. Our earlier studies have shown that treatment of cancer cells with Troglitazone (TZD), a synthetic ligand for Peroxisome Proliferator-activator receptor gamma can reduce cell proliferation and s-catenin expression. When combined with TZD, TRAIL was capable of inducing potent apoptosis in various TRAIL-resistant cancer cells. Aims: The present study was designed to determine the involvement of s-catenin during TRAIL-TZD-induced apoptosis of prostate cancer cells. Experimental procedures: Different prostate cancer cell lines (LNCaP, 22RV1, PC-3, DU145) were used to determine the effect of TRAIL-TZD on apoptosis and s-catenin pathway, utilizing Western Blots, Immunoprecipitation, and luciferase assays. Results: Treatment with a combination of TRAIL and TZD resulted in significant apoptosis (PARP, caspase-3 cleavage) and s-catenin cleavage in LNCaP but not in PC-3 and DU145 cells, and 22RV1 showed partial PARP cleavage. TRAIL-TZD-induced s-catenin cleavage was antagonized by caspase inhibitors, suggesting this to be downstream of caspase activation. Luciferase assays with s-catenin/TCF-responsive reporter indicated a significant reduction of luciferase activity with this treatment. Interestingly the cleaved s-catenin fragment retained strong interaction with E-Cadherin, as indicated by immunoprecipitation studies. Detergent fractionation of the cell extracts treated with the drug combination revealed that s-catenin cleavage was enriched in the cytosolic fraction. To understand any participation of HDACs, TRAIL treatment was performed in combination with various HDAC inhibitors. These results showed a strong increase in apoptosis and s-catenin cleavage with TRAIL and valproic acid treatment, suggesting an involvement of HDACs in this apoptotic resistance. Conclusion: These results show that targeting s-catenin signaling pathway might be effective means of increasing TRAIL sensitivity in prostate cancer, and combining TRAIL with TZD or valproic acid might be a promising treatment regimen for drug-resistant cells, especially those with aberrant s-catenin expression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 251. doi:1538-7445.AM2012-251