Abstract 1964: Role of AMP kinase in TRAIL and PPARγ ligand combination-induced apoptosis and β-catenin cleavage

Abstract

Abstract Tumor necrosis factor related apoptosis inducing ligand (TRAIL) is a promising anticancer agent that preferentially induces apoptosis in cancer cells. However, many neoplasms are resistant to TRAIL by mechanisms that are poorly understood. Previous studies from our lab indicated that combinatorial treatment with TRAIL and a synthetic ligand of peroxisome proliferator-activator receptor gamma (PPARγ) Troglitazone (TZD), can induce significant apoptosis in TRAIL-resistant cancer cells. These studies identified the serine/threonine protein kinase, AMP-activated protein kinase (AMPK) as a potential target for TRAIL-TZD-induced apoptosis in androgen independent (DU145) and androgen dependent (LNCaP) prostate cancer cells. By using prostate cancer cells overexpressing AMPKα1-dominant negative (C42-DN cells) and by siRNA-mediated knockdown of endogenous AMPKα expression in DU145 and LNCaP cells, we demonstrated that TRAIL-TZD combination-induced apoptosis was significantly attenuated in the absence of AMPKα. Mutations and overexpression of β-catenin are associated with many cancers and it is known to play important roles in androgen receptor signaling. Our earlier studies have also shown that TRAIL-TZD-combination-induced apoptosis was associated with a reduction in the expression of full length β-catenin and appearance of a cleaved β-catenin protein downstream of caspase activation. In this study we found that TRAIL-TZD-induced β-catenin cleavage also involves AMPK. Knockdown of AMPKα showed strong reduction of the cleaved β-catenin product in both cell types. Since TZD is an agonist of PPARγ, we also determined its involvement in this apoptosis pathway. Endogenous expression of PPARγ showed significant differences between DU145 and LNCaP cells, with higher level expression in the DU145 cells. Knockdown of PPARγ in DU145 cells showed a reduction of cleaved caspase 3 levels whereas cleaved caspase 8, 9 and PARP levels were largely unaffected. Luciferase assays with PPARγ-responsive reporter (PPRE-luc) didn't show significant increase in activity with TZD concentrations that was optimal for apoptosis induction. These suggested a partial involvement of PPARγ in mediating this apoptosis pathway most likely through a PPRE-independent manner. A screening with various synthetic and natural PPARγ ligands indicated 15-deoxy-Delta12-14-PGJ2 (15d-PGJ2) and TRAIL as the most potent apoptotic combination in both DU145 and LNCaP cells. This was evidenced from a very high induction of apoptotic markers (caspase cleavage) and dramatic reduction in cell viability by MTT assay when treated with TRAIL-15d-PGJ2 combination. Our studies indicate AMPK as a major mediator of TRAIL-PPARγ ligand-induced apoptosis and β-catenin cleavage, and suggest that TRAIL-15d-PGJ2 might be a very effective combination to target androgen dependent and independent prostate cancer cells. Citation Format: Sreevidya Santha, Aninda Basu, Ajay Rana, Basabi Rana. Role of AMP kinase in TRAIL and PPARγ ligand combination-induced apoptosis and β-catenin cleavage. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1964. doi:10.1158/1538-7445.AM2015-1964