Abstract 3684: Differential mechanisms of green tea polyphenols-induced apoptosis in human prostate cancer cells: Role of p53.

Abstract

Abstract Tumor suppressor gene p53 is frequently inactivated in a variety of human cancers including prostate cancer and is associated with therapeutic resistance. We have previously demonstrated that green tea polyphenols (GTP) induces apoptosis in prostate cancer cells irrespective of p53 status (Carcinogenesis 33:377-84, 2012). However, the molecular mechanisms underlying these observations are not properly understood. In the present study we investigated the mechanisms of GTP-induced apoptosis in human prostate cancer cells with and without functional p53. Human prostate cancer LNCaP cells were stably transfected with short hairpin-53 (LNCaPshp53) and control vector (LNCaPshV), exposed to GTP in dose and time dependent manner. GTP exposure induced p53 stabilization and activation of downstream targets p21/waf1 and Bax in dose-dependent manner specifically in LNCaPshV cells. However, GTP-induced FAS upregulation through the activation of c-jun N-terminal kinase resulting in FADD phosphorylation, caspase-8 activation and truncation of BID leading to apoptosis was common in both LNCaPshV and LNCaPshp53 cells. In parallel, treatment of cells with GTP resulted in inhibition of survival pathway, mediated by Akt deactivation and loss of BAD phosphorylation more prominently in LNCaPshp53 cells. These distinct routes of cell death converged to a common pathway leading to loss of mitochondrial transmembrane potential, cytochrome c release and activation of terminal caspases resulting in PARP cleavage. GTP-induced apoptosis was attenuated with JNK inhibitor, SP600125 in both cell lines; whereas PI3K-Akt inhibitor, LY294002 resulted in increased cell death in LNCaPshp53 cells, establishing the role of two distinct pathways of GTP-mediated apoptosis. Furthermore, GTP exposure resulted in the inhibition of class I HDAC protein, accumulation of acetylated histone H3 in total cellular chromatin resulting in increased accessibility to bind with the promoter sequences of p21/waf1 and Bax irrespective of p53 status of cells, consistent with the effects elicited by HDAC inhibitor, trichostatin A. These results demonstrate that GTP induces prostate cancer cell death by two distinct mechanisms irrespective of p53 status, thus identifying for the first time through defined molecular targets for their chemopreventive and/or therapeutic actions. Citation Format: Karishma Gupta, Vijay S. Thakur, Natarajan Bhaskaran, Akbar Nawab, Melissa A. Babcook, Mark W. Jackson, Sanjay Gupta. Differential mechanisms of green tea polyphenols-induced apoptosis in human prostate cancer cells: Role of p53. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3684. doi:10.1158/1538-7445.AM2013-3684