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Critical roles for JNK, c‐Jun, and Fas/FasL‐Signaling in vitamin E analog‐induced apoptosis in human prostate cancer cells
Author(s) -
Jia Li,
Yu Weiping,
Wang Pei,
Li Jing,
Sanders Bob G.,
Kline Kimberly
Publication year - 2008
Publication title -
the prostate
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.295
H-Index - 123
eISSN - 1097-0045
pISSN - 0270-4137
DOI - 10.1002/pros.20716
Subject(s) - fadd , fas ligand , apoptosis , biology , lncap , signal transduction , chromatin immunoprecipitation , c jun , microbiology and biotechnology , caspase 8 , cancer research , jurkat cells , cancer cell , caspase 3 , immunology , programmed cell death , caspase , biochemistry , transcription factor , cancer , t cell , gene expression , promoter , immune system , genetics , gene
Background α‐Tocopherol ether‐linked acetic acid (α‐TEA), an analog of vitamin E (RRR‐α‐tocopherol), is a potent pro‐apoptotic agent for human cancer cells in vivo and in vitro. Methods α‐TEA‐induced apoptosis was investigated in LNCaP and PC‐3 human prostate cancer cells. Apoptosis was measured by DAPI‐staining and FACS analyses of the sub‐G1 fraction. Signaling molecules involved in apoptosis were measured by Western immunoblot analyses with or without prior immunoprecipitation, FACS analyses of cell surface membrane expression, RT‐PCR analyses of mRNA levels, and chromatin immunoprecipitation. Functional significance was determined using siRNAs, dominant negative mutant, chemical inhibitor, or neutralizing antibody. Results α‐TEA treatment increased Fas and Fas ligand mRNA and protein levels; as well as, levels of cell surface membrane Fas in both cell lines. Blockage of Fas signaling attenuated α‐TEA‐induced apoptosis. α‐TEA treatment also produced prolonged, elevated levels of activated (phosphorylated) c‐Jun N‐terminal kinase (JNK) and its substrate c‐Jun, both of which were demonstrated to be necessary for α‐TEA‐induced apoptosis. Chromatin immunoprecipitation results showed binding of c‐Jun to the promoters of both Fas and FasL in α‐TEA treated cells. Investigations of α‐TEA‐triggered apoptosis showed dual signaling from Fas with essential roles for both FADD and Daxx with FADD initiating the classical pathway mediated by caspase‐8 activation and Daxx initiating an alternate pathway involving activation of JNK, c‐Jun, and increased levels of Fas and FasL. Conclusions Collectively, data support critical roles for JNK, c‐Jun, and dual signaling from Fas/FasL via FADD and Daxx in α‐TEA‐induced apoptosis of human prostate cancer cells. Prostate 68: 427–441, 2008. © 2008 Wiley‐Liss, Inc.