Critical roles for JNK, c-Jun, and Fas/FasL-Signaling in vitamin E analog-induced apoptosis in human prostate cancer cells.
BACKGROUND
Alpha-tocopherol ether-linked acetic acid (alpha-TEA), an analog of vitamin E (RRR-alpha-tocopherol), is a potent pro-apoptotic agent for human cancer cells in vivo and in vitro.


METHODS
alpha-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
Alpha-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 alpha-TEA-induced apoptosis. alpha-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 alpha-TEA-induced apoptosis. Chromatin immunoprecipitation results showed binding of c-Jun to the promoters of both Fas and FasL in alpha-TEA treated cells. Investigations of alpha-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 alpha-TEA-induced apoptosis of human prostate cancer cells.
Jia
Li
L
Section of Molecular Genetics and Microbiology, School of Biological Sciences, The University of Texas at Austin, Austin, Texas 78712, USA.
Yu
Weiping
W
Wang
Pei
P
Li
Jing
J
Sanders
Bob G
BG
Kline
Kimberly
K
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D053181:Caspase 8 / Q000378:metabolism; D045744:Cell Line, Tumor; D056970:Co-Repressor Proteins; D053222:Fas Ligand Protein / Q000235:genetics / Q000378:metabolism*; D053200:Fas-Associated Death Domain Protein / Q000378:metabolism; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D018832:Molecular Chaperones; D009687:Nuclear Proteins / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology; D014810:Vitamin E / Q000031:analogs & derivatives / Q000494:pharmacology; D014815:Vitamins / Q000494:pharmacology; D024502:alpha-Tocopherol / Q000494:pharmacology; D019014:fas Receptor / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D056970:Co-Repressor Proteins; C106985:DAXX protein, human; C505533:FADD protein, human; C491901:FAS protein, human; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D053200:Fas-Associated Death Domain Protein; D018832:Molecular Chaperones; D009687:Nuclear Proteins; D016755:Proto-Oncogene Proteins c-jun; D014815:Vitamins; D019014:fas Receptor; D014810:Vitamin E; D048031:JNK Mitogen-Activated Protein Kinases; D053181:Caspase 8; D024502:alpha-Tocopherol