alpha-Tocopheryl succinate and derivatives mediate the transcriptional repression of androgen receptor in prostate cancer cells by targeting the PP2A-JNK-Sp1-signaling axis.
As part of our effort to understand the mechanism underlying alpha-tocopheryl succinate [vitamin E succinate (VES)]-mediated antitumor effects, we investigated the signaling pathway by which VES suppresses androgen receptor (AR) expression in prostate cancer cells. VES and, to a greater extent, its truncated derivative TS-1 mediated transcriptional repression of AR in prostate cancer cells but not in normal prostate epithelial cells; a finding that underscores the differential susceptibility of normal versus malignant cells to the antiproliferative effect of these agents. This AR repression was attributable to the ability of VES and TS-1 to facilitate the proteasomal degradation of the transcription factor Sp1. This mechanistic link was corroborated by the finding that proteasome inhibitors or ectopic expression of Sp1 protected cells against drug-induced AR ablation. Furthermore, evidence suggests that the destabilization of Sp1 by VES and TS-1 resulted from the inactivation of Jun N-terminal kinases (JNKs) as a consequence of increased phosphatase activity of protein phosphatase 2A (PP2A). Stable transfection of LNCaP cells with the dominant-negative JNK1 plasmid mimicked drug-induced Sp1 repression, whereas constitutive activation of JNK kinase activity or inhibition of PP2A activity by okadaic acid protected Sp1 from VES- and TS-1-induced degradation. From a mechanistic perspective, the ability of VES and TS-1 to activate PP2A activity underscores their broad spectrum of effects on multiple signaling mechanisms, including those mediated by Akt, mitogen-activated protein kinases, nuclear factor kappaB, Sp1 and AR. This pleiotropic effect in conjunction with low toxicity suggests the translational potential for developing TS-1 into potent PP2A-activating agents for cancer therapy.
Huang
Po-Hsien
PH
Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy and Comprehensive Cancer Center, Ohio State University, 500 West 12th Avenue, Columbus, OH 43210, USA.
Wang
Dasheng
D
Chuang
Hsiao-Ching
HC
Wei
Shuo
S
Kulp
Samuel K
SK
Chen
Ching-Shih
CS
D045744:Cell Line, Tumor; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008297:Male; D011471:Prostatic Neoplasms / Q000378:metabolism*; D054648:Protein Phosphatase 2 / Q000378:metabolism*; D011944:Receptors, Androgen / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D014158:Transcription, Genetic; D024502:alpha-Tocopherol / Q000031:analogs & derivatives* / Q000494:pharmacology*
D011944:Receptors, Androgen; D016329:Sp1 Transcription Factor; D048031:JNK Mitogen-Activated Protein Kinases; D054648:Protein Phosphatase 2; D024502:alpha-Tocopherol