FOXO3a mediates the androgen-dependent regulation of FLIP and contributes to TRAIL-induced apoptosis of LNCaP cells.
Androgen-withdrawal-induced apoptosis (AWIA) is deregulated in androgen refractory prostate cancer. Androgens have been shown to positively regulate expression of the antiapoptotic FADD-like interleukin-1beta-converting enzyme (FLICE)-like inhibitory protein (FLIP), and reduced FLIP expression precedes apoptosis after androgen withdrawal. Here, we show that FLIP protein expression is downregulated in castrated rats, while in LNCaP cells, androgens regulate FLIP in a manner that is dependent on phosphoinositol-3-kinase (PI3K) and Akt signaling. Specifically, treatment of LNCaP cells with LY294002, or expression of either PTEN or a non-phosphorylatable form of FOXO3a (FOXO3aTM), downregulates FLIP protein and mRNA. Conversely, treatment with androgens in the absence of PI3/Akt signaling, or following expression of FOXO3aTM, leads to increased FLIP expression. A FOXO3a binding site was identified in the FLIP promoter and shown necessary for the combined effects of androgens and FOXO3a on FLIP transcription. FOXO3a binds the androgen receptor, suggesting that the transcriptional synergy depends on an interaction between these proteins. Finally, LNCaP cells are sensitized to TRAIL-induced apoptosis by PTEN or LY294002, and rescued by androgens. FOXO3aTM also sensitizes cells to androgen-inhibited TRAIL apoptosis. Androgen rescue was diminished when either FOXO3a or FLIP was reduced by siRNA. These data support a role for FOXO3a in AWIA.
Cornforth
A N
AN
Department of Pathology and Laboratory Medicine, University of California, Irvine, CA 92697-4800, USA.
Davis
J S
JS
Khanifar
E
E
Nastiuk
K L
KL
Krolewski
J J
JJ
D000728:Androgens / Q000502:physiology*; D017209:Apoptosis / Q000187:drug effects*; D001665:Binding Sites; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000032:analysis / Q000235:genetics* / Q000502:physiology; D045744:Cell Line, Tumor; D002867:Chromones / Q000494:pharmacology; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D009025:Morpholines / Q000494:pharmacology; D051059:PTEN Phosphohydrolase / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011401:Promoter Regions, Genetic; D011467:Prostate / Q000737:chemistry; D011471:Prostatic Neoplasms / Q000737:chemistry / Q000188:drug therapy* / Q000473:pathology; D011944:Receptors, Androgen / Q000032:analysis / Q000378:metabolism; D015398:Signal Transduction; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology*
D000728:Androgens; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002867:Chromones; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D009025:Morpholines; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011944:Receptors, Androgen; D053221:TNF-Related Apoptosis-Inducing Ligand; C499517:FOXO3 protein, human; C505653:TNFSF10 protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494929:PTEN protein, human