FLICE-like inhibitory protein blocks transforming growth factor beta 1-induced caspase activation and apoptosis in prostate epithelial cells.
Androgen withdrawal induces the regression of human prostate cancers, but such cancers eventually become androgen-independent and metastasize. Thus, deciphering the mechanism of androgen withdrawal-induced apoptosis is critical to designing new therapies for prostate cancer. Previously, we showed that in the rat, castration-induced apoptosis is accompanied by a reduction in the expression of the apical caspase inhibitor FLICE-like inhibitory protein (FLIP). To test the functional role of FLIP in inhibiting prostate epithelial cell apoptosis, we employed the rat prostate epithelial cell line NRP-152, which differentiates to a secretory phenotype in a low-mitogen medium and then undergoes apoptosis following the addition of transforming growth factor beta1 (TGFbeta1), mimicking androgen withdrawal-induced apoptosis. FLIP levels decline with TGFbeta1 treatment, suggesting that apoptosis is mediated by caspase-8 and indeed the caspase inhibitor crmA blocks TGFbeta1-induced apoptosis. Small interfering RNA-mediated knockdown of FLIP recapitulates and enhances TGFbeta1-induced cell death. NRP-152 cells stably transfected with constitutively expressed FLIP were refractory to TGFbeta1-induced apoptosis. TGFbeta1-induced caspase-3 activity is proportional to the level of cell death and inversely proportional to the level of FLIP expression in various clones. Moreover, neither caspase-3 nor PARP is cleaved in clones expressing high levels of FLIP. Furthermore, insulin, which inhibits differentiation, increases FLIP and inhibits TGFbeta-induced death in a FLIP-dependent manner. Although neither Fas-Fc, sTNFRII-Fc, nor DR5-Fc blocked TGFbeta1-induced cell death, there is a significant increase in tumor necrosis factor mRNA following TGFbeta stimulation, suggesting both an unexpected role for tumor necrosis factor in this model system and the possibility that FLIP blocks another unknown caspase-dependent mediator of apoptosis.
Nastiuk
Kent L
KL
Department of Pathology and Laboratory Medicine, School of Medicine, University of California Irvine, Medical Sciences I D450, Irvine, CA 92697-4800, USA.
Yoo
Kiwon
K
Lo
Karen
K
Su
Kevin
K
Yeung
Patricia
P
Kutaka
Julia
J
Danielpour
David
D
Krolewski
John J
JJ
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000378:metabolism*; D020169:Caspases / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D004847:Epithelial Cells / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D000068800:Etanercept; D053222:Fas Ligand Protein / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007074:Immunoglobulin G / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D008297:Male; D051379:Mice; D011467:Prostate / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000235:genetics / Q000378:metabolism; D018124:Receptors, Tumor Necrosis Factor; D012995:Solubility / Q000187:drug effects; D014162:Transfection; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology*
D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D053222:Fas Ligand Protein; D007074:Immunoglobulin G; D007328:Insulin; D012333:RNA, Messenger; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D018124:Receptors, Tumor Necrosis Factor; D053773:Transforming Growth Factor beta1; D020169:Caspases; D000068800:Etanercept