Targeting the short form of cFLIP by RNA interference is sufficient to enhance TRAIL sensitivity in PC3 prostate carcinoma cells.
The pro-apoptotic death receptor ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has received significant attention as a novel cancer therapeutic, since it selectively induces apoptosis in malignant and not normal cells. Unfortunately, prostate cancer cells display little if any susceptibility to TRAIL-induced apoptosis. However, sensitivity to TRAIL is enhanced by doxorubicin, which correlated with a decrease in expression of the caspase-8 inhibitor cFLIP (Kelly et al., Cancer Biol Ther 1:520). In this study we show that doxorubicin induces a time- and dose-dependent loss of cFLIP protein, but does not affect steady-state mRNA levels. Proteasome inhibition stabilized cFLIPL in the presence of doxorubicin. Although proteasome inhibitors increased basal levels of short cFLIP isoforms, cFLIPS declined at a similar rate in the absence or presence of proteasome inhibition during doxorubicin treatment. Ectopic expression of a cFLIPSGFP fusion protein protected PC3 cells from TRAIL-induced apoptosis in the absence or presence of doxorubicin, whereas downregulation of cFLIPS by RNA interference resulted in sensitization to TRAIL-induced apoptosis. We conclude that doxorubicin-mediated downregulation of cFLIPS, which occurs at the post-transcriptional level independent of proteasome-mediated pathways, is sufficient to enhance TRAIL sensitivity in PC3 prostate carcinoma cells.
White
Shai J
SJ
Department of Microbiology and Immunology, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
Lu
Ping
P
Keller
Gina M
GM
Voelkel-Johnson
Christina
C
D017209:Apoptosis; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000235:genetics*; D045744:Cell Line, Tumor; D017931:DNA Primers; D003630:Daunorubicin / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000235:genetics*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000502:physiology; D014162:Transfection
D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D017931:DNA Primers; D034741:RNA, Small Interfering; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D004317:Doxorubicin; D003630:Daunorubicin