Cellular FLICE-like inhibitory protein (c-FLIP): a novel target for Taxol-induced apoptosis.
It is known that by binding to the FAS-associated death domain (FADD) protein and/or caspases-8 and -10 at the level of the death-inducing signaling complex (DISC), cellular FLICE-like inhibitory protein (c-FLIP) can prevent apoptosis triggered by death-inducing ligands. We investigated whether the c-FLIP splice variants, c-FLIP long [c-FLIP(L)] and c-FLIP short [c-FLIP(S)], play a role in Taxol-induced apoptosis. Our results showed that low Taxol concentrations triggered caspase-8- and caspase-10-dependent apoptosis in the CCRF-HSB-2 human lymphoblastic leukemia cell line, and induced the down-regulation of c-FLIP(S) and c-FLIP(L). Taxol decreased the expression of c-FLIP by a post-transcriptional and caspase-independent mechanism. To explore the distinct functions of the c-FLIP variants in Taxol-induced apoptosis, we transfected the cells with expression vectors carrying c-FLIP(L) and c-FLIP(S) in the sense orientation or c-FLIP(S) in the antisense orientation [c-FLIP(S)-AS]. Caspases-8 and -10 were more efficiently activated in the c-FLIP(S)-AS strain treated with 5-50nM Taxol, which revealed that c-FLIP regulates Taxol-induced apoptosis by interacting with these caspases. Furthermore, our data showed that increased expression of c-FLIP(L) or c-FLIP(S) reduced apoptosis at 5-50nM Taxol concentrations suggesting that both isoforms of c-FLIP prevent Taxol-induced apoptosis. These results revealed that Taxol induces apoptosis by down-regulating c-FLIP(S) and c-FLIP(L) expression.
Department of Pharmacology and Toxicology, Indiana University Cancer Research Institute, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
Travis W
TW
Day
Farhad
F
Najafi
Ching-Huang
CH
Wu
Ahmad R
AR
Safa
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D053455:Caspase 10; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000502:physiology; D015459:Leukemia-Lymphoma, Adult T-Cell / Q000188:drug therapy / Q000473:pathology; D017239:Paclitaxel / Q000494:pharmacology*
D000972:Antineoplastic Agents, Phytogenic; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D047908:Intracellular Signaling Peptides and Proteins; C505530:CASP8 protein, human; D053455:Caspase 10; D053181:Caspase 8; D020169:Caspases; C506438:CASP10 protein, human; D017239:Paclitaxel