c-FLIP knockdown induces ligand-independent DR5-, FADD-, caspase-8-, and caspase-9-dependent apoptosis in breast cancer cells.
Cellular-FLICE inhibitory protein (c-FLIP) is an inhibitor of apoptosis downstream of the death receptors Fas, DR4, and DR5, and is expressed as long (c-FLIP(L)) and short (c-FLIP(S)) splice forms. We found that the knockdown of c-FLIP using small interfering RNA (siRNA) triggered ligand-independent caspase-8- and -9-dependent spontaneous apoptosis and decreased the proliferation of MCF-7 breast cancer cells. Further analysis revealed that an apoptotic inhibitory complex (AIC) comprised of DR5, FADD, caspase-8, and c-FLIP(L) exists in MCF-7 cells, and the absence of c-FLIP(L) from this complex induces DR5- and FADD-mediated caspase-8 activation in the death inducing signaling complex (DISC). c-FLIP(S) was not detected in the AIC, and using splice form-specific siRNAs we showed that c-FLIP(L) but not c-FLIP(S) is required to prevent spontaneous death signaling in MCF-7 cells. These results clearly show that c-FLIP(L) prevents ligand-independent death signaling and provides direct support for studying c-FLIP as a relevant therapeutic target for breast cancers.
Day
Travis W
TW
Department of Pharmacology and Toxicology, Indiana University Simon Cancer Center, Indiana University School of Medicine, 1044 West Walnut Street R4-119, Indianapolis, IN 46202, USA.
Huang
Su
S
Safa
Ahmad R
AR
D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000737:chemistry / Q000188:drug therapy / Q000473:pathology*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000037:antagonists & inhibitors* / Q000235:genetics; D053181:Caspase 8 / Q000378:metabolism*; D053453:Caspase 9 / Q000378:metabolism*; D045744:Cell Line, Tumor; D053200:Fas-Associated Death Domain Protein / Q000378:metabolism*; D020868:Gene Silencing; D006801:Humans; D008024:Ligands; D020033:Protein Isoforms; D034741:RNA, Small Interfering / Q000494:pharmacology*; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*
D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D053200:Fas-Associated Death Domain Protein; D008024:Ligands; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D053181:Caspase 8; D053453:Caspase 9