RIP1 is required for IAP inhibitor-mediated sensitization for TRAIL-induced apoptosis via a RIP1/FADD/caspase-8 cell death complex.
Inhibitor of apoptosis (IAP) proteins represent promising therapeutic targets due to their high expression in many cancers. Here, we report that small-molecule IAP inhibitors at subtoxic concentrations cooperate with monoclonal antibodies against TRAIL receptor 1 (Mapatumumab) or TRAIL-R2 (Lexatumumab) to induce apoptosis in neuroblastoma cells in a highly synergistic manner (combination index <0.1). Importantly, we identify receptor-activating protein 1 (RIP1) as a critical mediator of this synergism. RIP1 is required for the formation of a RIP1/FADD/caspase-8 complex that drives caspase-8 activation, cleavage of Bid into tBid, mitochondrial outer membrane permeabilization, full activation of caspase-3 and caspase-dependent apoptosis. Indeed, knockdown of RIP1 abolishes formation of the RIP1/FADD/caspase-8 complex, caspase activation and apoptosis upon combination treatment. Similarly, inhibition of RIP1 kinase activity by Necrostatin-1 inhibits IAP inhibitor- and TRAIL receptor-triggered apoptosis. In contrast, overexpression of the dominant-negative superrepressor IκBα-SR or addition of the tumor necrosis factor (TNF)α-blocking antibody Enbrel do not interfere with cotreatment-induced apoptosis, pointing to a nuclear factor-κB- and TNFα-independent mechanism. Of note, IAP inhibitor also sensitizes primary cultured neuroblastoma cells for TRAIL receptor-mediated loss of viability, underscoring the clinical relevance. By identifying RIP1 as a critical mediator of IAP inhibitor-mediated sensitization for Mapatumumab- or Lexatumumab-induced apoptosis, our findings provide new insights into the synergistic interaction of IAP inhibitors together with TRAIL receptor agonists.
Institute for Experimental Cancer Research in Pediatrics, Goethe-University, Frankfurt, Germany.
B A
BA
Abhari
S
S
Cristofanon
R
R
Kappler
D
D
von Schweinitz
R
R
Humphreys
S
S
Fulda
D000911:Antibodies, Monoclonal / Q000008:administration & dosage; D061067:Antibodies, Monoclonal, Humanized; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D015153:Blotting, Western; D053181:Caspase 8 / Q000378:metabolism*; D045744:Cell Line, Tumor; D004357:Drug Synergism; D024202:Electrophoretic Mobility Shift Assay; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D053200:Fas-Associated Death Domain Protein / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D051034:Inhibitor of Apoptosis Proteins / Q000037:antagonists & inhibitors; D028861:Nuclear Pore Complex Proteins / Q000378:metabolism*; D034622:RNA Interference; D016601:RNA-Binding Proteins / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism
C119724:AGFG1 protein, human; D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D004791:Enzyme Inhibitors; D053200:Fas-Associated Death Domain Protein; D051034:Inhibitor of Apoptosis Proteins; D028861:Nuclear Pore Complex Proteins; D016601:RNA-Binding Proteins; D053221:TNF-Related Apoptosis-Inducing Ligand; C510234:lexatumumab; D053181:Caspase 8; C507357:mapatumumab