Oncogene. 2012 Aug 13. doi: 10.1038/onc.2012.337.

RIP1 is required for IAP inhibitor-mediated sensitization for TRAIL-induced apoptosis via a RIP1/FADD/caspase-8 cell death complex.External

Abhari, B. A., Cristofanon, S., Kappler, R., von Schweinitz, D., Humphreys, R., Fulda, S.,
--- - Institute for Experimental Cancer Research in Pediatrics, Goethe-University, Frankfurt, Germany.
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 IkappaBalpha-SR or addition of the tumor necrosis factor (TNF)alpha-blocking antibody Enbrel do not interfere with cotreatment-induced apoptosis, pointing to a nuclear factor-kappaB- and TNFalpha-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.Oncogene advance online publication, 13 August 2012; doi:10.1038/onc.2012.337.
PMID: 22890322External
Arrow2 In vitro interaction Arrow2 In vivo interaction Arrow2 Characterization Arrow2 Functional role Arrow2 top
In vivo interaction
  Endogenous
expression
Overexpression DD1 DD2 Reference
Family DD1 DD2 Method Species Region Species Region
DED Caspase8 Link FADD Co-immunoprecipitation SH-EP 22890322
DED Caspase8 Link FADD Co-immunoprecipitation LAN-5 22890322
(Link: click this icon to show interactions only between the two corresponding DDs)
Arrow2 In vitro interaction Arrow2 In vivo interaction Arrow2 Characterization Arrow2 Functional role Arrow2 top
Functional Role
Family DD1 DD2 Method Death-related Death-unrelated Reference
DED Caspase8 Link FADD MTT assay Apoptosis (DISC) 22890322
(Link: click this icon to show interactions only between the two corresponding DDs)