Caspase-8 and caspase-10 activate NF-κB through RIP, NIK and IKKα kinases

NF-κB regulates the expression of various genes involved in cell growth and differentiation, immune response and inhibition of apoptosis. Recently, some death effector domain (DED)-containing proteins, such as FADD and c-FLIP were reported to activate NF-κB. We previously reported that the prodomain-only isoforms of caspase-8 and -10 (PDCasp8/10), containing two DED motifs, could inhibit Fas-mediated apoptosis. Here, we demonstrate that these isoforms also activate NF-κB, implying this to be one of the mechanisms by which these polypeptides inhibit apoptosis. The GST pull-down assay revealed that, among upstream kinases that activate NF-κB, only NIK and RIP, but not RICK or IKKα/β, could directly bind to PDCasp8/10. In addition, both modules ofDED in PDCasp8/10 were required for these interactions as well as NF-κB activation. Experiments using a kinase-dead mutant of IKKα and an RIP mutant lacking a kinase domain, both of whichfunction as dominant-negative mutants for their wild-type counterparts, blocked PDCasp8/10-mediated NF-κB activation. Using small interfering RNA technology, we further demonstrate that the down-regulation of IKKα but not IKKβ significantly inhibits PDCasp8-mediated NF-κB activation. Taken together, these results suggest that caspase-8 and -10 have roles in a non- or anti-apoptotic signaling pathway leading to NF-κB activation through RIP, NIK and IKKα.