Modulation of tumor necrosis factor apoptosis-inducing ligand-induced NF-kappa B activation by inhibition of apical caspases

Tumor necrosis factor (TNF) apoptosis-inducing ligand (TRAIL), a member of the TNF family, induces apoptosis in many transformed cells. We report TRAI L-induced NF-kappaB activation, concomitant with production of the pro-infl ammatory cytokine Interleukin-8 in the relatively TRAIL-insensitive cell li ne, HEK293. In contrast, TRAIL-induced NF-kappaB activation occurred in HeL a cells only upon pretreatment with the caspase inhibitor, benzyloxycarbony l-Val-Ala-Asp-(OMe) fluoromethyl ketone (z-VAD.fmk), indicating that this w as due to a caspase-sensitive component of TRAIL-induced NF-kappaB activati on. NF-kappaB activation was mediated by the death receptors, TRAIL-R1 and -R2, but not by TRAIL-R3 or -R4 and was only observed in HeLa cells in the presence of z-VAD.fmk. Receptor-interacting protein, an obligatory componen t of TNF-alpha -induced NF-kappaB activation, was cleaved during TRAIL-indu ced apoptosis. We show that receptor-interacting protein is recruited to th e native TRAIL death-inducing signaling complex (DISC) and that recruitment is enhanced in the presence of z-VAD.fmk, thus providing an explanation fo r the potentiation of TRAIL-induced NF-kappaB activation by z-VAD.fmk in TR AIL-sensitive cell lines. Examination of the TRAIL DISC in sensitive and re sistant cells suggests that a high ratio of c-FLIP to caspase-8 may partial ly explain cellular resistance to TRAIL-induced apoptosis. Sensitivity to T RAIL-induced apoptosis was also modulated by inhibition or activation of NF -kappaB. Thus, in some contexts, modulation of NF-kappaB activation possibl y at the level of apical caspase activation at the DISC may be a key determ inant of sensitivity to TRAIL-induced apoptosis.