Abstract B29: SMAC-mimetic induced apoptosis of SKOV3 cells requires NIK and activation of canonical NFκB signaling

Abstract

Abstract By stimulating the autoubiquitination and proteosome mediated degradation of CIAP1, Smac mimetics hypersensitize tumor cells to TNFα mediated apoptosis. Indeed, Smac mimetics induce the production of TNFα in sensitive but not insensitive tumor cell lines. The precise mechanism of NFκB activation and subsequent TNFα induction is not well understood, and identifying the mechanism by which LBW242 induces TNFα may provide potential biomarkers for patient stratification. Paradoxically, these agents have been reported to both activate and inhibit the canonical NFκB pathway and to activate the non-canonical pathway. To elucidate this mechanism, we knocked down nodes of the canonical and non-canonical NFκB pathways and assessed activation of an NFκB/p65-reporter, induction of TNFα expression and cell death after treatment with the Smac mimetic compound LBW242. In the canonical pathway, knockdown of IKKB and p65 ablated TNF induction and rescued SKOV cells from LBW242-mediated cell death, suggesting that activation of the canonical pathway is required for LBW242-mediated cell death. In the noncanonical pathway, knockdown of NIK, but surprisingly not RelB, rescued SKOV cells from LBW242-mediated cell death. This data suggests a role for NIK in LBW242-mediated activation of the canonical but not the non-canonical NFκB pathway. Consistent with this model, we find overexpression of NIK is sufficient to activate the p65 reporter. Moreover, activation of the non-canonical NFκB pathway was robustly observed in both sensitive and insensitive tumor cell lines, further invalidating the contribution of the non-canonical arm to Smac mimetic induced TNF production. We propose NIK-mediated activation of the canonical NFκB signaling is responsible for Smac mimetic induced TNFα production. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B29.