IAP Antagonists Target cIAP1 to Induce TNFα-Dependent Apoptosis

Abstract

XIAP prevents apoptosis by binding to and inhibiting caspases, and this inhibition can be relieved by IAP antagonists, such as Smac/DIABLO. IAP antagonist compounds (IACs) have therefore been designed to inhibit XIAP to kill tumor cells. Because XIAP inhibits postmitochondrial caspases, caspase 8 inhibitors should not block killing by IACs. Instead, we show that apoptosis caused by an IAC is blocked by the caspase 8 inhibitor crmA and that IAP antagonists activate NF-κB signaling via inhibtion of cIAP1. In sensitive tumor lines, IAP antagonist induced NF-κB-stimulated production of TNFα that killed cells in an autocrine fashion. Inhibition of NF-κB reduced TNFα production, and blocking NF-κB..