IAP Suppression of Apoptosis Involves Distinct Mechanisms: the TAK1/JNK1 Signaling Cascade and Caspase Inhibition

Abstract

The antiapoptotic properties of the inhibitor of apoptosis (IAP) family of proteins have been linked to caspase inhibition. We have previously described an alternative mechanism of XIAP inhibition of apoptosis that depends on the selective activation of JNK1. Here we report that two other members of the IAP family, NAIP and ML-IAP, both activate JNK1. Expression of catalytically inactive JNK1 blocks NAIP and ML-IAP protection against ICE- and TNF-α-induced apoptosis, indicating that JNK1 activation is necessary for the antiapoptotic effect of these proteins. The MAP3 kinase, TAK1, appears to be an essential component of this antiapoptotic pathway since IAP-mediated activation of JNK1, as well as protection against TNF-α- and ICE-induced apoptosis, is inhibited when catalytically inactive TAK1 is expressed. In addition, XIAP, NAIP, and JNK1 bind to TAK1. Importantly, expression of catalytically inactive TAK1 did not affect XIAP inhibition of caspase activity. These data suggest that XIAP's antiapoptotic activity is achieved by two separate mechanisms: one requiring TAK1-dependent JNK1 activation and the second involving caspase inhibition.

We thank C. Duckett for providing mouse Survivin and the MCF7-Fas cells, D. Altieri for the human Survivin, N. Roy and J. Reed for the NAIP-BIR1-3-expressing vector, and F. Mercurio for the JNK3 construct. We also thank C. Fearns and A. Ghetti for critical reading of the manuscript and for helpful discussions.

Nicolas Schrantz is a recipient of a fellowship from The Association pour la Recherche Contre le Cancer. This work was supported by grants GM36796, GM28485, and AI15136.