Regulation of the Copper Chaperone CCS by XIAP-Mediated Ubiquitination

Abstract

In order to balance the cellular requirements for copper with its toxic properties, an elegant set of mechanisms has evolved to regulate and buffer intracellular copper. The X-linked inhibitor of apoptosis (XIAP) protein was recently identified as a copper-binding protein and regulator of copper homeostasis, although the mechanism by which XIAP binds copper in the cytosol is unclear. Here we describe the identification of the copper chaperone for superoxide dismutase (CCS) as a mediator of copper delivery to XIAP in cells. We also find that CCS is a target of the E3 ubiquitin ligase activity of XIAP, although interestingly, ubiquitination of CCS by XIAP was found to lead to enhancement of its chaperone activity toward its physiologic target, superoxide dismutase 1, rather than proteasomal degradation. Collectively, our results reveal novel links among apoptosis, copper metabolism, and redox regulation through the XIAP-CCS complex.

This work was supported in part by Department of Defense Prostate Cancer Research Program predoctoral award W81XWH-08-1-0211 to G.F.B. and National Institutes of Health grant GM067827 and an American Asthma Foundation award to C.S.D.

We are grateful to Ezra Burstein for providing reagents and protocols, as well as helpful advice and discussions. We also thank Casey Wright and John Wilkinson and members of the Duckett laboratory for insightful discussions and critical reading of the manuscript and David Baltimore, Leo Klomp, and Prim de Bie for plasmids.