Interaction of heat-shock protein 90β isoform (HSP90β) with cellular inhibitor of apoptosis 1 (c-IAP1) is required for cell differentiation

Abstract

Members of the inhibitor of apoptosis protein (IAP) family have demonstrated functions in cell death, cell signalling, cell migration and mitosis. Several of them are E3 enzymes in the ubiquitination of proteins that leads to their degradation by the proteosomal machinery. We previously reported that one of them, cellular inhibitor of apoptosis protein-1 (c-IAP1), migrated from the nucleus to the surface of the Golgi apparatus in cells undergoing differentiation. Here, we show that c-IAP1 is a client protein of the stress protein HSP90b. In three distinct cellular models, the two proteins interact and migrate from the nucleus to the cytoplasm along the differentiation process through a leptomycin B-sensitive pathway. Inhibition of HSP90 proteins by small chemical molecules and specific depletion of HSP90b isoform by siRNA both lead to auto-ubiquitination of c-IAP1 and its degradation by the proteasome machinery. This chaperone function of HSP90 towards c-IAP1 is specific of its b isoform as specific depletion of HSP90a does not affect c-IAP1 content. Chemical inhibition of HSP90 or siRNA-mediated depletion of HSP90b both inhibit cell differentiation, which can be reproduced by siRNA-mediated depletion of c-IAP1. Altogether, these results suggest that HSP90b prevents auto-ubiquitination and degradation of its client protein c-IAP1, whose depletion would be sufficient to inhibit cell differentiation. Members of the inhibitor of apoptosis protein (IAP) family were initially described as a series of natural inhibitors of cell death. Among the eight human proteins of this family, X-linked IAP (XIAP) demonstrated to be the bona fide caspase inhibitor 1 whereas the others demonstrated, for the most part, functions in cell signalling 2 and mitosis. 3 Several of these proteins harbour a Really Interesting New Gene (RING) domain at the carboxy terminus and function as an E3 enzyme in the cascade of ubiquitination that targets proteins to the ubiquitinproteasome degradation machinery. 4 One of these IAP with a RING domain is cellular IAP1 (c-IAP1) that was initially described as a signalling molecule. 2 Although c-IAP1 has subsequently been described as a direct inhibitor of caspases, this remains a controversial issue. 5,6 Due to its E3 function, c-IAP1 is responsible for the ubiquitination and subsequent degradation of the adaptor protein TNF receptor associated factor 2 7 and the serinethreonine apoptosis signal-regulating kinase 1 8 in the tumour necrosis factor alpha (TNFa) signalling pathway. In this TNFa pathway, c-IAP1 was reported also to interact with the serinethreonine kinases receptor interacting protein 2 and nuclear factor kappaB (NF-kB) essential modifier, upstream of NF-kB, 9 and to block caspase-8 activation, downstream of NF-kB. 10 Deletion experiments in Drosophila melanogaster have revealed other functions of IAPs in cell differentiation, 11 cell migration, 12 and immune response. 13 In mammals, c-IAP1-deficient mice develop normally. However, cells from c-IAP1À/À mice express markedly elevated levels ...

cIAP1-dependent TRAF2 degradation regulates the differentiation of monocytes into macrophages and their response to CD40 ligand

“…8,12,13 We have previously shown that cIAP1 is required for optimal differentiation of monocytes into macrophages. 25 We show here that cIAP1 is one of the E3 ligases involved in the proteasome-dependent degradation of TRAF2 along this differentiation process. Because the effect of cIAP1 inhibition on differentiation-associated TRAF2 down-regulation was only partial, we cannot rule out a function for TRAF2 itself, Siah2, or other E3 in this event.…”

“…12,13,[22][23][24] We have previously shown that cIAP1 was required for macrophage differentiation. 25 We have also shown that cIAP1 migrated from the nucleus to the cytoplasm to concentrate at the surface of the Golgi apparatus in monocytes undergoing differentiation into macrophages. 26 However, the role of cIAP1 and the functional significance of its differentiation-associated redistribution remained unknown.…”

IAPS : More than just inhibitors of apoptosis proteins

“…More over, the expression and stability of IAPs are regulated by molecular chaperone such as heatshock proteins. 72,73 The molecular mechanisms of caspase regulation by BIRC4/XIAP have been extensively investigated in biochemical and structural studies (reviewed in ref. 11).…”

Role of Melanoma Inhibitor of Apoptosis (ML-IAP) Protein, a Member of the Baculoviral IAP Repeat (BIR) Domain Family, in the Regulation of C-RAF Kinase and Cell Migration

“…Our current data with ML-IAP also suggest that IAPs synergize with the chaperone machinery to regulate C-RAF levels. In fact, cIAP1 has been shown to be associated with Hsp90 during cellular differentiation (46). Further, silencing of CHIP expression has also led to an increase in C-RAF levels in these melanoma cell lines (data not shown).…”