Docking-dependent Ubiquitination of the Interferon Regulatory Factor-1 Tumor Suppressor Protein by the Ubiquitin Ligase CHIP

Abstract

Characteristically for a regulatory protein, the IRF-1 tumor suppressor turns over rapidly with a half-life of between 20 -40 min. This allows IRF-1 to reach new steady state protein levels swiftly in response to changing environmental conditions. Whereas CHIP (C terminus of Hsc70-interacting protein), appears to chaperone IRF-1 in unstressed cells, formation of a stable IRF-1⅐CHIP complex is seen under specific stress conditions. Complex formation, in heat-or heavy metaltreated cells, is accompanied by a decrease in IRF-1 steady state levels and an increase in IRF-1 ubiquitination. CHIP binds directly to an intrinsically disordered domain in the central region of IRF-1 (residues 106 -140), and this site is sufficient to form a stable complex with CHIP in cells and to compete in trans with full-length IRF-1, leading to a reduction in its ubiquitination. The study reveals a complex relationship between CHIP and IRF-1 and highlights the role that direct binding or "docking" of CHIP to its substrate(s) can play in its mechanism of action as an E3 ligase.

A Multiprotein Binding Interface in an Intrinsically Disordered Region of the Tumor Suppressor Protein Interferon Regulatory Factor-1

“…We recently discovered that the E3-ubiquitin ligase CHIP binds to a site (amino acids 106 -140) within the major disordered domain of IRF-1 (Fig. 1C), facilitating ubiquitination of IRF-1 under specific stress conditions (33). Because disordered domains appear to favor multiple protein interactions, we speculated that the major disordered domain in IRF-1 may bind to other components of the IRF-1 regulatory network.…”

“…2, A and B). These two peptides also contain the CHIPdocking site (33), suggesting that they may form a multiprotein binding interface on IRF-1. We have named this the Mf2 (multifunctional 2) domain (Fig.…”

The interferon regulatory factors as novel potential targets in the treatment of cardiovascular diseases

“…These two protein-modification events can occur rapidly through dedicated enzymes, and often act cooperatively in mobilizing particular cellular pathways in response to extracellular signals (Ben-Neriah, 2002;Wang and Maldonado, 2006). For IRF1, under certain stress conditions, the C-terminus of Hsc70-interacting protein binds to and forms a stable complex with IRF1, allowing an increase in IRF1 ubiquitination and a decrease in IRF1 steady-state levels (Narayan et al, 2011). Following the removal of the C-terminal 70 amino acids from IRF1, which could be recognized by an E3 ligase, its degradation and polyubiquitination can be inhibited, suggesting that the C-terminal of IRF1 promotes ubiquitination.…”

Inhibition of Histone Deacetylase Activity Suppresses IFN-γ Induction of Tripartite Motif 22 via CHIP-Mediated Proteasomal Degradation of IRF-1

“…Importantly, further studies revealed that CHIP overexpression enhanced, whereas CHIP knockdown attenuated, TSA-mediated IRF-1 degradation. Although Narayan et al (41) reported that CHIP could bind IRF-1 directly, their data did not rule out the possibility that CHIP interacts with IRF-1 through HSP70. Because our data showed that TSA treatment enhanced the interaction between HSP70 and IRF-1 markedly (Fig.…”

“…CHIP was identified as an E3 ligase for IRF-1 as well as a number of HSP70-associated proteins, such as ErbB2 and PTEN (47,48); however, it was reported that CHIP acted as the chaperone for IRF-1 in unstressed cells. Only under special conditions in which the interaction between CHIP and IRF-1 gets enhanced will CHIP target IRF-1 for ubiquitination and degradation (41). We therefore first determined the effect of TSA on the association between CHIP and IRF-1 by coimmunoprecipitation assays.…”