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Review
. 2007 Mar 15;6(6):656-9.
doi: 10.4161/cc.6.6.3981. Epub 2007 Mar 7.

RACK1 vs. HSP90: competition for HIF-1 alpha degradation vs. stabilization

Affiliations
Review

RACK1 vs. HSP90: competition for HIF-1 alpha degradation vs. stabilization

Ye V Liu et al. Cell Cycle. .

Abstract

Oxygen homeostasis represents an essential organizing principle of metazoan evolution and biology. Hypoxia-inducible factor 1 (HIF-1) regulates transcription in response to changes in O2 concentration. HIF-1 is a heterodimeric transcription factor that consists of HIF-1alpha and HIF-1beta subunits. O2 -dependent degradation of the HIF-1alpha subunit is mediated by prolyl hydroxylase (PHD), the von Hippel-Lindau (VHL)/Elongin-C/Elongin-B E3 ubiquitin ligase, and the proteasome. Inhibitors of heat shock protein 90 (HSP90) dissociate HSP90 from HIF-1alpha and induce O2/PHD/VHL-independent degradation of HIF-1alpha. Recently, we reported the identification of receptor of activated protein C kinase (RACK1) as a novel HIF-1alpha interacting protein. RACK1 promotes the O2/PHD/VHL-independent and proteasome-dependent degradation of HIF-1alpha. RACK1 competes with HSP90 for binding to the PAS-A domain of HIF-1alpha. RACK1 activity is required for the mechanism of action for the HSP90 inhibitor 17-allylaminogeldanamycin to induce HIF-1alpha degradation. RACK1 binds to Elongin-C and recruits Elongin-B and other components of E3 ubiquitin ligase to HIF-1alpha. The ubiquitination and degradation of HIF-1alpha are promoted by RACK1. RACK1 is an essential component of an O2/PHD/VHL-independent system for regulating HIF-1alpha stability through competition with HSP90 and recruitment of the Elongin-C/B ubiquitin ligase complex. Here we discuss how this system may be regulated.

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