RACK1 competes with HSP90 for binding to HIF-1alpha and is required for O(2)-independent and HSP90 inhibitor- induced degradation of HIF-1alpha.
Hypoxia-inducible factor 1 (HIF-1) regulates transcription in response to changes in O(2) concentration. O(2)-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 complex, and the proteasome. Inhibition of heat-shock protein 90 (HSP90) leads to O(2)/PHD/VHL-independent degradation of HIF-1alpha. We have identified the receptor of activated protein kinase C (RACK1) as a HIF-1alpha- interacting protein that promotes PHD/VHL-independent proteasomal degradation of HIF-1alpha. RACK1 competes with HSP90 for binding to the PAS-A domain of HIF-1alpha in vitro and in human cells. HIF-1alpha degradation induced by the HSP90 inhibitor 17-allylaminogeldanamycin is abolished by RACK1 loss of function. RACK1 binds to Elongin-C and promotes ubiquitination of HIF-1alpha. Elongin-C- binding sites in RACK1 and VHL show significant sequence similarity. Thus, RACK1 is an essential component of an O(2)/PHD/VHL-independent mechanism for regulating HIF-1alpha stability through competition with HSP90 and recruitment of the Elongin-C/B ubiquitin ligase complex.[1]References
- RACK1 competes with HSP90 for binding to HIF-1alpha and is required for O(2)-independent and HSP90 inhibitor-induced degradation of HIF-1alpha. Liu, Y.V., Baek, J.H., Zhang, H., Diez, R., Cole, R.N., Semenza, G.L. Mol. Cell (2007) [Pubmed]
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