In this study, we investigated the role of Nur77, an orphan nuclear receptor, in HIF-alpha transcriptional activity. We found that Nur77 associates and stabilizes HIF-1alpha via indirect interaction. Nur77 was found to interact with pVHL in vivo via the alpha-domain of pVHL. By binding to pVHL, Nur77 competed with elongin C for pVHL binding. Moreover, Nur77-binding to pVHL inhibited the pVHL-mediated ubiquitination of HIF-1alpha and ultimately increased the stability and transcriptional activity of HIF-1alpha. The ligand-binding domain of Nur77 was found to interact with pVHL and the expression of this ligand-binding domain was sufficient to stabilize and transactivate HIF-1alpha. Under the conditions that cobalt chloride was treated or pVHL was knocked down, Nur77 could not stabilize HIF-alpha. Moreover, Nur77 could not further stabilize HIF-2alpha in A498/VHL stable cells, which is consistent with our finding that Nur77 indirectly stabilizes HIF-alpha by binding to pVHL. Thus, our results suggest that an orphan nuclear receptor Nur77 binds to pVHL, thereby stabilizes and increases HIF-alpha transcriptional activity under the non- hypoxic conditions.
Animals ; DNA-Binding Proteins/chemistry/*metabolism ; Humans ; Hypoxia-Inducible Factor 1, alpha Subunit/*genetics ; Models, Biological ; PC12 Cells ; Protein Binding ; *Protein Processing, Post-Translational ; Protein Structure, Tertiary ; Rats ; Receptors, Cytoplasmic and Nuclear/chemistry/*metabolism ; Receptors, Steroid/chemistry/*metabolism ; Thermodynamics ; Transcription Factors/chemistry/*metabolism ; Transcriptional Activation/genetics ; Ubiquitination ; Up-Regulation/*genetics ; Von Hippel-Lindau Tumor Suppressor Protein/*antagonists & inhibitors/chemistry/*metabolism