Dynamic, site-specific interaction of hypoxia-inducible factor-1alpha with the von Hippel-Lindau tumor suppressor protein.

Hypoxia-inducible factor (HIF)-1alpha is a transcription factor that plays a critical role in regulating genes involved in erythropoiesis and angiogenesis. Recent evidence indicates that the von Hippel-Lindau tumor suppressor protein (VHL) is part of a ubiquitin ligase complex that promotes the degradation of HIF-1alpha under normoxic conditions. Under hypoxic conditions, HIF-1alpha is markedly stabilized. A critical issue in understanding the hypoxic response is the identification of hypoxia-regulated steps. We show here that hypoxia and cobalt treatment modulate the capacity of a HIF-1alpha fragment comprising residues 531-652 to coimmunoprecipitate with VHL. Hypoxia and cobalt both significantly diminish the interaction, and furthermore, normoxia treatment after hypoxia rapidly normalizes it. This HIF-1alpha fragment confers hypoxia and cobalt inducibility on a heterologous protein. Significantly, contained within this fragment is a short 27-residue sequence that behaves identically in all respects noted above. Finally, evidence is provided to show that cobalt and hypoxia both induce a posttranslational modification (or loss of one) in HIF-1alpha that affects its binding to VHL. We propose that dynamic, site-specific interaction of HIF-1alpha with VHL provides one mechanism by which HIF-1alpha can be regulated.