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

Hypoxia-inducible factor (HIF)-1 alpha is a transcription factor that plays a critical role in regulating genes involved in erythropoiesis and angioge nesis, Recent evidence indicates that the von Hippel-Lindau tumor suppresso r protein (VHL) is part of a ubiquitin ligase complex that promotes the deg radation of HIF-1 alpha under normoxic conditions. Under hypoxic conditions , HIF-1 alpha 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-1 al pha fragment comprising residues 531-652 to coimmunoprecipitate with VHL, H ypoxia and cobalt both significantly diminish the interaction, and furtherm ore, normoxia treatment after hypoxia rapidly normalizes it. This HIF-1 alp ha fragment confers hypoxia and cobalt inducibility on a heterologous prote in. Significantly, contained within this fragment is a short 27-residue seq uence that behaves identically in all respects noted above. Finally, eviden ce is provided to show that cobalt and hypoxia both induce a posttranslatio nal modification (or loss of one) in HIF-1 alpha that affects its binding t o VHL. We propose that dynamic, site-specific interaction of HIF-1 alpha wi th VHL provides one mechanism by which HIF-1 alpha can be regulated.