title: Heat induction of the unphosphorylated form of hypoxia-inducible factor-1alpha is dependent on heat shock protein-90 activity.
abstract: Hypoxia-inducible factor (HIF)-1alpha is the oxygen-sensitive subunit of HIF-1, a transcriptional master regulator of oxygen homeostasis. Oxygen-dependent prolyl hydroxylation targets HIF-1alpha for ubiquitinylation and proteasomal degradation. Unexpectedly, we found that exposing mice to elevated temperatures resulted in a strong HIF-1alpha induction in kidney, liver, and spleen. To elucidate the molecular mechanisms responsible for this effect, HepG2 hepatoma cells were exposed to different temperatures (34-42 degrees C) under normoxic (20% O(2)) or hypoxic (3% O(2)) conditions. Heat was sufficient to stabilize mainly a phosphatase-resistant, low molecular weight form of HIF-1alpha (termed HIF-1alpha(a)). Heat-induced HIF-1alpha(a) accumulated in the nucleus but neither bound to DNA nor trans-activated reporter or target gene expression, demonstrating the need for post-translational modifications for these functions. The protein banding pattern of heat-induced HIF-1alpha in immunoblot analyses was clearly distinct from the HIF-1alpha pattern after prolyl hydroxylase inhibition (by hypoxia or iron chelation/replacement) or following proteasome inhibition, suggesting that heat stabilizes HIF-1alpha by a novel mechanism. Inhibition of the ATP-dependent chaperone activity of HSP90 by novobiocin or geldanamycin prevented heat-induced as well as hypoxia-induced HIF-1alpha accumulation, indicating a common role of the HSP90 chaperone activity in HIF-1alpha stabilization by these two environmental parameters.
authors.affiliation: Institute of Physiology and Department of Anaesthesiology, Medical University of Lübeck, Ratzeburger Allee 160, D-23538 Lübeck, Germany. katschinski@physio.mu-luebeck.de
authors.forename: Dorthe M
authors.initials: DM
authors.lastname: Katschinski
authors.forename: Lu
authors.initials: L
authors.lastname: Le
authors.forename: Daniel
authors.initials: D
authors.lastname: Heinrich
authors.forename: Klaus F
authors.initials: KF
authors.lastname: Wagner
authors.forename: Thomas
authors.initials: T
authors.lastname: Hofer
authors.forename: Susann G
authors.initials: SG
authors.lastname: Schindler
authors.forename: Roland H
authors.initials: RH
authors.lastname: Wenger
mesh_terms: D000818:Animals; D001692:Biological Transport; D015687:Cell Hypoxia; D002467:Cell Nucleus / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000502:physiology; D018841:HSP90 Heat-Shock Proteins / Q000502:physiology*; D006358:Hot Temperature; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051379:Mice; D009097:Multienzyme Complexes / Q000502:physiology; D010766:Phosphorylation; D011393:Procollagen-Proline Dioxygenase / Q000502:physiology; D046988:Proteasome Endopeptidase Complex; D014157:Transcription Factors / Q000096:biosynthesis* / Q000737:chemistry; D014407:Tumor Cells, Cultured
chemical_list: C497442:HIF1A protein, human; D018841:HSP90 Heat-Shock Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009097:Multienzyme Complexes; D014157:Transcription Factors; D011393:Procollagen-Proline Dioxygenase; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex