PHDs overactivation during chronic hypoxia “desensitizes” HIFα and protects cells from necrosis

doi:10.1073/pnas.0705680105

PHDs overactivation during chronic hypoxia “desensitizes” HIFα and protects cells from necrosis

*Institute of Signaling, Developmental Biology, and Cancer Research, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 6543, University of Nice, Centre Antoine Lacassagne, 06189 Nice, France; and
^†Cell Biology and Stem Cells Unit, Cooperative Research Centre on Biosciences, Technology Park of Bizkaia, Building 801A, 48160 Derio, Spain

Edited by Salvador Moncada, University of London, London, United Kingdom, and approved February 8, 2008 (received for review June 18, 2007)

Abstract

Cell adaptation to changes in oxygen (O₂) availability is controlled by two subfamilies of O₂-dependent enzymes: the hypoxia inducible factor (HIF)–prolyl and asparaginyl hydroxylases [prolyl hydroxylases domain (PHDs) and factor inhibiting HIF (FIH)]. These oxygen sensors regulate the activity of the HIF, a transcriptional complex central in O₂ homeostasis. In well oxygenated cells, PHDs hydroxylate the HIFα subunits, thereby targeting them for proteasomal degradation. In contrast, acute hypoxia inhibits PHDs, leading to HIFα stabilisation. However, here we show that chronic hypoxia induces HIF1/2α“desensitization” in cellulo and in mice. At the basis of this general adaptative mechanism, we demonstrate that chronic hypoxia not only increases the pool of PHDs but also overactivates the three PHD isoforms. This overactivation appears to be mediated by an increase in intracellular O₂ availability consequent to the inhibition of mitochondrial respiration. By using in cellulo and in vivo siRNA, we found that the PHDs are the key enzymes triggering HIFα desensitization, a feedback mechanism required to protect cells against necrotic cell death and thus to adapt them across a chronic hypoxia. Hence, PHDs serve as dual enzymes, for which inactivation and later overactivation is necessary for cell survival in acute or chronic hypoxia, respectively.

Footnotes

^‡To whom correspondence should be addressed. E-mail: eberra{at}cicbiogune.es
Author contributions: A.G. and E.B. designed research; A.G., K.I., N.M., and E.B. performed research; A.G., J.P., and E.B. analyzed data; and A.G. and E.B. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.