Transport of hypoxia-inducible factor HIF-1alpha into the nucleus involves importins 4 and 7

Biochem Biophys Res Commun. 2009 Dec 11;390(2):235-40. doi: 10.1016/j.bbrc.2009.09.093. Epub 2009 Sep 27.

Abstract

Hypoxia-inducible transcription factor 1 (HIF-1) mediates the cellular response to hypoxia. HIF-1 activity is controlled via the synthesis, degradation or intracellular localization of its alpha subunit. HIF-1alpha contains a C-terminal bipartite basic NLS that interacts with importins alpha. We have recently shown that HIF-1alpha also contains an atypical hydrophobic CRM1- and phosphorylation-dependent NES and can therefore shuttle in and out of the nucleus. We now report that C-terminal NLS mutants of HIF-1alpha can still enter the nucleus when CRM1-dependent nuclear export is inhibited, indicating that HIF-1alpha contains an additional functional nuclear import signal. Using an in vitro nuclear import assay, we further show that importins 4 and 7 accomplish nuclear import of HIF-1alpha more efficiently than the classical importin alpha/beta NLS receptor. Binding assays confirmed the specific physical interaction between HIF-1alpha and importins 4 and 7. Moreover, the interaction of importin 7 with HIF-1alpha is mapped at its N-terminal part encompassing the bHLH-PAS(A) domain. By expressing functional HIF-1 in yeast, we show that Nmd5, the yeast orthologue of importin 7, is required for HIF-1alpha nuclear accumulation and activity. Taken together, our data show that shuttling of HIF-1alpha between cytoplasm and nucleus is a complex process involving several members of the nuclear transport receptor family.

MeSH terms

  • Active Transport, Cell Nucleus
  • Cell Nucleus / metabolism*
  • Cytoplasm / metabolism
  • HeLa Cells
  • Humans
  • Hypoxia-Inducible Factor 1, alpha Subunit / genetics
  • Hypoxia-Inducible Factor 1, alpha Subunit / metabolism*
  • Karyopherins / genetics
  • Karyopherins / metabolism*
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / metabolism*
  • Receptors, Cytoplasmic and Nuclear / genetics
  • Receptors, Cytoplasmic and Nuclear / metabolism*

Substances

  • HIF1A protein, human
  • Hypoxia-Inducible Factor 1, alpha Subunit
  • IPO4 protein, human
  • IPO7 protein, human
  • Karyopherins
  • Membrane Transport Proteins
  • Receptors, Cytoplasmic and Nuclear