Transport of hypoxia-inducible factor HIF-1alpha into the nucleus involves importins 4 and 7.
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.
Chachami
Georgia
G
Laboratory of Biochemistry, School of Medicine, University of Thessaly, Mezourlo, 41110 Larissa, Greece.
Paraskeva
Efrosyni
E
Mingot
José-Manuel
JM
Braliou
Georgia G
GG
Görlich
Dirk
D
Simos
George
G
D021581:Active Transport, Cell Nucleus; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*
C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C545055:IPO4 protein, human; C466996:IPO7 protein, human; D028884:Karyopherins; D026901:Membrane Transport Proteins; D018160:Receptors, Cytoplasmic and Nuclear