title: Regulation of the Drosophila hypoxia-inducible factor alpha Sima by CRM1-dependent nuclear export.
abstract: Hypoxia-inducible factor alpha (HIF-alpha) proteins are regulated by oxygen levels through several different mechanisms that include protein stability, transcriptional coactivator recruitment, and subcellular localization. It was previously reported that these transcription factors are mainly nuclear in hypoxia and cytoplasmic in normoxia, but so far the molecular basis of this regulation is unclear. We show here that the Drosophila melanogaster HIF-alpha protein Sima shuttles continuously between the nucleus and the cytoplasm. We identified the relevant nuclear localization signal and two functional nuclear export signals (NESs). These NESs are in the Sima basic helix-loop-helix (bHLH) domain and promote CRM1-dependent nuclear export. Site-directed mutagenesis of either NES provoked Sima nuclear retention and increased transcriptional activity, suggesting that nuclear export contributes to Sima regulation. The identified NESs are conserved and probably functional in the bHLH domains of several bHLH-PAS proteins. We propose that rapid nuclear export of Sima regulates the duration of cellular responses to hypoxia.
authors.affiliation: Instituto Leloir and FBMC, FCEyN, Universidad de Buenos Aires, CONICET, Patricias Argentinas 435, Buenos Aires 1405, Argentina.
authors.forename: Nuria M
authors.initials: NM
authors.lastname: Romero
authors.forename: Maximiliano
authors.initials: M
authors.lastname: Irisarri
authors.forename: Peggy
authors.initials: P
authors.lastname: Roth
authors.forename: Ana
authors.initials: A
authors.lastname: Cauerhff
authors.forename: Christos
authors.initials: C
authors.lastname: Samakovlis
authors.forename: Pablo
authors.initials: P
authors.lastname: Wappner
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D049790:Nuclear Export Signals / Q000235:genetics; D019913:Nuclear Localization Signals / Q000737:chemistry / Q000235:genetics; D011499:Protein Processing, Post-Translational; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D000097606:Exportin 1 Protein
chemical_list: D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D028884:Karyopherins; D049790:Nuclear Export Signals; D019913:Nuclear Localization Signals; D018160:Receptors, Cytoplasmic and Nuclear; D000097606:Exportin 1 Protein; C100429:Sima protein, Drosophila