title: Structural and functional analysis of amphioxus HIFα reveals ancient features of the HIFα family.
abstract: Hypoxia-inducible factors (HIFs) are master regulators of the transcriptional response to hypoxia. To gain insight into the structural and functional evolution of the HIF family, we characterized the HIFα gene from amphioxus, an invertebrate chordate, and identified several alternatively spliced HIFα isoforms. Whereas HIFα Ia, the full-length isoform, contained a complete oxygen-dependent degradation (ODD) domain, the isoforms Ib, Ic, and Id had 1 or 2 deletions in the ODD domain. When tagged with GFP and tested in mammalian cells, the amphioxus HIFα Ia protein level increased in response to hypoxia or CoCl2 treatment, whereas HIFα Ib, Ic, and Id showed reduced or no hypoxia regulation. Deletion of the ODD sequence in HIFα Ia up-regulated the HIFα Ia levels under normoxia. Gene expression analysis revealed HIFα Ic to be the predominant isoform in embryos and larvae, whereas isoform Ia was the most abundant form in the adult stage. The expression levels of Ib and Id were very low. Hypoxia treatment of adults had no effect on the mRNA levels of these HIFα isoforms. Functional analyses in mammalian cells showed all 4 HIFα isoforms capable of entering the nucleus and activating hypoxia response element-dependent reporter gene expression. The functional nuclear location signal (NLS) mapped to 3 clusters of basic residues. (775)KKARL functioned as the primary NLS, but (737)KRK and (754)KK also contributed to the nuclear localization. All amphioxus HIFα isoforms had 2 functional transactivation domains (TADs). Its C-terminal transactivation (C-TAD) shared high sequence identity with the human HIF-1α and HIF-2α C-TAD. This domain contained a conserved asparagine, and its mutation resulted in an increase in transcriptional activity. These findings reveal many ancient features of the HIFα family and provide novel insights into the evolution of the HIFα family.
authors.affiliation: 3Department of Molecular, Cellular and Developmental Biology, University of Michigan, Natural Science Bldg., Ann Arbor, MI 48109-1048, USA. cduan@umich.edu.
authors.forename: Shan
authors.initials: S
authors.lastname: Gao
authors.forename: Ling
authors.initials: L
authors.lastname: Lu
authors.forename: Yan
authors.initials: Y
authors.lastname: Bai
authors.forename: Peng
authors.initials: P
authors.lastname: Zhang
authors.forename: Weibo
authors.initials: W
authors.lastname: Song
authors.forename: Cunming
authors.initials: C
authors.lastname: Duan
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000196:embryology / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D000860:Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D015151:Immunoblotting; D064175:Lancelets / Q000196:embryology / Q000235:genetics* / Q000254:growth & development; D007814:Larva / Q000235:genetics / Q000254:growth & development; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D020033:Protein Isoforms; D049452:Green Fluorescent Proteins
keywords: cephalochordate; nuclear localization signal; oxygen-dependent degradation; transactivation domain