title: Overexpression of PH-4, a novel putative proline 4-hydroxylase, modulates activity of hypoxia-inducible transcription factors.
abstract: Hypoxia-inducible transcription factors (HIFs) are important for transcriptional adaptation to hypoxia. Availability of HIFs is regulated via posttranslational modification of their alpha subunits (HIF-1alpha and HIF-2alpha). Under normoxia, two highly conserved proline residues within the oxygen-dependent degradation domain (ODDD) are hydroxylated by oxoglutarate-dependent proline 4-hydroxylases EGLN1-3. Hydroxylated HIF-alpha interacts with the pVHL-E3 ubiquitin ligase complex and, subsequently, is degraded via the proteasomal pathway. We identified a novel putative proline 4-hydroxylase, PH-4, with an aminoterminal EF-hand motif and a carboxyterminal catalytic domain, which was highly expressed in most organs, and-unlike EGLNs which localize to the cytoplasm and nucleus-was associated with the endoplasmic reticulum. Like EGLNs, PH-4 overexpressed in cellular reporter assays suppressed the HIF transactivation activity, dependent on the consensus ODDD proline residues. Suppression of transactivation was correlated with decrease of cellular contents of HIF. Thus, PH-4 might be related to cellular oxygen sensing.
authors.affiliation: Bayer AG, Institut für Herz-/Kreislauf-Forschung, Aprather Weg 18a, Wuppertal, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: Oehme
authors.forename: Peter
authors.initials: P
authors.lastname: Ellinghaus
authors.forename: Peter
authors.initials: P
authors.lastname: Kolkhof
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Smith
authors.forename: Shyam
authors.initials: S
authors.lastname: Ramakrishnan
authors.forename: Joachim
authors.initials: J
authors.lastname: Hütter
authors.forename: Matthias
authors.initials: M
authors.lastname: Schramm
authors.forename: Ingo
authors.initials: I
authors.lastname: Flamme
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D017930:Genes, Reporter; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008969:Molecular Sequence Data; D010100:Oxygen / Q000378:metabolism*; D011393:Procollagen-Proline Dioxygenase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D014018:Tissue Distribution; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D011393:Procollagen-Proline Dioxygenase; D010100:Oxygen