title: Abundance of aspargynyl-hydroxylase FIH is regulated by Siah-1 under normoxic conditions.
abstract: The activity of hypoxia-inducible factors-1alpha (HIF-1alpha) is regulated by two types of hydroxylases, prolyl-hydroxylase (PHD) and aspargynyl-hydroxylase factor inhibiting HIF-1alpha (FIH). Hydroxylation of HIF-1alpha by PHD and FIH causes proteasomal degradation and transcriptional inhibition of HIF-1alpha, respectively. Siah ubiquitin ligases regulate the abundance of PHD via targeting for proteasomal degradation. The present study investigated the role of Siah-1 in the regulation of FIH abundance under normoxic conditions. Immunohistochemical analysis of the rat brains revealed that both Siah-1 and FIH were widely distributed in the central nervous system including the cerebral cortex, the hippocampus, the striatum, the olfactory bulb, the putamen, the thalamus, the celleberum, and the brain stem. In the hippocampus, both Siah-1 and FIH predominantly expressed in neurons. Siah-1 and FIH localized mostly in the cytoplasm. In mammalian cells, FIH expression levels were increased in the presence of a proteasomal inhibitor MG132, suggesting that FIH is degraded by the ubiquitin-proteasome system. Immunoprecipitation assay and ubiquitination assay revealed that Siah-1 interacted with, and ubiquitinated FIH. Under normoxic conditions, Siah-1 facilitated degradation of FIH. On the other hand, when endogenous Siah-1 expression was suppressed using siRNA, FIH expression levels were increased, as compared to control. These results suggest that Siah-1 might play a role as a regulator of FIH abundance under normoxic conditions.
authors.affiliation: Department of Clinical Neuroscience and Therapeutics, Hiroshima University Graduate School of Biomedical Sciences, 1-2-3 Kasumi, Hiroshima 734-8551, Japan. hi31fukuba@iris.ocn.ne.jp
authors.forename: Hiromasa
authors.initials: H
authors.lastname: Fukuba
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Takahashi
authors.forename: Hong Guo
authors.initials: HG
authors.lastname: Jin
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Kohriyama
authors.forename: Masayasu
authors.initials: M
authors.lastname: Matsumoto
mesh_terms: D000818:Animals; D001921:Brain / Q000033:anatomy & histology / Q000378:metabolism*; D002460:Cell Line; D015536:Down-Regulation / Q000235:genetics; D006801:Humans; D002534:Hypoxia, Brain / Q000378:metabolism* / Q000503:physiopathology; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D007150:Immunohistochemistry; D006899:Mixed Function Oxygenases; D009474:Neurons / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D012097:Repressor Proteins / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination / Q000502:physiology; D000098563:Seven in Absentia Proteins
chemical_list: C497444:Hif1a protein, rat; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D014157:Transcription Factors; D006899:Mixed Function Oxygenases; C439790:HIF1AN protein, human; C000606147:HIF1AN protein, rat; D044767:Ubiquitin-Protein Ligases; D000098563:Seven in Absentia Proteins; D046988:Proteasome Endopeptidase Complex; D010100:Oxygen