title: Bilirubin activates transcription of HIF-1α in human proximal tubular cells cultured in the physiologic oxygen content.
abstract: The expression of hypoxia-inducible factor (HIF) is influenced by reactive oxygen species (ROS). Effect of bilirubin on HIF-1 expression in proximal tubular cells was investigated under physiological oxygen concentration, which is relative hypoxic condition mimicking oxygen content in the medulla of renal tissue. The human kidney (HK2) cells were cultured in 5% oxygen with or without bilirubin. HIF-1α protein expression was increased by bilirubin treatment at 0.01-0.2 mg/dL concentration. The messenger RNA expression of HIF-1α was increased by 1.69±0.05 folds in the cells cultured with 0.1 mg/dL bilirubin, compared to the control cells. The inhibitors of PI3K/mTOR, PI3K/AKT, and ERK 1/2 pathways did not attenuate increased HIF-1α expression by bilirubin. HIF-1α expression decreased by 10 µM exogenous hydrogen peroxide (H2O2); scavenger of ROS with or without bilirubin in the HK2 cells increased HIF-1α concentration more than that in the cells without bilirubin. Exogenous H2O2 decreased the phosphorylation of P70S6 kinase, which was completely reversed by bilirubin treatment. Knockdown of NOX4 gene by small interfering RNA (siRNA) increased HIF-1α mRNA expression. In coonclusion, bilirubin enhances HIF-1α transcription as well as the up-regulation of HIF-1α protein translation through the attenuation of ROS and subunits of NADPH oxidase.
authors.affiliation: Department of Internal Medicine, Hallym University College of Medicine, Seoul, Korea. ; Department of Immunology, Seoul National University Postgraduate School, Seoul, Korea.
authors.forename: Sung Gyun
authors.identifier: 0000-0002-5034-0527
authors.initials: SG
authors.lastname: Kim
authors.affiliation: Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: Shin-Young
authors.identifier: 0000-0002-6844-0614
authors.initials: SY
authors.lastname: Ahn
authors.affiliation: Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: Eun Seong
authors.identifier: 0000-0001-6237-9528
authors.initials: ES
authors.lastname: Lee
authors.affiliation: Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: Sejoong
authors.identifier: 0000-0002-7238-9962
authors.initials: S
authors.lastname: Kim
authors.affiliation: Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea. ; Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Ki Young
authors.identifier: 0000-0002-8872-8236
authors.initials: KY
authors.lastname: Na
authors.affiliation: Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea. ; Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea.
authors.forename: Dong-Wan
authors.identifier: 0000-0001-9401-892X
authors.initials: DW
authors.lastname: Chae
authors.affiliation: Department of Immunology, Seoul National University Postgraduate School, Seoul, Korea. ; Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam, Korea. ; Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Korea. ; Renal Institute, Seoul National University Medical Research Center, Seoul, Korea.
authors.forename: Ho Jun
authors.identifier: 0000-0003-1185-2631
authors.initials: HJ
authors.lastname: Chin
mesh_terms: D001663:Bilirubin / Q000494:pharmacology*; D002460:Cell Line; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000633:toxicity; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000166:cytology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034622:RNA Interference; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects*; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D001663:Bilirubin; D006861:Hydrogen Peroxide; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases; D010100:Oxygen; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C498910:NOX4 protein, human; C546842:MTOR protein, human
keywords: Bilirubin; HIF-1; Proximal Tubular Cell; ROS