title: Hypoxic induction of human erythroid-specific δ-aminolevulinate synthase mediated by hypoxia-inducible factor 1.
abstract: Hypoxia-inducible factor 1 (HIF1) is a heterodimeric basic helix-loop-helix transcription factor that regulates many key genes. δ-Aminolevulinate synthase (ALAS) catalyzes the first and rate-limiting reaction in the heme biosynthetic pathway. In this study, we show that hypoxia-induced expression of erythroid-specific ALAS2 is mediated by HIF1 in erythroid cells. Under hypoxic conditions, significantly increased ALAS2 mRNA and protein levels were detected in K562 cells and erythroid induction cultures of CD34+ hematopoietic stem/progenitor cells. Enforced HIF1α expression increased the level of ALAS2 expression, while HIF1α knockdown by RNA interference decreased the level of ALAS2 expression. In silico analysis revealed three potential hypoxia-response elements (HREs) that are located 611, 621, and 741 bp downstream of the ALAS2 gene. The results from reporter gene and mutation analysis suggested that these elements are necessary for a maximal hypoxic response. Chromatin immunoprecipitation and polymerase chain reaction showed that the HREs could be recognized and bound by HIF1α in vivo. These results demonstrate that the upregulation of ALAS2 during hypoxia is directly mediated by HIF1. We hypothesize that HIF1-mediated ALAS2 upregulation promotes erythropoiesis to satisfy the needs of an organism under hypoxic conditions. This may be accomplished via increased heme levels and an interaction between ALAS2 and erythropoietin.
authors.affiliation: National Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China.
authors.forename: Feng-Lin
authors.initials: FL
authors.lastname: Zhang
authors.forename: Guo-Min
authors.initials: GM
authors.lastname: Shen
authors.forename: Xiao-Ling
authors.initials: XL
authors.lastname: Liu
authors.forename: Fang
authors.initials: F
authors.lastname: Wang
authors.forename: Hua-Lu
authors.initials: HL
authors.lastname: Zhao
authors.forename: Jia
authors.initials: J
authors.lastname: Yu
authors.forename: Jun-Wu
authors.initials: JW
authors.lastname: Zhang
mesh_terms: D000624:5-Aminolevulinate Synthetase / Q000096:biosynthesis* / Q000235:genetics; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D015687:Cell Hypoxia / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D004790:Enzyme Induction / Q000502:physiology; D041905:Erythroid Cells / Q000201:enzymology* / Q000378:metabolism; D004920:Erythropoiesis / Q000235:genetics / Q000502:physiology; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000378:metabolism / Q000502:physiology*; D020014:K562 Cells; D008954:Models, Biological; D009928:Organ Specificity / Q000235:genetics; D011485:Protein Binding; D020218:Response Elements / Q000235:genetics / Q000502:physiology; D054928:Validation Studies as Topic
chemical_list: D051793:Hypoxia-Inducible Factor 1; D000624:5-Aminolevulinate Synthetase; C480079:ALAS2 protein, human