Hypoxic up-regulation of erythroid 5-aminolevulinate synthase.
The erythroid-specific isoform of 5-aminolevulinate synthase (ALAS2) catalyzes the rate-limiting step in heme biosynthesis. The hypoxia-inducible factor-1 (HIF-1) transcriptionally up-regulates erythropoietin, transferrin, and transferrin receptor, leading to increased erythropoiesis and hematopoietic iron supply. To test the hypothesis that ALAS2 expression might be regulated by a similar mechanism, we exposed murine erythroleukemia cells to hypoxia (1% O(2)) and found an up to 3-fold up-regulation of ALAS2 mRNA levels and an increase in cellular heme content. A fragment of the ALAS2 promoter ranging from -716 to +1 conveyed hypoxia responsiveness to a heterologous luciferase reporter gene construct in transiently transfected HeLa cells. In contrast, iron depletion, known to induce HIF-1 activity but inhibit ALAS2 translation, did not increase ALAS2 promoter activity. Mutation of a previously predicted HIF-1-binding site (-323/-318) within this promoter fragment and DNA-binding assays revealed that hypoxic up-regulation is independent of this putative HIF-1 DNA-binding site.
Hofer
Thomas
T
Institute of Veterinary Physiology, University of Zurich, Switzerland.
Wenger
Roland H
RH
Kramer
Marianne F
MF
Ferreira
Gloria C
GC
Gassmann
Max
M
D000624:5-Aminolevulinate Synthetase / Q000235:genetics*; D000818:Animals; D004268:DNA-Binding Proteins; D004912:Erythrocytes / Q000201:enzymology*; D006367:HeLa Cells; D006418:Heme / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000201:enzymology*; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007501:Iron / Q000494:pharmacology; D051379:Mice; D009687:Nuclear Proteins; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis; D014157:Transcription Factors; D015854:Up-Regulation
D004268:DNA-Binding Proteins; C497442:HIF1A protein, human; C497443:Hif1a protein, mouse; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009687:Nuclear Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D006418:Heme; D007501:Iron; D000624:5-Aminolevulinate Synthetase