Hypoxic up-regulation of erythroid 5-aminolevulinate synthase

• Published in: Blood 2003-01, Vol.101 (1), p.348-350
• Main Authors: Hofer, Thomas, Wenger, Roland H., Kramer, Marianne F., Ferreira, Gloria C., Gassmann, Max
• Format: Article
• Language: English
• Subjects: 5-Aminolevulinate Synthetase - genetics; Animals; Biological and medical sciences; Cell differentiation, maturation, development, hematopoiesis; Cell physiology; DNA-Binding Proteins; Erythrocytes - enzymology; Fundamental and applied biological sciences. Psychology; HeLa Cells; Heme - metabolism; Humans; Hypoxia - enzymology; Hypoxia-Inducible Factor 1; Hypoxia-Inducible Factor 1, alpha Subunit; Iron - pharmacology; Mice; Molecular and cellular biology; Nuclear Proteins; Promoter Regions, Genetic; RNA, Messenger - biosynthesis; Transcription Factors; Up-Regulation
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2002-03-0773

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% O2) 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.