The Mouse Gene for Hypoxia-Inducible Factor-1α

Genomic Organization, Expression and Characterization of an Alternative First Exon and 5′ Flanking Sequence

Authors


  • Note. The novel nucleotide sequences reported in this paper have been deposited with the EMBL/GenBank/DDBJ data bases and are available under accession numbers Y09085 and Y09086.

R. H. Wenger, Physiologisches Institut der Universität Zürich-Irchel, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
Fax: +41 1 364 05 64.
E-mail: labbauer@physiol.unizh.ch
URL:http://www.unizh.ch/physiol

Abstract

The ubiquitously expressed hypoxia-inducible factor-1 (HIF-1) is involved in expression of a large number of oxygen-regulated genes. HIF-1 is a heterodimer consisting of an α and a β subunit, both belonging to the basic-helix-loop-helix Per-aryl hydrocarbon receptor nuclear translocator-Sim (PAS) family of transcription factors. Whereas HIF-1α is a novel member of this family, HIF-1β is identical to the aryl hydrocarbon receptor nuclear translocator, previously recognized to be involved in xenobiotic metabolism. cDNA cloning revealed that mouse HIF-1α can be expressed as two mRNA isoforms containing alternative 5′ untranslated regions and two different predicted translational start sites. We cloned and characterized 20.5 kb of the mouse HIF-1α gene (Hifla) containing exon II–XV. The two alternative first exons, I.1 and I.2, are separated from exon II by approximately 24 kb and 17 kb, respectively. We also sequenced Hifla exon I.1 and flanking regions, and mapped a single exon I.1 transcription initiation site. Reverse transcription PCR analysis of total RNA derived from normoxic and hypoxic mouse hepatoma and fibroblast cell lines suggested that the two alternative mRNA isoforms are constitutively co-expressed in these cells, and that two different promoters drive transcription of HIF-1α. A minimal exon I.1 promoter was identified which moderately activated heterologous gene expression, indicating that additional cis-elements are required for efficient HIF-1α transcription in vivo.

Abbreviations.
AhR

aryl hydrocarbon receptor

ARNT

AhR nuclear translocator

bHLH

basic-helix-loop-helix

EMS A

electrophoretic mobility shift assay

HIF

hypoxia-inducible factor

PAS

Per-ARNT-Sim

RACE

rapid amplification of cDNA ends

RT

reverse transcriptase

UTR

untranslated region

VEGF

vascular endothelial growth factor

Ancillary