Efficient translation of mouse hypoxia-inducible factor-1alpha under normoxic and hypoxic conditions.
The heterodimeric hypoxia-inducible factor-1 (HIF-1), consisting of the subunits HIF-1alpha and HIF-1beta/ARNT, is a master transcriptional regulator of oxygen homeostasis. Under hypoxic conditions, HIF-1alpha levels very rapidly increase, mostly due to protein stabilization. However, translational regulation of HIF-1alpha has not been directly analyzed so far. Mouse HIF-1alpha exists as two mRNA isoforms (termed mHIF-1alphaI.1 and mHIF-1alphaI. 2) containing structurally different 5'-termini which might modulate translation initiation. Whereas the in vitro translation efficiency of these two mRNA isoforms was about equal, the mHIF-1alphaI.2 5'-untranslated region (5'-UTR) conferred significantly higher in vivo luciferase reporter gene activity than the mHIF-1alphaI.1 5'-UTR. Similar corresponding luciferase mRNA levels indicate translational rather than transcriptional alterations. Reporter gene expression was not affected upon exposure of transiently transfected cells to hypoxia (1% oxygen). Direct assessment of translational regulation by polysomal profile analysis of HeLaS3 cells showed that HIF-1alpha (and to a lower extent ARNT) mRNA was found mainly in the translationally active polyribosomal fractions under both normoxic and hypoxic conditions. In contrast, the association of mRNAs for beta-actin and ribosomal protein L28 with the polyribosomal fractions was substantially reduced under hypoxic conditions, suggesting decreased overall protein synthesis. Thus, efficient translation of mouse HIF-1alpha in a situation where the general translation efficiency is reduced represents a prerequisite for the very rapid accumulation of HIF-1alpha protein upon exposure to hypoxia.
Görlach
A
A
Institute of Physiology, University of Zürich-Irchel, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
Camenisch
G
G
Kvietikova
I
I
Vogt
L
L
Wenger
R H
RH
Gassmann
M
M
D000818:Animals; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D015687:Cell Hypoxia; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D019281:Dimerization; D005091:Exons; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006367:HeLa Cells; D006801:Humans; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051379:Mice; D009687:Nuclear Proteins / Q000096:biosynthesis* / Q000235:genetics; D010957:Plasmids; D014176:Protein Biosynthesis; D020033:Protein Isoforms / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D018336:Receptors, Aryl Hydrocarbon; D014157:Transcription Factors / Q000235:genetics; D014162:Transfection
C497396:ARNT protein, human; C497397:Arnt protein, mouse; 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; D020033:Protein Isoforms; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D014157:Transcription Factors; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator