Hypoxia-inducible factor-1alpha mRNA contains an internal ribosome entry site that allows efficient translation during normoxia and hypoxia.
HIF-1alpha is the regulated subunit of the HIF-1 transcription factor, which induces transcription of a number of genes involved in the cellular response to hypoxia. The HIF-1alpha protein is rapidly degraded in cells supplied with adequate oxygen but is stabilized in hypoxic cells. Using polysome profile analysis, we found that translation of HIF-1alpha mRNA in NIH3T3 cells is spared the general reduction in translation rate that occurs during hypoxia. To assess whether the 5'UTR of the HIF-1alpha mRNA contains an internal ribosome entry site (IRES), we constructed a dicistronic reporter with the HIF-1alpha 5'UTR inserted between two reporter coding regions. We found that the HIF-1alpha 5'UTR promoted translation of the downstream reporter, indicating the presence of an IRES. The IRES had activity comparable to that of the well-characterized c-myc IRES. IRES activity was not affected by hypoxic conditions that caused a reduction in cap-dependent translation, and IRES activity was less affected by serum-starvation than was cap-dependent translation. These data indicate that the presence of an IRES in the HIF-1alpha 5'UTR allows translation to be maintained under conditions that are inhibitory to cap-dependent translation.
Lang
Kenneth J D
KJ
Hanson Centre for Cancer Research, Institute of Medical and Veterinary Science, Adelaide, South Australia 5000, Australia.
Kappel
Andreas
A
Goodall
Gregory J
GJ
D016475:3T3 Cells; D020121:5' Untranslated Regions; D000818:Animals; D016895:Culture Media, Serum-Free; D016228:Endothelial Growth Factors / Q000235:genetics; D016259:Genes, myc; D006367:HeLa Cells; D006801:Humans; D000860:Hypoxia / Q000378:metabolism; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics; D008222:Lymphokines / Q000235:genetics; D051379:Mice; D010100:Oxygen / Q000378:metabolism*; D014176:Protein Biosynthesis; D012333:RNA, Messenger; D012270:Ribosomes / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics*; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
D020121:5' Untranslated Regions; D016895:Culture Media, Serum-Free; D016228:Endothelial Growth Factors; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines; D012333:RNA, Messenger; D014157:Transcription Factors; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D010100:Oxygen