Hypoxia-inducible Factor-1α mRNA Contains an Internal Ribosome Entry Site That Allows Efficient Translation during Normoxia and Hypoxia

• DOI: 10.1091/mbc.02-02-0017
• Publication Date: 2002-07-26T22:19:52Z
• Authors: Kenneth J. D. Lang; Andreas Kappel; Gregory J. Goodall
• Keywords: Vascular Endothelial Growth Factor A; Messenger; Genes, myc; 610; Endothelial Growth Factors; alpha Subunit; Culture Media, Serum-Free; Serum-Free; Mice; 03 medical and health sciences; Animals; Humans; RNA, Messenger; Hypoxia; Lymphokines; 0303 health sciences; Vascular Endothelial Growth Factors; 3T3 Cells; myc; Hypoxia-Inducible Factor 1, alpha Subunit; Culture Media; 3. Good health; Oxygen; Genes; Hela Cells; Protein Biosynthesis; RNA; Intercellular Signaling Peptides and Proteins; Hypoxia-Inducible Factor 1; 5' Untranslated Regions; Ribosomes; HeLa Cells; Transcription Factors

HIF-1α 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-1α 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-1α 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-1α mRNA contains an internal ribosome entry site (IRES), we constructed a dicistronic reporter with the HIF-1α 5′UTR inserted between two reporter coding regions. We found that the HIF-1α 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-1α 5′UTR allows translation to be maintained under conditions that are inhibitory to cap-dependent translation.