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

• Published in: Molecular biology of the cell Vol. 13; no. 5; pp. 1792 - 1801
• Main Authors: Lang, Kenneth J. D., Kappel, Andreas, Goodall, Gregory J.
• Format: Journal Article
• Language: English
• Published: The American Society for Cell Biology 01.05.2002
• ISSN: 1059-1524; 1939-4586
• DOI: 10.1091/mbc.02-02-0017

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.