Hypoxia-mediated selective mRNA translation by an internal ribosome entry site-independent mechanism.
Although it is advantageous for hypoxic cells to inhibit protein synthesis and conserve energy, it is also important to translate mRNAs critical for adaptive responses to hypoxic stress. Because internal ribosome entry sites (IRES) have been postulated to mediate this preferential synthesis, we analyzed the 5 '-untranslated regions from a panel of stress-regulated mRNAs for m(7)GTP cap-independent translation and identified putative IRES elements in encephalomyocarditis virus, vascular endothelial growth factor, hypoxia-inducible factors (HIFs) 1alpha and 2alpha, glucose transporter-like protein 1, p57(Kip2), La, BiP, and triose phosphate isomerase transcripts. However, when capped and polyadenylated dicistronic RNAs were synthesized in vitro and transfected into cells, cellular IRES-mediated translation accounted for less than 1% that of the level of cap-dependent translation. Moreover, hypoxic stress failed to activate cap-independent synthesis, indicating that it is unlikely that this is the primary mechanism for the maintenance of the translation of these mRNAs under low O(2). Furthermore, although HIF-1alpha is frequently cited as an example of an mRNA that is preferentially translated, we demonstrate that under different levels and durations of hypoxic stress, changes in newly synthesized HIF-1alpha and beta-actin protein levels mirror alterations in corresponding mRNA abundance. In addition, our data suggest that cyclin-dependent kinase inhibitor p57(Kip2) and vascular endothelial growth factor mRNAs are selectively translated by an IRES-independent mechanism under hypoxic stress.
Young
Regina M
RM
Abramson Family Cancer Research Institute, Departments of Genetics and Medicine, University of Pennsylvania School of Medicine, and Howard Hughes Medical Institute, University of Pennsylvania, Philadelphia Pennsylvania 19104, USA.
Wang
Shang-Jui
SJ
Gordan
John D
JD
Ji
Xinjun
X
Liebhaber
Stephen A
SA
Simon
M Celeste
MC
D000199:Actins / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D050761:Cyclin-Dependent Kinase Inhibitor p57 / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D000860:Hypoxia; D051379:Mice; D041681:NIH 3T3 Cells; D011132:Polyribosomes / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
D000199:Actins; D050761:Cyclin-Dependent Kinase Inhibitor p57; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; D006160:Guanosine Triphosphate; D005947:Glucose