The polypyrimidine tract-binding protein stimulates HIF-1alpha IRES-mediated translation during hypoxia.
When oxygen supply is restricted, protein synthesis is rapidly abrogated owing to inhibition of global translation. However, HIF-1alpha protein expression can persist during hypoxia, owing to an internal ribosome entry site (IRES) in the 5'-untranslated region of its mRNA. Here, we report on the molecular mechanism of HIF-1alpha IRES-mediated translation during oxygen deprivation. Using RNA affinity chromatography and UV-crosslinking experiments, we show that the polypyrimidine tract binding protein (PTB) can specifically interact with the HIF-1alpha IRES, and that this interaction is enhanced in hypoxic conditions. Overexpression of PTB enhanced HIF-1alpha IRES activity, whereas RNA interference-mediated downregula-tion of PTB protein expression inhibited HIF-1alpha IRES activity. Furthermore, hypoxia-induced stimulation of the HIF-1alpha IRES was reduced in cells in which PTB function was downregulated. In agreement with these results, the IRES activity of HIF-1alpha IRES deletion mutants that are deficient in PTB-binding could not be stimulated by oxygen deprivation. All together, our data suggest that PTB plays a stimulatory role in the IRES-mediated translation of HIF-1alpha when oxygen supply is limited.
Schepens
Bert
B
Department for Molecular Biomedical Research, VIB-Ghent University, Unit of Molecular Signal Transduction in Inflammation, B-9052 Gent-Zwijnaarde, Belgium.
Tinton
Sandrine A
SA
Bruynooghe
Yanik
Y
Beyaert
Rudi
R
Cornelis
Sigrid
S
D020121:5' Untranslated Regions / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D015687:Cell Hypoxia; D002460:Cell Line; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis / Q000235:genetics*; D051379:Mice; D038941:Polypyrimidine Tract-Binding Protein / Q000378:metabolism*; D014176:Protein Biosynthesis; D011743:Pyrimidines / Q000378:metabolism
D020121:5' Untranslated Regions; C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011743:Pyrimidines; D038941:Polypyrimidine Tract-Binding Protein