An oxygen-regulated switch in the protein synthesis machinery

Abstract

Protein synthesis involves the translation of ribonucleic acid information into proteins, the building blocks of life. The initial step of protein synthesis is the binding of the eukaryotic translation initiation factor 4E (eIF4E) to the 7-methylguanosine (m7-GpppG) 5′ cap of messenger RNAs1,2. Low oxygen tension (hypoxia) represses cap-mediated translation by sequestering eIF4E through mammalian target of rapamycin (mTOR)-dependent mechanisms3,4,5,6. Although the internal ribosome entry site is an alternative translation initiation mechanism, this pathway alone cannot account for the translational capacity of hypoxic cells7,8. This raises a fundamental question in biology as to how proteins are synthesized in periods of oxygen scarcity and eIF4E inhibition9. Here we describe an oxygen-regulated translation initiation complex that mediates selective cap-dependent protein synthesis. We show that hypoxia stimulates the formation of a complex that includes the oxygen-regulated hypoxia-inducible factor 2α (HIF-2α), the RNA-binding protein RBM4 and the cap-binding eIF4E2, an eIF4E homologue. Photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation (PAR-CLIP)10 analysis identified an RNA hypoxia response element (rHRE) that recruits this complex to a wide array of mRNAs, including that encoding the epidermal growth factor receptor. Once assembled at the rHRE, the HIF-2α–RBM4–eIF4E2 complex captures the 5′ cap and targets mRNAs to polysomes for active translation, thereby evading hypoxia-induced repression of protein synthesis. These findings demonstrate that cells have evolved a program by which oxygen tension switches the basic translation initiation machinery.

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Figure 1: HIF-2α activates EGFR mRNA translation by interacting with its 3′ UTR.
Figure 2: RBM4 recruits HIF-2α to the 3′ UTR for hypoxic translation.
Figure 3: HIF-2α–RBM4 recruits the m 7 -GTP cap by means of an interaction with eIF4E2.
Figure 4: An oxygen-regulated switch from eIF4E- to eIF4E2-dependent protein synthesis.

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Gene Expression Omnibus

Data deposits

Illumina sequencing data are deposited in the Gene Expression Omnibus (http://www.ncbi.nlm.nih.gov/geo/) under accession number GSE36247.

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Acknowledgements

We thank J. Côté, W. Kaelin, C. Kennedy and T. Tuschl for reagents and technical advice. This work was funded by the Canadian Institutes of Health Research (S.L. and M.H.). J.U. is a Research Fellow of the Terry Fox Foundation (Canadian Cancer Society Award no. 700014). A.F. was supported by a Terry Fox Foundation Studentship from the Canadian Cancer Society.

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J.U. performed most experiments and made most of the plasmid constructs, with assistance from C.E.H. (who identified RBM4 interaction with HIF-2α, participated in PAR-CLIP experiments, and made some luciferase contructs), G.L. (who performed experiments with human renal proximal tubular epithelial cells), A.F. (who performed actinomycin D experiments on total hypoxic EGFR levels, created stable shHIF-2α and shHIF-1α cell lines and some plasmid constructs), M.D.J. (who created luciferase constructs for CGG mutagenesis and rHRE mapping and created HIF-2α truncation mutants), M.R.F. (who performed eIF4E2 co-IP assays) and J.P. (who created some luciferase constructs). J.U., C.E.H., G.L., A.F., M.R.F., M.H., A.P. and S.L. conceived the experiments and analysed the data. J.U. and S.L. wrote the paper.

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Correspondence to Stephen Lee.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Figures 1-30, Supplementary Tables 1-2 and Supplementary Methods. (PDF 3520 kb)

Supplementary Data 1

This file contains a list of RBM4 PAR-CLIP mRNA targets. (XLS 638 kb)

Supplementary Data 2

This file contains a list of HIF-2α/RBM4 PAR-CLIP mRNA targets. (XLS 246 kb)

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Uniacke, J., Holterman, C., Lachance, G. et al. An oxygen-regulated switch in the protein synthesis machinery. Nature 486, 126–129 (2012). https://doi.org/10.1038/nature11055

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