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The VEGF IRESes are differentially susceptible to translation inhibition by miR-16
Zeïneb S Karaa1, Jason S Iacovoni, Amandine Bastide
1Institut National de la Santé et de la Recherche Médicale, Toulouse, France.
Abstract:
Experiments with EMCV (Encephalomyocarditis virus) internal ribosome entry sites (IRESes) have shown that microRNAs (miRs) are unable to inhibit IRES driven translation. However, it is accepted that miRs can inhibit translation through multiple mechanisms, only some of which require interaction with the 5' cap structure. In this report, we first validate the targeting of miR-16 to a predicted binding site in the VEGF 3'UTR. We developed a series of experiments to ascertain whether or not miR-16 can inhibit translation of transcripts driven by either of the VEGF IRESes. Our results indicate that cellular IRESes can be classified as both sensitive and insensitive to miR control. While VEGF IRES-A activity was not altered by miR-16 targeting to the 3'UTR, IRES-B was susceptible to miR-16 inhibition. Taken together with previous results that show that IRES-B selectively translates the CUG initiated VEGF-121 isoform, we can conclude that the existence of two differentially susceptible IRESes in the VEGF 5'UTR leads to even more complex regulatory control of VEGF isoform production. This study demonstrates for the first time the inhibition of cellular IRES driven translation by a miR.
Insights
MicroRNAs (miRs) can inhibit translation, but not all internal ribosome entry sites (IRESes) are affected. This study shows that one VEGF IRES is sensitive to miR-16, revealing complex regulation of gene expression.
Area of Science:
- Molecular Biology
- Gene Regulation
- RNA Biology
Background:
- MicroRNAs (miRs) are known regulators of gene expression, typically inhibiting translation.
- Previous studies suggested microRNAs cannot inhibit translation driven by internal ribosome entry sites (IRESes).
- The vascular endothelial growth factor (VEGF) gene utilizes multiple IRES elements for translation initiation.
Purpose of the Study:
- To investigate whether microRNA-16 (miR-16) can inhibit translation mediated by VEGF IRES elements.
- To determine if cellular IRES elements exhibit differential sensitivity to microRNA-mediated translational repression.
- To elucidate the regulatory mechanisms controlling VEGF isoform production.
Main Methods:
- Validated miR-16 binding to the VEGF 3' untranslated region (3'UTR).
- Constructed reporter systems to assess translation driven by VEGF IRES-A and IRES-B.
- Quantified the effect of miR-16 on IRES-driven translation.
Main Results:
- Confirmed miR-16 targets a specific site within the VEGF 3'UTR.
- Demonstrated that VEGF IRES-A activity is not affected by miR-16.
- Showed that VEGF IRES-B is susceptible to miR-16-mediated translational inhibition.
- Identified differential miR sensitivity between the two VEGF IRES elements.
Conclusions:
- Cellular IRES elements can be classified as either sensitive or insensitive to microRNA regulation.
- VEGF IRES-B, which drives translation of the VEGF-121 isoform, is subject to miR-16 inhibition.
- The presence of differentially regulated IRESes in the VEGF 5'UTR provides a complex mechanism for controlling VEGF isoform production.
- This study provides the first evidence of microRNA-mediated inhibition of cellular IRES-driven translation.
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