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Unlike for cellular mRNAs and other viral internal ribosome entry sites (IRESs), the eIF3 subunit e is not required for the translational activity of the HCV IRES.
J Biol Chem, 295(7):1843-1856.
Viruses depend on the host cell translation machinery for their replication, andone common strategy is the presence of internal ribosome entry sites (IRESs) inthe viral RNAs, using different sets of host translation initiation factors. Thehepatitis C virus (HCV) IRES binds eukaryotic translation initiation factor 3(eIF3), but the exact functional role of the eIF3 complex and of its subunitsremains to be precisely defined. Toward this goal, here we focused on eIF3subunit e. We used an in vitro assay combining a ribosome-depleted rabbitreticulocyte lysate and ribosomes prepared from HeLa or Huh-7.5 cells transfectedwith either control or eIF3e siRNAs. eIF3e silencing reduced translation mediatedby the 5'UTR of various cellular genes and HCV-like IRESs. However, this effectwas not observed with the bona fide HCV IRES. Silencing of eIF3e reduced theintracellular levels of the c, d, and l subunits of eIF3 and their associationwith the eIF3 core subunit a. A pulldown analysis of eIF3 subunits associatedwith the HCV IRES disclosed similar effects and that the a subunit is criticalfor binding to the HCV IRES. Carrying out HCV infections of control andeIF3e-silenced Huh-7.5 cells, we found that in agreement with the in vitrofindings, eIF3e silencing does not reduce HCV replication and viral proteinexpression. We conclude that unlike for host cellular mRNAs, the entire eIF3 isnot required for HCV RNA translation, favoring viral expression under conditionsof low eIF3e levels.
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