Ribosomal Protein S25 Dependency Reveals a Common Mechanism for Diverse Internal Ribosome Entry Sites and Ribosome Shunting

Abstract

During viral infection or cellular stress, cap-dependent translation is shut down. Proteins that are synthesized under these conditions use alternative mechanisms to initiate translation. This study demonstrates that at least two alternative translation initiation routes, internal ribosome entry site (IRES) initiation and ribosome shunting, rely on ribosomal protein S25 (RPS25). This suggests that they share a mechanism for initiation that is not employed by cap-dependent translation, since cap-dependent translation is not affected by the loss of RPS25. Furthermore, we demonstrate that viruses that utilize an IRES or a ribosome shunt, such as hepatitis C virus, poliovirus, or adenovirus, have impaired amplification in cells depleted of RPS25. In contrast, viral amplification of a virus that relies solely on cap-dependent translation, herpes simplex virus, is not hindered. We present a model that explains how RPS25 can be a nexus for multiple alternative translation initiation pathways.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.00879-12.

ACKNOWLEDGMENTS

We thank David Bedwell for careful reading of the manuscript. We thank Peter Sarnow (Stanford School of Medicine) for the HCV plasmid, Jacqueline N. Parker (University of Alabama at Birmingham) for HSV-1, and Charles Rice (Rockefeller University) for the NS5A antibody.

This work is supported by the National Institutes of Health (grants R01GM084547 and 3R01GM084547-01A1S1 to S.R.T.) and a UAB Cancer Center HIV-Associated Malignancy pilot research grant (UAB Comprehensive Cancer Center core support grant P30 CA13148) to S.R.T.

We declare that we have no conflict of interest.