Dual mechanism for the translation of subgenomic mRNA from Sindbis virus in infected and uninfected cells

• Published in: PloS one Vol. 4; no. 3; p. e4772
• Main Authors: Sanz, Miguel Angel, Castelló, Alfredo, Ventoso, Iván, Berlanga, Juan José, Carrasco, Luis
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 10.03.2009; Public Library of Science (PLoS)
• Subjects: Alphavirus Infections - genetics; Alphavirus Infections - virology; Animals; Arsenic compounds; Arsenite; Cell Line; Cloning; Codon, Initiator; Codons; Confocal microscopy; Cricetinae; Deactivation; Eukaryotic Initiation Factor-2 - metabolism; Eukaryotic Initiation Factor-4G - metabolism; Gene expression; Genomes; Glycoproteins; Health aspects; Inactivation; Infection; Infections; Inhibition; Initiation factor eIF-4G; Initiation factors; Mesocricetus; Messenger RNA; Microscopy; Molecular Biology/Translation Mechanisms; Molecular Biology/Translational Regulation; mRNA; Mutagenesis; Phosphorylation; Proteases; Protein Biosynthesis; Protein synthesis; Proteins; Ribonucleic acid; Ribosomes; RNA; RNA Viruses; RNA, Messenger - genetics; RNA, Viral - genetics; Sindbis Virus - genetics; Structural proteins; Translation; Translation (Genetics); Virology/Effects of Virus Infection on Host Gene Expression; Virus replication; Viruses
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0004772

Infection of BHK cells by Sindbis virus (SV) gives rise to a profound inhibition of cellular protein synthesis, whereas translation of viral subgenomic mRNA that encodes viral structural proteins, continues for hours. To gain further knowledge on the mechanism by which this subgenomic mRNA is translated, the requirements for some initiation factors (eIFs) and for the presence of the initiator AUG were examined both in infected and in uninfected cells. To this end, BHK cells were transfected with different SV replicons or with in vitro made SV subgenomic mRNAs after inactivation of some eIFs. Specifically, eIF4G was cleaved by expression of the poliovirus 2A protease (2A(pro)) and the alpha subunit of eIF2 was inactivated by phosphorylation induced by arsenite treatment. Moreover, cellular location of these and other translation components was analyzed in BHK infected cells by confocal microscopy. Cleavage of eIF4G by poliovirus 2A(pro) does not hamper translation of subgenomic mRNA in SV infected cells, but bisection of this factor blocks subgenomic mRNA translation in uninfected cells or in cell-free systems. SV infection induces phosphorylation of eIF2alpha, a process that is increased by arsenite treatment. Under these conditions, translation of subgenomic mRNA occurs to almost the same extent as controls in the infected cells but is drastically inhibited in uninfected cells. Notably, the correct initiation site on the subgenomic mRNA is still partially recognized when the initiation codon AUG is modified to other codons only in infected cells. Finally, immunolocalization of different eIFs reveals that eIF2 alpha and eIF4G are excluded from the foci, where viral RNA replication occurs, while eIF3, eEF2 and ribosomes concentrate in these regions. These findings support the notion that canonical initiation takes place when the subgenomic mRNA is translated out of the infection context, while initiation can occur without some eIFs and even at non-AUG codons in infected cells.