The Poly(A) Binding Protein Is Internalized in Virus-Induced Vesicles or Redistributed to the Nucleolus during Turnip Mosaic Virus Infection

Infection of cells by herpes simplex virus type 1 (HSV-1) triggers host cell shutoff whereby mRNAs are degraded and cellular protein synthesis is diminished. However, virus protein translation continues because the translational apparatus in HSV-infected cells is maintained in an active state. Surprisingly, poly(A)-binding protein 1 (PABP1), a predominantly cytoplasmic protein that is required for efficient translation initiation, is partially relocated to the nucleus during HSV-1 infection. This relocalization occurred in a time-dependent manner with respect to virus infection. Since HSV-1 infection causes cell stress, we examined other cell stress inducers and found that oxidative stress similarly relocated PABP1. An examination of stress-induced kinases revealed similarities in HSV-1 infection and oxidative stress activation of JNK and p38 mitogen-activated protein (MAP) kinases. Importantly, PABP relocalization in infection was found to be independent of the viral protein ICP27. The depletion of PABP1 by small interfering RNA (siRNA) knockdown had no significant effect on viral replication or the expression of selected virus late proteins, suggesting that reduced levels of cytoplasmic PABP1 are tolerated during infection.The lytic replication cycle of herpes simplex virus type 1 (HSV-1) can be divided into three phases, immediate-early (IE), early (E), and late (L), that occur in a coordinated sequential gene expression program. IE proteins can regulate E and L gene expression, which produces proteins involved in DNA replication, capsid production, and virion assembly. HSV infection results in host cell shutoff to facilitate the efficient production of viral proteins. First, mRNA is degraded by the virion-associated vhs protein, and then ICP27, a multifunctional regulator of gene expression, inhibits pre-mRNA splicing. As most viral mRNAs are intronless, this abrogates the production of stable cellular mRNAs that can be exported to the cytoplasm and compete for translation with viral mRNAs (44).HSV mRNAs are capped and polyadenylated and so are translated via a normal cap-dependent mechanism. Translation initiation, during which translationally active ribosomes are assembled, is a tightly regulated process (21). Eukaryotic initiation factor 4F (eIF4F) (composed of eIF4E, eIF4G, and eIF4A) that binds the cap at the 5Ј end of the mRNA promotes the recruitment of the 40S ribosomal subunit and associated factors, including eIF2-GTP initiator tRNA. The recognition of the start codon then promotes large ribosomal subunit joining. Poly(A)-binding protein 1 (PABP1), which binds and multimerizes on mRNA poly(A) tails, enhances translation initiation through interactions with the eIF4G component of the eIF4F cap-binding complex (20,29,32,51) to circularize the mRNA in a "closed-loop" conformation (24). Key protein-RNA and protein-protein interactions in the translation initiation complex are strengthened by this PABP1-mediated circularization (12).HSV-1 maintains active viral translation in the face of host translatio...

Section: Resultsmentioning

confidence: 99%

Poly(A)-Binding Protein 1 Partially Relocalizes to the Nucleus during Herpes Simplex Virus Type 1 Infection in an ICP27-Independent Manner and Does Not Inhibit Virus Replication

Salaün

MacDonald

Larralde

et al. 2010

“…The 6K, NIb, and cylindrical inclusion (CI) cistrons of TuMV were amplified from infectious clone TuMV::6K-GFP by PCR. The 6K-NIa cistron of TuMV was amplified from the plasmids containing TuMV 6K-NIa, which had been modified at the junction of 6K2 and the viral genomelinked protein (VPg) and at the active site of NIa-Pro to prevent proteolysis (5,24). All these fragments were recombined into pDONR221 and then into the binary destination vector pEarleygate101 (12) and pGWB554 (28) to produce plasmids 6K-yellow fluorescent protein (6K-YFP), 6K-NIa-monomeric red fluorescent protein (mRFP), NIb-mRFP, and CI-mRFP, respectively.…”

Section: Methodsmentioning

confidence: 99%

Sequential Recruitment of the Endoplasmic Reticulum and Chloroplasts for Plant Potyvirus Replication

Wèi

Huang

McNeil

et al. 2010

Self Cite

203

225

The replication of positive-strand RNA viruses occurs in cytoplasmic membrane-bound virus replication complexes (VRCs). Depending on the virus, distinct cellular organelles such as the endoplasmic reticulum (ER), chloroplast, mitochondrion, endosome, and peroxisome are recruited for the formation of VRC-associated membranous structures. Previously, the 6,000-molecular-weight protein (6K) of plant potyviruses was shown to be an integral membrane protein that induces the formation of 6K-containing membranous vesicles at endoplasmic reticulum (ER) exit sites for potyvirus genome replication. Here, we present evidence that the 6K-induced vesicles predominantly target chloroplasts, where they amalgamate and induce chloroplast membrane invaginations. The vesicular transport pathway and actomyosin motility system are involved in the trafficking of the 6K vesicles from the ER to chloroplasts. Viral RNA, double-stranded RNA, and viral replicase components are concentrated at the 6K vesicles that associate with chloroplasts in infected cells, suggesting that these chloroplast-bound 6K vesicles are the site for potyvirus replication. Taken together, these results suggest that plant potyviruses sequentially recruit the ER and chloroplasts for their genome replication.The replication of eukaryotic positive-strand RNA viruses in infected cells is closely associated with unique virus-induced intracellular membranous vesicles (22). These membranous vesicles have been proposed to provide a scaffold for anchoring the virus replication complex (VRC), confine the process of RNA replication to a specific safeguarded cytoplasmic location, and prevent the activation of certain host defense mechanisms that can be triggered by double-stranded RNA (dsRNA) intermediates during virus replication (33, 47). Depending on the type of virus, the virus-induced membranous vesicles are derived from various intracellular organelles in the host. Many plant and animal viruses remodel and utilize the endoplasmic reticulum (ER) in VRCs (1,6,17,33,34,36,38,39,46). Other cellular organelles such as endosomes, lysomes, chloroplasts, peroxisomes, and mitochondria have also been suggest to be the replication site for togaviruses, tymoviruses, and tombusviruses, respectively (25,27,31). Given that the ER appears to be the site where the host cell translation machinery is hijacked for the biosynthesis of the first set of viral proteins, the subcellular location of virus replication (either in the vicinity of the ER or elsewhere) and the mechanism of transport to locations other than the ER are poorly understood.Plant potyviruses, accounting for ϳ30% of known plant viruses including many agriculturally important viruses, e.g., Turnip mosaic virus (TuMV), Maize dwarf mosaic virus (MDMV), Tobacco etch virus (TEV), and Potato virus Y (PVY), are related to picornaviruses and picorna-like viruses (20,21,43). The potyviral genome is a single-stranded positive-sense RNA of about 10 kb in length and encodes at least 11 mature viral proteins (8, 43). Of these 11 protei...

“…Several potential translational components are associated with RCs of TuMV, including eIF(iso)4E, PABP, eEF1A, and AtRH8 (16)(17)(18)63), but their roles have remained elusive. They may function to regulate viral translation (64), as translation is coupled with replication (35) and RCs (65) during potyvirus infection.…”

Section: Fig 10mentioning

confidence: 99%

“…The model virus of this study, Potato virus A (PVA), is a positive-stranded RNA virus belonging to the genus Potyvirus. Several host proteins that function in translation have been associated with RCs of Turnip mosaic virus (TuMV) (genus Potyvirus), including eIF(iso)4E, PABP, and eEF1A (16)(17)(18). Since both PABP and eEF1A interact with the TuMV RNA-dependent RNA polymerase (RdRp), PABP and eEF1A may function in RNA replication (18,19).…”

mentioning

confidence: 99%

Ribosomal Protein P0 Promotes Potato Virus A Infection and Functions in Viral Translation Together with VPg and eIF(iso)4E

Hafrén

Eskelin

Mäkinen

2013

We report here that the acidic ribosomal protein P0 is a component of the membrane-associated Potato virus A (PVA) ribonucleoprotein complex. As a constituent of the ribosomal stalk, P0 functions in translation. Although the ribosomal stalk proteins P0, P1, P2, and P3 are all important for PVA infection, P0 appears to have a distinct role from those of the other stalk proteins in infection. Our results indicate that P0 also regulates viral RNA functions as an extraribosomal protein. We reported previously that PVA RNA can be targeted by VPg to a specific gene expression pathway that protects the viral RNA from degradation and facilitates its translation. Here, we show that P0 is essential for this activity of VPg, similar to eIF4E/eIF(iso)4E. We also demonstrate that VPg, P0, and eIF(iso)4E synergistically enhance viral translation. Interestingly, the positive effects of VPg and P0 on viral translation were negatively correlated with the cell-to-cell spread of infection, suggesting that these processes may compete for viral RNA.