The HTLV-1 Tax protein inhibits formation of stress granules by interacting with histone deacetylase 6

In this report, we analyzed whether the degradation of mRNAs by the nonsense-mediated mRNA decay (NMD) pathway was affected in human T-lymphotropic virus type 1 (HTLV-1)-infected cells. This pathway was indeed strongly inhibited in C91PL, HUT102, and MT2 cells, and such an effect was also observed by the sole expression of the Tax protein in Jurkat and HeLa cells. In line with this activity, Tax binds INT6/EIF3E (here called INT6), which is a subunit of the translation initiation factor eukaryotic initiation factor 3 (eIF3) required for efficient NMD, as well as the NMD core factor upstream frameshift protein 1 (UPF1). It was also observed that Tax expression alters the morphology of processing bodies (P-bodies), the cytoplasmic structures which concentrate RNA degradation factors. The presence of UPF1 in these subcellular compartments was increased by Tax, whereas that of INT6 was decreased. In line with these effects, the level of the phosphorylated form of UPF1 was increased in the presence of Tax. Analysis of several mutants of the viral protein showed that the interaction with INT6 is necessary for NMD inhibition. The alteration of mRNA stability was observed to affect viral transcripts, such as that coding for the HTLV-1 basic leucine zipper factor (HBZ), and also several cellular mRNAs sensitive to the NMD pathway. Our data indicate that the effect of Tax on viral and cellular gene expression is not restricted to transcriptional control but can also involve posttranscriptional regulation. Human T-lymphotropic virus type 1 (HTLV-1) infection is associated with the onset of severe diseases, mainly adult Tcell leukemia (ATL) and tropical spastic paraparesis, also named HTLV-1-associated myelopathy, in 2 to 5% of patients (for a review, see reference 44). These conditions are characterized by a long latency, with infection often occurring in childhood and disease development at an adult age. Accordingly, it is estimated that the development of ATL involves several phases, ending in the acute proliferation of monoclonal ATL cells. At the initial stage, lymphocytes are infected by viral particles, leading to provirus integration and the expression of various viral proteins. Among them, Tax plays an important role both by inducing the transcription of the provirus and by stimulating the proliferation of the host cell. Tax, which is present in both the nucleus and the cytoplasm, exerts these functions by directly binding or by modulating the expression of several key cellular proteins involved in transcriptional control, cell cycle progression, genomic stability, cell adherence and migration, protein degradation, and RNA metabolism (7).Among these various cellular proteins bound by Tax, we have previously characterized INT6, also known as EIF3E, one the 13 subunits of the translation initiation factor eukaryotic initiation factor 3 (eIF3) (16). The complex between both proteins was found to be cytoplasmic, whereas in normal cells, INT6 is present in both the cytoplasm and the nucleus (16,27,64). In mammalian cell...

Section: Discussionmentioning

confidence: 99%

The Human T-Lymphotropic Virus Type 1 Tax Protein Inhibits Nonsense-Mediated mRNA Decay by Interacting with INT6/EIF3E and UPF1

Mocquet

Neusiedler

Rende

et al. 2012

“…Previous studies of HIV-1 and HTLV-1 demonstrated that stress granule formation was inhibited in infected cells (54,55). In contrast, yeast LTR retrotransposons Ty1 and Ty3 assemble RNP complexes in the cytoplasm in conjunction with mRNA processing factors that include orthologs of mammalian stress granule and P-body proteins (10,11).…”

Section: Constitutive Colocalization Of Mmtv Gag With Yb-1mentioning

confidence: 99%

A Murine Retrovirus Co-Opts YB-1, a Translational Regulator and Stress Granule-Associated Protein, To Facilitate Virus Assembly

Bann

Beyer

Parent

2014

The Gag protein of the murine retrovirus mouse mammary tumor virus (MMTV) orchestrates the assembly of immature virus particles in the cytoplasm which are subsequently transported to the plasma membrane for release from the cell. The morphogenetic pathway of MMTV assembly is similar to that of Saccharomyces cerevisiae retrotransposons Ty1 and Ty3, which assemble virus-like particles (VLPs) in intracytoplasmic ribonucleoprotein (RNP) complexes. Assembly of Ty1 and Ty3 VLPs depends upon cellular mRNA processing factors, prompting us to examine whether MMTV utilizes a similar set of host proteins to facilitate viral capsid assembly. Our data revealed that MMTV Gag colocalized with YB-1, a translational regulator found in stress granules and P bodies, in intracytoplasmic foci. The association of MMTV Gag and YB-1 in cytoplasmic granules was not disrupted by cycloheximide treatment, suggesting that these sites were not typical stress granules. However, the association of MMTV Gag and YB-1 was RNA dependent, and an MMTV RNA reporter construct colocalized with Gag and YB-1 in cytoplasmic RNP complexes. Knockdown of YB-1 resulted in a significant decrease in MMTV particle production, indicating that YB-1 plays a role in MMTV capsid formation. Analysis by live-cell imaging with fluorescence recovery after photobleaching (FRAP) revealed that the population of Gag proteins localized within YB-1 complexes was relatively immobile, suggesting that Gag forms stable complexes in association with YB-1. Together, our data imply that the formation of intracytoplasmic Gag-RNA complexes is facilitated by YB-1, which promotes MMTV virus assembly. IMPORTANCECellular mRNA processing factors regulate the posttranscriptional fates of mRNAs, affecting localization and utilization of mRNAs under normal conditions and in response to stress. RNA viruses such as retroviruses interact with cellular mRNA processing factors that accumulate in ribonucleoprotein complexes known as P bodies and stress granules. This report shows for the first time that mouse mammary tumor virus (MMTV), a mammalian retrovirus that assembles intracytoplasmic virus particles, commandeers the cellular factor YB-1, a key regulator of translation involved in the cellular stress response. YB-1 is essential for the efficient production of MMTV particles, a process directed by the viral Gag protein. We found that Gag and YB-1 localize together in cytoplasmic granules. Functional studies of Gag/YB-1 granules suggest that they may be sites where virus particles assemble. These studies provide significant insights into the interplay between mRNA processing factors and retroviruses.

“…Other viruses including human T cell leukemia virus type 1, mammalian orthoreovirus, and Semliki Forest virus, have the ability to manipulate SG formation to benefit their replicative cycle and to regulate the shutdown of host protein synthesis (38,50,57). In addition, the growth of herpes simplex virus 1 (HSV-1), Sindbis virus, and vesicular stomatitis virus is considerably enhanced in TIA-1 knockout cells compared to parental cells (39).…”

mentioning

confidence: 99%

Herpes Simplex Virus 2 Infection Impacts Stress Granule Accumulation

Finnen

Pangka

Banfield

2012

Interference with stress granule (SG) accumulation is gaining increased appreciation as a common strategy used by diverse viruses to facilitate their replication and to cope with translational arrest. Here, we examined the impact of infection by herpes simplex virus 2 (HSV-2) on SG accumulation by monitoring the localization of the SG components T cell internal antigen 1 (TIA-1), Ras-GTPase-activating SH3-domain-binding protein (G3BP), and poly(A)-binding protein (PABP). Our results indicate that SGs do not accumulate in HSV-2-infected cells and that HSV-2 can interfere with arsenite-induced SG accumulation early after infection. Surprisingly, SG accumulation was inhibited despite increased phosphorylation of eukaryotic translation initiation factor 2␣ (eIF2␣), implying that HSV-2 encodes previously unrecognized activities designed to maintain translation initiation downstream of eIF2␣. SG accumulation was not inhibited in HSV-2-infected cells treated with pateamine A, an inducer that works independently of eIF2␣ phosphorylation. The SGs that accumulated following pateamine A treatment of infected cells contained G3BP and PABP but were largely devoid of TIA-1. We also identified novel nuclear structures containing TIA-1 that form late in infection. These structures contain the RNA binding protein 68-kDa Src-associated in mitosis (Sam68) and were noticeably absent in infected cells treated with inhibitors of viral DNA replication, suggesting that they arise as a result of late events in the virus replicative cycle.