Manipulation of Cellular Processing Bodies and Their Constituents by Viruses

The processing bodies (PBs) are a form of cytoplasmic aggregates that house the cellular RNA decay machinery as well as many RNA-binding proteins and mRNAs. The PBs are constitutively present in eukaryotic cells and are involved in maintaining cellular homeostasis by regulating RNA metabolism, cell signaling, and survival. Virus infections result in modification of the PBs and their constituents. Many viruses induce compositionally altered PBs, while many others use specific components of the PBs for their replication. PB constituents are also known to restrict virus replication by a variety of mechanisms. Further, continuing studies in this rapidly emerging field of PB-virus interactions will undoubtedly provide important clues to the understanding of the role of PBs in cellular homeostasis as well as their role in virus infections and innate immune signaling

Manipulation of Cellular Processing Bodies and Their Constituents by Viruses

The processing bodies (PBs) are a form of cytoplasmic aggregates that house the cellular RNA decay machinery as well as many RNA-binding proteins and mRNAs. The PBs are constitutively present in eukaryotic cells and are involved in maintaining cellular homeostasis by regulating RNA metabolism, cell signaling, and survival. Virus infections result in modification of the PBs and their constituents. Many viruses induce compositionally altered PBs, while many others use specific components of the PBs for their replication. PB constituents are also known to restrict virus replication by a variety of mechanisms. Further, continuing studies in this rapidly emerging field of PB-virus interactions will undoubtedly provide important clues to the understanding of the role of PBs in cellular homeostasis as well as their role in virus infections and innate immune signaling

Host Cell Functions In Vesicular Stomatitis Virus Replication

Vesicular stomatitis virus (VSV), the prototypic rhabdovirus, has been used as an excellent paradigm for understanding the mechanisms of virus replication, pathogenesis, host response to virus infection and also for myriads of studies on cellular and molecular biology. Biochemical studies as well as high-throughput genomics, proteomics, and chemical approaches have revealed a plethora of cellular factors and pathways that regulate replication of VSV. These factors include those that support virus replication and also those that restrict its replication. This chapter discusses the role(s) of many of these host cell factors and pathways involved in VSV replication. Although mechanistic understanding of the roles of some of these factors in VSV replication has been obtained, the roles of many others need to be investigated for a better understanding of the virus-host cell interactions

Trim21 regulates Nmi-IFI35 complex-mediated inhibition of innate antiviral response

In this study, using an immunoprecipitation coupled with mass spectrometry approach, we have identified the E3 ubiquitin ligase Trim21 as an interacting partner of IFI35 and Nmi. We found that this interaction leads to K63-linked ubiquitination on K22 residue of Nmi, but not IFI35. Using domain deletion analysis, we found that the interaction is mediated via the coiled-coil domain of Nmi and the carboxyl-terminal SPRY domain of Trim21. Furthermore, we show that depletion of Trim21 leads to significantly reduced interaction of Nmi with IFI35, which results in the abrogation of the negative regulatory function of the Nmi-IFI35 complex on innate antiviral signaling. Thus, Trim21 appears to be a critical regulator of the functions of the Nmi-IFI35 complex. Overall, the results presented here uncover a new mechanism of regulation of the Nmi-IFI35 complex by Trim21, which may have implications for various autoimmune diseases associated uncontrolled antiviral signaling

Host Cell Functions In Vesicular Stomatitis Virus Replication

Vesicular stomatitis virus (VSV), the prototypic rhabdovirus, has been used as an excellent paradigm for understanding the mechanisms of virus replication, pathogenesis, host response to virus infection and also for myriads of studies on cellular and molecular biology. Biochemical studies as well as high-throughput genomics, proteomics, and chemical approaches have revealed a plethora of cellular factors and pathways that regulate replication of VSV. These factors include those that support virus replication and also those that restrict its replication. This chapter discusses the role(s) of many of these host cell factors and pathways involved in VSV replication. Although mechanistic understanding of the roles of some of these factors in VSV replication has been obtained, the roles of many others need to be investigated for a better understanding of the virus-host cell interactions

Heterogeneous Nuclear Ribonucleoprotein K Supports Vesicular Stomatitis Virus Replication by Regulating Cell Survival and Cellular Gene Expression

The heterogeneous nuclear ribonucleoprotein K (hnRNP K) is a member of the family of hnRNPs and was recently shown in a genome-wide small interfering RNA (siRNA) screen to support vesicular stomatitis virus (VSV) growth. To decipher the role of hnRNP K in VSV infection, we conducted studies which suggest that the protein is required for VSV spreading. Virus binding to cells, entry, and nucleocapsid uncoating steps were not adversely affected in the absence of hnRNP K, whereas viral genome transcription and replication were reduced slightly. These results indicate that hnRNP K is likely involved in virus assembly and/or release from infected cells. Further studies showed that hnRNP K suppresses apoptosis of virus-infected cells, resulting in increased cell survival during VSV infection. The increased survival of the infected cells was found to be due to the suppression of proapoptotic proteins such as Bcl-X5 and Bik in a cell-type-dependent manner. Additionally, depletion of hnRNP K resulted in not only significantly increased levels of T-cell-restricted intracellular antigen 1 (TIA1) but also switching of the expression of the two isoforms of the protein (TIA1a and TIA1b), both of which inhibited VSV replication. hnRNP K was also found to support expression of several cellular proteins known to be required for VSV infection. Overall, our studies demonstrate hnRNP K to be a multifunctional protein that supports VSV infection via its role(s) in suppressing apoptosis of infected cells, inhibiting the expression of antiviral proteins, and maintaining the expression of proteins required for the virus

A single amino acid change resulting in loss of fluorescence of eGFP in a viral fusion protein confers fitness and growth advantage to the recombinant vesicular stomatitis virus

Using a recombinant vesicular stomatitis virus encoding eGFP fused in-frame with an essential viral replication protein, the phosphoprotein P, we show that during passage in culture, the virus mutates the nucleotide C289 within eGFP of the fusion protein PeGFP to A or T, resulting in R97S/C amino acid substitution and loss of fluorescence. The resultant non-fluorescent virus exhibits increased fitness and growth advantage over its fluorescent counterpart. The growth advantage of the non-fluorescent virus appears to be due to increased transcription and replication activities of the PeGFP protein carrying the R97S/C substitution. Further, our results show that the R97S/C mutation occurs prior to accumulation of mutations that can result in loss of expression of the gene inserted at the G-L gene junction. These results suggest that fitness gain is more important for the recombinant virus than elimination of expression of the heterologous gene

The Minor Envelope Glycoproteins GP2a and GP4 of Porcine Reproductive and Respiratory Syndrome Virus Interact with the Receptor CD163

Porcine reproductive and respiratory syndrome virus (PRRSV) contains the major glycoprotein, GP5, as well as three other minor glycoproteins, namely, GP2a, GP3, and GP4, on the virion envelope, all of which are required for generation of infectious virions. To study their interactions with each other and with the cellular receptor for PRRSV, we have cloned each of the viral glycoproteins and CD163 receptor in expression vectors and examined their expression and interaction with each other in transfected cells by coimmunoprecipitation (co-IP) assay using monospecific antibodies. Our results show that a strong interaction exists between the GP4 and GP5 proteins, although weak interactions among the other minor envelope glycoproteins and GP5 have been detected. Both GP2a and GP4 proteins were found to interact with all the other GPs, resulting in the formation of multiprotein complex. Our results further show that the GP2a and GP4 proteins also specifically interact with the CD163 molecule. The carboxy-terminal 223 residues of the CD163 molecule are not required for interactions with either the GP2a or the GP4 protein, although these residues are required for conferring susceptibility to PRRSV infection in BHK-21 cells. Overall, we conclude that the GP4 protein is critical for mediating interglycoprotein interactions and, along with GP2a, serves as the viral attachment protein that is responsible for mediating interactions with CD163 for virus entry into susceptible host cell

A single amino acid change resulting in loss of fluorescence of eGFP in a viral fusion protein confers fitness and growth advantage to the recombinant vesicular stomatitis virus

Using a recombinant vesicular stomatitis virus encoding eGFP fused in-frame with an essential viral replication protein, the phosphoprotein P, we show that during passage in culture, the virus mutates the nucleotide C289 within eGFP of the fusion protein PeGFP to A or T, resulting in R97S/C amino acid substitution and loss of fluorescence. The resultant non-fluorescent virus exhibits increased fitness and growth advantage over its fluorescent counterpart. The growth advantage of the non-fluorescent virus appears to be due to increased transcription and replication activities of the PeGFP protein carrying the R97S/C substitution. Further, our results show that the R97S/C mutation occurs prior to accumulation of mutations that can result in loss of expression of the gene inserted at the G-L gene junction. These results suggest that fitness gain is more important for the recombinant virus than elimination of expression of the heterologous gene

Posttranslational Modification of Vesicular Stomatitis Virus Glycoprotein, but Not JNK Inhibition, Is the Antiviral Mechanism of SP600125

Vesicular stomatitis virus (VSV), a negative-sense single-stranded-RNA rhabdovirus, is an extremely promising oncolytic agent for cancer treatment. Since oncolytic virotherapy is moving closer to clinical application, potentially synergistic combinations of oncolytic viruses and molecularly targeted antitumor agents are becoming a meaningful strategy for cancer treatment. Mitogenactivated protein kinase (MAPK) inhibitors have been shown to impair liver cell proliferation and tumor development, suggesting their potential use as therapeutic agents for hepatocellular carcinoma (HCC). In this work, we show that the impairment of MAPK in vitro did not interfere with the oncolytic properties of VSV in HCC cell lines. Moreover, the administration of MAPK inhibitors did not restore the responsiveness of HCC cells to alpha/beta interferon (IFN-α/β). In contrast to previous reports, we show that JNK inhibition by the inhibitor SP600125 is not responsible for VSV attenuation in HCC cells and that this compound acts by causing a posttranslational modification of the viral glycoprotein