Deletion of the Pseudorabies Virus gE/gI-US9p complex disrupts kinesin KIF1A and KIF5C recruitment during egress, and alters the properties of microtubule-dependent transport in vitro.

During infection of neurons by alphaherpesviruses including Pseudorabies virus (PRV) and Herpes simplex virus type 1 (HSV-1) viral nucleocapsids assemble in the cell nucleus, become enveloped in the cell body then traffic into and down axons to nerve termini for spread to adjacent epithelia. The viral membrane protein US9p and the membrane glycoprotein heterodimer gE/gI play critical roles in anterograde spread of both HSV-1 and PRV, and several models exist to explain their function. Biochemical studies suggest that PRV US9p associates with the kinesin-3 motor KIF1A in a gE/gI-stimulated manner, and the gE/gI-US9p complex has been proposed to recruit KIF1A to PRV for microtubule-mediated anterograde trafficking into or along the axon. However, as loss of gE/gI-US9p essentially abolishes delivery of alphaherpesviruses to the axon it is difficult to determine the microtubule-dependent trafficking properties and motor-composition of Δ(gE/gI-US9p) particles. Alternatively, studies in HSV-1 have suggested that gE/gI and US9p are required for the appearance of virions in the axon because they act upstream, to help assemble enveloped virions in the cell body. We prepared Δ(gE/gI-US9p) mutant, and control parental PRV particles from differentiated cultured neuronal or porcine kidney epithelial cells and quantitated the efficiency of virion assembly, the properties of microtubule-dependent transport and the ability of viral particles to recruit kinesin motors. We find that loss of gE/gI-US9p has no significant effect upon PRV particle assembly but leads to greatly diminished plus end-directed traffic, and enhanced minus end-directed and bidirectional movement along microtubules. PRV particles prepared from infected differentiated mouse CAD neurons were found to be associated with either kinesin KIF1A or kinesin KIF5C, but not both. Loss of gE/gI-US9p resulted in failure to recruit KIF1A and KF5C, but did not affect dynein binding. Unexpectedly, while KIF5C was expressed in undifferentiated and differentiated CAD neurons it was only found associated with PRV particles prepared from differentiated cells.

Microtubule-Dependent Trafficking of Alphaherpesviruses in the Nervous System: The Ins and Outs.

The Alphaherpesvirinae include the neurotropic pathogens herpes simplex virus and varicella zoster virus of humans and pseudorabies virus of swine. These viruses establish lifelong latency in the nuclei of peripheral ganglia, but utilize the peripheral tissues those neurons innervate for productive replication, spread, and transmission. Delivery of virions from replicative pools to the sites of latency requires microtubule-directed retrograde axonal transport from the nerve terminus to the cell body of the sensory neuron. As a corollary, during reactivation newly assembled virions must travel along axonal microtubules in the anterograde direction to return to the nerve terminus and infect peripheral tissues, completing the cycle. Neurotropic alphaherpesviruses can therefore exploit neuronal microtubules and motors for long distance axonal transport, and alternate between periods of sustained plus end- and minus end-directed motion at different stages of their infectious cycle. This review summarizes our current understanding of the molecular details by which this is achieved.

Dengue virus non-structural 1 protein interacts with heterogeneous nuclear ribonucleoprotein H in human monocytic cells.

OBJECTIVE: To study protein-protein interaction between heterogeneous nuclear ribonucleoprotein H (hnRNP H) and Dengue virus (DENV) proteins. METHODS: DENV proteins were screened against the host hnRNP H protein, in order to identify the host-viral protein-protein interactions in DENV infected THP-1 cells by co-immunoprecipitation. The co-localization of the interacting proteins was further confirmed by immunofluorescence microscopy. RESULTS: The host protein hnRNP H was found to interact with DENV non-structural 1 protein and help the virus to multiply in the cell. CONCLUSIONS: The non-structural 1 glycoprotein is a key modulator of host immune response and is also involved in viral replication. Therefore, disruption of this key interaction between hnRNP H and DENV non-structural 1 could be an important therapeutic strategy for management of DENV infection.

Effect of modulation of unfolded protein response pathway on dengue virus infection.

The unfolded protein response (UPR) is a cascade of events that helps restoring cellular homeostasis under stressful conditions. It is activated when there is an imbalance in the protein load and protein folding capacity of the endoplasmic reticulum (ER) as a result of an increase in the naïve, unfolded, or misfolded protein content of the cell. Dengue virus (DENV) utilizes the host machinery to synthesize viral proteins and replicates in the cell. During DENV infection, up-regulation of viral proteins increases the protein pool of the cell, resulting in the induction of UPR pathway. In this study, we have tried to understand the consequence of UPR induction during DENV infection in human monocytic cells. To fulfill this objective, we have used VER-155008 (VER), a known inhibitor of the 78 kDa glucose-regulated protein (GRP78), which is the master regulator of the UPR pathway. After VER treatment, cells were infected with DENV, and the induction of the UPR elements and their downstream activation was studied by western blotting and RT-PCR analysis. Interestingly, inhibition of GRP78 via VER treatment led to the decreased expression of DENV envelope protein through the activation of the UPR elements, protein kinase-like ER resident kinase, activating transcription factor 6, and inositol-requiring enzyme 1 (IRE1), and then led to the activation of innate immune factors such as double-stranded RNA-activated protein kinase (PKR), interferon regulated factor 3 (IRF3), nuclear factor-κB (NF-κB) and interleukin 1ß (IL-1ß). This strategy may be used to decrease viral infection transiently. Thus UPR elements could be important therapeutic targets for decreasing DENV multiplication.

Protein disulfide isomerase mediates dengue virus entry in association with lipid rafts.

Dengue virus (DENV) causes a febrile disease, infecting around 50-100 million people annually. The relationship between DENV proteins and host cellular responses during infection is unclear. This study investigated the interaction of host protein disulfide isomerase (PDI) with DENV proteins and role of lipid rafts in viral immunopathogenesis. Host viral protein interactions were studied by co-immunoprecipitation and co-localization. It was found that PDI interacts with DENV nonstructural protein 1 (NS1) intracellularly as well as on the surface in the lipid raft domain. Disruption of this key interaction between PDI and NS1 could be an important therapeutic strategy to block DENV infection.

Rhodiola inhibits dengue virus multiplication by inducing innate immune response genes RIG-I, MDA5 and ISG in human monocytes.

Recognition of virus infection by retinoic acid-inducible gene (RIG) I and melanoma differentiation-associated protein (MDA) 5, which are RNA helicases, and interferon-stimulated gene (ISG) 15 activates cascades of signal transduction pathways leading to production of type I interferons and proinflammatory cytokines that orchestrate the elimination of the viruses. However, it has been demonstrated that RNA-helicase-mediated innate immunity plays an essential role in defending the host from infection. In our efforts to identify plant-derived antivirals that selectively enhance ISG- and RNA-helicase-mediated antiviral immune responses, we identified a plant, rhodiola, that significantly promoted ISG, RIG-I and MDA 5 gene expression and an antiviral immune response against dengue virus (DENV) infection. Rhodiola induced interferon (IFN) ß and other cytokines, including IL-1ß, TNF-α, IL-6 and IL-8, in infected cells. It was also found that rhodiola upregulated phosphorylated eIF-2α, PKR and NF-kB in infected cells. In addition, the number of NK cells was also increased by rhodiola treatment in dengue-virus-infected human PBMCs. Treatment with a crude extract of rhodiola (RAE) resulted in effects in the 20 % range, which is similar to the magnitude of the same effects observed in DENV infections. Taken together, our results imply that rhodiola induces pharmacological modulation of RIG-I, MDA 5 and ISG signal transduction pathways in favor of the induction of a beneficial antiviral immune response against dengue virus, which can be a novel therapeutic strategy for management of infection.

Dengue virus infection induces upregulation of hn RNP-H and PDIA3 for its multiplication in the host cell.

The pathogenic mechanism of Dengue virus (DENV) infection is related to the host responses within target cells and therefore, we assessed intracellular changes in host cell proteins following DENV infection. This study provides evidence that heterogeneous nuclear ribonucleoprotein H (hnRNP-H) and protein disulfide isomerase A3 (PDIA3) helps in DENV multiplication by suppressing TNF-α production in human monocytic THP1 cells. Proteomic analysis of infected cells, identified upregulation of the host cell proteins PDIA3 and hnRNP-H in comparison to mock infected cells. The functional role of hnRNP-H and PDIA3 in DENV infection was identified by down regulating hnRNP-H and PDIA3 genes with their specific siRNA duplexes which lead to decreased intracellular viral load. It also resulted in increased TNF-α level which mediates antiviral effect. This is the first study, which reports the role of PDIA3 and hnRNP-H in TNF-α production in DENV infected cells. Collectively, these results suggest that increased level of hnRNP-H and PDIA3 expression in DENV infected THP1 cells assist in the viral replication by suppressing the TNF-α production.