A vaccinia virus-driven interplay between the MKK4/7-JNK1/2 pathway and cytoskeleton reorganization. J Virol. 2012;86:172-184. [PMID: 22031940 DOI: 10.1128/jvi.05638-11]

Ribosomes in poxvirus infection

Poxviruses are large double-stranded DNA viruses that encode their own DNA replication, transcription, and mRNA biogenesis machinery, which underlies their ability to replicate entirely in the cytoplasm. However, like all other viruses, poxviruses remain dependent on host ribosomes to translate their mRNAs into the viral proteins needed to complete their replication cycle. While earlier studies established a fundamental understanding of how poxviruses wrestle with their hosts for control of translation initiation and elongation factors that guide ribosome recruitment and mRNA decoding, recent work has begun to reveal the extent to which poxviruses directly target the ribosome itself. This review summarizes our current understanding of the regulation of ribosomes and translation in poxvirus infection.

RACK1 Regulates Poxvirus Protein Synthesis Independently of Its Role in Ribosome-Based Stress Signaling

Receptor for activated C kinase 1 (RACK1) is a small ribosomal subunit protein that is phosphorylated by vaccinia virus (VacV) to maximize translation of postreplicative (PR) mRNAs that harbor 5' polyA leaders. However, RACK1 is a multifunctional protein that both controls translation directly and acts as a scaffold for signaling to and from the ribosome. This includes stress signaling that is activated by ribosome-associated quality control (RQC) and ribotoxic stress response (RSR) pathways. As VacV infection activates RQC and stress signaling, whether RACK1 influences viral protein synthesis through its effects on translation, signaling, or both remains unclear. Examining the effects of genetic knockout of RACK1 on the phosphorylation of key mitogenic and stress-related kinases, we reveal that loss of RACK1 specifically blunts the activation of c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) at late stages of infection. However, RACK1 was not required for JNK recruitment to ribosomes, and unlike RACK1 knockout, JNK inhibitors had no effect on viral protein synthesis. Moreover, reduced JNK activity during infection in RACK1 knockout cells contrasted with the absolute requirement for RACK1 in RSR-induced JNK phosphorylation. Comparing the effects of RACK1 knockout alongside inhibitors of late stage replication, our data suggest that JNK activation is only indirectly affected by the absence of RACK1 due to reduced viral protein accumulation. Cumulatively, our findings in the context of infection add further support for a model whereby RACK1 plays a specific and direct role in controlling translation of PR viral mRNAs that is independent of its role in ribosome-based stress signaling. IMPORTANCE Receptor for activated C kinase 1 (RACK1) is a multifunctional ribosomal protein that regulates translation directly and mediates signaling to and from the ribosome. While recent work has shown that RACK1 is phosphorylated by vaccinia virus (VacV) to stimulate translation of postreplicative viral mRNAs, whether RACK1 also contributes to VacV replication through its roles in ribosome-based stress signaling remains unclear. Here, we characterize the role of RACK1 in infected cells. In doing so, we find that RACK1 is essential for stress signal activation by ribotoxic stress responses but not by VacV infection. Moreover, although the loss of RACK1 reduces the level of stress-associated JNK activation in infected cells, this is an indirect consequence of RACK1's specific requirement for the synthesis of postreplicative viral proteins, the accumulation of which determines the level of cellular stress. Our findings reveal both the specific role of RACK1 and the complex downstream effects of its control of viral protein synthesis in the context of infection.

Deletion of immunomodulatory genes as a novel approach to oncolytic vaccinia virus development

Vaccinia virus (VV) has emerged as a promising platform for oncolytic virotherapy. Many clinical VV candidates, such as the double-deleted VV, vvDD, are engineered with deletions that enhance viral tumor selectivity based on cellular proliferation rates. An alternative approach is to exploit the dampened interferon-based innate immune responses of tumor cells by deleting one of the many VV immunomodulatory genes expressed to dismantle the antiviral response. We hypothesized that such a VV mutant would be attenuated in non-tumor cells but retain the ability to effectively propagate in and kill tumor cells, yielding a tumor-selective oncolytic VV with significant anti-tumor potency. In this study, we demonstrated that VVs with a deletion in one of several VV immunomodulatory genes (N1L, K1L, K3L, A46R, or A52R) have similar or improved in vitro replication, spread, and cytotoxicity in colon and ovarian cancer cells compared to vvDD. These deletion mutants are tumor selective, and the best performing candidates (ΔK1L, ΔA46R, and ΔA52R VV) are associated with significant improvement in survival, as well as immunomodulation, within the tumor environment. Overall, we show that exploiting the diminished antiviral responses in tumors serves as an effective strategy for generating tumor-selective and potent oncolytic VVs, with important implications in future oncolytic virus (OV) design.

The role of herpesvirus 6A and 6B in multiple sclerosis and epilepsy

Human herpesvirus 6A (HHV‐6A) and 6B (HHV‐6B) are two closely related viruses that can infect cells of the central nervous system (CNS). The similarities between these viruses have made it difficult to separate them on serological level. The broad term HHV‐6 remains when referring to studies where the two species were not distinguished, and as such, the seroprevalence is over 90% in the adult population. HHV‐6B has been detected in up to 100% of infants with the primary infection roseola infantum, but less is known about the primary infection of HHV‐6A. Both viruses are neurotropic and have capacity to establish lifelong latency in cells of the central nervous system, with potential to reactivate and cause complications later in life. HHV‐6A infection has been associated with an increased risk of multiple sclerosis (MS), whereas HHV‐6B is indicated to be involved in pathogenesis of epilepsy. These two associations show how neurological diseases might be caused by viral infections, but as suggested here, through completely different molecular mechanisms, in an autoimmune disease, such as MS, by triggering an overreaction of the immune system and in epilepsy by hampering internal cellular functions when the immune system fails to eliminate the virus. Understanding the viral mechanisms of primary infection and reactivation and their spectrum of associated symptoms will aid our ability to diagnose, treat and prevent these severe and chronic diseases. This review explores the role of HHV‐6A and HHV‐6B specifically in MS and epilepsy, the evidence to date and the future directions of this field.

Cell-to-cell spread of vaccinia virus is promoted by TGF-β-independent Smad4 signalling

The induction of Smad signalling by the extracellular ligand TGF-β promotes tissue plasticity and cell migration in developmental and pathological contexts. Here, we show that vaccinia virus (VACV) stimulates the activity of Smad transcription factors and expression of TGF-β/Smad-responsive genes at the transcript and protein levels. Accordingly, infected cells share characteristics to those undergoing TGF-β/Smad-mediated epithelial-to-mesenchymal transition (EMT). Depletion of the Smad4 protein, a common mediator of TGF-β signalling, results in an attenuation of viral cell-to-cell spread and reduced motility of infected cells. VACV induction of TGF-β/Smad-responsive gene expression does not require the TGF-β ligand or type I and type II TGF-β receptors, suggesting a novel, non-canonical Smad signalling pathway. Additionally, the spread of ectromelia virus, a related orthopoxvirus that does not activate a TGF-β/Smad response, is enhanced by the addition of exogenous TGF-β. Together, our results indicate that VACV orchestrates a TGF-β-like response via a unique activation mechanism to enhance cell migration and promote virus spread.

The small molecule AZD6244 inhibits dengue virus replication in vitro and protects against lethal challenge in a mouse model

Dengue virus (DENV) is the most common mosquito-borne viral disease. The World Health Organization estimates that 400 million new cases of dengue fever occur every year. Approximately 500,000 individuals develop severe and life-threatening complications from dengue fever, such as dengue shock syndrome (DSS) and dengue hemorrhagic fever (DHF), which cause 22,000 deaths yearly. Currently, there are no specific licensed therapeutics to treat DENV illness. We have previously shown that the MEK/ERK inhibitor U0126 inhibits the replication of the flavivirus yellow fever virus. In this study, we demonstrate that the MEK/ERK inhibitor AZD6244 has potent antiviral efficacy in vitro against DENV-2, DENV-3, and Saint Louis encephalitis virus (SLEV). We also show that it is able to protect AG129 mice from a lethal challenge with DENV-2 (D2S20). The molecule is currently undergoing phase III clinical trials for the treatment of non-small-cell lung cancer. The effect of AZD6244 on the DENV life cycle was attributed to a blockade of morphogenesis. Treatment of AG129 mice twice daily with oral doses of AZD6244 (100 mg/kg/day) prevented the animals from contracting dengue hemorrhagic fever (DHF)-like lethal disease upon intravenous infection with 1 × 10⁵ PFU of D2S20. The effectiveness of AZD6244 was observed even when the treatment of infected animals was initiated 1-2 days postinfection. This was also followed by a reduction in viral copy number in both the serum and the spleen. There was also an increase in IL-1β and TNF-α levels in mice that were infected with D2S20 and treated with AZD6244 in comparison to infected mice that were treated with the vehicle only. These data demonstrate the potential of AZD6244 as a new therapeutic agent to treat DENV infection and possibly other flavivirus diseases.

The Virology of Taterapox Virus In Vitro

Taterapox virus (TATV) is phylogenetically the closest related virus to variola—the etiological agent of smallpox. Despite the similarity, few studies have evaluated the virus. In vivo, TATV can infect several animals but produces an inapparent infection in wild-type mice; however, TATV does cause morbidity and mortality in some immunocompromised strains. We employed in vitro techniques to compare TATV to ectromelia (ECTV) and vaccinia (VACV) viruses. Both ECTV and TATV replicate efficiently in primate cell lines but TATV replicates poorly in murine cells lines. Furthermore, TATV induces cytopathic effects, but to a lesser extent than ECTV, and changes cytoskeletal networks differently than both ECTV and VACV. Bioinformatic studies revealed differences in several immunomodulator open reading frames that could contribute to the reduced virulence of TATV, which were supported by in vitro cytokine assays.

The effect of human herpesvirus 6B infection on the MAPK pathway

BACKGROUND

Human herpesvirus 6B (HHV-6B) is a neurotropic virus that has been repeatedly associated with mesial temporal lobe epilepsy (MTLE). However, the mechanism behind this suggested association is not known. Therefore, the aim of this study was to investigate what genes were affected by HHV-6B, possibly revealing HHV-6B induced disease causing mechanisms.

MATERIAL AND METHOD

First, gene expression in MTLE tissue positive for HHV-6B DNA (n = 10) and negative for HHV-6B DNA (n = 14) was compared using the Affymetrix® Human Gene 2.1 ST Array. Secondly, in vitro experiments were conducted where Molt-3 T cells were infected with HHV-6B and gene expression of MAP2K4 (MKK4) and 89 other genes in the MAPK signaling pathway was investigated using qPCR. In addition, phosphorylated MKK4 was assessed using IFA and the DNA methylation investigated with Illumina Infinium HumanMethylation450 BeadChip array.

RESULTS

MAP2K4 was one of the most differently expressed genes in the Affymetrix array, suggesting an upregulation by HHV-6B infection in MTLE tissue. No gene reached statistical significance but MAP2K4 was selected for further investigation in vitro, where it was clearly upregulated by HHV-6B infection both on gene expression and protein expression level. Further investigating expression of genes in the MAPK pathways in vitro revealed that several genes were affected by HHV-6B infection, but none of these genes displayed viral induced changes in DNA methylation.

CONCLUSIONS

As the MAPK pathways are involved in transforming different stimuli (like stress) into a cellular responses (like apoptosis or inflammation), it may not be surprising that genes in these pathways are affected by virus infection. This is the first report of HHV-6B's effect on these signaling cascades and given that both dysregulation of the MAPK pathways and an association with HHV-6B have been previously observed in epilepsy, a possible link of infection induced dysregulation of MAPK in epilepsy warrant further investigation.

How Does Vaccinia Virus Interfere With Interferon?

Interferons (IFNs) are secreted glycoproteins that are produced by cells in response to virus infection and other stimuli and induce an antiviral state in cells bearing IFN receptors. In this way, IFNs restrict virus replication and spread before an adaptive immune response is developed. Viruses are very sensitive to the effects of IFNs and consequently have evolved many strategies to interfere with interferon. This is particularly well illustrated by poxviruses, which have large dsDNA genomes and encode hundreds of proteins. Vaccinia virus is the prototypic poxvirus and expresses many proteins that interfere with IFN and are considered in this review. These proteins act either inside or outside the cell and within the cytoplasm or nucleus. They function by restricting the production of IFN by blocking the signaling pathways leading to transcription of IFN genes, stopping IFNs binding to their receptors, blocking IFN-induced signal transduction leading to expression of interferon-stimulated genes (ISGs), or inhibiting the antiviral activity of ISG products.

Hazard Characterization of Modified Vaccinia Virus Ankara Vector: What Are the Knowledge Gaps?

Modified vaccinia virus Ankara (MVA) is the vector of choice for human and veterinary applications due to its strong safety profile and immunogenicity in vivo. The use of MVA and MVA-vectored vaccines against human and animal diseases must comply with regulatory requirements as they pertain to environmental risk assessment, particularly the characterization of potential adverse effects to humans, animals and the environment. MVA and recombinant MVA are widely believed to pose low or negligible risk to ecosystem health. However, key aspects of MVA biology require further research in order to provide data needed to evaluate the potential risks that may occur due to the use of MVA and MVA-vectored vaccines. The purpose of this paper is to identify knowledge gaps in the biology of MVA and recombinant MVA that are of relevance to its hazard characterization and discuss ongoing and future experiments aimed at providing data necessary to fill in the knowledge gaps. In addition, we presented arguments for the inclusion of uncertainty analysis and experimental investigation of verifiable worst-case scenarios in the environmental risk assessment of MVA and recombinant MVA. These will contribute to improved risk assessment of MVA and recombinant MVA vaccines.

c-Jun integrates signals from both MEK/ERK and MKK/JNK pathways upon vaccinia virus infection

Usurpation of the host's signalling pathways is a common strategy employed by viruses to promote their successful replication. Here we show that infection with the orthopoxvirus vaccinia virus (VACV) leads to sustained stimulation of c-Jun activity during the entire infective cycle. This stimulation is temporally regulated through MEK/ERK or MKK/JNK pathways, i.e. during the early/mid phase (1 to 6 hpi) and in the late phase (9 to 24 hpi) of the infective cycle, respectively. As a transcriptional regulator, upon infection with VACV, c-Jun is translocated from the cytoplasm to the nucleus, where it binds to the AP-1 DNA sequence found at the promoter region of its target genes. To investigate the role played by c-Jun during VACV replication cycle, we generated cell lines that stably express a c-Jun-dominant negative (DNc-Jun) mutation. Our data revealed that c-Jun is required during early infection to assist with viral DNA replication, as demonstrated by the decreased amount of viral DNA found in the DNc-Jun cells. We also demonstrated that c-Jun regulates the expression of the early growth response gene (egr-1), a gene previously shown to affect VACV replication mediated by MEK/ERK signalling. VACV-induced stimulation of the MKK/JNK/JUN pathway impacts viral dissemination, as we observed a significant reduction in both viral yield, during late stages of infection, and virus plaque size. Collectively, our data suggest that, by modulating the host's signalling pathways through a common target such as c-Jun, VACV temporally regulates its infective cycle in order to successfully replicate and subsequently spread.

Vaccinia virus G1 protein: absence of autocatalytic self-processing

Vaccinia virus relies on a series of proteolytic cleavage events involving two viral proteins, I7 and G1, to complete its life cycle. Furthermore, G1 itself is cleaved during vaccinia virus infection. However, convincing evidence is lacking to show whether G1 participates in autoproteolysis or is a substrate of another protease. We employed both biochemical and cell-based approaches to investigate G1 cleavage. G1, when expressed in bacteria, rabbit reticulocyte lysates or HeLa cells, was not processed. Moreover, G1 was cleaved in infected cells, but only in the presence of virus late gene expression; cleavage was strongly inhibited by proteasome inhibitors. Thus, these results imply a more complex G1 cleavage reaction than previously envisaged.

MKK7 confers different activities to viral infection of Singapore grouper iridovirus (SGIV) and nervous necrosis virus (NNV) in grouper

Mitogen-activated protein kinase 7 (MKK7) is one of the major stress-activated protein kinase (SAPK)-activating kinases in response to environmental or physiological stimuli. Here a MKK7 named as Ec-MKK7 was identified from orange-spotted grouper, Epinephelus coioides. The full-length cDNA of Ec-MKK7 was 1853 bp, with an open reading frame (ORF) of 1272 bp encoding a putative protein of 423 amino acids. A characteristic S-K-A-K-T motif was contained in the domain of dual-specificity protein kinase, mitogen-activated protein kinase kinase 7 (PKc_MKK7). Intracellular localization showed that Ec-MKK7 was localized in both the cytoplasm and the nucleus of grouper spleen (GS) and/or grouper brain (EAGB) cells. Moreover, Ec-MKK7 was universally expressed in all examined tissues and showed expression modulation to challenges of lipopolysacchride (LPS), Singapore grouper iridovirus (SGIV) and polyriboinosinic polyribocytidylic acid (poly I:C) in vivo. A gene targeting strategy over-expressing Ec-MKK7 was performed to examine the activities of MKK7 to viral infection in vitro. Our data showed that Ec-MKK7 was involved in the evasion and replication of SGIV but played an antiviral role to the infection of nervous necrosis virus (NNV). All results demonstrated that Ec-MKK7 could play important roles in grouper innate immunity and show distinct functions on virus infection.

Vaccinia virus dissemination requires p21-activated kinase 1

The orthopoxvirus vaccinia virus (VACV) interacts with both actin and microtubule cytoskeletons in order to generate and spread progeny virions. Here, we present evidence demonstrating the involvement of PAK1 (p21-activated kinase 1) in the dissemination of VACV. Although PAK1 activation has previously been associated with optimal VACV entry via macropinocytosis, its absence does not affect the production of intracellular mature virions (IMVs) and extracellular enveloped virions (EEVs). Our data demonstrate that low-multiplicity infection of PAK1(-/-) MEFs leads to a reduction in plaque size followed by decreased production of both IMVs and EEVs, strongly suggesting that virus spread was impaired in the absence of PAK1. Confocal and scanning electron microscopy showed a substantial reduction in the amount of VACV-induced actin tails in PAK1(-/-) MEFs, but no significant alteration in the total amount of cell-associated enveloped virions (CEVs). Furthermore, the decreased VACV dissemination in PAK1(-/-) cells was correlated with the absence of phosphorylated ARPC1 (Thr21), a downstream target of PAK1 and a key regulatory subunit of the ARP2/3 complex, which is necessary for the formation of actin tails and viral spread. We conclude that PAK1, besides its role in virus entry, also plays a relevant role in VACV dissemination.

Multiple Bcl-2 family immunomodulators from vaccinia virus regulate MAPK/AP-1 activation

Vaccinia virus (VACV) is a poxvirus and encodes many proteins that modify the host cell metabolism or inhibit the host response to infection. For instance, it is known that VACV infection can activate the mitogen-activated protein kinase (MAPK)/activator protein 1 (AP-1) pathway and inhibit activation of the pro-inflammatory transcription factor NF-κB. Since NF-κB and MAPK/AP-1 share common upstream activators we investigated whether six different VACV Bcl-2-like NF-κB inhibitors can also influence MAPK/AP-1 activation. Data presented show that proteins A52, B14 and K7 each contribute to AP-1 activation during VACV infection, and when expressed individually outwith infection. B14 induced the greatest stimulation of AP-1 and further investigation showed B14 activated mainly the MAPKs ERK (extracellular signal-regulated kinase) and JNK (Jun N-terminal kinase), and their substrate c-Jun (a component of AP-1). These data indicate that the same viral protein can have different effects on distinct signalling pathways, in blocking NF-κB activation whilst leading to MAPK/AP-1 activation.

The role of microtubule-associated protein 1B in axonal growth and neuronal migration in the central nervous system

In this review, we discuss the role of microtubule-associated protein 1B (MAP1B) and its phosphorylation in axonal development and regeneration in the central nervous system. MAP1B exhibits similar functions during axonal development and regeneration. MAP1B and phosphorylated MAP1B in neurons and axons maintain a dynamic balance between cytoskeletal components, and regulate the stability and interaction of microtubules and actin to promote axonal growth, neural connectivity and regeneration in the central nervous system.

Subversion of cellular stress responses by poxviruses

Cellular stress responses are powerful mechanisms that prevent and cope with the accumulation of macromolecular damage in the cells and also boost host defenses against pathogens. Cells can initiate either protective or destructive stress responses depending, to a large extent, on the nature and duration of the stressing stimulus as well as the cell type. The productive replication of a virus within a given cell places inordinate stress on the metabolism machinery of the host and, to assure the continuity of its replication, many viruses have developed ways to modulate the cell stress responses. Poxviruses are among the viruses that have evolved a large number of strategies to manipulate host stress responses in order to control cell fate and enhance their replicative success. Remarkably, nearly every step of the stress responses that is mounted during infection can be targeted by virally encoded functions. The fine-tuned interactions between poxviruses and the host stress responses has aided virologists to understand specific aspects of viral replication; has helped cell biologists to evaluate the role of stress signaling in the uninfected cell; and has tipped immunologists on how these signals contribute to alert the cells against pathogen invasion and boost subsequent immune responses. This review discusses the diverse strategies that poxviruses use to subvert host cell stress responses.

Heat shock protein 72 confers protection in retinal ganglion cells and lateral geniculate nucleus neurons via blockade of the SAPK/JNK pathway in a chronic ocular-hypertensive rat model

Optic nerve transection increased the expression of heat shock protein 72 (HSP72) in the lateral geniculate body, indicating that this protein is involved in the prevention of neuronal injury. Zinc sulfate and quercetin induced and inhibited the expression of HSP72, respectively. Intraperitoneal injections of zinc sulfate, SP600125 (c-Jun N-terminal kinase inhibitor), or quercetin were performed on retinal ganglion cells in a Wistar rat model of chronic ocular hypertension. Our results showed that compared with the control group, the expression of HSP72 in retinal ganglion cells and the lateral geniculate body was increased after the injection of zinc sulfate, but was decreased after the injection of quercetin. The expression of phosphorylated c-Jun N-terminal kinases and phosphorylated c-Jun were visible 3 days after injection in the control group, and reached a peak at 7 days. Zinc sulfate and SP600125 significantly decreased the expression of p-c-Jun, whereas quercetin significantly enhanced the expression of this protein. These results suggest that HSP72 protects retinal ganglion cells and lateral geniculate body in a rat model of chronic ocular hypertension from injury by blocking the activation of the stress-activated kinase/c-Jun N-terminal kinase apoptotic pathway.

TRAF2 facilitates vaccinia virus replication by promoting rapid virus entry

Tumor necrosis factor receptor (TNFR)-associated factor 2 (TRAF2) is a pivotal intracellular mediator of signaling pathways downstream of TNFR1 and -2 with known pro- and antiviral effects. We investigated its role in the replication of the prototype poxvirus vaccinia virus (VACV). Loss of TRAF2 expression, either through small interfering RNA treatment of HeLa cells or through genetic knockout in murine embryonic fibroblasts (MEFs), led to significant reductions in VACV growth following low-multiplicity infection. In single-cycle infections, there was delayed production of both early and late VACV proteins as well as accelerated virus-induced alterations to cell morphology, indicating that TRAF2 influences early stages of virus replication. Consistent with an early role, uncoating assays showed normal virus attachment but delayed virus entry in the absence of TRAF2. Although alterations to c-Jun N-terminal kinase (JNK) signaling were apparent in VACV-infected TRAF2^−/− MEFs, treatment of wild-type cells with a JNK inhibitor did not affect virus entry. Instead, treatment with an inhibitor of endosomal acidification greatly reduced virus entry into TRAF2^−/− MEFs, suggesting that VACV is reliant on the endosomal route of entry in the absence of TRAF2. Thus, TRAF2 is a proviral factor for VACV that plays a role in promoting efficient viral entry, most likely via the plasma membrane.

IMPORTANCE Tumor necrosis factor receptor-associated factors (TRAFs) are key facilitators of intracellular signaling with roles in innate and adaptive immunity and stress responses. We have discovered that TRAF2 is a proviral factor in vaccinia virus replication in both HeLa cells and mouse embryonic fibroblasts and that its influence is exercised through promotion of efficient virus entry.

Study of vaccinia and cowpox viruses' replication in Rac1-N17 dominant-negative cells

Interfering with cellular signal transduction pathways is a common strategy used by many viruses to create a propitious intracellular environment for an efficient replication. Our group has been studying cellular signalling pathways activated by the orthopoxviruses Vaccinia (VACV) and Cowpox (CPXV) and their significance to viral replication. In the present study our aim was to investigate whether the GTPase Rac1 was an upstream signal that led to the activation of MEK/ERK1/2, JNK1/2 or Akt pathways upon VACV or CPXV' infections. Therefore, we generated stable murine fibroblasts exhibiting negative dominance to Rac1-N17 to evaluate viral growth and the phosphorylation status of ERK1/2, JNK1/2 and Akt. Our results demonstrated that VACV replication, but not CPXV, was affected in dominant-negative (DN) Rac1-N17 cell lines in which viral yield was reduced in about 10-fold. Viral late gene expression, but not early, was also reduced. Furthermore, our data showed that Akt phosphorylation was diminished upon VACV infection in DN Rac1-N17 cells, suggesting that Rac1 participates in the phosphoinositide-3 kinase pathway leading to the activation of Akt. In conclusion, our results indicate that while Rac1 indeed plays a role in VACV biology, perhaps another GTPase may be involved in CPXV replication.

Study of vaccinia and cowpox viruses' replication in Rac1-N17 dominant-negative cells

Interfering with cellular signal transduction pathways is a common strategy used by many viruses to create a propitious intracellular environment for an efficient replication. Our group has been studying cellular signalling pathways activated by the orthopoxviruses Vaccinia (VACV) and Cowpox (CPXV) and their significance to viral replication. In the present study our aim was to investigate whether the GTPase Rac1 was an upstream signal that led to the activation of MEK/ERK1/2, JNK1/2 or Akt pathways upon VACV or CPXV' infections. Therefore, we generated stable murine fibroblasts exhibiting negative dominance to Rac1-N17 to evaluate viral growth and the phosphorylation status of ERK1/2, JNK1/2 and Akt. Our results demonstrated that VACV replication, but not CPXV, was affected in dominant-negative (DN) Rac1-N17 cell lines in which viral yield was reduced in about 10-fold. Viral late gene expression, but not early, was also reduced. Furthermore, our data showed that Akt phosphorylation was diminished upon VACV infection in DN Rac1-N17 cells, suggesting that Rac1 participates in the phosphoinositide-3 kinase pathway leading to the activation of Akt. In conclusion, our results indicate that while Rac1 indeed plays a role in VACV biology, perhaps another GTPase may be involved in CPXV replication.

Viral interactions with microtubules: orchestrators of host cell biology?

Viral interaction with the microtubule (MT) cytoskeleton is critical to infection by many viruses. Most data regarding virus–MT interaction indicate key roles in the subcellular transport of virions/viral genomic material to sites of replication, assembly and egress. However, the MT cytoskeleton orchestrates diverse processes in addition to subcellular cargo transport, including regulation of signaling pathways, cell survival and mitosis, suggesting that viruses, expert manipulators of the host cell, may use the virus–MT interface to control multiple aspects of cell biology. Several lines of evidence support this idea, indicating that specific viral proteins can modify MT dynamics and/or structure and regulate processes such as apoptosis and innate immune signaling through MT-dependent mechanisms. Here, the authors review general aspects of virus–MT interactions, with emphasis on viral mechanisms that modify MT dynamics and functions to affect processes beyond virion transport. The emerging importance of discrete viral protein–MT interactions in pathogenic processes indicates that these interfaces may represent new targets for future therapeutics and vaccine development.

Paxillin is the target of c-Jun N-terminal kinase in Schwann cells and regulates migration

During development of the peripheral nervous system (PNS), Schwann cells migrate along axons, wrapping individual axons to form a myelin sheath. This process is all mediated by the intercellular signaling between neurons and Schwann cells. As yet, little is known about the intracellular signaling mechanisms controlling these morphological changes including Schwann cell migration. We previously showed that c-Jun N-terminal kinase (JNK) plays a key role in Schwann cell migration before the initiation of myelination. Here we show that JNK, acting through phosphorylation of the cytoskeletal protein paxillin, regulates Schwann cell migration and that it mediates dorsal root ganglion (DRG) neuronal conditioned medium (CM). Phosphorylation of paxillin at the Ser-178 position, the JNK phosphorylation site, is observed following stimulation with neuronal CM. Phosphorylation is also detected as a result of stimulation with each of growth factors contained in neuronal CM. Knockdown of paxillin with the specific small interfering RNA (siRNA) inhibits migration. The reintroduction of paxillin reverses siRNA-mediated inhibition of migration, whereas paxillin harboring the Ser-178-to-Ala mutation fails to reverse it. In addition, while JNK binds to the N-terminal region (called LD1), the deletion of LD1 blocks migration. Together, JNK binds and phosphorylates paxillin to regulate Schwann cell migration, illustrating that paxillin provides one of the convergent points of intracellular signaling pathways controlling Schwann cell migration.