Tyrosine phosphorylation events during coxsackievirus B3 replication

Analysis and identification of tyrosine phosphorylated proteins in hemocytes of Litopenaeus vannamei infected with WSSV

Previous studies have demonstrated that protein tyrosine phosphorylation plays an important role in WSSV infection. In the present work, in order to further elucidate the potential role of protein tyrosine phosphorylation in white spot syndrome virus (WSSV) infection. The expression variation of tyrosine phosphorylated proteins in hemocytes of shrimp (Litopenaeus vannamei) after WSSV infection were examined by flow cytometric immunofluorescence assay (FCIFA) and enzyme linked immunosorbent assay (ELISA), and results showed that the level of protein tyrosine phosphorylation in hemocytes fluctuated significantly after WSSV infection and exhibited two peaks at 6 and 24 h post infection (hpi). Meanwhile, tyrosine phosphorylated proteins in hemocytes after WSSV infection were also detected by cell immunofluorescence, and results showed that the fluorescence intensity in hemocytes was altered with the course of WSSV infection and showed stronger fluorescent signals at 6 and 24 hpi compared to other time points. Furthermore, two dimensional gel electrophoresis (2-DE) and 2-DE western blotting were applied to identify the differentially expressed tyrosine phosphorylated proteins in hemocytes before and after WSSV infection. The result of 2-DE western blotting showed that there were nine tyrosine phosphorylated proteins in the hemocytes of healthy shrimp, whereas twenty-one tyrosine phosphorylated proteins were detected in the hemocytes of shrimp at 6hpi. Then, the differential tyrosine phosphorylated proteins were analyzed by Mass Spectrometry (MS), and eight of them were identified to be sodium/potassium-transporting ATPase subunit alpha, ubiquitin/ribosomal L40 fusion protein, actin-D, phosphopyruvate hydratase, beta-actin, ATP synthase subunit beta, receptor for activated protein kinase c1 and protein disulfide-isomerase. Moreover, the expression levels of sodium/potassium-transporting ATPase subunit alpha, ubiquitin/ribosomal L40 fusion protein, phosphopyruvate hydratase, ATP synthase subunit beta, receptor for activated protein kinase c1 and protein disulfide-isomerase were examined to be up-regulated post WSSV infection by quantitative real-time RT-PCR. Taken together, these results demonstrated that protein tyrosine phosphorylation was involved in the process of WSSV infection, which might play an important role in the immune response to WSSV infection in shrimp.

Enterovirus 71 infection caused neuronal cell death and cytokine expression in cultured rat neural cells

Fatal enterovirus type-71 (EV71) cases are associated with central nervous system infection characterized by inflammatory cell infiltration and activation, cytokine overproduction, and neuronal cell death. Although EV71 antigen has been detected in neurons and glia, the molecular mechanisms underlying EV71-associated neuroinflammation and neuronal cell death are not fully understood. Using cultured rodent neural cell models, we found that EV71 infection preferentially caused cell death in neurons but not brain-resident immune cells astrocytes and microglia. Neurons, astrocytes, and microglia responded to EV71 infection by releasing distinct profiles of cytokines, including nitric oxide (NO), tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, regulated on activation normal T cell expressed and secreted (RANTES), and glutamate. EV71 infection-induced neuronal cell death correlated well with the elevated production of NO, TNF-α, IL-1β, and glutamate as well as activation of microglia. Exogenous addition studies further demonstrated the neurotoxic potential of NO, TNF-α, IL-1β, and glutamate. EV71 infection-induced cytokine expression was accompanied by activation of protein tyrosine phosphorylation, mitogen-activated protein kinases (MAPKs), and NF-κB. Intriguingly, EV71 susceptibility was accompanied by infection-elevated neuronal human scavenger receptor class B member 2 expression in cultured neural cells with age-dependent manner. Biochemical and pharmacological studies revealed that after EV71 infection, microglia and accompanied cytokines play an active role in triggering bystander damage to neurons involving the tyrosine kinase/MAPKs/NF-κB signaling cascade. These data suggest that bystander damage caused by activated glia particularly the microglia could be an alternative mechanism of EV71-associated neuronal cell death. However, its clinical importance and implication require further investigation.

Coxsackievirus B3 replication and pathogenesis

ABSTRACT 

Viruses such as coxsackievirus B3 (CVB3) are entirely host cell-dependent parasites. Indeed, they must cleverly exploit various compartments of host cells to complete their life cycle, and consequently launch disease. Evolution has equipped this pico-rna-virus, CVB3, to use different strategies, including CVB3-induced direct damage to host cells followed by a host inflammatory response to CVB3 infection, and cell death to super-additively promote target organ tissue injury, and dysfunction. In this update, the patho-stratagems of CVB3 are explored from molecular, and systems-level approaches. In summarizing recent developments in this field, we focus particularly on mechanisms by which CVB3 can harness different host cell processes including kinases, host cell-killing and cell-eating machineries, matrix metalloproteinases and miRNAs to promote disease.

The antiviral effect of jiadifenoic acids C against coxsackievirus B3

Coxsackievirus B type 3 (CVB3) is one of the major causative pathogens associated with viral meningitis and myocarditis, which are widespread in the human population and especially prevalent in neonates and children. These infections can result in dilated cardiomyopathy (DCM) and other severe clinical complications. There are no vaccines or drugs approved for the prevention or therapy of CVB3-induced diseases. During screening for anti-CVB3 candidates in our previous studies, we found that jiadifenoic acids C exhibited strong antiviral activities against CVB3 as well as other strains of Coxsackie B viruses (CVBs). The present studies were carried out to evaluate the antiviral activities of jiadifenoic acids C. Results showed that jiadifenoic acids C could reduce CVB3 RNA and proteins synthesis in a dose-dependent manner. Jiadifenoic acids C also had a similar antiviral effect on the pleconaril-resistant variant of CVB3. We further examined the impact of jiadifenoic acids C on the synthesis of viral structural and non-structural proteins, finding that jiadifenoic acids C could reduce VP1 and 3D protein production. A time-course study with Vero cells showed that jiadifenoic acids C displayed significant antiviral activities at 0-6 h after CVB3 inoculation, indicating that jiadifenoic acids C functioned at an early step of CVB3 replication. However, jiadifenoic acids C had no prophylactic effect against CVB3. Taken together, we show that jiadifenoic acids C exhibit strong antiviral activities against all strains of CVB, including the pleconaril-resistant variant. Our study could provide a significant lead for anti-CVB3 drug development.

The prostacyclin agonist iloprost aggravates fibrosis and enhances viral replication in enteroviral myocarditis by modulation of ERK signaling and increase of iNOS expression

Enteroviruses, such as coxsackieviruses of group B (CVB), are able to induce a chronic inflammation of the myocardium, which may finally lead to the loss of functional tissue, remodeling processes and the development of fibrosis, thus affecting the proper contractile function of the heart. In other fibrotic diseases like scleroderma, the prostacyclin agonist iloprost was found to inhibit the extracellular signal-regulated kinase (ERK, p44/42 MAPK), a mitogen-activated protein kinase, and consecutively, the expression of the profibrotic cytokine connective tissue growth factor (CTGF), thereby preventing the development of fibrosis. As CTGF was found to mediate fibrosis in chronic CVB3 myocarditis as well, we evaluated whether the in vivo application of iloprost is capable to reduce the development of ERK/CTGF-mediated fibrosis in enteroviral myocarditis. Unexpectedly, the application of iloprost resulted in a prolonged myocardial inflammation and an aggravated fibrosis and failed to reduce activation of ERK and expression of CTGF at later stages of the disease. In addition, viral replication was found to be increased in iloprost-treated mice. Notably, the expression of cardiac inducible nitric oxide synthase (iNOS), which is known to aggravate myocardial damage in CVB3-infected mice, was strongly enhanced by iloprost. Using cultivated bone marrow macrophages (BMM), we confirmed these results, proving that iloprost potentiates the expression of iNOS mRNA and protein in CVB3-infected and IFN-gamma stimulated BMM. In conclusion, these results suggest a critical reflection of the clinical use of iloprost, especially in patients possibly suffering from an enteroviral myocarditis.

Tripeptidyl peptidase II serves as an alternative to impaired proteasome to maintain viral growth in the host cells

The ubiquitin-proteasome system is known to be utilized by coxsackievirus to facilitate its propagation within the host cells. The present study explores the role of tripeptidyl peptidase II (TPPII), a serine peptidase contributing to protein turnover by acting downstream of the proteasome, in regulating coxsackievirus infection. Inhibition of TPPII does not affect virus replication in cells with functional proteasome. However, when the proteasome is impaired, TPPII appears to serve as an alternative to maintain low levels of virus infection. Our results suggest an important function of TPPII in the maintenance of viral growth and may have implications for anti-viral therapy.

Proteasome activator REGgamma enhances coxsackieviral infection by facilitating p53 degradation

Coxsackievirus B3 (CVB3) is a small RNA virus associated with diseases such as myocarditis, meningitis, and pancreatitis. We have previously demonstrated that proteasome inhibition reduces CVB3 replication and attenuates virus-induced myocarditis. However, the underlying mechanisms by which the ubiquitin/proteasome system regulates CVB replication remain unclear. In this study, we investigated the role of REGγ, a member of the 11S proteasome activator, in CVB3 replication. We showed that overexpression of REGγ promoted CVB3 replication but that knockdown of REGγ led to reduced CVB3 replication. We further demonstrated that REGγ-mediated p53 proteolysis contributes, as least in part, to the proviral function of REGγ. Although total protein levels of REGγ remained unaltered after CVB3 infection, virus infection induced a redistribution of REGγ from the nucleus to the cytoplasm, rendering an opportunity for a direct interaction of REGγ with viral proteins and/or host proteins (e.g., p53), which controls viral growth and thereby enhances viral infectivity. Further analyses suggested a potential modification of REGγ by SUMO following CVB3 infection, which was verified by both in vitro and in vivo sumoylation assays. Sumoylation of REGγ may play a role in its nuclear export during CVB3 infection. Taken together, our results present the first evidence that the host REGγ pathway is utilized and modified during CVB3 infection to promote efficient viral replication.

Molecular biology and pathogenesis of viral myocarditis

Myocarditis is a cardiac disease associated with inflammation and injury of the myocardium. Several viruses have been associated with myocarditis in humans. However, coxsackievirus B3 is still considered the dominant etiological agent. The observed pathology in viral myocarditis is a result of cooperation or teamwork between viral processes and host immune responses at various stages of disease. Both innate and adaptive immune responses are crucial determinants of the severity of myocardial damage, and contribute to the development of chronic myocarditis and dilated cardiomyopathy following acute viral myocarditis. Advances in genomics and proteomics, and in the use of informatics and biostatistics, are allowing unbiased initial evaluations that can be the basis for testable hypotheses about virus pathogenesis and new therapies.

Japanese encephalitis virus infection stimulates Src tyrosine kinase in neuron/glia

Japanese encephalitis virus (JEV) is a neurotropic virus. The clinically manifestation of JEV-induced encephalitis is characterized by the brain inflammation and neuronal dysfunction and/or destruction. Currently, the cellular signaling molecules that underlie JEV-induced cerebral inflammation and cellular alterations are not well understood. Protein tyrosine phosphorylation events are key regulators of cellular signaling processes, including inflammation. We investigated whether Src protein tyrosine kinase (PTK) function in JEV-induced cellular changes in neuron/glia cultures. JEV infection modulated tyrosine phosphorylation events. Src PTK was hyperphosphorylated at the early stage of infection. Biochemical studies demonstrated that both inhibitors of the Src family PTK and Ras attenuated JEV-induced extracellular signal-regulated kinase (ERK) activation. Our results further revealed that PTK, Ras, and ERK inhibitors effectively suppressed JEV-induced pro-inflammatory cytokine expression and neurotoxicity. Pharmacological studies suggested that microglia secreted pro-inflammatory cytokine via Src/Ras/ERK pathway in responding to JEV infection. Another interesting observation was that nonstructural protein 3 (NS3) was able to interact with Src and showed tyrosine phosphorylation. However, the biological consequences of their interaction and exact control of NS3 tyrosine phosphorylation required further investigation. Our results suggest that the Src/Ras/ERK signaling cascade is involved in JEV-induced pro-inflammatory cytokine expression and neurotoxicity.

Tyrosine kinase inhibitors attenuate Japanese encephalitis virus-induced neurotoxicity

The cellular signaling molecules that underlie Japanese encephalitis virus (JEV)-induced inflammation and neurotoxicity are not well understood. We examined whether protein tyrosine kinase (PTK) inhibitors play roles in JEV replication and cytopathic effect in neuron/glia cultures. JEV infection caused significant neuronal injury. PTK inhibitors, genistein, herbimycin A, and PP2, attenuated JEV-induced neurotoxicity but failed to affect JEV replication. Infection of neuron/glia cultures with JEV produced elevated levels of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta). PTK inhibitors suppressed JEV-induced TNF-alpha and IL-1beta production at the transcriptional level. Neutralizing antibodies against TNF-alpha and IL-1beta partially suppressed JEV-induced neurotoxicity. JEV infection modulated tyrosine phosphorylation events within the course of infection. Currently, the nature of the affected phosphorylated proteins was not characterized. Our results suggest that PTKs, especially Src-related PTK, play roles in the production of TNF-alpha and IL-1beta during JEV infection and in the induction of neuronal death in neuron/glia cultures.

Virus-receptor interactions of coxsackie B viruses and their putative influence on cardiotropism

Specific virus-receptor interactions are important determinants in the pathogenesis of viral infections, influencing the location and initiation of primary infection as well as the viral spread to other target organs in the postviremic phase. Coxsackieviruses of group B (CVB) specifically interact with at least two receptor proteins, the coxsackievirus-adenovirus receptor (CAR) and the decay-accelerating factor (DAF), and cause a broad spectrum of diseases, including acute and chronic myocarditis. In the human heart, CAR is predominantly expressed in intercalated discs, regions of utmost importance for the functional integrity of the heart. Since DAF is abundantly expressed in epithelial and endothelial cells, interaction of cardiotropic CVB with the DAF coreceptor protein, in addition to CAR, could therefore be advantageous to the virus by enhancing viral entry into the heart.

Bcl-2 and Bcl-xL overexpression inhibits cytochrome c release, activation of multiple caspases, and virus release following coxsackievirus B3 infection

Coxsackievirus B3, a cytopathic virus in the family Picornaviridae, induces degenerative changes in host cell morphology. Here we demonstrate cytochrome c release and caspases-2, -3, -6, -7, -8, and -9 processing. Enforced Bcl-2 and Bcl-xL expression markedly reduced release of cytochrome c, presentation of the mitochondrial epitope 7A6, and depressed caspase activation following infection. In comparison, cell death using TRAIL ligand caused caspase-8 processing prior to cytochrome c release and executioner caspases and cell death was only partially rescued by Bcl-2 and Bcl-xL overexpression. Disruption of the mitochondrial inner membrane potential following CVB3 infection was not inhibited by zVAD.fmk treatment. Bcl-2 or Bcl-xL overexpression or zVAD.fmk treatment delayed the loss of host cell viability and decreased progeny virus release following infection. Our data suggest that mitochondrial release of cytochrome c may be an important early event in caspase activation in CVB3 infection, and, as such, may contribute to the loss of host-cell viability and progeny virus release.

Effect of p38 mitogen-activated protein kinase on the replication of encephalomyocarditis virus

Cellular phosphorylation events during viral infection are necessary for effective viral replication. Encephalomyocarditis (EMC) virus has been used for studies on the molecular mechanisms of viral replication, but little is known about the cellular signaling pathways involved. This investigation was initiated to determine whether mitogen-activated protein kinases (MAPKs), which are central components of signal transduction pathways in the regulation of cell proliferation, play a role in the replication of EMC virus. We examined the phosphorylation of MAPKs, including extracellular signal-regulated kinase (ERK1/2), p38 MAPK, and stress-activated protein kinase 1/c-Jun NH(2)-terminal kinase (SAPK/JNK) in EMC virus-infected L929 cells and found that p38 MAPK and SAPK-JNK, but not ERK1/2, were activated during viral infection. We then examined the effect of these kinases on the replication of EMC virus in L929 cells by using specific inhibitors, including genistein or herbimycin A for tyrosine kinase, SB203580 or SB202190 for p38 MAPK, and PD98059 for ERK1/2. We found that the tyrosine kinase and p38 MAPK inhibitors, but not the ERK1/2 inhibitor, suppressed viral replication and that the inhibitory effect was primarily on viral protein synthesis. Finally, we examined whether p38 MAPK is involved in the translation of EMC viral transcripts by using L929 cells transfected with a gene construct containing the internal ribosomal entry site (IRES) of EMC virus and a luciferase reporter gene. We found that the p38 MAPK inhibitor suppressed the translation of EMC viral RNA. On the basis of these observations, we conclude that p38 MAPK plays a critical role in the replication of EMC virus, probably in the translation of viral RNA.

Human rhinovirus selectively modulates membranous and soluble forms of its intercellular adhesion molecule-1 (ICAM-1) receptor to promote epithelial cell infectivity

Human rhinoviruses are responsible for many upper respiratory tract infections. 90% of rhinoviruses utilize intercellular adhesion molecule-1 (ICAM-1) as their cellular receptor, which also plays a critical role in recruitment of immune effector cells. Two forms of this receptor exist; membrane-bound (mICAM-1) and soluble ICAM-1 (sICAM-1). The soluble receptor may be produced independently from the membrane-bound form or it may be the product of proteolytic cleavage of mICAM-1. The ratio of airway epithelial cell expression of mICAM-1 to the sICAM-1 form may influence cell infectivity and outcome of rhinovirus infection. We therefore investigated the effect of rhinovirus on expression of both ICAM-1 receptors in normal human bronchial epithelial cells. We observed separate distinct messenger RNA transcripts coding for mICAM-1 and sICAM-1 in these cells, which were modulated by virus. Rhinovirus induced mICAM-1 expression on epithelial cells while simultaneously down-regulating sICAM-1 release, with consequent increase in target cell infectivity. The role of protein tyrosine kinases was investigated as a potential mechanistic pathway. Rhinovirus infection induced rapid phosphorylation of intracellular tyrosine kinase, which may be critical in up-regulation of mICAM-1. Elucidation of the underlying molecular mechanisms involved in differential modulation of both ICAM-1 receptors may lead to novel therapeutic strategies.

Enhanced ERK-1/2 activation in mice susceptible to coxsackievirus-induced myocarditis

Group B coxsackieviral (CVB) infection commonly causes viral myocarditis. Mice are protected from CVB3 myocarditis by gene-targeted knockout of p56(Lck)(Lck), the Src family kinase (Src) essential for T cell activation. Extracellular signal-regulated kinase 1 and 2 (ERK-1/2) can influence cell function downstream of Lck. Using T cell lines and neonatal cardiac myocytes we investigated the role of ERK-1/2 in CVB3 infection. In Jurkat T cells ERK-1/2 is rapidly activated by CVB3; but, this response is absent in Lck-negative JCaM T cells. Inhibition of ERK-1/2 with UO126 reduced CVB3 titers in Jurkat cells, but not in JCaM cells. In cardiac myocytes CVB3 activation of ERK-1/2 is blocked by the Src inhibitor PP2. In addition, viral production in myocytes is decreased by Src or ERK-1/2 inhibition. In vitro, in both immune and myocardial cells, ERK-1/2 is activated by CVB3 downstream of Lck and other Src's and is necessary for efficient CVB3 replication. In vivo, following CVB3 infection, ERK-1/2 activation is evident in the myocardium. ERK-1/2 activation is intense in the hearts of myocarditis-susceptible A/J mice. In contrast, significantly less ERK-1/2 activation is found in the hearts of myocarditis-resistant C57BL/6 mice. Therefore, the ERK-1/2 response to CVB3 infection may contribute to differential host susceptibility to viral myocarditis.

Apoptosis in coxsackievirus B3-caused diseases: interaction between the capsid protein VP2 and the proapoptotic protein siva

Coxsackievirus B3 (CVB3) is a common factor in human myocarditis. Apoptotic events are present in CVB3-induced disease, but it is unclear how CVB3 is involved in apoptosis and which viral proteins may induce the apoptotic pathway. In this report we demonstrate that the human and murine proapoptotic protein Siva specifically interact with the CVB3 capsid protein VP2. Furthermore, the transcription of Siva is strongly induced in tissue of CVB3-infected mice and is present in the same area which is positively stained for apoptosis, CD27, and CD70. It has been proposed that Siva is involved in the CD27/CD70-transduced apoptosis. Therefore, we suggest a molecular mechanism through which apoptotic events contributes to CVB3-caused pathogenesis.

Mechanisms and consequences of enterovirus persistence in cardiac myocytes and cells of the immune system

In humans and experimental murine models enteroviruses, and in particular coxsackieviruses of group B (CVB), may induce chronic myocarditis associated with a persistent type of heart muscle infection. Persistent myocardial infection has been characterized by restricted viral replication and gene expression, which is capable of sustaining chronic inflammation. Altered replication and transcription of the virus, in addition to an immune response insufficient to recognize and clear infected cells entirely, are essential mechanisms for initiation and maintenance of persistent heart muscle infection. Viral cytotoxicity was found to be crucial for organ pathology both during acute and persistent infection, indicating that enterovirus myocarditis is a virus-induced rather than an immune-mediated disease. Notably, resistance to the development of persistent heart muscle infection is not linked to the H-2 haplotype of the host. In addition to persistently infected myocytes, detection of the replicative minus-strand RNA intermediate provided evidence for virus replication in lymphoid cells of the spleen, predominantly in splenic B lymphocytes, during the course of the disease. Whereas viral RNA was also detected in certain CD4+ helper T cells and Mac1+ macrophages, no enteroviral genomes were identified in CD8+ T cells. Detection of infected activated B lymphocytes both in heart tissue of CVB3-infected immunocompetent mice and syngenic SCID mice receiving splenocytes from CVB3-infected donors support the concept that B cell traffic may contribute to maintenance of chronic disease. Dissection of the diversity of viral and host-specific determinants in susceptible and resistant hosts will allow us to define the protective mechanisms that mediate resistance to the development of life-threatening acute and chronic enterovirus myocarditis.

Cleavage of RasGAP and phosphorylation of mitogen-activated protein kinase in the course of coxsackievirus B3 replication

Recently, we reported on tyrosine phosphorylation of distinct cellular proteins in the course of enterovirus infections (M. Huber, H.-C. Selinka, and R. Kandolf, J. Virol. 71:595-600, 1997). These phosphorylation events were mediated by Src-like kinases and were shown to be necessary for effective virus replication. That study is now extended by examination of the interaction of the adapter protein Sam68, a cellular target of Src-like kinases which has been shown to interact with the poliovirus 3D polypeptide, with cellular signaling proteins as well as the function of the latter during infection. Here, we report that the RNA-binding and protein-binding protein Sam68 associates with the p21(ras) GTPase-activating protein RasGAP. Remarkably, RasGAP is cleaved during infections with different strains of coxsackievirus B3 as well as with echovirus 11 and echovirus 12, yielding a 104-kDa protein fragment. This cleavage event, which cannot be prevented by the general caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone, may promote the activation of the Ras pathway, as shown by the activating dual phosphorylation of the mitogen-activated protein kinases Erk-1 and Erk-2 in the late phase of infection. Moreover, downstream targets of the mitogen-activated protein kinases, i.e., the p21(ras) exchange factor Sos-1 and cytoplasmic phospholipase A2, are phosphorylated with parallel time courses during infection. Activation or inhibition of cellular signaling pathways may play a general role in regulating effective enterovirus replication and pathogenesis, and the results of this study begin to unravel the molecular cross talk between enterovirus infection and key cellular signaling networks.

Caspase activation and specific cleavage of substrates after coxsackievirus B3-induced cytopathic effect in HeLa cells

Coxsackievirus B3 (CVB3), an enterovirus in the family Picornaviridae, induces cytopathic changes in cell culture systems and directly injures multiple susceptible organs and tissues in vivo, including the myocardium, early after infection. Biochemical analysis of the cell death pathway in CVB3-infected HeLa cells demonstrated that the 32-kDa proform of caspase 3 is cleaved subsequent to the degenerative morphological changes seen in infected HeLa cells. Caspase activation assays confirm that the cleaved caspase 3 is proteolytically active. The caspase 3 substrates poly(ADP-ribose) polymerase, a DNA repair enzyme, and DNA fragmentation factor, a cytoplasmic inhibitor of an endonuclease responsible for DNA fragmentation, were degraded at 9 h following infection, yielding their characteristic cleavage fragments. Inhibition of caspase activation by benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (ZVAD.fmk) did not inhibit the virus-induced cytopathic effect, while inhibition of caspase activation by ZVAD.fmk in control apoptotic cells induced by treatment with the porphyrin photosensitizer benzoporphyrin derivative monoacid ring A and visible light inhibited the apoptotic phenotype. Caspase activation and cleavage of substrates may not be responsible for the characteristic cytopathic effect produced by picornavirus infection yet may be related to late-stage alterations of cellular homeostatic processes and structural integrity.

Coxsackie B virus and its interaction with permissive host cells

BACKGROUND

Observations in humans and the results of experiments on laboratory animals have provided evidence that coxsackieviruses of group B (CVB) are major etiologic agents of acute and chronic enterovirus myocarditis and various other virus-induced diseases.

OBJECTIVE

This minireview briefly summarizes the investigations to elucidate various molecular mechanisms for the induction and maintenance of persistent CVB infections. With regard to the recent findings that CVB may use several different receptor proteins, this article focuses on virus-host cell interactions and the potential impact of these interactions for enteroviral replication.

STUDY DESIGN

The interaction of CVB with specific cell surface proteins was analyzed in cultured cell lines and murine tissues at the level of virus attachment and virus internalization. As example for the interaction of CVB with intracellular proteins, the state of p21rasGTPase-activating protein (RasGAP) was investigated in mock-infected and CVB3-infected HeLa cells.

RESULTS AND CONCLUSIONS

The experiments to elucidate the virus receptor interactions revealed the necessity to differentiate between CVB attachment proteins and proteins involved in virus internalization. Since more than one protein may be required to initiate the uptake of CVB into permissive host cells, a model of the putative interaction of these proteins within a multimeric receptor complex is proposed. It is further tempting to speculate that the presence of multiple attachment proteins may influence the tissue tropism of CVB as well as pathogenicity.

Myocarditis as systemic disease: new perspectives on pathogenesis

1. Myocarditis may be an early indicator of or may subsequently lead to dilated cardiomyopathy in humans. This hypothesis has evolved from research on viruses that induce myocarditis, wherein the coxsackie B group viruses (CVB) in the family Picornaviridae are the most common known viral infectants of heart muscle. 2. Many competing hypotheses exist as to the pathogenesis of CVB3-induced myocarditis, including direct virus-induced myocyte damage and immunopathological disease with autoimmune sequelae. Evidence to support the direct-damage and viral RNA-persistence hypothesis is derived from in situ hybridization and gene amplification studies. 3. Recent use of terminal deoxynucleotidyl transferase-mediated nick-end labelling indicates that this injury in target organs is largely non-apoptotic in nature. Most apoptotic bodies in cardiac tissue are derived from immune cells. 4. Beyond infection of heart muscle, CVB3 can also associate with, infect and persist in cells of immune origin. The CVB3 localizes to follicles in spleens and lymph nodes of the murine host and this particular localization may continue in mice susceptible to more aggressive myocarditis. Whether virus-immune cell association in these compartments is advantageous (or essential) to the host in the evolution of anti-viral immune responses or whether it is more advantageous to the virus in immunosuppression of the host is not known. 5. We suggest that CVB3 can directly perturb or alter the immune response, thereby delaying viral clearance from vulnerable systemic organs. Both host and viral genetic factors can influence susceptibility, persistence and disease progression. 6. Picornaviruses use a unique method for the initiation of translation, involving the internal binding of the ribosome on a sequence element of the 5' untranslated region, termed an internal ribosome entry site (IRES). 7. The IRES of CVB3 is located at approximately stem loops G, H and I, spanning nucloetides 530 and 630. Arrest of host translation is also a feature of picornavirus infection. Such regulation of host cell translation machinery no doubt fosters viral replication at the expense of the host cell. 8. Differences between cell types in the mechanisms, along with those at other key steps in the viral life cycle and in signalling via kinase pathways, may determine viral tropism and cellular destruction and the physiological outcome of neighbouring cells.