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

Pathogenesis of Autographa californica multiple nucleopolyhedrovirus in fifth-instar Anticarsia gemmatalis larvae

We have investigated infection and pathogenesis of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) in Anticarsia gemmatalis (velvetbean caterpillar) larvae using a lacZ recombinant virus (AcMNPV-hsp70/lacZ) to track the temporal progression of infection in the midgut intestine and haemocoel. A. gemmatalis was highly resistant to fatal infection by occlusion bodies (OBs; LD(50)>5.5 x 10(5) OB) and budded virus (BV; LD(50)>3 x 10(5) BV) administered via oral and systemic routes, respectively. Orally administered occlusion-derived virus (ODV) efficiently attached and fused to midgut cells; however, high levels of infection-induced apoptosis limited infection in the midgut. Transcriptional analysis of AcMNPV genes expressed in the midgut of OB-inoculated A. gemmatalis larvae showed high levels of mRNA encoding the major capsid protein VP39 in the absence of immediate-early transactivator 1 (ie-1) expression. In the midgut, virus was efficiently transferred from infected midgut epithelial cells to nearby tracheolar cells and circulating haemocytes to initiate systemic infection in the haemocoel. However, haemocoelic BV did not efficiently disseminate infection and only cuticular epidermal cells displayed high levels of viral infection. Flow cytometry analysis of haemocytes isolated from BV-inoculated A. gemmatalis larvae showed low-level expression of the BV envelope protein GP64 on the cell surface, suggesting that A. gemmatalis haemocytes have a limited capacity for amplifying virus. These results show that AcMNPV is not an effective biological control agent for limiting crop damage caused by A. gemmatalis larvae.

Antiapoptotic activity of the cardiovirus leader protein, a viral "security" protein

Apoptosis is a common antiviral defensive mechanism that potentially limits viral reproduction and spread. Many viruses possess apoptosis-suppressing tools. Here, we show that the productive infection of HeLa cells with encephalomyocarditis virus (a cardiovirus) was not accompanied by full-fledged apoptosis (although the activation of caspases was detected late in infection) but rather elicited a strong antiapoptotic state, as evidenced by the resistance of infected cells to viral and nonviral apoptosis inducers. The development of the antiapoptotic state appeared to depend on a function(s) of the viral leader (L) protein, since its mutational inactivation resulted in the efflux of cytochrome c from mitochondria, the early activation of caspases, and the appearance of morphological and biochemical signs of apoptosis in a significant proportion of infected cells. Infection with both wild-type and L-deficient viruses induced the fragmentation of mitochondria, which in the former case was not accompanied with cytochrome c efflux. Although the exact nature of the antiapoptotic function(s) of cardioviruses remains obscure, our results suggested that it includes previously undescribed mechanisms operating upstream and possibly downstream of the mitochondrial level, and that L is involved in the control of these mechanisms. We propose that cardiovirus L belongs to a class of viral proteins, dubbed here security proteins, whose roles consist solely, or largely, in counteracting host antidefenses. Unrelated L proteins of other picornaviruses as well as their highly variable 2A proteins also may be security proteins. These proteins appear to be independent acquisitions in the evolution of picornaviruses, implying multiple cases of functional (though not structural) convergence.

Theiler's murine encephalomyelitis virus leader protein is the only nonstructural protein tested that induces apoptosis when transfected into mammalian cells

Theiler's murine encephalomyelitis virus (TMEV) induces two distinct cell death programs, necrosis and apoptosis. The apoptotic pathway is of particular interest because TMEV persists in the central nervous system of mice, largely in infiltrating macrophages, which undergo apoptosis. Infection of murine macrophages in culture induces apoptosis that is Bax dependent through the intrinsic or mitochondrial pathway, restricting infectious-virus yields and raising the possibility that apoptosis represents a mechanism to attenuate TMEV yet promote macrophage-to-macrophage spread during persistent infection. To help define the cellular stressors and upstream signaling events leading to apoptosis during TMEV infection, we screened baby hamster kidney (BHK-21) cells transfected to express individual nonstructural genes (except 3B) of the low-neurovirulence BeAn virus strain for cell death. Only expression of the leader protein led to apoptosis, as assessed by fluorescence-activated cell sorting analysis of propidium iodide- and annexin V-stained transfected cells, immunoblot analysis of poly(ADP-ribose) polymerase and caspase cleavages, electron microscopy, and inhibition of apoptosis by the pancaspase inhibitor qVD-OPh. After transfection, Bak and not Bax expression increased, suggesting that the apical pathway leading to activation of these Bcl-2 multi-BH-domain proapoptotic proteins differs in BeAn virus infection versus L transfection. Mutation to remove the CHCC Zn finger motif from L, a motif required by L to mediate inhibition of nucleocytoplasmic trafficking, significantly reduced L-protein-induced apoptosis in both BHK-21 and M1-D macrophages.

Apoptosis in animal models of virus-induced disease

Apoptosis is associated with virus-induced human diseases of the central nervous system, heart and liver, and causes substantial morbidity and mortality. Although virus-induced apoptosis is well characterized in individual cells in cell culture, virus-induced apoptosis in vivo and the role of apoptosis in virus-induced disease is not well established. This review focuses on animal models of virus-induced diseases of the central nervous system, heart and liver that provide insights into the role of apoptosis in pathogenesis, the pathways involved and the potential therapeutic implications.

Proapoptotic protein Siva binds to the muscle protein telethonin in cardiomyocytes during coxsackieviral infection

AIMS

Coxsackievirus B3 (CVB3) is known to cause a variety of human diseases including acute and chronic myocarditis as well as dilated cardiomyopathy (DCM). However, the mechanisms by which CVB3 causes diseases are not well understood.

METHODS AND RESULTS

Studies identifying protein-protein interactions during CVB3 infection are useful in delineating the pathogenesis of acute or chronic myocarditis. Screening a human heart cDNA library revealed a yet unknown interaction partner of the proapoptotic protein Siva. We demonstrate that Siva specifically interacts with the heart and skeletal muscle protein telethonin. The expression of Siva is increased in heart tissue of CVB3-infected mice and the proteins colocalize in cardiomyocytes.

CONCLUSION

telethonin might be involved in CVB3-mediated cell damage and in the resulting cardiac dysfunction due to the interaction with Siva. We suggest a molecular mechanism through which coxsackieviral infection contributes to the pathogenesis of chronic myocarditis and in particular of acquired forms of DCM.

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.

The Siva protein is a novel intracellular ligand of the CD4 receptor that promotes HIV-1 envelope-induced apoptosis in T-lymphoid cells

In addition to its positive signaling function in the antigen presentation process, CD4 acts as the primary receptor for HIV-1. Contact between CD4 and the viral envelope leads to virus entry, but can also trigger apoptosis of uninfected CD4+ T-cells through a mechanism that is poorly understood. We show that Siva-1, a death domain-containing proapoptotic protein, associates with the cytoplasmic domain of CD4. This interaction is mediated by the cysteine-rich region found in the C-terminal part of the Siva-1 protein. Expression of Siva-1 specifically increases the susceptibility of both T-cell lines and unstimulated human primary CD4+ T-lymphocytes to CD4-mediated apoptosis triggered by the HIV-1 envelope, and results in activation of a caspase-dependent mitochondrial pathway. The same susceptibility is observed in T-cells expressing a truncated form of CD4 that is able to recruit Siva-1 but fails to associate with p56Lck, indicating that Siva-1 participates in a pathway independent of the p56Lck kinase activity. Altogether, these results suggest that Siva-1 might participate in the CD4-initiated signaling apoptotic pathway induced by the HIV-1 envelope in T-lymphoid cells.

Influence of pan-caspase inhibitors on coxsackievirus B3-infected CD19+ B lymphocytes

Coxsackievirus B3 (CVB3), together with other enteroviruses of the picornavirus family, is associated with a wide variety of acute and chronic forms of human diseases. Using the murine model of CVB3-caused myocarditis, this pathogen can be detected not only in solid organs but also in different types of immune cells, preferentially in B lymphocytes. Therefore, these cells could represent a non-cardiac virus reservoir and may play an important role with regard to viral dissemination in the infected host. In addition, the infection of specific immune cells might modulate the severity of tissue injury and the pattern of virus-caused pathology in susceptible or resistant individuals. In the present study it could be demonstrated that CVB3 was capable to infect productively a certain percentage of murine CD19(+) B cells. In vivo studies revealed that CVB3 invaded murine CD19(+) B cells during an acute infection. Three days p. i. approximately 0.5-1.0% of these cells were productively infected. This proportion could be decreased up to 45%, if 3 days p. i. mice were intravenously treated with the pan-caspase inhibitors Z-VAD-FMK or Q-VD-OPH. These data were compared with results obtained from CVB3-infected human Raji cells.

The human fatty acid synthase: a new therapeutic target for coxsackievirus B3-induced diseases?

Coxsackievirus is linked to a large variety of severe human and animal diseases such as myocarditis. The interplay between host factors and virus components is crucial for the fate of the infected cells. However, host proteins which may play a role in coxsackievirus-induced diseases are ill-defined. Two-dimensional gel electrophoresis of protein extracts obtained from coxsackievirus B3 (CVB3)-infected and uninfected HeLa or HepG2 cells combined with spot analysis revealed several proteins which are exclusively up-regulated in infected cells. One of these proteins was identified as the fatty acid synthase (FAS). By using cerulenin and C75, two known inhibitors of FAS we were able to significantly block CVB3 replication. FAS appears to be directly involved in CVB3-caused pathology and is therefore suitable as a therapeutic target in CVB3-induced diseases.

Coxsackievirus B3 proteases 2A and 3C induce apoptotic cell death through mitochondrial injury and cleavage of eIF4GI but not DAP5/p97/NAT1

By transfection of Coxsackievirus B3 (CVB3) individual protease gene into HeLa cells, we demonstrated that 2A(pro) and 3C(pro) induced apoptosis through multiple converging pathways. Firstly, both 2A(pro) and 3C(pro) induced caspase-8-mediated activation of caspase-3 and dramatically reduced cell viability. Secondly, they both activated the intrinsic mitochondria-mediated apoptosis pathway leading to cytochrome c release from mitochondria and activation of caspase-9. However, 3C(pro) induced these events via both up-regulation of Bax and cleavage of Bid, and 2A(pro) induced these events via cleavage of Bid only. Nevertheless, neither altered Bcl-2 expression. Thirdly, both proteases induced cell death through cleavage or down regulation of cellular factors for translation and transcription: both 2A(pro) and 3C(pro) cleaved eukaryotic translation initiation factor 4GI but their cleavage products are different, indicating different cleavage sites; further, both 2A(pro) and 3C(pro) down-regulated cyclic AMP responsive element binding protein, a transcription factor, with 2A(pro) exhibiting a stronger effect than 3C(pro). Surprisingly, neither could cleave DAP5/p97/NAT1, a translation regulator, although this cleavage was observed during CVB3 infection and could not be blocked by caspase inhibitor z-VAD-fmk. Taken together, these data suggest that 2A(pro) and 3C(pro) induce apoptosis through both activation of proapoptotic mediators and suppression of translation and transcription.

Antiviral effects of pan-caspase inhibitors on the replication of coxsackievirus B3

The induction of apoptosis during coxsackievirus B3 (CVB3) infection is well documented. In order to study whether the inhibition of apoptosis has an impact on CVB3 replication, the pan-caspase inhibitor Z-VAD-FMK was used. The decreased CVB3 replication is based on reduced accumulation of both viral RNA and viral proteins. These effects are due to an inhibitory influence of Z-VAD-FMK on the proteolytic activity of the CVB3 proteases 2A and 3C, which was demonstrated by using the target protein poly(A)-binding protein (PABP). The antiviral effect of the structurally different pan-caspase inhibitor Q-VD-OPH was independently of the viral protease inhibition and resulted in suppression of virus progeny production and impaired release of newly produced CVB3 from infected cells. A delayed release of cytochrome c into the cytoplasm was detected in Q-VD-OPH-treated CVB3-infected cells pointing to an involvement of caspases in the initial steps of mitochondrial membrane-permeabilization.

Proteome alterations in human host cells infected with coxsackievirus B3

Coxsackievirus B3 (CVB3) is a common factor in human myocarditis. The interplay between host factors and virus components is crucial for the fate of the infected cells. Despite that, host protein responses, which characterize CVB3-induced diseases, have not yet been determined in detail. To investigate the nature of modified protein patterns in infected human cells compared with uninfected cells, two-dimensional gel electrophoresis in combination with matrix-assisted laser desorption/ionization-mass spectrometry were used. The regulated proteins, e.g. nucleophosmin (nucleolar protein B23), lamin, the RNA-binding protein UNR and the p38 mitogen-activated protein kinase, were sorted according to their functional groups and interpreted in the context of the myocarditis process.

The zinc containing pro-apoptotic protein siva interacts with the peroxisomal membrane protein pmp22

Host answers to pathogen attacks define the course of pathogenic events and decide about the fate of the host organism. Infection with coxsackievirus B3 (CVB3) can induce severe myocarditis and pancreatitis. The interplay between host factors and virus components is crucial for the fate of the infected host. As we have shown before, expression of the pro-apoptotic host protein Siva is significantly increased after CVB3 infection, and infected cells are removed by programmed cell death. Analysis of Siva expressed in Escherichia coli revealed that this protein binds three zinc ions, suggesting a rather complex three-dimensional structure. By screening a human heart cDNA library we found a new interaction partner of Siva. The peroxisomal membrane protein PMP22 may be involved in the host response against CVB3. Previous investigations showed that Siva interacts with the cytoplasmic C-terminus of CD27, a member of the tumor necrosis factor receptor group, and transmits an apoptotic signal. With the help of directed two-hybrid assays we determined the N-terminal part of Siva as the binding region for CD27.

Coxsackievirus targets proliferating neuronal progenitor cells in the neonatal CNS

Type B coxsackieviruses (CVB) frequently infect the CNS and, together with other enteroviruses, are the most common cause of viral meningitis in humans. Newborn infants are particularly vulnerable, and CVB also can infect the fetus, leading to mortality, or to neurodevelopmental defects in surviving infants. Using a mouse model of neonatal CVB infection, we previously demonstrated that coxsackievirus B3 (CVB3) could infect neuronal progenitor cells in the subventricular zone (SVZ). Here we extend these findings, and we show that CVB3 targets actively proliferating (bromodeoxyuridine+, Ki67+) cells in the SVZ, including type B and type A stem cells. However, infected cells exiting the SVZ have lost their proliferative capacity, in contrast to their uninfected companions. Despite being proliferation deficient, the infected neuronal precursors could migrate along the rostral migratory stream and radial glia, to reach their final destinations in the olfactory bulb or cerebral cortex. Furthermore, infection did not prevent cell differentiation, as determined by cellular morphology and the expression of maturation markers. These data lead us to propose a model of CVB infection of the developing CNS, which may explain the neurodevelopmental defects that result from fetal infection.

Siva-1 negatively regulates NF-kappaB activity: effect on T-cell receptor-mediated activation-induced cell death (AICD)

Ligation of TCRs on stimulated T cells leads to activation-induced cell death (AICD) resulting in the downregulation of immune responses, a process essential for T-cell homeostasis. In this study, using transformed T-cell lines such as Jurkat and Do11.10 as cellular models of TCR-mediated AICD, we have demonstrated that the proapoptotic protein Siva-1 is required for TCR-induced apoptosis. Knockdown of Siva-1 rendered T cells specifically resistant to anti-CD3 but not Fas-induced apoptosis. Further, we observed that in Siva-1 knockout Jurkat cells, TCR-mediated activation of the canonical and non-canonical limbs of the NF-kappaB pathway are significantly enhanced as reflected by elevated nuclear levels of p65 and RelB, respectively. In addition, loss of endogenous Siva-1 also resulted in the enhanced expression of NF-kappaB- responsive anti-apoptotic genes such as Bcl-xL and c-FLIP. Interestingly, the c-FLIP(short) was detected only in TCR-ligated Siva-1 knockdown Jurkat cells. These results demonstrate a significant role for endogenous Siva-1, through its inhibitory effect on NF-kappaB activity, in TCR-mediated AICD with implications in peripheral tolerance, T-cell homeostasis and cancer.

Picornaviruses and cell death

Members of the picornavirus family, including poliovirus and foot-and-mouth disease virus, are widespread pathogens of humans and domestic animals. Recent global developments in the resurgence of poliovirus infection and in the control of foot-and-mouth disease infection highlight the problems caused by the ability of picornaviruses to alter the apoptotic machinery of host cells and establish persistent infections. Despite the medical, economic and social impact of this family of viruses, little information exists that integrates the mechanisms of cell death and damage induced by related family members. Fortunately, examination of the reported roles and functions of individual viral proteins from multiple picornaviruses makes it possible to surmise canonical functions for these proteins. This review analyzes the canonical function of picornavirus proteins involved in the alteration of apoptotic homeostasis in infected host cells.

Host and virus determinants of picornavirus pathogenesis and tropism

The family Picornaviridae contains some notable members, including rhinovirus, which infects humans more frequently than any other virus; poliovirus, which has paralysed or killed millions over the years; and foot-and-mouth-disease virus, which led to the creation of dedicated institutes throughout the world. Despite their profound impact on human and animal health, the factors that regulate pathogenesis and tissue tropism are poorly understood. In this article, we review the clinical and economic challenges that these agents pose, summarize current knowledge of host-pathogen interactions and highlight a few of the many outstanding questions that remain to be answered.

Gamma interferon-inducible protein 10 induces HeLa cell apoptosis through a p53-dependent pathway initiated by suppression of human papillomavirus type 18 E6 and E7 expression

Gamma interferon-inducible protein 10 (IP10) is a member of the CXC family of chemokines. By differential mRNA display, we have demonstrated the upregulation of IP10 in coxsackievirus B3 (CVB3)-infected mouse hearts. Functional characterization of the IP10 gene in IP10-transfected Tet-On HeLa cells has found that IP10 induced cell apoptosis and inhibited viral replication. In the characterization of the IP10-induced apoptotic pathway, we found that overexpression of IP10 upregulated p53 and resulted in altered expression of p53-responsive genes such as the p21Cip1, p27kip1, NF-kappaB, Bax, and PUMA genes and the mitochondrial translocation of Bax. However, transduction of the IP10 cells with adenovirus expressing dominant negative p53 not only ablated p53-triggered gene expression but also abolished IP10-induced apoptosis and restored CVB3 replication to the control levels. These data suggest a novel mechanism by which IP10 inhibits viral replication through the induction of host cell death via a p53-mediated apoptotic pathway. We also found that constantly high-level expression of p53 in these tumor cells is attributed to the IP10-induced suppression of human papillomavirus E6 and E7 oncogene expression. Taken together, these data reveal not only a previously unrecognized link between chemokine IP10 and p53 in antiviral defense but also a mechanism by which IP10 inhibits tumor cell growth.

Expression of Siva-1 protein or its putative amphipathic helical region enhances cisplatin-induced apoptosis in breast cancer cells: effect of elevated levels of BCL-2

cis-Diaminedichloroplatinum (II) (cisplatin) is routinely used to treat various types of cancers; however, a significant number develop resistance. One of the underlying factors that contribute to cisplatin resistance is the elevated level of BCL-2 and/or BCL-XL, which promotes cell survival. A potential method of overcoming such resistance is to use a potentiator that is capable of neutralizing the antiapoptotic effects of BCL-2/BCL-XL, such as Siva-1. We previously cloned the proapoptotic protein Siva-1 and showed a possible role for it in both extrinsic and intrinsic apoptosis. Using an adenovirus-based expression system, we now show that Siva-1 can synergize with cisplatin in inducing apoptosis in MCF7 and MDA-MB-231 breast cancer cells. In an anchorage-independent clonogenicity assay, MCF7/caspase-3 cells stably expressing Siva-1, but not the control cells, showed a dramatic decrease in the number of colonies formed on one-time cisplatin treatment. Further, we show that the unique putative amphipathic helical region (SAH) in Siva-1 (amino acid residues 36-55) is necessary and sufficient for the observed enhancement in cisplatin-induced apoptosis by Siva-1. Although cisplatin treatment results in significant elevation in the expression of Fas ligand and intracellular p21 levels, expression of Siva-1 has no additional benefit. Instead, the enhancement in apoptosis seems to be due to activation of intrinsic pathway that involves caspase-9 activation. Moreover, Siva-1 augments cisplatin-mediated cell death in MCF7 cells stably expressing BCL-2. We therefore propose that Siva-1 or its SAH region can be used as a potentiator of cisplatin-based chemotherapy.

Targeting 2A protease by RNA interference attenuates coxsackieviral cytopathogenicity and promotes survival in highly susceptible mice

BACKGROUND

Enteroviridae such as coxsackievirus B3 (CVB3) are important infectious agents involved in viral heart disease, hepatitis, and pancreatitis, but no specific antiviral therapy is available.

METHODS AND RESULTS

The aim of the present study was to evaluate the impact of RNA interference on viral replication, cytopathogenicity, and survival. Small interfering RNA (siRNA) molecules were designed against the viral 2A region (siRNA-2A), which is considered to be highly conserved and essential for both virus maturation and host cytopathogenicity. siRNA-2A exhibited a significant protective effect on cell viability mediated by marked inhibition of CVB3 gene expression and viral replication. In highly susceptible type I interferon receptor-knockout mice, siRNA-2A led to significant reduction of viral tissue titers, attenuated tissue damage, and prolonged survival. Repeated siRNA-2A transfection was associated with a further improvement of survival. Various control siRNA molecules had no protective effect in vitro or in vivo.

CONCLUSIONS

RNA interference directed against the 2A protease encoding genomic region effectively confers intracellular immunity toward CVB3-mediated cell injury and improves survival, suggesting a potential role for RNA interference for future treatment options targeting enteroviral diseases.

Myocarditis susceptibility in female mice depends upon ovarian cycle phase at infection

Female BALB/c mice were infected with coxsackievirus B3 in the diestrus, proestrus, estrus, or metestrus phases of the ovarian cycle. Cycle stage was determined by vaginal smear. All mice were killed 7 days after infection. Females infected in the diestrus and especially the proestrus phases developed myocarditis. CD4+ T cells expressing interferon-gamma (IFNgamma) infiltrate the myocardium in these two phases, whereas CD4+ T cells expressing IL-4 are more frequent during estrus. Cardiac virus titers were determined 15 h and 7 days after infection. No differences in virus titer were seen at 7 days. These studies show that natural hormone variations can have substantial effects on viral pathogenicity presumably due to hormone effects on the immune system.

Role of Apoptosis in the Pathogenesis of Asian and South American Foot-and-Mouth Disease Viruses in Swine

In this study, we performed experiments to evaluate the extend of the process of apoptotic cell death by foot-and-mouth disease virus (FMDV). Apoptosis can also occur in some virus-infected cells, and ability of viruses to either inhibit or promote apoptosis may influence the pathologic outcome of infection. In this study, to determine if apoptosis plays a role in the outcome of FMDV infection in swine, we evaluated apoptosis in diseased tissues collected from pigs inoculated with two different stains of FMDV (O1 Campos and O Taiwan). And host cell DNA fragmentation in diseased tissue from animals which were infected with either virus was evaluated by occurrence of a laddering pattern characteristic of apoptosis. Infection of cultured keratinocytes from swine tongue failed to demonstrate apoptosis in the first few hours of infection, suggesting that cell-to-cell correlation between viral antigen and apoptotic changes, e.g. cytokine secretions by immune system cells, could be critical to initiating apoptosis. Consistent with this finding, we were able to detect the pro-inflammatory cytokine TNF-alpha in diseased tissues. A clear difference in the pathogenicity of the two different FMDV isolates to pigs was not demonstrated in our study.

Variability in apoptotic response to poliovirus infection

In several cell types, poliovirus activates the apoptotic program, implementation of which is suppressed by viral antiapoptotic functions. In such cells, productive infection leads to a necrotic cytopathic effect (CPE), while abortive reproduction, associated with inadequate viral antiapoptotic functions, results in apoptosis. Here, we describe two other types of cell response to poliovirus infection. Murine L20B cells expressing human poliovirus receptor responded to the infection by both CPE and apoptosis concurrently. Interruption of productive infection decreased rather than increased the proportion of apoptotic cells. Productive infection was accompanied by the early efflux of cytochrome c from the mitochondria in a proportion of cells and by activation of DEVD-specific caspases. Inactivation of caspase-9 resulted in a marked, but incomplete, prevention of the apoptotic response of these cells to viral infection. Thus, the poliovirus-triggered apoptotic program in L20B cells was not completely suppressed by the viral antiapoptotic functions. In contrast, human rhabdomyosarcoma RD cells did not develop appreciable apoptosis during productive or abortive infection, exhibiting inefficient efflux of cytochrome c from mitochondria and no marked activation of DEVD-specific caspases. The cells were also refractory to several nonviral apoptosis inducers. Nevertheless, typical caspase-dependent signs of apoptosis in a proportion of RD cells were observed after cessation of viral reproduction. Such "late" apoptosis was also observed in productively infected HeLa cells. In addition, a tiny proportion of all studied cells were TUNEL positive even in the presence of a caspase inhibitor. Degradation of DNA in such cells appeared to be a postmortem phenomenon. Biological relevance of variable host responses to viral infection is discussed.

Coxsackievirus B3 infection induces cyr61 activation via JNK to mediate cell death

Coxsackievirus B3 (CVB3), an enterovirus in the Picornavirus family, is the most common human pathogen associated with myocarditis and idiopathic dilated cardiomyopathy. We found upregulation of the cysteine-rich protein gene (cyr61) after CVB3 infection in HeLa cells with a cDNA microarray approach, which is confirmed by Northern blot analysis. It is also revealed that the extracellular amount of Cyr61 protein was increased after CVB3 infection in HeLa cells. cyr61 is an early-transcribed gene, and the Cyr61 protein is secreted into the extracellular matrix. Its function is related to cell adhesion, migration, and neuronal cell death. Here, we show that activation of the cyr61 promoter by CVB3 infection is dependent on JNK activation induced by CVB3 replication and viral protein expression in infected cells. To explore the role of Cyr61 protein in infected HeLa cells, we transiently overexpressed cyr61 and infected HeLa cells with CVB3. This increased CVB3 growth in the cells and promoted host cell death by viral infection, whereas down-expression of cyr61 with short interfering RNA reduced CVB3 growth and showed resistance to cell death by CVB3 infection. In conclusion, we have demonstrated a new role for cyr61 in HeLa cells infected with CVB3, which is associated with the cell death induced by virus infection. These data thus expand our understanding of the physiological functions of cyr61 in virus-induced cell death and provide new insights into the cellular factors involved.

Intranasal delivery of chitosan-DNA vaccine generates mucosal SIgA and anti-CVB3 protection

Coxsackievirus B3 infections are common causes of acute and chronic myocarditis with no effective prophylactic treatment available. We describe here a prophylactic strategy using chitosan-DNA intranasal immunization to induce CVB3 specific immune responses. Intranasal administration with chitosan-DNA complex prepared by votexing DNA with chitosan, a natural mucus absorption enhancer, resulted in transgenic DNA expression in mouse nasopharynx. Mice immunized with chitosan-DNA (pcDNA3-VP1) encoding VP1, major structural protein of CVB3, produced much higher levels of serum IgG and mucosal secretory IgA compared to mice treated with pcDNA3-VP1 or pcDNA3. Increased virus-specific cytotoxic activity of spleen cells derived from chitosan-DNA vaccinated mice was also determined. Chitosan-pcDNA3-VP1 intranasal immunization resulted in 42.9% protection of mice against lethal CVB3 challenge and a significant reduction of viral load after acute CVB3 infection. Meanwhile no myonecrosis or infiltrating immune cells indicating ongoing myocarditis was detected in hearts of surviving mice treated with chitosan-DNA. Together, Our data show that intranasal delivery of chitosan-DNA vaccine successfully induced mucosal SIgA secretion and might be a promising vaccine candidate to protect against CVB3 infection.

Coxsackievirus-induced pancreatitis

In humans, infections with the group B coxsackieviruses (CVBs) range from asymptomatic infections to chronic, debilitating diseases. The CVBs are associated with chronic inflammatory diseases of the pancreas, heart, and central nervous system. A major focus in CVB pathogenesis is to understand the mechanisms by which these viruses cause acute diseases that resolve or acute diseases that progress to chronic diseases. The present review explores CVB infections in the development of acute and chronic pancreatitis. Mouse models of CVB-induced pancreatitis share many features with the human diseases and are providing insight into the multi-faceted processes of pancreatic tissue repair and irreversible tissue destruction. The development and progression of CVB-induced pancreatic inflammatory disease is an extremely complex process, involving both viral and host factors. The review examines the roles of the virus and host in contributing to the disease process. Recent studies of global gene expression during CVB-induced pancreatitis have increased our understanding of host factors that influence the outcome of infection and have highlighted interrelationships among complex biological programs. As we unravel the complexity of the disease process, the information gained will lead to the design of therapeutics that not only prevent the progression of chronic inflammatory disease, but that also restore functionality of affected tissues and organs.

T cells in coxsackievirus-induced myocarditis

Myocarditis is a complex disease in which distinct immunopathogenic mechanisms cause tissue injury. In some but not all cases, autoimmunity is a major pathogenic factor. Cross-reactivity between viral and myosin epitopes underlies both cellular and humoral autoimmunity in myocarditis. Thus, the genetics of the host as well as the virus determine disease pathogenicity. Innate immunity, as represented by gammadelta+ T cells, is important in determining disease susceptibility. The innate effectors rapidly localize in the infected myocardium and through release of IFNgamma (Vgamma4+ cells; BALB/c) or IL-4 (Vgamma1+ cells; C57Bl/6), modulate the developing adaptive immune response to either a Th1 or Th2 response, respectively. The Vgamma4+ cells in BALB/c mice recognize CD1d, a major histocompatibility complex class I-like antigen. The ligand for Vgamma1+ cells is unknown. Only infected myocytes up-regulate CD1d. Signaling through both infection (double stranded RNA) and TNFalpha is required for CD1d up-regulation.

Siva-1 and an alternative splice form lacking the death domain, Siva-2, similarly induce apoptosis in T lymphocytes via a caspase-dependent mitochondrial pathway

Siva-1 is a death domain-containing proapoptotic protein identified as an intracellular ligand of CD27 and of the glucocorticoid-induced TNFR family-related gene, which are two members of the TNFR family expressed on lymphoid cells. Although Siva-1 expression is up-regulated in multiple pathological processes, little is known about the signaling pathway underlying the Siva-induced apoptosis. In this study, we investigated the mechanism of the proapoptotic activity of Siva-1 and an alternative splice form lacking the death domain of Siva-1, Siva-2, in T lymphocytes in which Siva proteins, CD27, and glucocorticoid-induced TNFR family-related gene are primarily expressed. Overexpression of Siva proteins triggers a typical apoptotic process manifested by cell shrinkage and surface exposure of phosphatidylserine, and confirmed by ultrastructural features. Siva-induced apoptosis is related to the CD27-mediated apoptotic pathway and results in activation of both initiator and effector caspases. This pathway involves a mitochondrial step evidenced by activation of Bid and cytochrome c release, and is modulated by overexpression of Bcl-2 or Bcl-x(L). The determinants for Siva-induced apoptosis are not contained within the death domain found in the central part of Siva-1, but rather in both the N-terminal and C-terminal regions shared by both Siva proteins. The N-terminal region also participates in the translocation of both Siva proteins into the nuclear compartment. These results indicate that Siva-1 and Siva-2 mediate apoptosis in T lymphocytes via a caspase-dependent mitochondrial pathway that likely involves both cytoplasmic and nuclear events.

Recruitment of Hsp70 chaperones: a crucial part of viral survival strategies

Virus proliferation depends on the successful recruitment of host cellular components for their own replication, protein synthesis, and virion assembly. In the course of virus particle production a large number of proteins are synthesized in a relatively short time, whereby protein folding can become a limiting step. Most viruses therefore need cellular chaperones during their life cycle. In addition to their own protein folding problems viruses need to interfere with cellular processes such as signal transduction, cell cycle regulation and induction of apoptosis in order to create a favorable environment for their proliferation and to avoid premature cell death. Chaperones are involved in the control of these cellular processes and some viruses reprogram their host cell by interacting with them. Hsp70 chaperones, as central components of the cellular chaperone network, are frequently recruited by viruses. This review focuses on the function of Hsp70 chaperones at the different stages of the viral life cycle emphasizing mechanistic aspects.

Increased susceptibility of male BALB/c mice to coxsackievirus B3-induced myocarditis: role for CD1d

BALB/c male mice infected with the H3 variant of coxsackievirus B3 (CVB3) develop fulminant myocarditis. Age-matched female mice show little myocarditis due to decreased virus receptor expression on cardiac cells. TNFalpha and IL-1beta levels were increased in males by 3 days after infection. IFNgamma levels increased more slowly throughout the 7-day observation period. CD4+, CD8+, macrophage (Mac3+) and gammadelta+ cells all accumulated in male hearts, with gammadelta+ cells showing early (day 3) infiltration. Females also accumulated CD4+ cells, but few of the other cell types. CD4+ cells in male hearts predominately produced IFNgamma, indicating a Th1 cell phenotype, whereas CD4+ cells in females produced IL-4, but little IFNgamma, indicating a Th2 phenotype. CD1d, a major histocompatibility complex I-like molecule often implicated in innate immunity, was increased in CVB3-infected male but not female cardiocytes both in vivo and in vitro. These results demonstrate that CVB3 infections produce gender-specific differences in both innate and adaptive immunity, which may explain the difference in disease susceptibility.

Glutathione depletion and cardiomyocyte apoptosis in viral myocarditis

BACKGROUND

The course of viral myocarditis is highly variable. Oxidative stress and Bcl-2 family genes may play a role in its pathogenesis by regulating the amount of cardiomyocyte apoptosis. Apoptosis is difficult to detect and quantify in vivo. Therefore, we set to look for indicators of this potentially preventable form of cell death during various phases of experimental murine coxsackievirus B3 myocarditis.

METHODS

BALB/c mice were infected with the cardiotropic coxsackievirus B3 variant. Glutathione (HPLC), cardiomyocyte apoptosis (TUNEL and caspase-3 cleavage), Bax and Bcl-X(L) mRNA expression (real time RT-PCR), histopathology and viral replication (plaque assay and real time RT-PCR) were measured from day 3 to day 20 after infection.

RESULTS

Infection caused severe myocarditis and led to progressive decrease of plasma glutathione levels. Myocardial mRNA levels of pro-apoptotic Bax and antiapoptotic Bcl-X(L) were significantly increased from day 3 onwards. Bax mRNA and ratio of Bax to Bcl-X(L) correlated with cardiomyocyte apoptosis (r = 0.77, P = < 0.001 and r 0.51, P < 0.01, respectively). Cardiomyocyte apoptosis was highest on day 5, coinciding with a rapid decline in plasma glutathione (r = -0.52, P = 0.003).

CONCLUSIONS

Systemic oxidative stress as indicated by decreased plasma glutathione levels coincides with cardiomyocyte apoptosis in experimental coxsackievirus myocarditis. Decreased plasma glutathione levels and changes in cardiac Bax and Bcl-X(L) mRNA expression identify a phase of myocarditis in which the potentially preventable cardiomyocyte apoptosis is mostly observed.

Avian encephalomyelitis virus nonstructural protein 2C induces apoptosis by activating cytochrome c /caspase-9 pathway

The nonstructural protein 2C is highly conserved among picornaviruses and plays an important role in the assembly of mature virions, membrane association, and viral RNA synthesis. The investigation of other potential functions of nonstructural protein 2C from avian encephalomyelitis virus (AEV) resulted in identifying for the first time that the protein 2C is involved in apoptosis. Expression of the protein 2C on chick embryo brain (CEB) and Cos-7 cells produced TUNEL-positive cells characterized by a cleavage of cellular DNA and the formation of membrane-enclosed apoptotic bodies. Analysis of the protein 2C showed that the N-terminal domain containing 35 amino acid (aa) residues (between 46 and 80 aa) is associated with apoptotic function. Transfection of the deletion mutant lacking this 35 aa's into CEB and Cos-7 cells failed to induce apoptosis. Furthermore, the protein 2C induced apoptosis in the transfected CEB and Cos-7 cells through activation of caspase-9 rather than caspase-8 followed by activation of caspase-3 pathway. Analysis of the Western blots of caspase-3 and caspase-9 showed the characteristics of active caspase-3 and -9 in the 2C-transfected CEB and Cos-7 cells as seen in the AEV-infected CEB cells while they were in the form of procaspase-3 and procaspase-9 in the 2C mutant-transfected cells. To further elucidate the mechanism of the 2C-induced apoptosis, the 2C-transfected CEB and Cos-7 cells were fractionated into mitochondria and cytosol and subjected for Western blotting, located cytochrome c in the mitochondria as well as the cytosol fractions, while it was only sequestered in the mitochondrial fraction in the mutant 2C-transfected cells. The protein 2C was located in the mitochondria and cytosol of the transfected/infected CEB and transfected Cos-7 cells, but the mutant lost its ability to localize to the mitochondria. Altogether, the results demonstrate that the protein 2C localized to the mitochondria of the transfected cells triggered the efflux of cytochrome c into the cytosol in turn activating the upstream caspase-9 and then the downstream caspase-3, thus leading to apoptosis in the cells.

Direct interferon-gamma-mediated protection caused by a recombinant coxsackievirus B3

Coxsackievirus B3 (CVB3) is one of the most important causes of viral myocarditis. Cytokines are involved in the control of CVB3 replication and pathogenesis. Local expression of specific cytokines by recombinant CVB3 confers prevention of virus-caused myocarditis. Expression of IFN-gamma by CVB3(IFN-gamma) protected BALB/c and C57BL/6 mice when the lethal infection with the highly pathogenic CVB3H3 variant was given directly after or prior to CVB3(IFN-gamma) inoculation by decreasing the viral load and spread as well as tissue destruction. This direct effect was not restricted to the homologous virus. In vitro, cocultivation of CVB3(IFN-gamma)-infected cells induced a reduction of CVB3H3 replication and virus-induced cytopathogenicity.

Coxsackievirus B3 and the neonatal CNS: the roles of stem cells, developing neurons, and apoptosis in infection, viral dissemination, and disease

Neonates are particularly susceptible to coxsackievirus infections of the central nervous system (CNS), which can cause meningitis, encephalitis, and long-term neurological deficits. However, viral tropism and mechanism of spread in the CNS have not been examined. Here we investigate coxsackievirus B3 (CVB3) tropism and pathology in the CNS of neonatal mice, using a recombinant virus expressing the enhanced green fluorescent protein (eGFP). Newborn pups were extremely vulnerable to coxsackievirus CNS infection, and this susceptibility decreased dramatically by 7 days of age. Twenty-four hours after intracranial infection of newborn mice, viral genomic RNA and viral protein expression were detected in the choroid plexus, the olfactory bulb, and in cells bordering the cerebral ventricles. Many of the infected cells bore the anatomical characteristics of type B stem cells, which can give rise to neurons and astrocytes, and expressed the intermediate filament protein nestin, a marker for progenitor cells. As the infection progressed, viral protein was identified in the brain parenchyma, first in cells expressing neuron-specific class III beta-tubulin, an early marker of neuronal differentiation, and subsequently in cells expressing NeuN, a marker of mature neurons. At later time points, viral protein expression was restricted to neurons in specific regions of the brain, including the hippocampus, the entorhinal and temporal cortex, and the olfactory bulb. Extensive neuronal death was visible, and appeared to result from virus-induced apoptosis. We propose that the increased susceptibility of the neonatal CNS to CVB infection may be explained by the virus' targeting neonatal stem cells; and that CVB is carried into the brain parenchyma by developing neurons, which continue to migrate and differentiate despite the infection. On full maturation, some or all of the infected neurons undergo apoptosis, and the resulting neuronal loss can explain the longer-term clinical picture.

Inhibition of translation and induction of apoptosis by Bunyaviral nonstructural proteins bearing sequence similarity to reaper

Members of the California serogroup of bunyaviruses (family Bunyaviridae) are the leading cause of pediatric viral encephalitis in North America. Significant cell death is observed as part of the infection pathology. We now report that a Bunyaviral nonstructural protein termed NSs shows sequence similarity to Reaper, a proapoptotic protein from Drosophila. Although NSs proteins lack the Reaper N-terminal motif critical for IAP inhibition, they do retain other functions of Reaper that map to conserved C-terminal regions. Like Reaper, NSs proteins induce mitochondrial cytochrome c release and caspase activation in cell-free extracts and promote neuronal apoptosis and mortality in a mouse model. Independent of caspase activation, Bunyavirus NSs proteins also share with Reaper the ability to directly inhibit cellular protein translation. We have found that the shared capacity to inhibit translation and induce apoptosis resides in common sequence motifs present in both Reaper and NSs proteins. Data presented here suggest that NSs induce apoptosis through a mechanism similar to that used by Reaper, as both proteins bind to an apoptotic regulator called Scythe and can relieve Scythe inhibition of Hsp70. Thus, bunyavirus NSs proteins have multiple Reaper-like functions that likely contribute to viral pathogenesis by promoting cell death and/or inhibiting cellular translation.

Cardiomyocyte apoptosis in experimental coxsackievirus B3 myocarditis

INTRODUCTION

Viruses are known to induce apoptosis in their host cells. We studied whether cardiomyocyte apoptosis occurs upon coxsackievirus B3 (CVB3) infection and whether virus-associated apoptosis plays a role in the pathogenesis of experimental myocarditis.

METHODS

BALB/c mice were infected with two variants of CVB3 causing either mild or severe myocarditis. Myocardial and serum samples were collected from Day 1 to Day 14 after virus inoculation. Apoptosis was detected in myocardial tissue sections using the terminal transferase-mediated DNA nick end labelling (TUNEL) assay and staining of active caspase 3, and compared with the presence of infectious CVB3 and viral proteins in cardiomyocytes.

RESULTS

Compared with the noninfected control mice, infection with either CVB3 variant resulted in significantly increased cardiomyocyte apoptosis, which peaked on Day 5 after infection. At this time, the average percentages of apoptotic cardiomyocytes were 0.17% (SD 0.04; P=.03) and 0.77% (SD 0.11; P<.01) in mild and severe disease forms, respectively. The amount of apoptosis correlated with titers of infectious CVB3 in the heart muscle. Viral proteins were detected in the TUNEL-positive cells by immunohistochemistry. In the late stages of disease, apoptosis, together with inflammatory infiltrates persisted only in the severe disease form.

CONCLUSIONS

CVB3-associated myocardial damage involves cardiomyocyte apoptosis. In the early stages of the disease, it appears to be triggered by viral replication in the cardiomyocytes.

High-neurovirulence GDVII virus induces apoptosis in murine astrocytes through tumor necrosis factor (TNF)-receptor and TNF-related apoptosis-inducing ligand

We carried out a study to determine if the high-neurovirulence GDVII strain of Theiler's murine encephalomyelitis virus (TMEV) and the demyelinating, low-neurovirulence BeAn strain induced apoptosis in murine astrocytes. Astrocytes, the major glial cell population of the central nervous system, were semipermissive for GDVII virus replication. Programmed cell death, demonstrated by apoptosis-specific caspase-3 protease activity, was maximal 8 h after GDVII infection at an m.o.i. of 1. Purified TMEV capsid proteins VP1, VP2, and VP3 did not induce apoptosis but antibodies to VP1 and VP2 inhibited it. Antibody inhibition of caspase-3 activity as well as flow cytometry experiments implicated TNF-related apoptosis-inducing ligand (TRAIL) and TNF-alpha-receptor (TNF-R) in apoptosis signaling. Conversely, TNF-alpha and the TRAIL-receptor were not upregulated. Furthermore, the number of functional TNF-alpha receptors, but not their affinity, was increased in apoptotic GDVII virus-infected astrocytes, as confirmed in binding experiments with 125I-labeled recombinant murine TNF-alpha. In vivo studies showed that most of the cells loaded with the virus when injected in the brains of SJL mice were neurons but very few showed TUNEL costaining. Conversely, many of the apoptotic cells found were also positive for GFAP staining.

beta2-microglobulin-associated regulation of interferon-gamma and virus-specific immunoglobulin G confer resistance against the development of chronic coxsackievirus myocarditis

To gain insight into the strategies of the immune system to confer resistance against the development of chronic coxsackievirus B3 (CVB3) myocarditis we compared the course of the disease in C57BL/6 mice, beta2-microglobulin knockout (beta2m(-/-)) mice, and perforin-deficient (perforin(-/-)) mice. We found that perforin(-/-) mice as well as immunocompetent C57BL/6 mice reveal a resistant phenotype with complete elimination of the virus from the heart in the course of acute myocarditis. In contrast, myocardial CVB3 infection of beta2m(-/-) mice was characterized by a significantly higher virus load associated with a fulminant acute inflammatory response and, as a consequence of virus persistence, by the development of chronic myocarditis. Interferon-gamma secretion of stimulated spleen cells was found to be significantly delayed in beta2m(-/-) mice compared to perforin(-/-) mice and C57BL/6 control mice during acute myocarditis. In addition, generation of virus-specific IgG and neutralizing antibodies were found to be significantly decreased in beta2m(-/-) mice during acute infection. From these results we conclude that protection against the development of chronic myocarditis strongly depends on the expression of beta2m, influencing the catabolism of IgG as well as the production of protective cytokines, such as interferon-gamma. Moreover, CVB3-induced cardiac injury and prevention of chronic myocarditis was found to be unrelated to perforin-mediated cytotoxicity in our model system.

Caspase-3 activation and ERK phosphorylation during CVB3 infection of cells: influence of the coxsackievirus and adenovirus receptor and engineered variants

Caspase activation and MAP kinase signaling have been implicated in coxsackievirus B3 (CVB3) pathogenesis, and both have been demonstrated late in the virus life cycle. We studied activation of caspase-3, an effector protease of apoptosis, and ERK phosphorylation, indicative of MAPK signaling pathway activation, following CVB3 infection of cells that express the coxsackievirus and adenovirus receptor (CAR) or CAR constructs lacking the cytoplasmic domain, and cells which express no detectable CAR. These experiments showed that a burst of caspase-3 activity preceded lysis of CVB3-infected cells expressing CAR, irrespective of the CAR cytoplasmic domain. In RD cells, which were infected in the absence of detectable CAR, caspase-3 activity increased progressively over 52 h with no apparent burst. ERK phosphorylation also occurred late in the virus life cycle, preceding caspase-3 activation, and occurred in cells expressing full-length CAR but not in RD. These results show that ERK phosphorylation precedes caspase-3 activation, both occur late in the infection, and both are influenced by the presence of CAR.

A possible role for the loss of CD27-CD70 interaction in myelomagenesis

CD27 is a marker of memory B cells and its interaction with its ligand, CD70, is very important for differentiation into plasma cells. Although CD27 is detected on normal plasma cells, its expression is significantly reduced with the progression of multiple myeloma (MM), including monoclonal gammopathy of undetermined significance (MGUS). CD27+ myeloma cells are thought to represent an early phase of myeloma, as CD27+ plasma cells from MM patients were found to be composed of normal plasma cells (CD19+/CD38++) and myeloma cells (CD19-/CD38++), and monoclonality was detected in the CD27+/CD38++ fraction. Given that the lack of CD27 on plasma cells is related to myelomagenesis and that the pro-apoptotic protein Siva is thought to bind to the cytoplasmic tail of CD27, we analysed alterations of cell growth and genes caused by co-culturing CD27-transfected myeloma cell lines (U266, KMS-5) with CD70-transfected NIH3T3 cells. CD27-CD70 interaction could not induce apoptosis in either type of myeloma transfectant, and binding between Siva and CD27 was not detected. cDNA microarray (human apoptosis CHIP) analysis showed a significant upregulation of expression of the ectodermal neural cortex 1 (ENC1) gene by CD27-CD70 interaction compared with CD27 transfection alone. These findings show that the relationship between the loss of CD27 and oncogenesis of plasma cells is not simple. It remains unclear whether the lack of CD27 leads to evasion of apoptosis.

Nip21 gene expression reduces coxsackievirus B3 replication by promoting apoptotic cell death via a mitochondria-dependent pathway

Our previous studies, using differential mRNA display, suggested that the mouse Nip21 gene may be involved in myocarditis development in the coxsackievirus B3 (CVB3)-infected mouse heart. Sequence comparison indicated that the mouse Nip21 gene shares high sequence homology to human Nip2. This human protein is known to interact with both the apoptosis inhibitor Bcl-2 and a homologous protein, the adenovirus E1B 19-kDa protein. Such interactions implicate Nip21 gene in cell death pathways. To study the function of this gene, we have cloned Nip21 from mouse hearts and established a Tet-On doxycycline-inducible HeLa cell line and a cardiomyocyte H9c2 cell line expressing Nip21 to characterize gene function in relation to apoptosis. We demonstrated that Nip21 expression could induce apoptosis via caspase-depended mitochondria activation. To further determine the function of Nip21 in CVB3-induced apoptosis, the Tet-On/Nip21 HeLa cell line was induced by doxycycline followed by CVB3 infection. We found that activation of caspase-3 and cleavage of poly-(ADP-ribose) polymerase occurred 2 hours earlier than in vector-transfected control cells, suggesting that Nip21 expression enhances CVB3-induced apoptosis. We also demonstrated a significant decrease in HeLa cell and H9c2 cell viability. Particularly, as illustrated by viral plaque assay, CVB3 replication was dramatically reduced in Tet-On HeLa cells, due at least in part to the earlier killing of the host cells by Nip21 overexpression.

Infection with enterovirus 71 or expression of its 2A protease induces apoptotic cell death

Enterovirus 71 (EV71) is the causative agent of human diseases with distinct severity, from mild hand-foot-and-mouth disease to severe neurological syndromes, such as encephalitis and meningitis. Infection of several different cell lines with EV71 causes extensive cytopathic effect, leading to destruction of the entire monolayer and the death of infected cells. In this study, cell death processes during EV71 infection and the underlying mechanisms of them were investigated. The hallmarks of apoptosis, nuclear condensation and fragmentation, were observed 24 h after infection. Apoptosis in infected cells was also confirmed by detectable cleavage of cellular DNA and degradation of poly(ADP-ribose) polymerase. Transient expression of EV71 2A protease (2A(pro)) alone resulted in the induction of apoptotic change. Infection of EV71 or expression of EV71 2A(pro) leads to cleavage of the eukaryotic initiation factor 4GI, a key factor for host protein synthesis. This study added one more example to the growing list of human viruses that induce apoptosis by a virus-encoded protein.

Siva-1 binds to and inhibits BCL-X(L)-mediated protection against UV radiation-induced apoptosis

We previously cloned Siva-1 by using the cytoplasmic tail of CD27, a member of the tumor necrosis factor receptor family, as the bait in the yeast two-hybrid system. The Siva gene is organized into four exons that code for the predominant full-length Siva-1 transcript, whereas its alternate splice form, Siva-2, lacks exon 2 coding sequence. Various groups have demonstrated a role for Siva-1 in several apoptotic pathways. Interestingly, the proapoptotic properties of Siva-1 are lacking in Siva-2. The fact that Siva-1 is partly localized to mitochondria despite the absence of any mitochondrial targeting signal, it harbors a 20-aa-long putative amphipathic helical structure that is absent in Siva-2, and that its expression is restricted to double-positive (CD3(+), CD4(+), CD8(+)) thymocytes like BCL-X(L), prompted us to test for a potential interaction between Siva-1 and BCL-X(L). Here, we show that Siva-1 binds to and inhibits BCL-X(L)-mediated protection against UV radiation-induced apoptosis. Indeed, the unique amphipathic helical region (SAH) present in Siva-1 is required for its binding to BCL-X(L) and sensitizing cells to UV radiation. Natural complexes of Siva-1/BCL-X(L) are detected in HUT78 and murine thymocyte, suggesting a potential role for Siva-1 in regulating T cell homeostasis.

Cardiomyocyte apoptosis after antiviral WIN 54954 treatment in murine coxsackievirus B3 myocarditis

OBJECTIVE

Cardiomyocyte apoptosis (CA) is known to occur in experimental coxsackievirus B3 (CVB3) myocarditis. However, the mechanisms of CA induction are not well known. In this study we investigate the role of direct viral induction of CA in CVB3 myocarditis.

DESIGN

A/J mice were infected with the Woodruff strain of CVB3 and treated with WIN 54954 for 5 days thereafter. WIN 54954, a compound that inhibits early events of picornavirus infection, is known to dramatically reduce mortality in murine CVB3 myocarditis without abrogating systemic or myocardial inflammation. Presence of viral RNA (in situ hybridization), CA (TUNEL method) and histopathology were studied in transverse ventricular sections at day 7 post infection (n = 8 treated and n = 8 non-treated).

RESULTS

The proportion of cardiomyocytes containing viral RNA was 89% lower in WIN 54954 treated mice when compared with non-treated mice (0.29 +/- 0.56% vs 2.76 +/- 1.65%, p = 0.003). Treatment also reduced the amount of CA by 52% compared with non-treated mice (0.20 +/- 0.06% vs 0.42 +/- 0.06%, p < 0.001). The reduction of CA by WIN treatment did not result in any increase of necrosis, in fact treatment reduced the area of necrotic lesions by 77% (2.51 +/- 1.64% vs 11.10 +/- 8.76%, p = 0.028).

CONCLUSION

Taking the results of the reduced CA, necrosis and viral RNA with no effect on inflammation into account, our findings suggest the importance of direct viral effect in cardiomyocyte damage by both apoptosis and necrosis in CVB3 myocarditis.

Coxsackievirus B3 replication is reduced by inhibition of the extracellular signal-regulated kinase (ERK) signaling pathway

Coxsackievirus B3 (CVB3) is the most common human pathogen for viral myocarditis. We have previously shown that the signaling protein p21(ras) GTPase-activating protein (RasGAP) is cleaved and that mitogen-activated protein kinases (MAPKs) ERK1/2 are activated in the late phase of CVB3 infection. However, the role of intracellular signaling pathways in CVB3-mediated myocarditis and the relative advantages of such pathways to host or virus remain largely unclear. In this study we extended our prior studies by examining the interaction between CVB3 replication and intracellular signaling pathways in HeLa cells. We observed that CVB3 infection induced a biphasic activation of ERK1/2, early transient activation versus late sustained activation, which were regulated by different mechanisms. Infection by UV-irradiated, inactivated virus capable of receptor binding and endocytosis triggered early ERK1/2 activation, but was insufficient to trigger late ERK1/2 activation. By using a general caspase inhibitor (zVAD.fmk) we further demonstrated that late ERK1/2 activation was not a result of CVB3-mediated caspase cleavage. Treatment of cells with U0126, a selective inhibitor of MAPK kinase (MEK), significantly inhibited CVB3 progeny release and decreased virus protein production. Furthermore, inhibition of ERK1/2 activation circumvented CVB3-induced apoptosis and viral protease-mediated RasGAP cleavage. Taken together, these data suggest that ERK1/2 activation is important for CVB3 replication and contributes to virus-mediated changes in host cells. Our findings demonstrate coxsackievirus takeover of a particular host signaling mechanism and uncover a prospective approach to stymie virus spread and preserve myocardial integrity.