Coxsackievirus B3 activates nuclear factor kappa B transcription factor via a phosphatidylinositol-3 kinase/protein kinase B-dependent pathway to improve host cell viability

Identification of the proteolytic signature in CVB3-infected cells

Coxsackievirus B3 (CVB3) encodes proteinases that are essential for processing of the translated viral polyprotein. Viral proteinases also target host proteins to manipulate cellular processes and evade innate antiviral responses to promote replication and infection. While some host protein substrates of the CVB3 3C and 2A cysteine proteinases have been identified, the full repertoire of targets is not known. Here, we utilize an unbiased quantitative proteomics-based approach termed terminal amine isotopic labeling of substrates (TAILS) to conduct a global analysis of CVB3 protease-generated N-terminal peptides in both human HeLa and mouse cardiomyocyte (HL-1) cell lines infected with CVB3. We identified >800 proteins that are cleaved in CVB3-infected HeLa and HL-1 cells including the viral polyprotein, known substrates of viral 3C proteinase such as PABP, DDX58, and HNRNPs M, K, and D and novel cellular proteins. Network and GO-term analysis showed an enrichment in biological processes including immune response and activation, RNA processing, and lipid metabolism. We validated a subset of candidate substrates that are cleaved under CVB3 infection and some are direct targets of 3C proteinase in vitro. Moreover, depletion of a subset of TAILS-identified target proteins decreased viral yield. Characterization of two target proteins showed that expression of 3Cpro-targeted cleaved fragments of emerin and aminoacyl-tRNA synthetase complex-interacting multifunctional protein 2 modulated autophagy and the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway, respectively. The comprehensive identification of host proteins targeted during virus infection provides insights into the cellular pathways manipulated to facilitate infection.

IMPORTANCE

RNA viruses encode proteases that are responsible for processing viral proteins into their mature form. Viral proteases also target and cleave host cellular proteins; however, the full catalog of these target proteins is incomplete. We use a technique called terminal amine isotopic labeling of substrates (TAILS), an N-terminomics to identify host proteins that are cleaved under virus infection. We identify hundreds of cellular proteins that are cleaved under infection, some of which are targeted directly by viral protease. Revealing these target proteins provides insights into the host cellular pathways and antiviral signaling factors that are modulated to promote virus infection and potentially leading to virus-induced pathogenesis.

MG53 protects against Coxsackievirus B3-induced acute viral myocarditis in mice by inhibiting NLRP3 inflammasome-mediated pyroptosis via the NF-κB signaling pathway

Pyroptosis, a novel programmed cell death mediated by NOD-like receptor protein 3 (NLRP3) inflammasome, is a critical pathogenic process in acute viral myocarditis (AVMC). Mitsugumin 53 (MG53) is predominantly expressed in myocardial tissues and has been reported to exert cardioprotective effects through multiple pathways. Herein, we aimed to investigate the biological function of MG53 in AVMC and its underlying regulatory mechanism in pyroptosis. BALB/c mice and HL-1 cells were infected with Coxsackievirus B3 (CVB3) to establish animal and cellular models of AVMC. As inflammation progressed in the myocardium, we found a progressive decrease in myocardial MG53 expression, accompanied by a significant enhancement of cardiomyocyte pyroptosis. MG53 overexpression significantly alleviated myocardial inflammation, apoptosis, fibrosis, and mitochondrial damage, thereby improving cardiac dysfunction in AVMC mice. Moreover, MG53 overexpression inhibited NLRP3 inflammasome-mediated pyroptosis, reduced pro-inflammatory cytokines (IL-1β/18) release, and suppressed NF-κB signaling pathway activation both in vivo and in vitro. Conversely, MG53 knockdown reduced cell viability, facilitated cell pyroptosis, and increased pro-inflammatory cytokines release in CVB3-infected HL-1 cells by promoting NF-κB activation. These effects were partially reversed by applying the NF-κB inhibitor BAY 11-7082. In conclusion, our results suggest that MG53 acts as a negative regulator of NLRP3 inflammasome-mediated pyroptosis in CVB3-induced AVMC, partially by inhibiting the NF-κB signaling pathway. MG53 is a promising candidate for clinical applications in AVMC treatment.

MicroRNA-22-3p displaces critical host factors from the 5' UTR and inhibits the translation of Coxsackievirus B3 RNA

Coxsackievirus B3 (CVB3) is known to cause acute myocarditis and pancreatitis in humans. We investigated the microRNAs (miRNAs) that can potentially govern the viral life cycle by binding to the untranslated regions (UTRs) of CVB3 RNA. MicroRNA-22-3p was short-listed, as its potential binding site overlapped with the region crucial for recruiting internal ribosome entry site trans-acting factors (ITAFs) and ribosomes. We demonstrate that miR-22-3p binds CVB3 5' UTR, hinders recruitment of key ITAFs on viral mRNA, disrupts the spatial structure required for ribosome recruitment, and ultimately blocks translation. Likewise, cells lacking miR-22-3p exhibited heightened CVB3 infection compared to wild type, confirming its role in controlling infection. Interestingly, miR-22-3p level was found to be increased at 4 hours post-infection, potentially due to the accumulation of viral 2A protease in the early phase of infection. 2Apro enhances the miR-22-3p level to dislodge the ITAFs from the SD-like sequence, rendering the viral RNA accessible for binding of replication factors to switch to replication. Furthermore, one of the cellular targets of miR-22-3p, protocadherin-1 (PCDH1), was significantly downregulated during CVB3 infection. Partial silencing of PCDH1 reduced viral replication, demonstrating its proviral role. Interestingly, upon CVB3 infection in mice, miR-22-3p level was found to be downregulated only in the small intestine, the primary target organ, indicating its possible role in influencing tissue tropism. It appears miR-22-3p plays a dual role during infection by binding viral RNA to aid its life cycle as a viral strategy and by targeting a proviral protein to restrict viral replication as a host response.IMPORTANCECVB3 infection is associated with the development of end-stage heart diseases. Lack of effective anti-viral treatments and vaccines for CVB3 necessitates comprehensive understanding of the molecular players during CVB3 infection. miRNAs have emerged as promising targets for anti-viral strategies. Here, we demonstrate that miR-22-3p binds to 5' UTR and inhibits viral RNA translation at the later stage of infection to promote viral RNA replication. Conversely, as host response, it targets PCDH1, a proviral factor, to discourage viral propagation. miR-22-3p also influences CVB3 tissue tropism. Deciphering the multifaced role of miR-22-3p during CVB3 infection unravels the necessary molecular insights, which can be exploited for novel intervening strategies to curb infection and restrict viral pathogenesis.

Recent Developments in Cell Shipping Methods

As opposed to remarkable advances in the cell therapy industry, researches reveal inexplicable difficulties associated with preserving and post-thawing cell death. Post cryopreservation apoptosis is a common occurrence that has attracted the attention of scientists to use apoptosis inhibitors. Transporting cells without compromising their survival and function is crucial for any experimental cell-based therapy. Preservation of cells allows the safe transportation of cells between distances and improves quality control testing in clinical and research applications. The vitality of transported cells is used to evaluate the efficacy of transportation strategies. For many decades, the conventional global methods of cell transfer were not only expensive but also challenging and had adverse effects. The first determination of some projects is optimizing cell survival after cryopreservation. The new generation of cryopreservation science wishes to find appropriate and alternative methods for cell transportation to ship viable cells at an ambient temperature without dry ice or in media-filled flasks. The diversity of cell therapies demands new cell shipping methodologies and cryoprotectants. In this review, we tried to summarize novel improved cryopreservation methods and alternatives to cryopreservation with safe and viable cell shipping at ambient temperature, including dry preservation, hypothermic preservation, gel-based methods, encapsulation methods, fibrin microbeads, and osmolyte solution compositions. This article is protected by copyright. All rights reserved.

Prognostic utility of echocardiographically derived left ventricular strain in assessing neonatal enteroviral myocarditis outcome

BACKGROUND

Neonatal enteroviral myocarditis is a rare but potentially fatal illness. We sought to identify echocardiographic markers at diagnosis that could help risk-stratify infants for poor outcome and to characterise late sequelae.

METHODS

We reviewed data for infants <30 days of age diagnosed with enteroviral myocarditis between 1999 and 2019 at Children's Wisconsin. Echo measures were collected retrospectively from the initial neonatal study including left ventricular ejection fraction, shortening fraction, diastolic and systolic dimensions, and peak global circumferential and longitudinal strain.

RESULTS

Fourteen neonates were diagnosed at an average age of 11 days. All had abnormal left ventricular ejection fraction (mean 38%; range 22-53%) at diagnosis. Three infants died, and one required transplantation during initial hospital. The 10 transplant-free survivors had significantly better global circumferential strain and global longitudinal strain at the initial echo compared to the 4 who died or needed transplant (global circumferential strain -13.2% versus -6.8%, p = 0.005; global longitudinal strain -8.8% versus -4.7%, p = 0.016). All other measures of left ventricular systolic function/dimensions were similar between the two groups. Follow-up data were available for 8/10 survivors; 5/8 had a persistently abnormal echo at an average interval of 8.3 years. 4/8 developed a left ventricular aneurysm that was consistently localised to the posterior basal wall.

CONCLUSIONS

Neonatal enteroviral myocarditis carries a high risk of early mortality and late morbidity. Echo-derived left ventricular strain measures have utility in risk stratifying infants with enteroviral myocarditis. Most survivors continue to have late dysfunction necessitating cardiology surveillance and medical therapy.

Transcriptomic analysis reveals that coxsackievirus B3 Woodruff and GD strains use similar key genes to induce FoxO signaling pathway activation in HeLa cells

Coxsackievirus B3 (CVB3) is a major cause of viral myocarditis in humans. Although there have been studies on CVB3 infection and pathogenesis, the precise disease mechanism is still not clear. In this study, we used RNA-seq technology to compare the transcriptomic profile of virus-infected HeLa cells to that of uninfected cells to identify key genes involved in host-virus interaction. For this, two CVB3 strains, CVB3 Woodruff, an experimental strain, and GD16-69/GD/CHN/2016, a clinical strain, were selected to examine the common mechanisms underlying their infection. Transcriptomic profiles revealed increased expression of the cell cycle genes CCNG2, GADD45B, PIM1, RBM15, KLF10, and RIOK3 and decreased expression of CYBA. The autophagy-related genes ATG12 and YOD1 were found to be upregulated, while the expression of SOD2 and XPO1 increased slightly in infected cells, and only a minor change was observed in GABARAP expression. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed the FoxO signaling pathway to be enriched and showed a close interaction with differentially expressed genes (DEGs) in the protein-protein interaction network. DEGs associated with related pathways such as cell cycle, autophagy, and oxidative stress resistance were also confirmed by qRT-PCR. In summary, the FoxO signaling pathway was activated during infection with both CVB3 strains and was found to have a regulatory role in downstream pathways such as cell cycle, autophagy, oxidative stress resistance, and the antiviral immune response.

Covid-19 pathogenesis in prostatic cancer and TMPRSS2-ERG regulatory genetic pathway

Members of Coronaviridae family have been the source of respiratory illnesses. The outbreak of SARS-CoV-2 that produced a severe lung disease in afflicted patients in China and other countries was the reason for the incredible attention paid toward this viral infection. It is known that SARS-CoV-2 is dependent on TMPRSS2 activity for entrance and subsequent infection of the host cells and TMPRSS2 is a host cell molecule that is important for the spread of viruses such as coronaviruses.

Different factors can increase the risk of prostate cancer, including older age, a family history of the disease. Androgen receptor (AR) initiates a transcriptional cascade which plays a serious role in both normal and malignant prostate tissues. TMPRSS2 protein is highly expressed in prostate secretory epithelial cells, and its expression is dependent on androgen signals. One of the molecular signs of prostate cancer is TMPRSS2-ERG gene fusion. In TMPRSS2-ERG-positive prostate cancers different patterns of changed gene expression can be detected. The possible molecular relation between fusion positive prostate cancer patients and the increased risk of lethal respiratory viral infections especially SARS-CoV-2 can candidate TMPRSS2 as an attractive drug target. The studies show that some molecules such as nicotinamide, PARP1, ETS and IL-1R can be studied deeper in order to control SARS-CoV-2 infection especially in prostate cancer patients.

This review attempts to investigate the possible relation between the gene expression pattern that is produced through TMPRSS2-ERG fusion positive prostate cancer and the possible influence of these fluctuations on the pathogenesis and development of viral infections such as SARS-CoV-2.

Kruppel-like factor 10 protects against acute viral myocarditis by negatively regulating cardiac MCP-1 expression

Viral myocarditis (VMC) is a cardiac disease associated with myocardial inflammation and injury induced by virus infection. Cardiomyocytes have recently been regarded as key players in eliciting and modulating inflammation within the myocardium. Kruppel-like factor 10 (KLF10) is a crucial regulator of various pathological processes and plays different roles in a variety of diseases. However, its role in VMC induced by coxsackievirus B3 (CVB3) infection remains unknown. In this study, we report that cardiac KLF10 confers enhanced protection against viral myocarditis. We found that KLF10 expression was downregulated upon CVB3 infection. KLF10 deficiency enhanced cardiac viral replication and aggravated VMC progress. Bone marrow chimera experiments indicated that KLF10 expression in nonhematopoietic cells was involved in the pathogenesis of VMC. We further identified MCP-1 as a novel target of KLF10 in cardiomyocytes, and KLF10 cooperated with histone deacetylase 1 (HDAC1) to negatively regulate MCP-1 expression by binding its promoter, leading to activation of MCP-1 transcription and recruitment of Ly6C^high monocytes/macrophages into the myocardium. This novel mechanism of MCP-1 regulation by KLF10 might provide new insights into the pathogenesis of VMC and a potential therapeutic target for VMC.

Spatio-temporal characterization of the antiviral activity of the XRN1-DCP1/2 aggregation against cytoplasmic RNA viruses to prevent cell death

Host nucleases are implicated in antiviral response through the processing of pathogen-derived nucleic acids. Among many host RNases, decapping enzymes DCP1 and 2, and 5'→3' exonuclease XRN1, which are components of the RNA decay machinery, have been extensively studied in prokaryotes, plants, and invertebrates but less so in mammalian systems. As a result, the implication of XRN1 and DCPs in viral replication, in particular, the spatio-temporal dynamics during RNA viral infections remains elusive. Here, we highlight that XRN1 and DCPs play a critical role in limiting several groups of RNA viral infections. This antiviral activity was not obvious in wild-type cells but clearly observed in type I interferon (IFN-I)-deficient cells. Mechanistically, infection with RNA viruses induced the enrichment of XRN1 and DCPs in viral replication complexes (vRCs), hence forming distinct cytoplasmic aggregates. These aggregates served as sites for direct interaction between XRN1, DCP1/2, and viral ribonucleoprotein that contains viral RNA (vRNA). Although these XRN1-DCP1/2-vRC-containing foci resemble antiviral stress granules (SGs) or P-body (PB), they did not colocalize with known SG markers and did not correlate with critical PB functions. Furthermore, the presence of 5' mono- and 5' triphosphate structures on vRNA was not required for the formation of XRN1-DCP1/2-vRC-containing foci. On the other hand, single-, double-stranded, and higher-ordered vRNA species play a role but are not deterministic for efficient formation of XRN1-DCP1/2 foci and consequent antiviral activity in a manner proportional to RNA length. These results highlight the mechanism behind the antiviral function of XRN1-DCP1/2 in RNA viral infections independent of IFN-I response, protein kinase R and PB function.

Pyroptosis induced by enterovirus 71 and coxsackievirus B3 infection affects viral replication and host response

Enterovirus 71 (EV71) is the primary causative pathogen of hand, foot, and mouth disease (HFMD), affecting children with severe neurological complications. Pyroptosis is a programmed cell death characterized by cell lysis and inflammatory response. Although proinflammatory response has been implicated to play important roles in EV71-caused diseases, the involvement of pyroptosis in the pathogenesis of EV71 is poorly defined. We show that EV71 infection induced caspase-1 activation. Responding to the activation of caspase-1, the expression and secretion of both IL-1β and IL-18 were increased in EV71-infected cells. The treatment of caspase-1 inhibitor markedly improved the systemic response of the EV71-infected mice. Importantly, caspase-1 inhibitor suppressed EV71 replication in mouse brains. Similarly, pyroptosis was activated by the infection of coxsackievirus B3 (CVB3), an important member of the Enterovirus genus. Caspase-1 activation and the increased expression of IL-18 and NLRP3 were demonstrated in HeLa cells infected with CVB3. Caspase-1 inhibitor also alleviated the overall conditions of virus-infected mice with markedly decreased replication of CVB3 and reduced expression of caspase-1. These results indicate that pyroptosis is involved in the pathogenesis of both EV71 and CVB3 infections, and the treatment of caspase-1 inhibitor is beneficial to the host response during enterovirus infection.

Cleavage of osmosensitive transcriptional factor NFAT5 by Coxsackieviral protease 2A promotes viral replication

Nuclear factor of activated T cells 5 (NFAT5)/Tonicity enhancer binding protein (TonEBP) is a transcription factor induced by hypertonic stress in the kidney. However, the function of NFAT5 in other organs has rarely been studied, even though it is ubiquitously expressed. Indeed, although NFAT5 was reported to be critical for heart development and function, its role in infectious heart diseases has remained obscure. In this study, we aimed to understand the mechanism by which NFAT5 interferes with infection of Coxsackievirus B3 (CVB3), a major cause of viral myocarditis. Our initial results demonstrated that although the mRNA level of NFAT5 remained constant during CVB3 infection, NFAT5 protein level decreased because the protein was cleaved. Bioinformatic prediction and verification of the predicted site by site-directed mutagenesis experiments determined that the NFAT5 protein was cleaved by CVB3 protease 2A at Glycine 503. Such cleavage led to the inactivation of NFAT5, and the 70-kDa N-terminal cleavage product (p70-NFAT5) exerted a dominant negative effect on the full-length NFAT5 protein. We further showed that elevated expression of NFAT5 to counteract viral protease cleavage, especially overexpression of a non-cleavable mutant of NFAT5, significantly inhibited CVB3 replication. Ectopic expression of NFAT5 resulted in elevated expression of inducible nitric oxide synthase (iNOS), a factor reported to inhibit CVB3 replication. The necessity of iNOS for the anti-CVB3 effect of NFAT5 was supported by the observation that inhibition of iNOS blocked the anti-CVB3 effect of NFAT5. In a murine model of viral myocarditis, we observed that treatment with hypertonic saline or mannitol solution upregulated NFAT5 and iNOS expression, inhibited CVB3 replication and reduced tissue damage in the heart. Taken together, our data demonstrate that the anti-CVB3 activity of NFAT5 is impaired during CVB3 infection due to 2A-mediated cleavage of NFAT5. Thus induction of NFAT5 by hypertonic agents may be a promising strategy for the development of anti-CVB3 therapeutics.

TRAF6: A player in CVB3-induced myocarditis?

Coxsackievirus B3 (CVB3) is an important inducer of myocarditis, which, in susceptible individuals, can chronify and eventually lead to the development of dilated cardiomyopathy and heart failure. The respective mechanisms are not completely understood. Here, we analyzed expression of the TRAF6 gene, encoding TNF receptor-associated factor 6 (TRAF6), a signal transduction scaffold protein that acts downstream of cytokine receptors, in heart tissue of susceptible and non-susceptible mouse strains. We found that after infection, TRAF6 expression was upregulated in both non-susceptible C57BL/6 wildtype and susceptible A.BY/SnJ and C57BL/6-TLR3 (-/-) mice, however, to different degrees. In infected HeLa cells, we also found moderately elevated TRAF6 levels after infection, in addition, activity of the transcription factor nuclear factor kappa B (NFκB), which can be activated downstream of TRAF6, was strongly enhanced in infected cells. To functionally analyze the role of TRAF6 with regard to infection progression, TRAF6 expression was knocked down in cultured HeLa cells using specific siRNAs. We found that reduction of TRAF6 expression had no effect on NFκB activation in response to infection. Taken together, our data suggest that CVB3 infection enhances TRAF6 levels, however, this induction might not be necessary for infection-induced NFκB activation.

IL-33 enhances macrophage M2 polarization and protects mice from CVB3-induced viral myocarditis

Viral myocarditis is the inflammation caused by myocardial virus infection, and the coxsackievirus group B3 virus (CVB3) is the most common pathogen. An efficient therapeutic agent against viral myocarditis is currently unavailable. IL-33, a new member of the IL-1 cytokine superfamily, exhibits potential immunotherapeutic effect against inflammatory and autoimmune diseases. However, the functional role of IL-33 in viral myocarditis has not been investigated. To examine the therapeutic role of IL-33 in viral myocarditis, an IL-33 overexpression plasmid (pDisplay-IL-33) and IL-33 knockdown plasmid (pLL3.7-IL-33) were packaged with polyethylenimine and delivered intravenously at the orbital area of BALB/c male mice after CVB3 infection. Then, myocarditis severity was assessed 7days after infection. Results showed that IL-33 up-regulation significantly alleviated the severity of viral myocarditis with an increased cardiac contractive function and survival rate. Mechanistic studies demonstrated that IL-33 can stimulate ST2L⁺F4/80⁺ macrophages and ST2L⁺CD4⁺T cells in cardiac tissue to express IL-4, which is a potent inducer for macrophage M2 polarization. Mice with adoptive transfer of M2 macrophages exhibited less cardiac inflammation and attenuated myocarditis, suggesting the protective role of M2 macrophage in viral myocarditis. Additionally, IL-4 neutralization abolished the IL-33-mediated cardiac functional improvement in myocarditis mice. Collectively, our findings provide a novel therapeutic role for IL-33 in CVB3-induced myocarditis.

Enhanced enteroviral infectivity via viral protease-mediated cleavage of Grb2-associated binder 1

Coxsackievirus B3 (CVB3), an important human causative pathogen for viral myocarditis, pancreatitis, and meningitis, has evolved different strategies to manipulate the host signaling machinery to ensure successful viral infection. We previously revealed a crucial role for the ERK1/2 signaling pathway in regulating viral infectivity. However, the detail mechanism remains largely unknown. Grb2-associated binder 1 (GAB1) is an important docking protein responsible for intracellular signaling assembly and transduction. In this study, we demonstrated that GAB1 was proteolytically cleaved after CVB3 infection at G175 and G436 by virus-encoded protease 2A(pro), independent of caspase activation. Knockdown of GAB1 resulted in a significant reduction of viral protein expression and virus titers. Moreover, we showed that virus-induced cleavage of GAB1 is beneficial to viral growth as the N-terminal proteolytic product of GAB1 (GAB1-N1-174) further enhances ERK1/2 activation and promotes viral replication. Our results collectively suggest that CVB3 targets host GAB1 to generate a GAB1-N1-174 fragment that enhances viral infectivity, at least in part, via activation of the ERK pathway. The findings in this study suggest a novel mechanism that CVB3 employs to subvert the host signaling and facilitate consequent viral replication.

Protecting intestinal epithelial cell number 6 against fission neutron irradiation through NF-κB signaling pathway

The purpose of this paper is to explore the change of NF-κB signaling pathway in intestinal epithelial cell induced by fission neutron irradiation and the influence of the PI3K/Akt pathway inhibitor LY294002. Three groups of IEC-6 cell lines were given: control group, neutron irradiation of 4Gy group, and neutron irradiation of 4Gy with LY294002 treatment group. Except the control group, the other groups were irradiated by neutron of 4Gy. LY294002 was given before 24 hours of neutron irradiation. At 6 h and 24 h after neutron irradiation, the morphologic changes, proliferation ability, apoptosis, and necrosis rates of the IEC-6 cell lines were assayed and the changes of NF-κB and PI3K/Akt pathway were detected. At 6 h and 24 h after neutron irradiation of 4Gy, the proliferation ability of the IEC-6 cells decreased and lots of apoptotic and necrotic cells were found. The injuries in LY294002 treatment and neutron irradiation group were more serious than those in control and neutron irradiation groups. The results suggest that IEC-6 cells were obviously damaged and induced serious apoptosis and necrosis by neutron irradiation of 4Gy; the NF-κB signaling pathway in IEC-6 was activated by neutron irradiation which could protect IEC-6 against injury by neutron irradiation; LY294002 could inhibit the activity of IEC-6 cells.

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.

Mapping of a quantitative trait locus controlling susceptibility to Coxsackievirus B3-induced viral hepatitis

The pathogenesis of coxsackieviral infection is a multifactorial process involving host genetics, viral genetics and the environment in which they interact. We have used a mouse model of Coxsackievirus B3 infection to characterize the contribution of host genetics to infection survival and to viral hepatitis. Twenty-five AcB/BcA recombinant congenic mouse strains were screened. One, BcA86, was found to be particularly susceptible to early mortality; 100% of BcA86 mice died by day 6 compared with 0% of B6 mice (P=0.0012). This increased mortality was accompanied by an increased hepatic necrosis as measured by serum alanine aminotransferase (ALT) levels (19547±10556 vs 769±109, P=0.0055). This occurred despite a predominantly resistant (C57BL/6) genetic background. Linkage analysis in a cohort (n=210) of (BcA86x C56Bl/10)F2 animals revealed a new locus on chromosome 13 (peak linkage 101.2 Mbp, lod 4.50 and P=0.003). This locus controlled serum ALT levels as early as 48 h following the infection, and led to an elevated expression of type I interferon. Another locus on chromosome 17 (peak linkage 57.2 Mbp) was significantly linked to heart viral titer (lod 3.4 and P=0.046). These results provide new evidence for the presence of genetic loci contributing to the susceptibility of mice to viral hepatitis.

RASSF4 promotes EV71 replication to accelerate the inhibition of the phosphorylation of AKT

Enterovirus 71 (EV71) is a neurotropic virus that causes hand, foot and mouth disease (HFMD), occasionally leading to death. As a member of the RAS association domain family (RASSFs), RASSF4 plays important roles in cell death, tumor development and signal transduction. However, little is known about the relationship between RASSF4 and EV71. Our study reveals for the first time that RASSF4 promotes EV71 replication and then accelerates AKT phosphorylation inhibition in EV71-infected 293T cells, suggesting that RASSF4 may be a potential new target for designing therapeutic measures to prevent and control EV71 infection.

Make yourself at home: viral hijacking of the PI3K/Akt signaling pathway

As viruses do not possess genes encoding for proteins required for translation, energy metabolism or membrane biosynthesis, they are classified as obligatory intracellular parasites that depend on a host cell to replicate. This genome limitation forces them to gain control over cellular processes to ensure their successful propagation. A diverse spectrum of virally encoded proteins tackling a broad spectrum of cellular pathways during most steps of the viral life cycle ranging from the host cell entry to viral protein translation has evolved. Since the host cell PI3K/Akt signaling pathway plays a critical regulatory role in many cellular processes including RNA processing, translation, autophagy and apoptosis, many viruses, in widely varying ways, target it. This review focuses on a number of remarkable examples of viral strategies, which exploit the PI3K/Akt signaling pathway for effective viral replication.

Coxsackievirus B3-induced calpain activation facilitates the progeny virus replication via a likely mechanism related with both autophagy enhancement and apoptosis inhibition in the early phase of infection: an in vitro study in H9c2 cells

Calpain is a family of neutral cysteine proteinase involved in many physiological and pathological processes including virus replication, autophagy and apoptosis. Previous study has indicated the involvement of calpain in pathogenesis of coxsackievirus B3 (CVB3)-induced myocarditis. Besides, many studies demonstrated that host cell autophagy and apoptosis mechanisms participate in virus life cycle. However, role of calpain in CVB3 replication via autophagy/apoptosis mechanisms has not been reported, which was discussed here in H9c2 cardiomyocytes. The data demonstrated that calpain was activated following CVB3 infection. Calpain inhibition decreased autophagy, indicating role of calpain in enhancing autophagy during CVB3 infection. Both calpain activity and autophagy were involved in facilitating CVB3 replication demonstrated by virus titer and CVB3 capsid protein VP1 expression alterations resulting from calpain inhibitor ALLN and autophagy inhibitor 3MA intervention. We also found that both calpain activity and autophagy suppressed caspase3 activity and host cell apoptosis 5-10h post-infection (p.i.). In summary, the present study shows that CVB3 infection of H9c2 cells hinders caspase3 activity provocation and cell apoptosis at least in the early phase of infection (5-10h p.i.) via calpain-induced autophagy enhancement, which might be a mechanism facilitating CVB3 replication in host cells.

Overexpression of 4EBP1, p70S6K, Akt1 or Akt2 differentially promotes Coxsackievirus B3-induced apoptosis in HeLa cells

Our previous studies have shown that the inhibition of phosphatidylinositol 3-kinase (PI3K) or mTOR complex 1 can obviously promote the Coxsackievirus B3 (CVB3)-induced apoptosis of HeLa cells by regulating the expression of proapoptotic factors. To further illustrate it, Homo sapiens eIF4E-binding protein 1 (4EBP1), p70S6 kinase (p70S6K), Akt1 and Akt2 were transfected to HeLa cells, respectively. And then, we established the stable transfected cell lines. Next, after CVB3 infection, apoptosis in different groups was determined by flow cytometry; the expressions of Bim, Bax, caspase-9 and caspase-3 were examined by real-time fluorescence quantitative PCR and western blot analysis; the expression of CVB3 mRNA and viral capsid protein VP1 were also analyzed by real-time fluorescence quantitative PCR, western blot analysis and immunofluorescence, respectively. At the meantime, CVB3 replication was observed by transmission electron microscope. We found that CVB3-induced cytopathic effect and apoptosis in transfected groups were more obvious than that in controls. Unexpectedly, apoptosis rate in Akt1 group was higher than others at the early stage after viral infection and decreased with the viral-infected time increasing, which was opposite to other groups. Compared with controls, the expression of CVB3 mRNA was increased at 3, 6, 12 and 24 h postinfection (p. i.) in all groups. At the meantime, VP1 expression in 4EBP1 group was higher than control during the process of infection, while the expressions in the other groups were change dynamically. Moreover, overexpression of 4EBP1 did not affect the mRNA expressions of Bim, Bax, caspase-9 and caspase-3; while protein expressions of Bim and Bax were decreased, the self-cleavages of caspase-9 and caspase-3 were stimulated. Meanwhile, overexpression of p70S6K blocked the CVB3-induced Bim, Bax and caspase-9 expressions but promoted the self-cleavage of caspase-9. In the Akt1 group, it is noteworthy that the expressions of Bim protein were higher than controls at 3 and 6 h p. i. but lower at 24 h p. i., and the expression of Bax protein were higher at 6 and 24 h p. i., while their mRNA expressions were all decreased. Furthermore, overexpression of Akt1 stimulated the procaspase-9 and procaspase-3 expression but blocked their self-cleavages. Overexpression of Akt2, however, had little effect on Bim, Bax and caspase-3, while prevented caspase-9 from self-cleavage at the late stage of CVB3 infection. As stated above, our results demonstrated that overexpression of 4EBP1, p70S6K, Akt1 or Akt2 could promote the CVB3-induced apoptosis in diverse degree via different mediating ways in viral replication and proapoptotic factors in BcL-2 and caspase families. As 4EBP1, p70S6K and Akt are the important substrates of PI3K and mammalian target of rapamycin (mTOR), we further illustrated the role of PI3K/Akt/mTOR signaling pathway in the process of CVB3-induced apoptosis.

The AKT genes and their roles in various disorders

AKT (AK mouse plus Transforming or Thymoma) is a common oncogene expressed in most tissues. Both AKT2 and AKT3, although important, have more limited distributions. The regulation of all three genes depends on two receptors-a receptor tyrosine kinase with a growth factor ligand, and a G protein coupled receptor, also with a ligand together with an explanation of how their downsteam components function. AKT2 is amplified or overexpressed in cancer with a higher frequency than those found with AKT1. AKT1 is cardioprotective to the heart by supporting its physiological growth and function. AKT2 is closely linked to Type II diabetes and the implications of various types of mutations are discussed. Various AKT3 mutations are important in neurological disorders, such as microcephaly, hemimegalencephaly, and megalencephaly syndromes. Finally, a reduced level of AKT1 in the frontal cortex has been found during post-mortem brain studies of schizophrenic patients in the populations of many countries.

Molecular mechanism behind rotavirus NSP1-mediated PI3 kinase activation: interaction between NSP1 and the p85 subunit of PI3 kinase

Our previous study had reported on the interaction of rotavirus NSP1 with cellular phosphoinositide 3-kinase (PI3K) during activation of the PI3K pathway (P. Bagchi et al., J. Virol. 84:6834-6845, 2010). In this study, we have analyzed the molecular mechanism behind this interaction. Results showed that this interaction is direct and that both α and β isomers of the PI3K regulatory subunit p85 and full-length NSP1 are important for this interaction, which results in efficient activation of the PI3K/Akt pathway during rotavirus infection.

Immunogenic cell death and DAMPs in cancer therapy

Although it was thought that apoptotic cells, when rapidly phagocytosed, underwent a silent death that did not trigger an immune response, in recent years a new concept of immunogenic cell death (ICD) has emerged. The immunogenic characteristics of ICD are mainly mediated by damage-associated molecular patterns (DAMPs), which include surface-exposed calreticulin (CRT), secreted ATP and released high mobility group protein B1 (HMGB1). Most DAMPs can be recognized by pattern recognition receptors (PRRs). In this Review, we discuss the role of endoplasmic reticulum (ER) stress and reactive oxygen species (ROS) in regulating the immunogenicity of dying cancer cells and the effect of therapy-resistant cancer microevolution on ICD.

A20 (TNFAIP3) alleviates CVB3-induced myocarditis via inhibiting NF-κB signaling

Background

Viral myocarditis, which is most prevalently caused by Coxsackievirus B3 (CVB3) infection, is a serious clinical condition characterized by cardiac inflammation. However, efficient therapies targeting inflammation are still lacking and much needed. A20, also known as tumor necrosis factor alpha induced protein 3 (TNFAIP3) is a key negative regulator of inflammation. But whether A20 may affect cardiac inflammation during acute viral myocarditis remains to be elucidated. The aim of this study was to investigate the potential protective effect of A20 on CVB3-induced myocarditis.

Methodology/Principal Findings

Mice were intraperitoneally inoculated with CVB3 to establish acute viral myocarditis model. We found that the expression of pro-inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6 and monocyte chemotactic protein-1 (MCP-1) were markedly and persistently increased during the progression of CVB3-induced myocarditis, and positively correlated with the disease severity. Notably, intravenous injection in vivo with adenovirus expressed A20 (Ad-A20) remarkably reduced CVB3-induced pro-inflammatory cytokines production and alleviated the severity of myocarditis. Further, we observed that nuclear factor-kappaB (NF-κB) signaling which mediates inflammatory response was significantly inhibited in CVB3-infected mice with Ad-A20 treatment. Finally, we revealed that A20 was required to inhibit CVB3-induced NF-κB signaling by restricting TNF receptor associated factor 6 (TRAF6) ubiquitylation.

Conclusion/Significance

This study demonstrates the protective role of A20 against CVB3-induced myocarditis, which may provide a new therapeutic strategy for the treatment of viral myocarditis.

Inflammation in myocardial diseases

Inflammatory processes underlie a broad spectrum of conditions that injure the heart muscle and cause both structural and functional deficits. In this article, we address current knowledge regarding 4 common forms of myocardial inflammation: myocardial ischemia and reperfusion, sepsis, viral myocarditis, and immune rejection. Each of these pathological states has its own unique features in pathogenesis and disease evolution, but all reflect inflammatory mechanisms that are partially shared. From the point of injury to the mobilization of innate and adaptive immune responses and inflammatory amplification, the cellular and soluble mediators and mechanisms examined in this review will be discussed with a view that both beneficial and adverse consequences arise in these human conditions.

HijAkt: The PI3K/Akt pathway in virus replication and pathogenesis

As obligate parasites of cellular processes, viruses must take over cellular macromolecular machinery. It is also becoming clear that viruses routinely control intracellular signaling pathways through the direct or indirect control of kinases and phosphatases. This control of cellular phosphoproteins is important to promote a variety of viral processes, from control of entry to nuclear function to the stimulation of viral protein synthesis. This review focuses on the takeover of the cellular phosphatidylinositol-3-kinase (PI3K)/Akt signaling pathway by a variety of retroviruses, DNA viruses, and RNA viruses, highlighting the functions ascribed to virus activation of PI3K and Akt activity. This review also describes the role that the PI3K/Akt pathway plays in the host response, noting that it that can trigger anti- as well as proviral functions.

Encephalomyocarditis virus 2A protein is required for viral pathogenesis and inhibition of apoptosis

The encephalomyocarditis virus (EMCV), a Picornaviridae virus, has a wide host spectrum and can cause various diseases. EMCV virulence factors, however, are as yet ill defined. Here, we demonstrate that the EMCV 2A protein is essential for the pathogenesis of EMCV. Infection of mice with the B279/95 strain of EMCV resulted in acute fatal disease, while the clone C9, derived by serial in vitro passage of the B279/95 strain, was avirulent. C9 harbored a large deletion in the gene encoding the 2A protein. This deletion was incorporated into the cDNA of a pathogenic EMCV1.26 strain. The new virus, EMCV1.26Δ2A, was capable of replicating in vitro, albeit more slowly than EMCV1.26. Only mice inoculated with EMCV1.26 triggered death within a few days. Mice infected with EMCV1.26Δ2A did not exhibit clinical signs, and histopathological analyses showed no damage in the central nervous system, unlike EMCV1.26-infected mice. In vitro, EMCV1.26Δ2A presented a defect in viral particle release correlating with prolonged cell viability. Unlike EMCV1.26, which induced cytopathic cell death, EMCV1.26Δ2A induced apoptosis via caspase 3 activation. This strongly suggests that the 2A protein is required for inhibition of apoptosis during EMCV infection. All together, our data indicate that the EMCV 2A protein is important for the virus in counteracting host defenses, since Δ2A viruses were no longer pathogenic and were unable to inhibit apoptosis in vitro.

Myocardial AKT: the omnipresent nexus

One of the greatest examples of integrated signal transduction is revealed by examination of effects mediated by AKT kinase in myocardial biology. Positioned at the intersection of multiple afferent and efferent signals, AKT exemplifies a molecular sensing node that coordinates dynamic responses of the cell in literally every aspect of biological responses. The balanced and nuanced nature of homeostatic signaling is particularly essential within the myocardial context, where regulation of survival, energy production, contractility, and response to pathological stress all flow through the nexus of AKT activation or repression. Equally important, the loss of regulated AKT activity is primarily the cause or consequence of pathological conditions leading to remodeling of the heart and eventual decompensation. This review presents an overview compendium of the complex world of myocardial AKT biology gleaned from more than a decade of research. Summarization of the widespread influence that AKT exerts upon myocardial responses leaves no doubt that the participation of AKT in molecular signaling will need to be reckoned with as a seemingly omnipresent regulator of myocardial molecular biological responses.

Pairwise network mechanisms in the host signaling response to coxsackievirus B3 infection

Signal transduction networks can be perturbed biochemically, genetically, and pharmacologically to unravel their functions. But at the systems level, it is not clear how such perturbations are best implemented to extract molecular mechanisms that underlie network function. Here, we combined pairwise perturbations with multiparameter phosphorylation measurements to reveal causal mechanisms within the signaling network response of cardiomyocytes to coxsackievirus B3 (CVB3) infection. Using all possible pairs of six kinase inhibitors, we assembled a dynamic nine-protein phosphorylation signature of perturbed CVB3 infectivity. Cluster analysis of the resulting dataset showed repeatedly that paired inhibitor data were required for accurate data-driven predictions of kinase substrate links in the host network. With pairwise data, we also derived a high-confidence network based on partial correlations, which identified phospho-IκBα as a central "hub" in the measured phosphorylation signature. The reconstructed network helped to connect phospho-IκBα with an autocrine feedback circuit in host cells involving the proinflammatory cytokines, TNF and IL-1. Autocrine blockade substantially inhibited CVB3 progeny release and improved host cell viability, implicating TNF and IL-1 as cell autonomous components of CVB3-induced myocardial damage. We conclude that pairwise perturbations, when combined with network-level intracellular measurements, enrich for mechanisms that would be overlooked by single perturbants.

Toll-like receptor 4-mediated activation of p38 mitogen-activated protein kinase is a determinant of respiratory virus entry and tropism

Respiratory viruses exert a heavy toll of morbidity and mortality worldwide. Despite this burden there are few specific treatments available for respiratory virus infections. Since many viruses utilize host cell enzymatic machinery such as protein kinases for replication, we determined whether pharmacological inhibition of kinases could, in principle, be used as a broad antiviral strategy for common human respiratory virus infections. A panel of green fluorescent protein (GFP)-expressing recombinant respiratory viruses, including an isolate of H1N1 influenza virus (H1N1/Weiss/43), was used to represent a broad range of virus families responsible for common respiratory infections (Adenoviridae, Paramyxoviridae, Picornaviridae, and Orthomyxoviridae). Kinase inhibitors were screened in a high-throughput assay that detected virus infection in human airway epithelial cells (1HAEo-) using a fluorescent plate reader. Inhibition of p38 mitogen-activated protein kinase (MAPK) signaling was able to significantly inhibit replication by all viruses tested. Therefore, the pathways involved in virus-mediated p38 and extracellular signal-regulated kinase (ERK) MAPK activation were investigated using bronchial epithelial cells and primary fibroblasts derived from MyD88 knockout mouse lungs. Influenza virus, which activated p38 MAPK to approximately 10-fold-greater levels than did respiratory syncytial virus (RSV) in 1HAEo- cells, was internalized about 8-fold faster and more completely than RSV. We show for the first time that p38 MAPK is a determinant of virus infection that is dependent upon MyD88 expression and Toll-like receptor 4 (TLR4) ligation. Imaging of virus-TLR4 interactions showed significant clustering of TLR4 at the site of virus-cell interaction, triggering phosphorylation of downstream targets of p38 MAPK, suggesting the need for a signaling receptor to activate virus internalization.

Rotavirus nonstructural protein 1 suppresses virus-induced cellular apoptosis to facilitate viral growth by activating the cell survival pathways during early stages of infection

Following virus infection, one of the cellular responses to limit the virus spread is induction of apoptosis. In the present study, we report role of rotavirus nonstructural protein 1 (NSP1) in regulating apoptosis by activating prosurvival pathways such as phosphatidylinositol 3-kinase (PI3K)/Akt and NF-kappaB (nuclear factor kappaB) during early hours of infections (2 to 8 hpi). The NSP1 mutant strain A5-16 induces weak and transient activation of Akt (protein kinase B) and p65 NF-kappaB compared to the isogenic wild-type strain A5-13 in MA104 or HT29 cells. The weak NF-kappaB promoter activity or Akt phosphorylation after A5-16 infection could be complemented in cells transfected with plasmid expressing NSP1 after infection with the rotavirus A5-16 strain. In cells either infected with A5-13 or transfected with pcD-NSP1, coimmunoprecipitation of NSP1 with phosphoinositide 3-kinase (PI3K) was observed, indicating that strong activation of PI3K/Akt could be due to its interaction with NSP1. In addition, after infection with same multiplicity of infection, A5-16 showed reduced number of viral particles compared to the A5-13 strain at the end of the replication cycle. A lower growth rate could be due to weak induction of PI3K/Akt and NF-kappaB, since the A5-13 strain also showed reduced growth in the presence of PI3K or NF-kappaB inhibitors. This effect was interferon independent; however, it was partly due to significantly higher caspase-3 activity, poly-ADP ribose polymerase (PARP) cleavage, and apoptosis during earlier stages of infection with the NSP1 mutant. Thus, our data suggest that NSP1 positively supports rotavirus growth by suppression of premature apoptosis for improved virus growth after infection.

Difference in susceptibility to MxA protein between a coxsackievirus B1 isolate and prototype, impact of serial cell culture passage

Human enteroviruses (EVs) cause a broad spectrum of acute and chronic diseases including meningitis and myocarditis. The type I interferon-induced MxA protein has been shown to inhibit the replication of an EV, coxsackievirus B4 (CVB4), but not cardioviruses such as encephalomyocarditis virus and mengo virus, members of the Picornaviridae family. EVs consist of more than 60 distinct serotypes against which the antiviral activity of MxA was not investigated yet. The main aim of this study was to explore the antiviral activity of MxA protein against a clinical CVB1 isolate and other EV prototypes. Vero cells expressing constituvely MxA protein were infected with EVs, and the percentage of inhibiton of expression of enteroviral RNA and capsid VP1 protein was determined. Following infection of MxA-transfected Vero cells with EVs, the expression of enteroviral RNA was inhibited by up to 99%, and that of VP1 protein by up to 85%. However, there was a difference in the percentage of MxA inhibition of EV replication between the different EV prototypes. This difference in MxA sensitivity was not due to a difference in the viral replication rates. The MxA protein was inactive against the clinical CVB1 isolate, and the replication rate of CVB1 isolate in MxA-transfected Vero cells was higher than that in mock-transfected Vero cells. A serial passage of the clinical CVB1 isolate and other EV prototypes resulted in an increase in their susceptibility to MxA protein. These results suggest the presence of MxA-resistant EV variants that may escape innate immunity and cause disease. J. Med. Virol. 82:424-432, 2010. (c) 2010 Wiley-Liss, Inc.

Protein degradation systems in viral myocarditis leading to dilated cardiomyopathy

The primary intracellular protein degradation systems, including the ubiquitin-proteasome and the lysosome pathways, have been emerging as central regulators of viral infectivity, inflammation, and viral pathogenicity. Viral myocarditis is an inflammatory disease of the myocardium caused by virus infection in the heart. The disease progression of viral myocarditis occurs in three distinct stages: acute viral infection, immune cell infiltration, and cardiac remodelling. Growing evidence suggests a crucial role for host proteolytic machineries in the regulation of the pathogenesis and progression of viral myocarditis in all three stages. Cardiotropic viruses evolve different strategies to subvert host protein degradation systems to achieve successful viral replication. In addition, these proteolytic systems play important roles in the activation of innate and adaptive immune responses during viral infection. Recent evidence also suggests a key role for the ubiquitin-proteasome and lysosome systems as the primary effectors of protein quality control in the regulation of cardiac remodelling. This review summarizes the recent advances in understanding the direct interaction between cardiotropic viruses and host proteolytic systems, with an emphasis on coxsackievirus B3, one of the primary aetiological agents causing viral myocarditis, and highlights possible roles of the host degradation systems in the pathogenesis of viral myocarditis and its progression to dilated cardiomyopathy.

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.

Coxsackievirus B3 induction of NFAT: requirement for myocarditis susceptibility

Ultraviolet (u.v.) inactivated coxsackievirus B3 (CVB3) induces rapid calcium flux in naïve BALB/c CD4+ T cells. CD4+ cells lacking decay accelerating factor (DAF-/-) show little calcium flux indicating that virus cross-linking of this virus receptor protein is necessary for calcium signaling in CVB3 infection. Interaction of CVB3 with CD4+ cells also activates NFAT DNA binding. To show that NFAT activation is crucial to CVB3 induced disease, wild-type mice and transgenic mice expressing dominant-negative NFAT (dnNFAT) mutant in T cells were infected and evaluated for myocarditis and pancreatitis 7 days later. Inhibition of NFAT in T cells prevented myocarditis but had no effect on pancreatitis. Virus titers in pancreas were equivalent in wild-type and dnNFAT animals but cardiac virus titers were increased in dnNFAT mice. Interferon-gamma (IFN gamma) expression was reduced in both CD4+ and V gamma 4+ T cells from dnNFAT mice compared to controls. FasL expression by V gamma 4+ cells was also suppressed. Inhibition of FasL expression by V gamma 4+ cells is consistent with myocarditis protection in dnNFAT mice.

Focal adhesion kinase mediates the interferon-gamma-inducible GTPase-induced phosphatidylinositol 3-kinase/Akt survival pathway and further initiates a positive feedback loop of NF-kappaB activation

Interferon-gamma-inducible GTPase (IGTP) expression is upregulated in coxsackievirus B3 (CVB3)-infected murine heart and inhibits CVB3-induced apoptosis through activation of the PI3 kinase/Akt pathway. However, the mechanism of this pathway activation is unknown. In this study, using doxcycycline-inducible Tet-On HeLa cells that overexpress IGTP, we have demonstrated that focal adhesion kinase (FAK) is phosphorylated in response to IGTP expression and that transfection of the Tet-On HeLa cells with a dominant negative FAK (FRNK) blocks Akt activation. Furthermore, induction of IGTP also promoted the NF-kappaB activation as evidenced by its enhanced nuclear translocation, binding to transcriptional promoters and increased transcriptional activity. However, FRNK transfection and phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 both blocked the IGTP-induced translocation and NF-kappaB activation. Furthermore, silencing NF-kappaB with siRNAs significantly inhibited the phosphorylation of FAK and Akt, but not their total expression levels, indicating that NF-kappaB activation is required for the IGTP-induced activation of FAK and PI3K/Akt. Finally, blocking this survival pathway by transfection of FRNK or silencing of NF-kappaB reduced CVB3 replication and enhanced cell death during CVB3 infection. Taken together, these results suggest that FAK is a mediator upstream of PI3K/Akt and NF-kappaB functions as a downstream effector and also positively regulates the activity of upstream kinases.