Roles of cell signaling pathways in cell-to-cell contact-mediated Epstein-Barr virus transmission

Current Insights into the Maturation of Epstein-Barr Virus Particles

The three subfamilies of herpesviruses (alphaherpesviruses, betaherpesviruses, and gammaherpesviruses) appear to share a unique mechanism for the maturation and egress of virions, mediated by several budding and fusion processes of various organelle membranes during replication, which prevents cellular membrane disruption. Newly synthesized viral DNA is packaged into capsids within the nucleus, which are subsequently released into the cytoplasm via sequential fusion (primary envelopment) and budding through the inner and outer nuclear membranes. Maturation concludes with tegumentation and the secondary envelopment of nucleocapsids, which are mediated by budding into various cell organelles. Intracellular compartments containing mature virions are transported to the plasma membrane via host vesicular trafficking machinery, where they fuse with the plasma membrane to extracellularly release mature virions. The entire process of viral maturation is orchestrated by sequential interactions between viral proteins and intracellular membranes. Compared with other herpesvirus subfamilies, the mechanisms of gammaherpesvirus maturation and egress remain poorly understood. This review summarizes the major findings, including recently updated information of the molecular mechanism underlying the maturation and egress process of the Epstein-Barr virus, a ubiquitous human gammaherpesvirus subfamily member that infects most of the population worldwide and is associated with a number of human malignancies.

Advancing therapeutic strategies for Epstein-Barr virus-associated malignancies through lytic reactivation

Epstein-Barr virus (EBV) is a widespread human herpes virus associated with lymphomas and epithelial cell cancers. It establishes two separate infection phases, latent and lytic, in the host. Upon infection of a new host cell, the virus activates several pathways, to induce the expression of lytic EBV antigens and the production of infectious virus particles. Although the carcinogenic role of latent EBV infection has been established, recent research suggests that lytic reactivation also plays a significant role in carcinogenesis. In this review, we summarize the mechanism of EBV reactivation and recent findings about the role of viral lytic antigens in tumor formation. In addition, we discuss the treatment of EBV-associated tumors with lytic activators and the targets that may be therapeutically effective in the future.

Fascin in Gynecological Cancers: An Update of the Literature

Simple Summary

Fascin, an actin-binding protein, is upregulated in different types of human cancers. It is reportedly responsible for increasing the invasive and metastatic ability of cancer cells by reducing cell–cell adhesions. This review provides a brief overview of fascin and its interactions with other genes and oncoviruses to induce the onset and progression of cancer.

Abstract

Fascin is an actin-binding protein that is encoded by the FSCN1 gene (located on chromosome 7). It triggers membrane projections and stimulates cell motility in cancer cells. Fascin overexpression has been described in different types of human cancers in which its expression correlated with tumor growth, migration, invasion, and metastasis. Moreover, overexpression of fascin was found in oncovirus-infected cells, such as human papillomaviruses (HPVs) and Epstein-Barr virus (EBV), disrupting the cell–cell adhesion and enhancing cancer progression. Based on these findings, several studies reported fascin as a potential biomarker and a therapeutic target in various cancers. This review provides a brief overview of the FSCN1 role in various cancers with emphasis on gynecological malignancies. We also discuss fascin interactions with other genes and oncoviruses through which it might induce cancer development and progression.

Advances in pathogenesis and precision medicine for nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a squamous carcinoma with apparent geographical and racial distribution, mostly prevalent in East and Southeast Asia, particularly concentrated in southern China. The epidemiological trend over the past decades has suggested a substantial reduction in the incidence rate and mortality rate due to NPC. These results may reflect changes in lifestyle and environment, and more importantly, a deeper comprehension of the pathogenic mechanism of NPC, leading to much progress in the preventing, screening, and treating for this cancer. Herein, we present the recent advances on the key signal pathways involved in pathogenesis of NPC, the mechanism of Epstein‐Barr virus (EBV) entry into the cell, and the progress of EBV vaccine and screening biomarkers. We will also discuss in depth the development of various therapeutic approaches including radiotherapy, chemotherapy, surgery, targeted therapy, and immunotherapy. These research advancements have led to a new era of precision medicine in NPC.

Epstein-Barr Virus Exploits the Secretory Pathway to Release Virions

Herpesvirus egress mechanisms are strongly associated with intracellular compartment remodeling processes. Previously, we and other groups have described that intracellular compartments derived from the Golgi apparatus are the maturation sites of Epstein-Barr virus (EBV) virions. However, the mechanism by which these virions are released from the host cell to the extracellular milieu is poorly understood. Here, I adapted two independent induction systems of the EBV lytic cycle in vitro, in the context of Rab GTPase silencing, to characterize the EBV release pathway. Immunofluorescence staining revealed that p350/220, the major EBV glycoprotein, partially co-localized with three Rab GTPases: Rab8a, Rab10, and Rab11a. Furthermore, the knockdown of these Rab GTPases promoted the intracellular accumulation of viral structural proteins by inhibiting its distribution to the plasma membrane. Finally, the knockdown of the Rab8a, Rab10, and Rab11a proteins suppressed the release of EBV infectious virions. Taken together, these findings support the hypothesis that mature EBV virions are released from infected cells to the extracellular milieu via the secretory pathway, as well as providing new insights into the EBV life cycle.

Revisiting the Tissue Microenvironment of Infectious Mononucleosis: Identification of EBV Infection in T Cells and Deep Characterization of Immune Profiles

To aid understanding of primary EBV infection, we have performed an in depth analysis of EBV-infected cells and of local immune cells in tonsils from infectious mononucleosis (IM) patients. We show that EBV is present in approximately 50% of B-cells showing heterogeneous patterns of latent viral gene expression probably reflecting different stages of infection. While the vast majority of EBV+ cells are B-cells, around 9% express T-cell antigens, with a predominance of CD8+ over CD4+ cells. PD-L1 was expressed by a median of 14% of EBV+ cells. The numbers of EBER+PD-L1+ cells were directly correlated with the numbers of EBER+CD3+ and EBER+CD8+ cells suggesting a possible role for PD-L1 in EBV infection of T-cells. The microenvironment of IM tonsils was characterized by a predominance of M1-polarized macrophages over M2-polarized cells. However, at the T-cell level, a heterogeneous picture emerged with numerous Th1/cytotoxic cells accompanied and sometimes outnumbered by Th2/regulatory T-cells. Further, we observed a direct correlation between the numbers of Th2-like cells and EBV- B-cells. Also, a prevalence of cytotoxic T-cells over Th2-like cells was associated with an increased viral load. These observations point to contribution of B- and Th2-like cells to the control of primary EBV infection. 35% of CD8+ cells were differentiated CD8+TBET+ cells, frequently detected in post-capillary venules. An inverse correlation was observed between the numbers of CD8+TBET+ cells and viral load suggesting a pivotal role for these cells in the control of primary EBV infection. Our results provide the basis for a better understanding of immune reactions in EBV-associated tumors.

Microfluidic on-demand droplet generation, storage, retrieval, and merging for single-cell pairing

A multifunctional microfluidic platform combining on-demand aqueous-phase droplet generation, multi-droplet storage, and controlled merging of droplets selected from a storage library in a single integrated microfluidic device is described. A unique aspect of the technology is a microfluidic trap design comprising a droplet trap chamber and lateral bypass channels integrated with a microvalve that supports the capture and merger of multiple droplets over a wide range of individual droplet sizes. A storage unit comprising an array of microfluidic traps operates in a first-in first-out manner, allowing droplets stored within the library to be analyzed before sequentially delivering selected droplets to a downstream merging zone, while shunting other droplets to waste. Performance of the microfluidic trap is investigated for variations in bypass/chamber hydrodynamic resistance ratio, micro-chamber geometry, trapped droplet volume, and overall flow rate. The integrated microfluidic platform is then utilized to demonstrate the operational steps necessary for cell-based assays requiring the isolation of defined cell populations with single cell resolution, including encapsulation of individual cells within an aqueous-phase droplet carrier, screening or incubation of the immobilized cell-encapsulated droplets, and generation of controlled combinations of individual cells through the sequential droplet merging process. Beyond its utility for cell analysis, the presented platform represents a versatile approach to robust droplet generation, storage, and merging for use in a wide range of droplet-based microfluidics applications.

Infection of Epstein⁻Barr Virus in Type III Latency Modulates Biogenesis of Exosomes and the Expression Profile of Exosomal miRNAs in the Burkitt Lymphoma Mutu Cell Lines

Infection of Epstein–Barr virus (EBV), a ubiquitous human gamma herpesvirus, is associated with various malignancies in B lymphocytes and epithelial cells. EBV encodes 49 microRNAs in two separated regions, termed the BART and BHRF1 loci. Although accumulating evidence demonstrates that EBV infection regulates the profile of microRNAs in the cells, little is known about the microRNAs in exosomes released from infected cells. Here, we characterized the expression profile of intracellular and exosomal microRNAs in EBV-negative, and two related EBV-infected Burkitt lymphoma cell lines having type I and type III latency by next-generation sequencing. We found that the biogenesis of exosomes is upregulated in type III latently infected cells compared with EBV-negative and type I latently infected cells. We also observed that viral and several specific host microRNAs were predominantly incorporated in the exosomes released from the cells in type III latency. We confirmed that multiple viral microRNAs were transferred to the epithelial cells cocultured with EBV-infected B cells. Our findings indicate that EBV infection, in particular in type III latency, modulates the biogenesis of exosomes and the profile of exosomal microRNAs, potentially contributing to phenotypic changes in cells receiving these exosomes.

The Role of Transforming Growth Factor β in Cell-to-Cell Contact-Mediated Epstein-Barr Virus Transmission

Infection of Epstein–Barr virus (EBV), a ubiquitous human gamma herpesvirus, is closely linked to various lymphoid and epithelial malignancies. Previous studies demonstrated that the efficiency of EBV infection in epithelial cells is significantly enhanced by coculturing them with latently infected B cells relative to cell-free infection, suggesting that cell-to-cell contact-mediated viral transmission is the dominant mode of infection by EBV in epithelial cells. However, a detailed mechanism underlying this process has not been fully understood. In the present study, we assessed the role of transforming growth factor β (TGF-β), which is known to induce EBV's lytic cycle by upregulation of EBV's latent-lytic switch BZLF1 gene. We have found that 5 days of cocultivation facilitated cell-to-cell contact-mediated EBV transmission. Replication of EBV was induced in cocultured B cells both with and without a direct cell contact in a time-dependent manner. Treatment of a blocking antibody for TGF-β suppressed both induction of the lytic cycle in cocultured B cells and subsequent viral transmission. Cocultivation with epithelial cells facilitated expression of TGF-β receptors in B cells and increased their susceptibility to TGF-β. Finally, we confirmed the spontaneous secretion of TGF-β from epithelial cells, which was not affected by cell-contact. In contrast, the extracellular microvesicles, exosomes derived from cocultured cells partly contributed to cell-to-cell contact-mediated viral transmission. Taken together, our findings support a role for TGF-β derived from epithelial cells in efficient viral transmission, which fosters induction of the viral lytic cycle in the donor B cells.

Epstein-Barr Virus Acquires Its Final Envelope on Intracellular Compartments With Golgi Markers

Herpesvirus subfamilies typically acquire their final envelope in various cytoplasmic compartments such as the trans-Golgi network (TGN), and endosomes prior to their secretion into the extracellular space. However, the sites for the final envelopment of Epstein–Barr virus (EBV), a ubiquitous human gamma herpesvirus, are poorly understood. Here, we characterized the sites for the final envelopment of EBV in Burkitt’s lymphoma cell lines induced into the lytic cycle by crosslinking cell surface IgG. Electron microscopy revealed the various stages of maturation and egress of progeny virions including mature EBV in irregular cytoplasmic vesicles. Immunofluorescence staining showed that gp350/220, the major EBV glycoprotein, and the viral capsid antigen, p18, efficiently colocalized with a cis-Golgi marker, GM130. gp350/220 partly colocalized with the TGN, which was distributed in a fragmented and dispersed pattern in the cells induced into the lytic cycle. In contrast, limited colocalization was observed between gp350/220 and endosomal markers, such as a multi-vesicular bodies marker, CD63, a recycling endosome marker, Rab11, and a regulatory secretion vesicles marker, Rab27a. Finally, we observed that treatment of cells with brefeldin A, an inhibitor of vesicle trafficking between the endoplasmic reticulum and Golgi apparatus, resulted in the perinuclear accumulation of gp350/220 and inhibition of its distribution to the plasma membrane. Brefeldin A also inhibited the release of infectious EBV. Taken together, our findings support a model in which EBV acquires its final envelope in intracellular compartments containing markers of Golgi apparatus, providing new insights into how EBV matures.

Status of Epstein-Barr Virus Coinfection with Helicobacter pylori in Gastric Cancer

Epstein-Barr virus is a ubiquitous human herpesvirus whose primary infection causes mononucleosis, Burkett's lymphoma, nasopharyngeal carcinoma, autoimmune diseases, and gastric cancer (GC). The persistent infection causes malignancies in lymph and epithelial cells. Helicobacter pylori causes gastritis in human with chronic inflammation. This chronic inflammation is thought to be the cause of genomic instability. About 45%-word population have a probability of having both pathogens, namely, H. pylori and EBV. Approximately 180 per hundred thousand population is developing GC along with many gastric abnormalities. This makes GC the third leading cause of cancer-related death worldwide. Although lots of research are carried out individually for EBV and H. pylori, still there are very few reports available on coinfection of both pathogens. Recent studies suggested that EBV and H. pylori coinfection increases the occurrence of GC as well as the early age of GC detection comparing to individual infection. The aim of this review is to present status on coinfection of both pathogens and their association with GC.

The Tax-Inducible Actin-Bundling Protein Fascin Is Crucial for Release and Cell-to-Cell Transmission of Human T-Cell Leukemia Virus Type 1 (HTLV-1)

The delta-retrovirus Human T-cell leukemia virus type 1 (HTLV-1) preferentially infects CD4⁺ T-cells via cell-to-cell transmission. Viruses are transmitted by polarized budding and by transfer of viral biofilms at the virological synapse (VS). Formation of the VS requires the viral Tax protein and polarization of the host cytoskeleton, however, molecular mechanisms of HTLV-1 cell-to-cell transmission remain incompletely understood. Recently, we could show Tax-dependent upregulation of the actin-bundling protein Fascin (FSCN-1) in HTLV-1-infected T-cells. Here, we report that Fascin contributes to HTLV-1 transmission. Using single-cycle replication-dependent HTLV-1 reporter vectors, we found that repression of endogenous Fascin by short hairpin RNAs and by Fascin-specific nanobodies impaired gag p19 release and cell-to-cell transmission in 293T cells. In Jurkat T-cells, Tax-induced Fascin expression enhanced virus release and Fascin-dependently augmented cell-to-cell transmission to Raji/CD4⁺ B-cells. Repression of Fascin in HTLV-1-infected T-cells diminished virus release and gag p19 transfer to co-cultured T-cells. Spotting the mechanism, flow cytometry and automatic image analysis showed that Tax-induced T-cell conjugate formation occurred Fascin-independently. However, adhesion of HTLV-1-infected MT-2 cells in co-culture with Jurkat T-cells was reduced upon knockdown of Fascin, suggesting that Fascin contributes to dissemination of infected T-cells. Imaging of chronically infected MS-9 T-cells in co-culture with Jurkat T-cells revealed that Fascin’s localization at tight cell-cell contacts is accompanied by gag polarization suggesting that Fascin directly affects the distribution of gag to budding sites, and therefore, indirectly viral transmission. In detail, we found gag clusters that are interspersed with Fascin clusters, suggesting that Fascin makes room for gag in viral biofilms. Moreover, we observed short, Fascin-containing membrane extensions surrounding gag clusters and clutching uninfected T-cells. Finally, we detected Fascin and gag in long-distance cellular protrusions. Taken together, we show for the first time that HTLV-1 usurps the host cell factor Fascin to foster virus release and cell-to-cell transmission.

Human T-cell leukemia virus type 1 (HTLV-1) is the only human retrovirus causing cancer and is transmitted via breast feeding, sexual intercourse, and cell-containing blood products. Efficient infection of CD4⁺ T-cells occurs via polarized budding of virions or via cell surface transfer of viral biofilms at a tight, specialized cell-cell contact, the virological synapse (VS). The viral protein Tax and polarization of the host cell cytoskeleton are crucial for formation of the VS, however, only little is known about the link between Tax and remodeling of the cytoskeleton to foster viral spread. The actin-bundling protein Fascin has evolved as a therapeutic target in several types of cancer. Here, we show that Fascin is also crucial for release and transmission of the tumorvirus HTLV-1. Since Fascin is a transcriptional target gene of Tax in T-cells, our work provides a link between Tax’s activity and virus transmission. Visualization of cell-cell contacts between infected and uninfected T-cells suggests a role of Fascin in viral transmission potentially by facilitating the transport of viral proteins to budding sites. Thus, Fascin is not only crucial for metastasis of tumors, but also for transmission of HTLV-1 and is a new cellular target to counteract HTLV-1.

Isolation and expression analysis of an MAPKK gene from Fenneropenaeus chinensis in response to white spot syndrome virus infection

Mitogen-activated kinase kinase (MAPKK) is an important gene involved in the host-virus interaction process. To obtain a better understanding of MAPKK in the interaction process between the Chinese shrimp Fenneropenaeus chinensis and white spot syndrome virus (WSSV), we cloned the sequence of an MAPKK cDNA from F. chinensis (FcMAPKK) and investigated the effect of FcMAPKK on WSSV infection. The results showed that the FcMAPKK gene contained a 1227 bp open reading frame (ORF), which encoded a highly conserved protein with a serine/threonine protein kinase catalytic (S_TKc) domain. The deduced amino acid sequence of FcMAPKK shared identities between 11.9 and 92.6% with MAPKKs from vertebrate, invertebrate, plant and fungus species. The FcMAPKK was expressed in all the examined tissues in the normal F. chinensis. FcMAPKK expression level was highest in the hepatopancreas where it was approximately 2.6-fold the expression level in the gill, and lowest in the muscle where it was approximately 0.3-fold the expression level in the hepatopancreas. The FcMAPKK expression levels in the muscle, gill, and hepatopancreas were all changed post WSSV challenge. The FcMAPKK expression was significantly (P < 0.01) up-regulated in the muscle of F. chinensis at 48 h post WSSV infection. The WSSV began to replicate quickly in the normal F. chinensis at 48 h post infection, while the WSSV replication in the U0126-treated F. chinensis could be significantly (P < 0.05) inhibited. The results suggested that FcMAPKK might be involved in the WSSV infection process, and hijacking of FcMAPKK might be required for WSSV replication in F. chinensis.

Significance of Interviral Recombination as Novel Mechanism for Extending Viral Disease Repertoire

The recent observation of interviral recombination between members of two distinct classes of DNA viruses has opened the gates to a new field of human disease development. In all cases studied thus far interviral recombination is a rare event that requires special circumstances for intracellular interaction of participating viral genomes. The rarity and special requirements do not detract from the potential clinical significance of resulting recombinants, as exemplified by recombination between JC viral and Epstein-Barr viral genomes. This significance depends largely upon the mechanisms of recombination that would generate specific forms of recombinant viral genomes. At this time little is known regarding mechanisms of interviral recombination. DNA break-induced replication seems presently to be a highly plausible means of initiating formation of different, potentially active recombination products. Generalizing interviral recombination to a variety of viruses will open a fertile field for discovery as multiple diseases of mysterious etiology are investigated.

Opportunistic DNA Recombination With Epstein-Barr Virus at Sites of Control Region Rearrangements Mediating JC Virus Neurovirulence

We document a unique DNA recombination between polyomavirus JC (JC virus [JCV]) and Epstein-Barr virus (EBV) at sequences of JCV found infecting the brain. Archetype JCV is present in bone marrow and uroepithelial cells of most adults. During immunosuppression, JCV can infect the brain, causing a demyelinating disease, progressive multifocal leukoencephalopathy. Rearrangements in the archetype noncoding control region are necessary for neurovirulence. Two NCCR deletions and a duplication occur at sequences of homology with EBV, present latently in B cells, which may be coinfected with both viruses. Recombination between JCV and EBV occurs in B lymphoblasts at a sequence essential for JCV neurovirulence and in cerebrospinal fluid of immunosuppressed patients with multiple sclerosis, those susceptible to progressive multifocal leukoencephalopathy. Interviral recombination is a model for conferring advantages on JCV in the brain. It can alter a critical noncoding control region sequence and potentially facilitate use of EBV DNA abilities to transfer among different cell types.

Hepatitis B virus infection and risk of nasopharyngeal carcinoma in southern China

BACKGROUND

Whether or not hepatitis B virus (HBV) infection plays a role in the development of nasopharyngeal carcinoma (NPC) is largely unknown. Our study aimed to assess the association between HBV infection and the risk of NPC in Southern China.

METHODS

We conducted a case-control study including 711 NPC cases and two groups of controls. The first control group consisted of 656 individuals with other benign tumors unrelated to HBV infection and the second group consisted of 680 healthy population controls. Multivariable ORs and corresponding 95% confidence intervals (CI) for NPC were estimated by logistic regression.

RESULTS

Patients with NPC had higher prevalence of antibodies against hepatitis B core antigen-positive [anti-HBc-(+); 47.26%] compared with either benign tumor controls (39.33%; P < 0.01) or healthy controls (41.18%; P = 0.04). In multivariable models adjusting for a set of risk factors for NPC, anti-HBc-(+) was significantly associated with a higher risk of NPC [adjusted OR (AOR), 1.40; 95% CI, 1.12-1.74 compared with the benign tumor controls and AOR, 1.48; 95% CI, 1.05-2.08 compared with the healthy controls]. The association was not modified by hepatitis B surface antigen (HBsAg) status. Finally, compared with the healthy controls, individuals with both anti-HBc-(+) and EBV antibodies had largely increased risk of NPC (AOR, 141.82; 95% CI, 68.73-292.62).

CONCLUSION

Our study suggests that HBV infection is associated with NPC risk in Southern China.

IMPACT

Prevention for HBV infection may play a role in the development of NPC.

Orderly Steps in Progression of JC Virus to Virulence in the Brain

Progressive multifocal leukoencephalopathy is a neurodegenerative disease caused by demyelination in the brain. The demyelination is due to infection of oligodendroglial cells by polyomavirus JC, a circular DNA virus. The virus resides as an archetype form in uroepithelial cells and bone marrow of more than 70% of adults, in whom it seldom causes overt symptoms. The JC viral form infecting the brain differs from the archetype. This viral form contains two deletions and a duplication in the non-coding control region that are thought to be derived from the archetype. These rearrangements are necessary for neurovirulence. This review considers how these rearrangements occur in the context of transit to the brain and adaptation to infect glial cells.

In-cell infection: bringing uninvited guests

Cell-in-cell structures resulting from live cell engulfment were identified more than 100 years ago, but their physiological significance has remained largely obscure. Now Ni et al. identify a new role for cell-in-cell structure formation, called "in-cell infection" that spreads Epstein-Barr virus from infected B cells to epithelial cells, an activity that may predispose to cancer.

In-cell infection: a novel pathway for Epstein-Barr virus infection mediated by cell-in-cell structures

Epstein-Barr virus (EBV) can infect both susceptible B lymphocytes and non-susceptible epithelial cells (ECs). Viral tropism analyses have revealed two intriguing means of EBV infection, either by a receptor-mediated infection of B cells or by a cell-to-cell contact-mediated infection of non-susceptible ECs. Herein, we report a novel “in-cell infection” mechanism for EBV infection of non-susceptible ECs through the formation of cell-in-cell structures. Epithelial CNE-2 cells were invaded by EBV-infected Akata B cells to form cell-in-cell structures in vitro. Such unique cellular structures could be readily observed in the specimens of nasopharyngeal carcinoma. Importantly, the formation of cell-in-cell structures led to the autonomous activation of EBV within Akata cells and subsequent viral transmission to CNE-2 cells, as evidenced by the expression of viral genes and the presence of virion particles in CNE-2 cells. Significantly, EBV generated from in-cell infected ECs displayed altered tropism with higher infection efficacy to both B cells and ECs. In addition to CNE-2 tumor cells, cell-in-cell structure formation could also mediate EBV infection of NPEC1-Bmi1 cells, an immortalized nasopharyngeal epithelial cell line. Furthermore, efficient infection by this mechanism involved the activation of the PI3K/AKT signaling pathway. Thus, our study identified “in-cell infection” as a novel mechanism for EBV infection. Given the diversity of virus-infected cells and the prevalence of cell-in-cell structures during chronic infection, we speculate that “in-cell infection” is likely a general mechanism for EBV and other viruses to infect non-susceptible ECs.

Regulation of Epstein-Barr virus reactivation from latency

The Epstein-Barr virus (EBV) is a human gamma-herpesvirus that is implicated in various types of proliferative diseases. Upon infection, it predominantly establishes latency in B cells and cannot ever be eradicated; it persists for the host's lifetime. Reactivation of the virus from latency depends on expression of the viral immediate-early gene, BamHI Z fragment leftward open reading frame 1 (BZLF1). The BZLF1 promoter normally exhibits only low basal activity but is activated in response to chemical or biological inducers, such as 12-O-tetradecanoylphorbol-13-acetate, calcium ionophore, histone deacetylase inhibitor, or anti-Ig. Transcription from the BZLF1 promoter is activated by myocyte enhancer factor 2, specificity protein 1, b-Zip type transcription factors and mediating epigenetic modifications of the promoter, such as histone acetylation and H3K4me3. In contrast, repression of the promoter is mediated by transcriptional suppressors, such as ZEB, ZIIR-BP, and jun dimerization protein 2, causing suppressive histone modifications like histone H3K27me3, H3K9me2/3 and H4K20me3. Interestingly, there is little CpG DNA methylation of the promoter, indicating that DNA methylation is not crucial for suppression of BZLF1. This review will focus on the molecular mechanisms by which the EBV lytic switch is controlled and discuss the physiological significance of this switching for its survival and oncogenesis.

The tumor marker Fascin is induced by the Epstein-Barr virus-encoded oncoprotein LMP1 via NF-κB in lymphocytes and contributes to their invasive migration

Background

The actin-bundling protein Fascin (FSCN1) is a tumor marker that is highly expressed in numerous types of cancer including lymphomas and is important for migration and metastasis of tumor cells. Fascin has also been detected in B lymphocytes that are freshly-infected with Epstein-Barr virus (EBV), however, both the inducers and the mechanisms of Fascin upregulation are still unclear.

Results

Here we show that the EBV-encoded oncoprotein latent membrane protein 1 (LMP1), a potent regulator of cellular signaling and transformation, is sufficient to induce both Fascin mRNA and protein in lymphocytes. Fascin expression is mainly regulated by LMP1 via the C-terminal activation region 2 (CTAR2). Block of canonical NF-κB signaling using a chemical inhibitor of IκB kinase β (IKKβ) or cotransfection of a dominant-negative inhibitor of IκBα (NFKBIA) reduced not only expression of p100, a classical target of the canonical NF-κB-pathway, but also LMP1-induced Fascin expression. Furthermore, chemical inhibition of IKKβ reduced both Fascin mRNA and protein levels in EBV-transformed lymphoblastoid cell lines, indicating that canonical NF-κB signaling is required for LMP1-mediated regulation of Fascin both in transfected and transformed lymphocytes. Beyond that, chemical inhibition of IKKβ significantly reduced invasive migration of EBV-transformed lymphoblastoid cells through extracellular matrix. Transient transfection experiments revealed that Fascin contributed to LMP1-mediated enhancement of invasive migration through extracellular matrix. While LMP1 enhanced the number of invaded cells, functional knockdown of Fascin by two different small hairpin RNAs resulted in significant reduction of invaded, non-attached cells.

Conclusions

Thus, our data show that LMP1-mediated upregulation of Fascin depends on NF-κB and both NF-κB and Fascin contribute to invasive migration of LMP1-expressing lymphocytes.

Identification, cloning and characterization of an extracellular signal-regulated kinase (ERK) from Chinese shrimp, Fenneropenaeus chinensis

Extracellular signal-regulated kinase (ERK) is a serine/threonine-specific protein kinase, which participates in signaling transduction pathways that control intracellular events, including resumption of meiosis, embryogenesis, cell differentiation, cell proliferation, cell death and response to radiation. Some virus species evolved the ability to hijack the host cell ERK signaling transduction pathway for viral replications and gene expressions. To obtain a better understanding of ERK, we cloned a cDNA encoding ERK from the muscle of Fenneropenaeus chinensis (FcERK). The FcERK contained a 1098 bp open reading frame (ORF) encoding a protein of 365 amino acid residues with a conserved phosphorylation motif TEY in the kinase activation loop. Pair-wise and multiple sequence alignment revealed that ERK is highly conserved across taxa. The FcERK gene expressions in the hepatopancreas and gill were noticeably higher than the expression observed in the muscle. A challenge test was performed to reveal the responses of FcERK in different tissues to white spot syndrome virus (WSSV) infection. Post WSSV challenge, the FcERK expression in the gill significantly increased during the early stage of the viral infection, the FcERK expression in the muscle increased later than that in the gill, and the FcERK expression in the hepatopancreas significantly decreased. The FcERK gene expression profile accorded with the results that the virus primarily infects tissues originating from the ectoderm, with less infection of the tissues originating from the mesoderm, and hardly any infection in the tissues originating from the entoderm. Two single nucleotide polymorphisms (SNPs) were identified in the FcERK gene, involving C/T transition. The SNP genotypes of two groups of shrimps, respectively comprising 96 WSSV-resistant shrimps and 96 WSSV-susceptible shrimps were obtained using a high-resolution melting (HRM) method. In the two groups, the MAFs of both sites were greater than 0.05, and no site departed significantly (P < 0.05) from HWE. The genotype distributions of both mutation sites between the two groups were not significantly different. These results lead to a better understanding of the molecular mechanisms of the host-virus interaction and provide useful information for disease control.

Exosomes derived from Epstein-Barr virus-infected cells are internalized via caveola-dependent endocytosis and promote phenotypic modulation in target cells

Epstein-Barr virus (EBV), a human gammaherpesvirus, establishes a lifelong latent infection in B lymphocytes and epithelial cells following primary infection. Several lines of evidence suggest that exosomes derived from EBV-infected cells are internalized and transfer viral factors, including EBV-encoded latent membrane protein and microRNAs, to the recipient cells. However, the detailed mechanism by which exosomes are internalized and their physiological impact on the recipient cells are still poorly understood. In this study, we visualized the internalization of fluorescently labeled exosomes derived from EBV-uninfected and EBV-infected B cells of type I and type III latency into EBV-negative epithelial cells. In this way, we demonstrated that exosomes derived from all three cell types were internalized into the target cells in a similar fashion. Internalization of exosomes was significantly suppressed by treatment with an inhibitor of dynamin and also by the knockdown of caveolin-1. Labeled exosomes were colocalized with caveolae and subsequently trafficked through endocytic pathways. Moreover, we observed that exosomes derived from type III latency cells upregulated proliferation and expression of intercellular adhesion molecule 1 (ICAM-1) in the recipient cells more significantly than did those derived from EBV-negative and type I latency cells. We also identified the EBV latent membrane protein 1 (LMP1) gene as responsible for induction of ICAM-1 expression. Taken together, our data indicate that exosomes released from EBV-infected B cells are internalized via caveola-dependent endocytosis, which, in turn, contributes to phenotypic changes in the recipient cells through transferring one or more viral factors.

Epstein-Barr Virus (EBV)-associated gastric carcinoma

The ubiquitous Epstein-Barr virus (EBV) is associated with several human tumors, which include lymphoid and epithelial malignancies. It is known that EBV persistently infects the memory B cell pool of healthy individuals by activating growth and survival signaling pathways that can contribute to B cell lymphomagenesis. Although the monoclonal proliferation of EBV-infected cells can be observed in epithelial tumors, such as nasopharyngeal carcinoma and EBV-associated gastric carcinoma, the precise role of EBV in the carcinogenic progress is not fully understood. This review features characteristics and current understanding of EBV-associated gastric carcinoma. EBV-associated gastric carcinoma comprises almost 10% of all gastric carcinoma cases and expresses restricted EBV latent genes (Latency I). Firstly, definition, epidemiology, and clinical features are discussed. Then, the route of infection and carcinogenic role of viral genes are presented. Of particular interest, the association with frequent genomic CpG methylation and role of miRNA for carcinogenesis are topically discussed. Finally, the possibility of therapies targeting EBV-associated gastric carcinoma is proposed.