Epstein-Barr virus (EBV) infects cells in latent or lytic forms, but the role of lytic infection in EBV- DLBCL). Animals infected with the control virus developed tumors more frequently than Z-KO virus-infected animals. Specific immune responses against EBV-infected B cellswere generated in mice infected with either the control virus or the Z-KO virus. In both cases, forms of viral latency (type I and type IIB) were observed that are less immunogenic than the highly transforming form (type III) commonly found in tumors of immunocompromised hosts, suggesting that immune pressure contributed to the outcome of the infection. These results point to an important role for lytic EBV infection in the development of B cell lymphomas in the context of an active host immune response.

Epstein–Barr virus (EBV) infection contributes to the development of several different types of human malignancy, including Burkitt lymphoma, Hodgkin lymphoma, and nasopharyngeal carcinoma. As a herpesvirus, EBV can establish latent or lytic infection in cells. EBV-positive tumors are composed almost exclusively of cells with latent EBV infection. Strategies for inducing the lytic form of EBV infection in tumor cells are being investigated as a potential therapy for EBV-positive tumors. In this article, we review how cellular and viral proteins regulate the latent-lytic EBV switch in infected B cells and epithelial cells, and discuss how harnessing lytic viral reactivation might be used therapeutically.

Epstein-Barr virus (EBV), the causative agent of infectious mononucleosis, is a human herpesvirus associated with epithelial cell malignancies (nasopharyngeal carcinoma) as well as B-cell malignancies. Understanding how viral latency is disrupted is a central issue in herpesvirus biology. Epithelial cells are the major site of lytic EBV replication within the human host, and viral reactivation occurs in EBV-associated nasopharyngeal carcinomas. It Epstein-Barr virus (EBV) is a human herpesvirus associated with lymphoid and epithelial cell malignancies (1, 2). A critical aspect of herpesvirus biology is the maintenance and disruption of viral latency. EBV infection is generally latent in B cells but commonly productive in epithelial cells (3)(4)(5). EBV reactivation and replication in latently infected B cells can be activated by treatment with agents such as phorbol 12-myristate 13-acetate (PMA) or cross-linking of surface immunoglobulin (6, 7). These agents activate expression of the immediate-early (IE) protein, BZLF1 (Z) (8, 9). Z, a transcriptional activator, is a member of the basic leucine zipper (bZip) family which binds to APi-like Z-response elements in EBV early promoters (10-12). Expression of transfected Z in latently infected lymphocytes is sufficient to trigger the lytic cycle (13)(14)(15).In addition to Z, EBV has one other IE protein, BRLF1 (R). Like Z, R is a transcriptional activator and sequence-specific DNA-binding protein (16)(17)(18)(19)(20)(21)(22). A number of early EBV promoters contain upstream R binding sites (a G+C-rich motif) and are transcriptionally activated by R in transient transfection assays. Certain early viral promoters require both Z and R for maximal transcriptional activation (13,19,21). In contrast to Z, expression of transfected R in EBV-infected B cells does not disrupt latency (19).The finding that expression of Z is sufficient to disrupt viral latency has led to a model in which lytic EBV infection results from activation of BZLF1 transcription by cellular transcription factors (23). The Z protein can potentially be derived from two different promoters, Zp and Rp (16) (Fig. 1). The more proximal promoter, Zp (from which most, if not all, Z protein is derived), directs transcription of a 1.0-kb message encoding the Z protein alone. The distal promoter, Rp, directs transcription of a 2.8-kb message encoding the R protein, and potentially the Z protein as well (if the message can be bicistronically translated) (16). Zp and Rp are normally inactive in latently infected cells, but agents that disrupt viral latency such as PMA and anti-immunoglobulin activate expression of Zp, as well as Rp (8, 9), with similar kinetics.Although the phenotype of virus lacking Z or R has not been reported, it is likely that both Z and R are required for disruption of viral latency. Assuming that this is the case, transfected Z may activate Rp in latently infected B cells, and the resultant combination of Z and R then leads to disruption of viral latency. In contrast, transfected R...

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Although the immediate-early proteins of both herpes simplex virus (HSV) and cytomegalovirus (CMV) are known to modify promyelocytic leukemia (PML) (ND10) bodies in the nucleus of the host cell, it has been unclear whether lytic infection with gamma herpesviruses induces a similar effect. The PML protein is induced by interferon, involved in major histocompatibility complex class I presentation, and necessary for certain types of apoptosis. Therefore, it is likely that PML bodies function in an antiviral capacity. SUMO-1 modification of PML is known to be required for the formation of PML bodies. To examine whether Epstein-Barr virus (EBV) lytic replication interferes with PML bodies, we expressed the EBV immediate-early genes BZLF1 (Z) and BRLF1 (R) in EBV-positive cell lines and examined PML localization. Both Z and R expression resulted in PML dispersion in EBV-positive cells. Z but not R expression is sufficient to disrupt PML bodies in EBV-negative cell lines. We show that dispersion of PML bodies by Z requires a portion of the transcriptional activation domain of Z but not the DNA-binding function. As was previously reported for the HSV-1 ICP0 and CMV IE1 proteins, Z reduces the amount of SUMO-1-modified PML. We also found that Z itself is SUMO-1 modified (through amino acid 12) and that Z competes with PML for limiting amounts of SUMO-1. These results suggest that disruption of PML bodies is important for efficient lytic replication of EBV. Furthermore, Z may potentially alter the function of a variety of cellular proteins by inhibiting SUMO-1 modification.Epstein-Barr virus (EBV) is a member of the human herpesvirus family of viruses and infects approximately 90% of the world's population. EBV is responsible for the clinical syndrome infectious mononucleosis (66) and is found in various tumors, including nasopharyngeal carcinoma and Burkitt's lymphoma (66,88). Upon infection of the host, EBV initially replicates within epithelial cells in the oropharynx (44,52,66,71) and subsequently infects B cells trafficking through the pharynx. In B cells, the virus usually converts to a latent form and persists indefinitely in the host (44,52,66,71). During latency, only a small subset of EBV-encoded proteins are expressed. Occasionally, the latent virus within B cells switches back to the lytic mode of replication (66). Virus released from B cells then reinfects pharyngeal epithelial cells, resulting in the secretion of infectious virus into the saliva.The first EBV genes expressed during the lytic form of viral replication are the immediate-early genes BZLF1 (Z) and BRLF1 (R) (44). The Z and R proteins function as transcriptional activators and induce expression of the next tier of EBV genes, the early genes (14,15,16,28,32,33,36,41,53,64,67,68,75,78). The early genes encode the viral proteins required for EBV DNA replication (44). Viral DNA replication is followed by EBV late-gene expression and packaging of the virus (44).Viruses often manipulate their host's cellular environment in order to create favorable con...

A novel therapy for Epstein-Barr virus (EBV)-Most importantly, the combination of gemcitabine or doxorubicin and GCV was significantly more effective for the inhibition of EBV-driven lymphoproliferative disease in SCID mice than chemotherapy alone. In contrast, the combination of zidovudine and gemcitabine was no more effective than gemcitabine alone. These results suggest that the addition of GCV to either gemcitabine-or doxorubicin-containing chemotherapy regimens may enhance the therapeutic efficacy of these drugs for EBV-driven lymphoproliferative disease in patients.

Expression of either Epstein-Barr virus (EBV) immediate-early protein BZLF1 (Z) or BRLF1 (R) issufficient to convert EBV infection from the latent to lytic form. Disruption of viral latency requires transcriptional activation of the Z and R promoters. The Z and R proteins are transcriptional activators, and each immediate-early protein activates expression of the other immediate-early protein. Z activates the R promoter through a direct binding mechanism. However, R does not bind directly to the Z promoter. In this study, we demonstrate that the ZII element (a cyclic AMP response element site) in the Z promoter is required for efficient activation by R. The ZII element has been shown to be important for induction of lytic EBV infection by tetradecanoyl phorbol acetate and surface immunoglobulin cross-linking and is activated by Z through an indirect mechanism. We demonstrate that both R and Z activate the cellular stress mitogen-activated protein (MAP) kinases, p38 and JNK, resulting in phosphorylation (and activation) of the cellular transcription factor ATF2. Furthermore, we show that the ability of R to induce lytic EBV infection in latently infected cells is significantly reduced by inhibition of either the p38 kinase or JNK pathways. In contrast, inhibition of stress MAP kinase pathways does not impair the ability of Z expression vectors to disrupt viral latency, presumably because expression of Z under the control of a strong heterologous promoter bypasses the need to activate Z transcription. Thus, both R and Z can activate the Z promoter indirectly by inducing ATF2 phosphorylation, and this activity appears to be important for R-induced disruption of viral latency.Epstein-Barr virus (EBV) is a member of the human herpesvirus family of viruses and is the causative agent of infectious mononucleosis (61). EBV has also been found in association with a variety of cancers, including Burkitt's lymphoma and nasopharyngeal carcinoma (61, 82). Upon primary infection, EBV infects epithelial cells, where it undergoes lytic replication, and B cells, where it usually remains latent (37,45,61,67). However, in a small percentage of B cells, latent EBV can become reactivated and undergo lytic replication. This viral reactivation is initiated by the two EBV immediate-early proteins, BZLF1 and BRLF1 (5,8,36,57,62,63,69,77,80).The BZLF1 (Z) and BRLF1 (R) proteins function as transcriptional activators of the EBV early genes (9, 20, 28-30, 35, 46, 56, 74), and the expression of either Z or R is sufficient to induce lytic replication in both latently infected epithelial cells and B cells (5,8,57,69,77,80). Regardless of which immediate-early gene is initially transcribed, expression of one immediate-early protein leads to the expression of the other (80), and full activation of early genes requires the presence of both immediate-early proteins (1, 80). Z activates the R promoter by directly binding to Z-response elements (ZREs) (1, 66). However, the mechanism by which R activates Z expression remains unknown. Although the R ...