Interaction of Epstein-Barr Virus BZLF1 C-Terminal Tail Structure and Core Zipper Is Required for DNA Replication but Not for Promoter Transactivation

Elevated secretion of inflammatory factors is associated with latent Epstein-Barr virus (EBV) infection and the pathology of EBV-asso- Infection by the Epstein-Barr virus (EBV) causes infectious mononucleosis and several malignant cancers, including Burkitt's lymphoma, Hodgkin's lymphoma, nasopharyngeal carcinoma (NPC), and gastric carcinoma, as well as posttransplant lymphomas (1-5). EBV infection is persistent worldwide, but the frequency of EBV-associated NPC is highest in southern China, while Burkitt's lymphoma is most commonly found in equatorial Africa (2, 3). Although the exact mechanism by which EBV causes tumorigenesis remains to be fully defined, two important cofactors are strongly involved in EBV pathogenesis: genetic susceptibility and local diet. Unique polymorphisms of NPC-associated EBV have been identified in Chinese individuals, indicating the existence of EBV variants with higher pathogenic potential for NPC than that seen in the typical Western strains that cause infectious mononucleosis (6-8).Latent infection with limited gene expression is the default EBV cycle, whereas the lytic cycle is essential for transmission (1, 9). Lytic replication during primary infection or reactivation from the latent cycle is initiated by the expression of the immediate early (IE) viral transactivators BZLF1 and BRLF1. BZLF1, an EBV-encoded transcription factor of the basic-leucine zipper (b-ZIP) family, activates both viral and cellular genes by binding to BZLF1-responsive elements (ZREs), including several transcription factors and inflammatory factors (10).Inflammatory mediators have complex roles in cancer and infectious diseases, either limiting or promoting these disorders (11-15). Several proinflammatory factors have been fully characterized in experimental and clinical studies, including tumor necrosis factor alpha (TNF-␣), interferon gamma (IFN-␥), interleukin-1␣ (IL-1␣), and IL-1␤. TNF-␣ serves as an antiviral immune factor operating via two different mechanisms: induction of apoptosis in infected cells and activation of the antiviral response in uninfected cells (16)(17)(18)(19). For successful infection and replication, viruses employ multiple strategies to escape or hijack the host defenses, including innate immunity and the inflammatory response (15,17,20). The EBV lytic cycle evades the host inflammatory responses through the activity of BZLF1, which inhibits both IFN-␥ signaling and tumor necrosis factor receptor 1 (TNFR1) signaling (21-23). BZLF1 suppresses the NF-B signaling pathway by directly binding the p65 subunit (24, 25), acting as an

Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Bzlf1 Suppresses Expression Of Tnf-␣ and Proinflammatory Facmentioning

confidence: 99%

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Epstein-Barr Virus BZLF1-Mediated Downregulation of Proinflammatory Factors Is Essential for Optimal Lytic Viral Replication

Long

Yang

et al. 2016

“…No functions previously had been ascribed to this region, although a recent publication revealed a role for the interaction between position D236 in the C-terminal tail and the zipper for the viral lytic cycle (32).…”

Section: Discussionmentioning

confidence: 99%

Functional Interaction between Epstein-Barr Virus Replication Protein Zta and Host DNA Damage Response Protein 53BP1

Bailey¹,

Verrall²,

Schelcher³

et al. 2009

Epstein-Barr virus (EBV; human herpesvirus 4) poses major clinical problems worldwide. Following primary infection, EBV enters a form of long-lived latency in B lymphocytes, expressing few viral genes, and itpersists for the lifetime of the host with sporadic bursts of viral replication. The switch between latency and replication is governed by the action of a multifunctional viral protein Zta (also called BZLF1, ZEBRA, and Z). Using a global proteomic approach, we identified a host DNA damage repair protein that specifically interacts with Zta: 53BP1. 53BP1 is intimately connected with the ATM signal transduction pathway, which is activated during EBV replication. The interaction of 53BP1 with Zta requires the C-terminal ends of both proteins. A series of Zta mutants that show a wild-type ability to perform basic functions of Zta, such as dimer formation, interaction with DNA, and the transactivation of viral genes, were shown to have lost the ability to induce the viral lytic cycle. Each of these mutants also is compromised in the C-terminal region for interaction with 53BP1. In addition, the knockdown of 53BP1 expression reduced viral replication, suggesting that the association between Zta and 53BP1 is involved in the viral replication cycle.The Epstein-Barr virus (EBV) life cycle is divided temporally into two phases, latency and the lytic cycle. Following the infection of epithelial cells of the oropharynx, EBV enters the lytic cycle, where the expression of approximately 80 genes and numerous rounds of genome replication occur, culminating in the production of infectious virions. The infection of B lymphocytes results in the establishment of viral latency with a restricted gene expression pattern; these cells sporadically enter the lytic cycle and reproduce infectious virus (27,53).The EBV gene BZLF1 has been associated specifically with the disruption of latency (reviewed in references 34 and 50). This gene encodes the protein Zta (ZEBRA, BZLF1, Z), which has an undisputed role in activating the viral lytic cycle. Not only is the enforced expression of Zta in cells harboring the latent virus able to induce the viral lytic cycle, but a mutant virus where BZLF1 has been inactivated also is unable to replicate the viral genome (10). Zta has homology to the bZIP family of transcription factors whose general structure includes a transactivation domain and a bZIP domain consisting of a basic DNA contact region and a coiled-coil dimerization motif, termed a leucine zipper (24,49,50). Zta has a more complex dimerization domain than other bZIP family members, consisting of a dimeric leucine zipper entwined with an adjacent carboxyl-terminal region (35,38,44,50). Zta is multifunctional; through its basic region, it interacts with specific sequence DNA motifs (ZREs) that occur in the promoters of several viral and cellular genes (49) and in the viral origin of lytic replication (Ori-lyt) (46,47). Through its bZIP domain, Zta interacts with cellular transcription factors such as p53, RAR, NF-B, CBP, and C/EBP␣ (7), ...

“…Cells from this individual (donor B8; HLA-A2, A66, B4402, B49, Cw7) expressed HLA-B49, which is likely to be the restricting allele based on the binding motif of HLA-B49, which includes anchor residues Glu at position 2 and Leu at the C terminus. It is notable that McDonald and colleagues found the motif 209 SENDRLR 215 , located midway along the coiled-coil dimerization region, to play a key role in the BZLF1 structure and to be required for EBV DNA replication (29). In addition, the leucine at residue 217 is suggested to be important for dimerization, since it is positioned adjacent to the interacting faces of the helices (10).…”

Section: Discussionmentioning

confidence: 99%

T Cell Epitope Clustering in the Highly Immunogenic BZLF1 Antigen of Epstein-Barr Virus

Neller

Burrows

2015

Polymorphism in the human leukocyte antigen (HLA) loci ensures that the CD8؉ T cell response to viruses is directed against a diverse range of antigenic epitopes, thereby minimizing the impact of virus escape mutation across the population. The BZLF1 antigen of Epstein-Barr virus is an immunodominant target for CD8 ؉ T cells, but the response has been characterized only in the context of a limited number of HLA molecules due to incomplete epitope mapping. We have now greatly expanded the number of defined CD8 ؉ T cell epitopes from BZLF1, allowing the response to be evaluated in a much larger proportion of the population. Some regions of the antigen fail to be recognized by CD8 ؉ T cells, while others include clusters of overlapping epitopes presented by different HLA molecules. These highly immunogenic regions of BZLF1 include polymorphic sequences, such that up to four overlapping epitopes are impacted by a single amino acid variation common in different regions of the world. This focusing of the immune response to limited regions of the viral protein could be due to sequence similarity to human proteins creating "immune blind spots" through self-tolerance. This study significantly enhances the understanding of the immune response to BZLF1, and the precisely mapped T cell epitopes may be directly exploited in vaccine development and adoptive immunotherapy. IMPORTANCE Epstein-Barr virus (EBV) is an important human pathogen, associated with several malignancies, including nasopharyngeal carcinoma and Hodgkin lymphoma. T lymphocytes are critical for virus control, and clinical trials aimed at manipulating this armof the immune system have demonstrated efficacy in treating these EBV-associated diseases. These trials have utilized information on the precise location of viral epitopes for T cell recognition, for either measuring or enhancing responses. In this study, we have characterized the T cell response to the highly immunogenic BZLF1 antigen of EBV by greatly expanding the number of defined T cell epitopes. An unusual clustering of epitopes was identified, highlighting a small region of BZLF1 that is targeted by the immune response of a high proportion of the world's population. This focusing of the immune response could be utilized in developing vaccines/therapies with wide coverage, or it could potentially be exploited by the virus to escape the immune response.