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Ali A, Ohashi M, Casco A, Djavadian R, Eichelberg M, Kenney SC, Johannsen E. Rta is the principal activator of Epstein-Barr virus epithelial lytic transcription. PLoS Pathog 2022; 18:e1010886. [PMID: 36174106 PMCID: PMC9553042 DOI: 10.1371/journal.ppat.1010886] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Revised: 10/11/2022] [Accepted: 09/14/2022] [Indexed: 01/27/2023] Open
Abstract
The transition from latent Epstein-Barr virus (EBV) infection to lytic viral replication is mediated by the viral transcription factors Rta and Zta. Although both are required for virion production, dissecting the specific roles played by Rta and Zta is challenging because they induce each other's expression. To circumvent this, we constructed an EBV mutant deleted for the genes encoding Rta and Zta (BRLF1 and BZLF1, respectively) in the Akata strain BACmid. This mutant, termed EBVΔRZ, was used to infect several epithelial cell lines, including telomerase-immortalized normal oral keratinocytes, a highly physiologic model of EBV epithelial cell infection. Using RNA-seq, we determined the gene expression induced by each viral transactivator. Surprisingly, Zta alone only induced expression of the lytic origin transcripts BHLF1 and LF3. In contrast, Rta activated the majority of EBV early gene transcripts. As expected, Zta and Rta were both required for expression of late gene transcripts. Zta also cooperated with Rta to enhance a subset of early gene transcripts (Rtasynergy transcripts) that Zta was unable to activate when expressed alone. Interestingly, Rta and Zta each cooperatively enhanced the other's binding to EBV early gene promoters, but this effect was not restricted to promoters where synergy was observed. We demonstrate that Zta did not affect Rtasynergy transcript stability, but increased Rtasynergy gene transcription despite having no effect on their transcription when expressed alone. Our results suggest that, at least in epithelial cells, Rta is the dominant transactivator and that Zta functions primarily to support DNA replication and co-activate a subset of early promoters with Rta. This closely parallels the arrangement in KSHV where ORF50 (Rta homolog) is the principal activator of lytic transcription and K8 (Zta homolog) is required for DNA replication at oriLyt.
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Affiliation(s)
- Ahmed Ali
- Department of Oncology, McArdle Laboratory for Cancer Research, University of Wisconsin, Madison Wisconsin, United States of America
- National Center for Research, Khartoum, Sudan
| | - Makoto Ohashi
- Department of Oncology, McArdle Laboratory for Cancer Research, University of Wisconsin, Madison Wisconsin, United States of America
| | - Alejandro Casco
- Department of Oncology, McArdle Laboratory for Cancer Research, University of Wisconsin, Madison Wisconsin, United States of America
| | - Reza Djavadian
- Department of Oncology, McArdle Laboratory for Cancer Research, University of Wisconsin, Madison Wisconsin, United States of America
| | - Mark Eichelberg
- Department of Oncology, McArdle Laboratory for Cancer Research, University of Wisconsin, Madison Wisconsin, United States of America
| | - Shannon C. Kenney
- Department of Oncology, McArdle Laboratory for Cancer Research, University of Wisconsin, Madison Wisconsin, United States of America
- Department of Medicine, Division of Infectious Diseases, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Eric Johannsen
- Department of Oncology, McArdle Laboratory for Cancer Research, University of Wisconsin, Madison Wisconsin, United States of America
- Department of Medicine, Division of Infectious Diseases, University of Wisconsin, Madison, Wisconsin, United States of America
- * E-mail:
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Damania B, Kenney SC, Raab-Traub N. Epstein-Barr virus: Biology and clinical disease. Cell 2022; 185:3652-3670. [PMID: 36113467 PMCID: PMC9529843 DOI: 10.1016/j.cell.2022.08.026] [Citation(s) in RCA: 109] [Impact Index Per Article: 54.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Revised: 08/17/2022] [Accepted: 08/24/2022] [Indexed: 01/26/2023]
Abstract
Epstein-Barr virus (EBV) is a ubiquitous, oncogenic virus that is associated with a number of different human malignancies as well as autoimmune disorders. The expression of EBV viral proteins and non-coding RNAs contribute to EBV-mediated disease pathologies. The virus establishes life-long latency in the human host and is adept at evading host innate and adaptive immune responses. In this review, we discuss the life cycle of EBV, the various functions of EBV-encoded proteins and RNAs, the ability of the virus to activate and evade immune responses, as well as the neoplastic and autoimmune diseases that are associated with EBV infection in the human population.
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Affiliation(s)
- Blossom Damania
- Lineberger Comprehensive Cancer Center and Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
| | - Shannon C Kenney
- Department of Oncology, McArdle Laboratory for Cancer Research, and Department of Medicine, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, USA
| | - Nancy Raab-Traub
- Lineberger Comprehensive Cancer Center and Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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Chua HH, Kameyama T, Mayeda A, Yeh TH. Epstein-Barr Virus Enhances Cancer-Specific Aberrant Splicing of TSG101 Pre-mRNA. Int J Mol Sci 2022; 23:ijms23052516. [PMID: 35269659 PMCID: PMC8910672 DOI: 10.3390/ijms23052516] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 02/21/2022] [Accepted: 02/21/2022] [Indexed: 11/16/2022] Open
Abstract
Tumor viruses gain control of cellular functions when they infect and transform host cells. Alternative splicing is one of the cellular processes exploited by tumor viruses to benefit viral replication and support oncogenesis. Epstein-Barr virus (EBV) participates in a number of cancers, as reported mostly in nasopharyngeal carcinoma (NPC) and Burkitt lymphoma (BL). Using RT-nested-PCR and Northern blot analysis in NPC and BL cells, here we demonstrate that EBV promotes specific alternative splicing of TSG101 pre-mRNA, which generates the TSG101∆154-1054 variant though the agency of its viral proteins, such as EBNA-1, Zta and Rta. The level of TSG101∆154-1054 is particularly enhanced upon EBV entry into the lytic cycle, increasing protein stability of TSG101 and causing the cumulative synthesis of EBV late lytic proteins, such as VCA and gp350/220. TSG101∆154-1054-mediated production of VCA and gp350/220 is blocked by the overexpression of a translational mutant of TSG101∆154-1054 or by the depletion of full-length TSG101, which is consistent with the known role of the TSG101∆154-1054 protein in stabilizing the TSG101 protein. NPC patients whose tumor tissues express TSG101∆154-1054 have high serum levels of anti-VCA antibodies and high levels of viral DNA in their tumors. Our findings highlight the functional importance of TSG101∆154-1054 in allowing full completion of the EBV lytic cycle to produce viral particles. We propose that targeting EBV-induced TSG101 alternative splicing has broad potential as a therapeutic to treat EBV-associated malignancies.
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Affiliation(s)
- Huey-Huey Chua
- Department of Pediatrics, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 100226, Taiwan;
| | - Toshiki Kameyama
- Department of Physiology, School of Medicine, Fujita Health University, Toyoake 470-1192, Aichi, Japan;
| | - Akila Mayeda
- Division of Gene Expression Mechanism, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake 470-1192, Aichi, Japan
- Correspondence: (A.M.); (T.-H.Y.)
| | - Te-Huei Yeh
- Department of Otolaryngology, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 100225, Taiwan
- Correspondence: (A.M.); (T.-H.Y.)
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Kusano S, Ikeda M. Interaction of phospholipid scramblase 1 with the Epstein-Barr virus protein BZLF1 represses BZLF1-mediated lytic gene transcription. J Biol Chem 2019; 294:15104-15116. [PMID: 31434743 DOI: 10.1074/jbc.ra119.008193] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Revised: 08/15/2019] [Indexed: 11/06/2022] Open
Abstract
Human phospholipid scramblase 1 (PLSCR1) is strongly expressed in response to interferon (IFN) treatment and viral infection, and PLSCR1 has been suggested to play an important role in IFN-dependent antiviral responses. In this study, we showed that the basal expression of PLSCR1 was significantly elevated in Epstein-Barr virus (EBV)-infected nasopharyngeal carcinoma (NPC). PLSCR1 was observed to directly interact with the EBV immediate-early transactivator BZLF1 in vitro and in vivo, and this interaction repressed the BZLF1-mediated transactivation of an EBV lytic BMRF1 promoter construct. In addition, PLSCR1 expression decreased the BZLF1-mediated up-regulation of lytic BMRF1 mRNA and protein expression in WT and PLSCR1-knockout EBV-infected NPC cells. Furthermore, we showed that PLSCR1 represses the interaction between BZLF1 and CREB-binding protein (CBP), which enhances the BZLF1-mediated transactivation of EBV lytic promoters. These results reveal for the first time that PLSCR1 specifically interacts with BZLF1 and negatively regulates its transcriptional regulatory activity by preventing the formation of the BZLF1-CBP complex. This interaction may contribute to the establishment of latent EBV infection in EBV-infected NPC cells.
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Affiliation(s)
- Shuichi Kusano
- Division of Biological Information Technology, Joint Research Center for Human Retrovirus Infection, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima-shi, Kagoshima 890-8544, Japan
| | - Masanori Ikeda
- Division of Biological Information Technology, Joint Research Center for Human Retrovirus Infection, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima-shi, Kagoshima 890-8544, Japan
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Abstract
Epstein-Barr virus, which mainly infects B cells and epithelial cells, has two modes of infection: latent and lytic. Epstein-Barr virus infection is predominantly latent; however, lytic infection is detected in healthy seropositive individuals and becomes more prominent in certain pathological conditions. Lytic infection is divided into several stages: early gene expression, DNA replication, late gene expression, assembly, and egress. This chapter summarizes the most recent progress made toward understanding the molecular mechanisms that regulate the different lytic stages leading to production of viral progeny. In addition, the chapter highlights the potential role of lytic infection in disease development and current attempts to purposely induce lytic infection as a therapeutic approach.
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Affiliation(s)
- Jessica McKenzie
- Department of Pediatrics, Division of Infectious Diseases, Yale University School of Medicine, New Haven, CT, 06520, USA
| | - Ayman El-Guindy
- Department of Pediatrics, Division of Infectious Diseases, Yale University School of Medicine, New Haven, CT, 06520, USA.
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T cell epitope clustering in the highly immunogenic BZLF1 antigen of Epstein-Barr virus. J Virol 2014; 89:703-12. [PMID: 25355876 DOI: 10.1128/jvi.02642-14] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
UNLABELLED 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 arm of 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.
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Yang Y, Jia Y, Wang Y, Wang X, Sun Z, Luo B. Sequence analysis of EBV immediate-early gene BZLF1 and BRLF1 in lymphomas. J Med Virol 2014; 86:1788-95. [PMID: 24615673 DOI: 10.1002/jmv.23911] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/31/2014] [Indexed: 12/20/2022]
Abstract
The immediate-early (IE) genes, BZLF1 and BRLF1, play an important role in switching Epstein-Barr virus from the latent to the lytic state. The functions of the two IE genes and their respective proteins: ZEBRA and Rta have been well studied, but little is known about their DNA coding sequence variations and disease association. In order to investigate the sequence variation patterns and elucidate their association with lymphomas, BZLF1 and BRLF1 were analyzed in 26 and 33 lymphomas using PCR-direct sequencing method respectively. Three sequence variation types of BZLF1 gene were identified. The type BZLF1-A and BZLF1-B was detected in 34.6% (9/26) and 57.7% (15/26) of the tumor specimens, respectively. Among the three functional domains of ZEBRA, the transactivation domain had the most mutations. Three variation types were also identified in BRLF1 gene where type BR1-A and BR1-C were detected in 27.3% (9/33) and 69.7% (23/33) of specimens, respectively. Among the three functional domains of Rta, the dimerization domain was well conserved while multiple mutations were detected in both the DNA binding domain and the transactivation domain. The variation types BZLF1-B and BR1-C were more frequent in the lymphomas, compared with the throat washing samples from the healthy donors. These results suggest that the type BZLF1-B and BR1-C may be associated with the tumorigenesis of lymphoma.
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Affiliation(s)
- Ying Yang
- Department of Medical Microbiology, Qingdao University Medical College, Qingdao, 266021, China
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8
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Abstract
The Epstein-Barr virus (EBV) lytic transactivator Rta activates promoters through direct binding to cognate DNA sites termed Rta response elements (RREs). Rta also activates promoters that apparently lack Rta binding sites, notably Zp and Rp. Chromatin immunoprecipitation (ChIP) of endogenous Rta expressed during early replication in B95-8 cells was performed to identify Rta binding sites in the EBV genome. Quantitative PCR (qPCR) analysis showed strong enrichment for known RREs but little or no enrichment for Rp or Zp, suggesting that the Rta ChIP approach enriches for direct Rta binding sites. Rta ChIP combined with deep sequencing (ChIP-seq) identified most known RREs and several novel Rta binding sites. Rta ChIP-seq peaks were frequently upstream of Rta-responsive genes, indicating that these Rta binding sites are likely functioning as RREs. Unexpectedly, the BALF5 promoter contained an Rta binding peak. To assess whether BALF5 might be activated by an RRE-dependent mechanism, an Rta mutant (Rta K156A), deficient for DNA binding and RRE activation but competent for Zp/Rp activation, was used. Rta K156A failed to activate BALF5p, suggesting this promoter can be activated by an RRE-dependent mechanism. Rta binding to late gene promoters was not seen at early time points but was specifically detected at later times within the Rta-responsive BLRF2 and BFRF3 promoters, even when DNA replication was inhibited. Our results represent the first characterization of Rta binding to the EBV genome during replication, identify previously unknown RREs, such as one in BALF5p, and highlight the complexity of EBV late gene promoter activation by Rta.
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Robinson AR, Kwek SS, Kenney SC. The B-cell specific transcription factor, Oct-2, promotes Epstein-Barr virus latency by inhibiting the viral immediate-early protein, BZLF1. PLoS Pathog 2012; 8:e1002516. [PMID: 22346751 PMCID: PMC3276558 DOI: 10.1371/journal.ppat.1002516] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2011] [Accepted: 12/16/2011] [Indexed: 01/16/2023] Open
Abstract
The Epstein-Barr virus (EBV) latent-lytic switch is mediated by the BZLF1 immediate-early protein. EBV is normally latent in memory B cells, but cellular factors which promote viral latency specifically in B cells have not been identified. In this report, we demonstrate that the B-cell specific transcription factor, Oct-2, inhibits the function of the viral immediate-early protein, BZLF1, and prevents lytic viral reactivation. Co-transfected Oct-2 reduces the ability of BZLF1 to activate lytic gene expression in two different latently infected nasopharyngeal carcinoma cell lines. Furthermore, Oct-2 inhibits BZLF1 activation of lytic EBV promoters in reporter gene assays, and attenuates BZLF1 binding to lytic viral promoters in vivo. Oct-2 interacts directly with BZLF1, and this interaction requires the DNA-binding/dimerization domain of BZLF1 and the POU domain of Oct-2. An Oct-2 mutant (Δ262–302) deficient for interaction with BZLF1 is unable to inhibit BZLF1-mediated lytic reactivation. However, an Oct-2 mutant defective for DNA-binding (Q221A) retains the ability to inhibit BZLF1 transcriptional effects and DNA-binding. Importantly, shRNA-mediated knockdown of endogenous Oct-2 expression in several EBV-positive Burkitt lymphoma and lymphoblastoid cell lines increases the level of lytic EBV gene expression, while decreasing EBNA1 expression. Moreover, treatments which induce EBV lytic reactivation, such as anti-IgG cross-linking and chemical inducers, also decrease the level of Oct-2 protein expression at the transcriptional level. We conclude that Oct-2 potentiates establishment of EBV latency in B cells. Epstein-Barr virus (EBV) is a human herpesvirus associated with B-cell malignancies. EBV infection of cells can result in either lytic replication or latency. Memory B cells are the primary site of EBV latency within the human host, while oropharyngeal epithelial cells support the lytic form of infection. However, the cellular mechanism(s) that enable EBV to establish viral latency in a B-cell specific manner are not currently understood. In this report, we show that the B-cell specific cellular transcription factor, Oct-2, promotes viral latency by inhibiting the lytic form of infection. We find that Oct-2 interacts directly with the EBV immediate-early protein, BZLF1, and abrogates its ability to activate lytic viral gene transcription through protein-protein interactions off the DNA. Furthermore, knockdown of endogenous Oct-2 expression in several latently-infected Burkitt lymphoma B-cell lines increases EBV lytic protein expression. In addition, we show that certain stimuli which can prompt lytic EBV reactivation in B cells also decrease expression of endogenous Oct-2. Our results suggest that the cellular transcription factor, Oct-2, promotes EBV latency in a B-cell dependent manner.
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Affiliation(s)
- Amanda R. Robinson
- Department of Oncology, McArdle Laboratory for Cancer Research , University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
- Department of Cellular and Molecular Biology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
| | - Swee Sen Kwek
- Department of Oncology, McArdle Laboratory for Cancer Research , University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
| | - Shannon C. Kenney
- Department of Oncology, McArdle Laboratory for Cancer Research , University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
- Department of Medicine, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
- * E-mail:
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Huang Q, Gong C, Li J, Zhuo Z, Chen Y, Wang J, Hua ZC. Distance and helical phase dependence of synergistic transcription activation in cis-regulatory module. PLoS One 2012; 7:e31198. [PMID: 22299056 PMCID: PMC3267773 DOI: 10.1371/journal.pone.0031198] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2011] [Accepted: 01/03/2012] [Indexed: 01/21/2023] Open
Abstract
Deciphering of the spatial and stereospecific constraints on synergistic transcription activation mediated between activators bound to cis-regulatory elements is important for understanding gene regulation and remains largely unknown. It has been commonly believed that two activators will activate transcription most effectively when they are bound on the same face of DNA double helix and within a boundary distance from the transcription initiation complex attached to the TATA box. In this work, we studied the spatial and stereospecific constraints on activation by multiple copies of bound model activators using a series of engineered relative distances and stereospecific orientations. We observed that multiple copies of the activators GAL4-VP16 and ZEBRA bound to engineered promoters activated transcription more effectively when bound on opposite faces of the DNA double helix. This phenomenon was not affected by the spatial relationship between the proximal activator and initiation complex. To explain these results, we proposed the novel concentration field model, which posits the effective concentration of bound activators, and therefore the transcription activation potential, is affected by their stereospecific positioning. These results could be used to understand synergistic transcription activation anew and to aid the development of predictive models for the identification of cis-regulatory elements.
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Affiliation(s)
- Qilai Huang
- The State Key Laboratory of Pharmaceutical Biotechnology and Affiliated Stomatological Hospital, Nanjing University, Nanjing, People's Republic of China
- The State Key Laboratory of Quality Research in Chinese Medicine and Macau Institute for Applied Research in Medicine, Macau University of Science and Technology, Macau, People's Republic of China
- Changzhou High-Tech Research Institute of Nanjing University and Jiangsu TargetPharma Laboratories Inc., Changzhou, People's Republic of China
| | - Chenguang Gong
- The State Key Laboratory of Pharmaceutical Biotechnology and Affiliated Stomatological Hospital, Nanjing University, Nanjing, People's Republic of China
| | - Jiahuang Li
- The State Key Laboratory of Pharmaceutical Biotechnology and Affiliated Stomatological Hospital, Nanjing University, Nanjing, People's Republic of China
| | - Zhu Zhuo
- The State Key Laboratory of Pharmaceutical Biotechnology and Affiliated Stomatological Hospital, Nanjing University, Nanjing, People's Republic of China
| | - Yuan Chen
- The State Key Laboratory of Pharmaceutical Biotechnology and Affiliated Stomatological Hospital, Nanjing University, Nanjing, People's Republic of China
| | - Jin Wang
- The State Key Laboratory of Pharmaceutical Biotechnology and Affiliated Stomatological Hospital, Nanjing University, Nanjing, People's Republic of China
- * E-mail: (JW); (ZH)
| | - Zi-Chun Hua
- The State Key Laboratory of Pharmaceutical Biotechnology and Affiliated Stomatological Hospital, Nanjing University, Nanjing, People's Republic of China
- The State Key Laboratory of Quality Research in Chinese Medicine and Macau Institute for Applied Research in Medicine, Macau University of Science and Technology, Macau, People's Republic of China
- Changzhou High-Tech Research Institute of Nanjing University and Jiangsu TargetPharma Laboratories Inc., Changzhou, People's Republic of China
- * E-mail: (JW); (ZH)
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Katsumura KR, Maruo S, Takada K. EBV lytic infection enhances transformation of B-lymphocytes infected with EBV in the presence of T-lymphocytes. J Med Virol 2012; 84:504-10. [DOI: 10.1002/jmv.23208] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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12
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Luo B, Tang X, Jia Y, Wang Y, Chao Y, Zhao C. Sequence variation of Epstein-Barr virus (EBV) BZLF1 gene in EBV-associated gastric carcinomas and nasopharyngeal carcinomas in Northern China. Microbes Infect 2011; 13:776-82. [DOI: 10.1016/j.micinf.2011.04.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2010] [Revised: 03/19/2011] [Accepted: 04/06/2011] [Indexed: 12/23/2022]
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13
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Epstein-Barr virus Zta-induced immunomodulators from nasopharyngeal carcinoma cells upregulate interleukin-10 production from monocytes. J Virol 2011; 85:7333-42. [PMID: 21543473 DOI: 10.1128/jvi.00182-11] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
During lytic infection with Epstein-Barr virus (EBV), several viral lytic proteins function to evade immune recognition or to actively suppress immune cells. An EBV lytic transactivator, Zta, induces an immunosuppressive cytokine interleukin 10 (IL-10) in B cells, but whether it regulates IL-10 in the context of epithelial cells is unclear. In this study, we tested nasopharyngeal carcinoma (NPC) cell lines and found that Zta did not induce IL-10 in these epithelial cells. Interestingly, the conditioned medium of Zta-expressing NPC cells enhanced IL-10 production from monocytes. We further revealed that the IL-10-inducing effect involved at least two immunomodulators that were upregulated by Zta and secreted from NPC cells: granulocyte-macrophage colony-stimulating factor (GM-CSF) and prostaglandin E(2) (PGE(2)). Zta was recruited to and activated the GM-CSF promoter, thus upregulating GM-CSF expression. Zta also activated the promoter of cyclooxygenase-2 (COX-2), and Zta-induced COX-2 increased downstream PGE(2) production. Cotreatment with GM-CSF and PGE(2) synergistically induced IL-10 production from monocytes. The IL-10-inducing effect of the Zta-conditioned medium was reduced when GM-CSF or the COX-2/PGE(2) pathway was blocked. The conditioned medium of NPC cells with EBV lytic infection showed a similar increase of GM-CSF and PGE(2) levels as well as the IL-10-inducing effect on monocytes, and knockdown of Zta abolished all the effects. Therefore, through Zta-induced immunomodulators, EBV lytic infection in NPC cells can direct bystander monocytes to produce IL-10, which may be a novel way of EBV to promote local immunosuppression.
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14
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McDonald C, Karstegl CE, Kellam P, Farrell PJ. Regulation of the Epstein-Barr virus Zp promoter in B lymphocytes during reactivation from latency. J Gen Virol 2009; 91:622-9. [DOI: 10.1099/vir.0.017277-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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15
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Katsumura KR, Maruo S, Wu Y, Kanda T, Takada K. Quantitative evaluation of the role of Epstein-Barr virus immediate-early protein BZLF1 in B-cell transformation. J Gen Virol 2009; 90:2331-2341. [PMID: 19553389 DOI: 10.1099/vir.0.012831-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The Epstein-Barr virus (EBV) immediate-early transactivator BZLF1 plays a key role in switching EBV infection from the latent to the lytic form by stimulating the expression cascade of lytic genes; it also regulates the expression of several cellular genes. Recently, we reported that BZLF1 is expressed in primary human B cells early after EBV infection. To investigate whether this BZLF1 expression early after infection plays a role in the EBV-induced growth transformation of primary B cells, we generated BZLF1-knockout EBV and quantitatively evaluated its transforming ability compared with that of wild-type EBV. We found that the 50% transforming dose of BZLF1-knockout EBV was quite similar to that of wild-type EBV. Established lymphoblastoid cell lines (LCLs) harbouring BZLF1-knockout EBV were indistinguishable from LCLs harbouring wild-type EBV in their pattern of latent gene expression and in their growth in vitro. Furthermore, the copy numbers of EBV episomes were very similar in the LCLs harbouring BZLF1-knockout EBV and in those harbouring wild-type EBV. These data indicate that disrupting BZLF1 expression in the context of the EBV genome, and the resultant inability to enter lytic replication, have little impact on the growth of LCLs and the steady-state copy number of EBV episomes in established LCLs.
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Affiliation(s)
- Koichi Ricardo Katsumura
- Department of Tumor Virology, Institute for Genetic Medicine, Hokkaido University, Sapporo 060-0815, Japan
| | - Seiji Maruo
- Department of Tumor Virology, Institute for Genetic Medicine, Hokkaido University, Sapporo 060-0815, Japan
| | - Yi Wu
- Department of Tumor Virology, Institute for Genetic Medicine, Hokkaido University, Sapporo 060-0815, Japan
| | - Teru Kanda
- Research Center for Infection-Associated Cancer, Institute for Genetic Medicine, Hokkaido University, Sapporo 060-0815, Japan
| | - Kenzo Takada
- Department of Tumor Virology, Institute for Genetic Medicine, Hokkaido University, Sapporo 060-0815, Japan
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16
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Park R, Heston L, Shedd D, Delecluse HJ, Miller G. Mutations of amino acids in the DNA-recognition domain of Epstein-Barr virus ZEBRA protein alter its sub-nuclear localization and affect formation of replication compartments. Virology 2008; 382:145-62. [PMID: 18937960 DOI: 10.1016/j.virol.2008.09.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2008] [Revised: 07/31/2008] [Accepted: 09/08/2008] [Indexed: 11/18/2022]
Abstract
ZEBRA, a transcription factor and DNA replication protein encoded by the Epstein-Barr virus (EBV) BZLF1 gene, plays indispensable roles in the EBV lytic cycle. We recently described the phenotypes of 46 single amino acid substitutions introduced into the DNA-recognition region of ZEBRA [Heston, L., El-Guindy, A., Countryman, J., Dela Cruz, C., Delecluse, H.J., and Miller, G. 2006]. The 27 DNA-binding-proficient mutants exhibited distinct defects in their ability to activate expression of the kinetic classes of viral genes. Four phenotypic variants could be discerned: wild-type, defective at activating Rta, defective at activating early genes, and defective at activating late genes. Here we analyze the distribution of ZEBRA within the nucleus and the localization of EA-D (the viral DNA polymerase processivity factor), an indicator of the development of replication compartments, in representatives of each phenotypic group. Plasmids encoding wild-type (WT) and mutant ZEBRA were transfected into 293 cells containing EBV-bacmids. WT ZEBRA protein was diffusely and smoothly distributed throughout the nucleus, sparing nucleoli, and partially recruited to globular replication compartments. EA-D induced by WT ZEBRA was present diffusely in some cells and concentrated in globular replication compartments in other cells. The distribution of ZEBRA and EA-D proteins was identical to WT following transfection of K188R, a mutant with a conservative change. The distribution of S186A mutant ZEBRA protein, defective for activation of Rta and EA-D, was identical to WT, except that the mutant ZEBRA was never found in globular compartments. Co-expression of Rta with S186A mutant rescued diffuse EA-D but not globular replication compartments. The most striking observation was that several mutant ZEBRA proteins defective in activating EA-D (R179A, K181A and A185V) and defective in activating lytic viral DNA replication and late genes (Y180E and K188A) were localized to numerous punctate foci. The speckled appearance of R179A and Y180E was more regular and clearly defined in EBV-positive than in EBV-negative 293 cells. The Y180E late-mutant induced EA-D, but prevented EA-D from localizing to globular replication compartments. These results show that individual amino acids within the basic domain influence localization of the ZEBRA protein and its capacity to induce EA-D to become located in mature viral replication compartments. Furthermore, these mutant ZEBRA proteins delineate several stages in the processes of nuclear re-organization which accompany lytic EBV replication.
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Affiliation(s)
- Richard Park
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06520, USA
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17
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Epstein-Barr virus lytic transactivator Zta enhances chemotactic activity through induction of interleukin-8 in nasopharyngeal carcinoma cells. J Virol 2008; 82:3679-88. [PMID: 18234802 DOI: 10.1128/jvi.02301-07] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Epstein-Barr virus (EBV)-associated, undifferentiated type of nasopharyngeal carcinoma (NPC) is characterized by intensive leukocyte infiltration. Interaction between the infiltrating cells and the tumor cells has been considered crucial for NPC development. Recruitment of the infiltrates can be directed by certain chemokines present in the NPC tissues. It is unknown whether and how EBV lytic infection regulates expression of the chemokines. Using an antibody array, we first found that several chemokines secreted from EBV-infected NPC cells are increased upon EBV reactivation into the lytic cycle, and interleukin-8 (IL-8) is the chemokine upregulated most significantly and consistently. Further studies showed that the EBV lytic transactivator Zta is a potent inducer of IL-8 in NPC cells, augmenting secreted and intracellular IL-8 proteins, as well as IL-8 RNA. Zta upregulates Egr-1, a cellular transcription factor that has been involved in upregulation of IL-8, but the Zta-induced IL-8 expression is independent of Egr-1. The ability of Zta to transactivate the IL-8 promoter is important for the induction of IL-8, and we have identified two Zta-responsive elements in the promoter. Zta can bind to these two elements in vitro and can also be recruited to the IL-8 promoter in vivo. DNA-binding-defective Zta mutants can neither activate the IL-8 promoter nor induce IL-8 production. In addition, Zta-expressing NPC cells exert enhanced chemotactic activity that is mainly mediated by IL-8. Since IL-8 may contribute to not only leukocyte infiltration but also multiple oncogenic processes, the present study provides a potential link between EBV lytic infection and pathogenesis of NPC.
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18
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Asai R, Kato A, Kato K, Kanamori-Koyama M, Sugimoto K, Sairenji T, Nishiyama Y, Kawaguchi Y. Epstein-Barr virus protein kinase BGLF4 is a virion tegument protein that dissociates from virions in a phosphorylation-dependent process and phosphorylates the viral immediate-early protein BZLF1. J Virol 2007; 80:5125-34. [PMID: 16698993 PMCID: PMC1472150 DOI: 10.1128/jvi.02674-05] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Epstein-Barr virus (EBV) BGLF4 is a viral protein kinase that is expressed in the lytic phase of infection and is packaged in virions. We report here that BGLF4 is a tegument protein that dissociates from the virion in a phosphorylation-dependent process. We also present evidence that BGLF4 interacts with and phosphorylates BZLF1, a key viral regulator of lytic infection. These conclusions are based on the following observations. (i) In in vitro tegument release assays, a significant fraction of BGLF4 was released from virions in the presence of physiological NaCl concentrations. (ii) Addition of physiological concentrations of ATP and MgCl(2) to virions enhanced BGLF4 release, but phosphatase treatment of virions significantly reduced BGLF4 release. (iii) A recombinant protein containing a domain of BZLF1 was specifically phosphorylated by purified recombinant BGLF4 in vitro, and BGLF4 altered BZLF1 posttranslational modification in vivo. (iv) BZLF1 was specifically coimmunoprecipitated with BGLF4 in 12-O-tetradecanoylphorbol-13-acetate-treated B95-8 cells and in COS-1 cells transiently expressing both of these viral proteins. (v) BGLF4 and BZLF1 were colocalized in intranuclear globular structures, resembling the viral replication compartment, in Akata cells treated with anti-human immunoglobulin G. Our results suggest that BGLF4 functions not only in lytically infected cells by phosphorylating viral and cellular targets but also immediately after viral penetration like other herpesvirus tegument proteins.
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Affiliation(s)
- Risa Asai
- Division of Viral Infection, Department of Infectious Disease Control, International Research Center for Infectious Diseases, The Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
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19
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Heston L, El-Guindy A, Countryman J, Dela Cruz C, Delecluse HJ, Miller G. Amino acids in the basic domain of Epstein-Barr virus ZEBRA protein play distinct roles in DNA binding, activation of early lytic gene expression, and promotion of viral DNA replication. J Virol 2006; 80:9115-33. [PMID: 16940523 PMCID: PMC1563939 DOI: 10.1128/jvi.00909-06] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The ZEBRA protein of Epstein-Barr virus (EBV) drives the viral lytic cycle cascade. The capacity of ZEBRA to recognize specific DNA sequences resides in amino acids 178 to 194, a region in which 9 of 17 residues are either lysine or arginine. To define the basic domain residues essential for activity, a series of 46 single-amino-acid-substitution mutants were examined for their ability to bind ZIIIB DNA, a high-affinity ZEBRA binding site, and for their capacity to activate early and late EBV lytic cycle gene expression. DNA binding was obligatory for the protein to activate the lytic cascade. Nineteen mutants that failed to bind DNA were unable to disrupt latency. A single acidic replacement of a basic amino acid destroyed DNA binding and the biologic activity of the protein. Four mutants that bound weakly to DNA were defective at stimulating the expression of Rta, the essential first target of ZEBRA in lytic cycle activation. Four amino acids, R183, A185, C189, and R190, are likely to contact ZIIIB DNA specifically, since alanine or valine substitutions at these positions drastically weakened or eliminated DNA binding. Twenty-three mutants were proficient in binding to ZIIIB DNA. Some DNA binding-proficient mutants were refractory to supershift by BZ-1 monoclonal antibody (epitope amino acids 214 to 230), likely as the result of the increased solubility of the mutants. Mutants competent to bind DNA could be separated into four functional groups: the wild-type group (eight mutants), a group defective at activating Rta (five mutants, all with mutations at the S186 site), a group defective at activating EA-D (three mutants with the R179A, S186T, and K192A mutations), and a group specifically defective at activating late gene expression (seven mutants). Three late mutants, with a Y180A, Y180E, or K188A mutation, were defective at stimulating EBV DNA replication. This catalogue of point mutants reveals that basic domain amino acids play distinct functions in binding to DNA, in activating Rta, in stimulating early lytic gene expression, and in promoting viral DNA replication and viral late gene expression. These results are discussed in relationship to the recently solved crystal structure of ZEBRA bound to an AP-1 site.
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Affiliation(s)
- Lee Heston
- Department of Pediatrics, Yale University School of Medicine, New Haven, CT 06520, USA
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20
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El-Guindy AS, Paek SY, Countryman J, Miller G. Identification of constitutive phosphorylation sites on the Epstein-Barr virus ZEBRA protein. J Biol Chem 2005; 281:3085-95. [PMID: 16321978 DOI: 10.1074/jbc.m506076200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ZEBRA, the product of the Epstein-Barr virus gene bzlf1, and a member of the AP-1 subfamily of basic zipper (bZIP) transcription factors, is necessary and sufficient to disrupt viral latency and to initiate the viral lytic cycle. Two serine residues of ZEBRA, Ser167 and Ser173, are substrates for casein kinase 2 (CK2) and are constitutively phosphorylated in vivo. Phosphorylation of ZEBRA at its CK2 sites is required for proper temporal regulation of viral gene expression. Phosphopeptide analysis indicated that ZEBRA contains additional constitutive phosphorylation sites. Here we employed a co-migration strategy to map these sites in vivo. The cornerstone of this strategy was to correlate the migration of 32P- and 35S-labeled tryptic peptides of ZEBRA. The identity of the peptides was revealed by mutagenesis of methionine and cysteine residues present in each peptide. Phosphorylation sites within the peptide were identified by mutagenesis of serines and threonines. ZEBRA was shown to be phosphorylated at serine and threonine residues, but not tyrosine. Two previously unrecognized phosphorylation sites of ZEBRA were identified in the NH2-terminal region of the transactivation domain: a cluster of weak phosphorylation sites at Ser6, Thr7, and Ser8 and a strong phosphorylation site at Thr14. Thr14 was embedded in a MAP kinase consensus sequence and could be phosphorylated in vitro by JNK, despite the absence of a canonical JNK docking site. Thus ZEBRA is now known to be constitutively phosphorylated at three distinct sites.
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Affiliation(s)
- Ayman S El-Guindy
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, Connecticut 06520, USA
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21
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Bowling BL, Adamson AL. Functional interactions between the Epstein-Barr virus BZLF1 protein and the promyelocytic leukemia protein. Virus Res 2005; 117:244-53. [PMID: 16307818 DOI: 10.1016/j.virusres.2005.10.018] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2005] [Revised: 10/25/2005] [Accepted: 10/25/2005] [Indexed: 12/15/2022]
Abstract
The Epstein-Barr virus immediate-early protein BZLF1 (Z) has been shown to alter the cellular localization of the promyelocytic leukemia (PML) protein. PML has important implications for growth control, apoptosis, anti-viral effects and many more processes. Here we further examined the relationship between PML and the Epstein-Barr virus Z protein. We examined the effect of Z expression on PML protein levels, and the effect of increased PML protein levels on Z-mediated dispersion of PML bodies. We found that increased levels of PML protein, such as through interferon treatment, were able to suppress Z-mediated PML body dispersion. We also studied the consequences of PML dispersion by Z, by examining p21 transactivation, A20 transactivation, and MHC Class I presentation levels in Z-expressing cells. We found that, while Z-mediated dispersion of PML did not affect MHC Class I presentation, it did alter p21 and A20 expression. In addition, we found that increased levels of PML were able to prevent Z protein binding to mitotic chromosomes. Our work implies that the balance of PML and Z levels in cells may affect how each protein functions.
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Affiliation(s)
- Brandy L Bowling
- Department of Biology, University of North Carolina at Greensboro, Greensboro, NC 27402, USA
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22
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Abstract
Epstein-Barr virus (EBV) is a human herpesvirus that causes infectious mononucleosis and is associated with several types of cancers, including nasopharyngeal carcinoma and Burkitt's lymphoma. An EBV protein that plays an integral role during lytic replication is the immediate-early protein BZLF1. Our laboratory has found that BZLF1 (Z) localizes to host chromosomes during mitosis. Two Z-interacting proteins are also found localized to mitotic chromosomes in the presence of Z. The association between Z and mitotic chromosomes may lead to the sequestering of Z-interacting proteins within the cell and potentially cause an alteration of chromosome compaction or chromatin structure.
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Affiliation(s)
- Amy L Adamson
- Department of Biology, University of North Carolina at Greensboro, Greensboro, NC 27402, USA.
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23
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Morrison TE, Kenney SC. BZLF1, an Epstein-Barr virus immediate-early protein, induces p65 nuclear translocation while inhibiting p65 transcriptional function. Virology 2004; 328:219-32. [PMID: 15464842 DOI: 10.1016/j.virol.2004.07.020] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2004] [Revised: 05/27/2004] [Accepted: 07/14/2004] [Indexed: 10/26/2022]
Abstract
We have previously demonstrated that the Epstein-Barr virus immediate-early BZLF1 protein interacts with, and is inhibited by, the NF-kappaB family member p65. However, the effects of BZLF1 on NF-kappaB activity have not been intensively studied. Here we show that BZLF1 inhibits p65-dependent gene expression. BZLF1 inhibited the ability of IL-1, as well as transfected p65, to activate the expression of two different NF-kappaB-responsive genes, ICAM-1 and IkappaB-alpha. BZLF1 also reduced the constitutive level of IkappaB-alpha protein in HeLa and A549 cells, and increased the amount of nuclear NF-kappaB to a similar extent as tumor necrosis factor-alpha (TNF-alpha) treatment. In spite of this BZLF1-associated increase in the nuclear form of NF-kappaB, BZLF1 did not induce binding of NF-kappaB to NF-kappaB responsive promoters (as determined by chromatin immunoprecipitation assay) in vivo, although TNF-alpha treatment induced NF-kappaB binding as expected. Overexpression of p65 dramatically inhibited the lytic replication cycle of EBV in 293-EBV cells, confirming that NF-kappaB also inhibits BZLF1 transcriptional function. Our results are consistent with a model in which BZLF1 inhibits the transcriptional function of p65, resulting in decreased transcription of IkappaB-alpha, decreased expression of IkappaB-alpha protein, and subsequent translocation of NF-kappaB to the nucleus. This nuclear translocation of NF-kappaB may promote viral latency by negatively regulating BZLF1 transcriptional activity. In situations where p65 activity is limiting in comparison to BZLF1, the ability of BZLF1 to inhibit p65 transcriptional function may protect the virus from the host immune system during the lytic form of infection.
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Affiliation(s)
- Thomas E Morrison
- Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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24
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Yin Q, Jupiter K, Flemington EK. The Epstein–Barr virus transactivator Zta binds to its own promoter and is required for full promoter activity during anti-Ig- and TGF-beta1-mediated reactivation. Virology 2004; 327:134-43. [PMID: 15327904 DOI: 10.1016/j.virol.2004.06.026] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2004] [Revised: 05/27/2004] [Accepted: 06/14/2004] [Indexed: 12/01/2022]
Abstract
Transcription of the immediate early gene BZLF1 is mediated initially through the activation of cellular transcription factors. Reporter-based studies have provided evidence that following this initial activation, the BZLF1 gene product Zta may be involved in an autoactivation loop through binding to its promoter Zp. In contrast, other reports have shown that transfection of a Zta expression vector in latently infected cells does not activate endogenous Zp. Using chromatin immunoprecipitation (ChIP) assays, we show here that Zta binds to endogenous Zp following induction of the lytic cycle by anti-Ig and TGF-beta1 and that binding occurs early enough to play a role in the activation of Zp. We have also generated a dominant-negative Zta and shown that it inhibits activation of endogenous Zp. These data support a two-step model for Zp activation during reactivation involving initial activation by cellular factors followed by an autoactivation step.
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Affiliation(s)
- Qinyan Yin
- Tulane Cancer Center, Tulane Health Sciences Center, New Orleans, LA 70112, USA
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25
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Deng Z, Chen CJ, Chamberlin M, Lu F, Blobel GA, Speicher D, Cirillo LA, Zaret KS, Lieberman PM. The CBP bromodomain and nucleosome targeting are required for Zta-directed nucleosome acetylation and transcription activation. Mol Cell Biol 2003; 23:2633-44. [PMID: 12665567 PMCID: PMC152567 DOI: 10.1128/mcb.23.8.2633-2644.2003] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2002] [Accepted: 01/13/2003] [Indexed: 11/20/2022] Open
Abstract
The Epstein-Barr virus (EBV)-encoded lytic activator Zta is a bZIP protein that can stimulate nucleosomal histone acetyltransferase (HAT) activity of the CREB binding protein (CBP) in vitro. We now show that deletion of the CBP bromo- and C/H3 domains eliminates stimulation of nucleosomal HAT activity in vitro and transcriptional coactivation by Zta in transfected cells. In contrast, acetylation of free histones was not affected by the addition of Zta or by deletions in the bromo or C/H3 domain of CBP. Zta stimulated acetylation of oligonucleosomes assembled on supercoiled DNA and dinucleosomes assembled on linear DNA, but Zta-stimulated acetylation was significantly reduced for mononucleosomes. Western blotting and amino-terminal protein sequencing indicated that all lysine residues in the H3 and H4 amino-terminal tails were acetylated by CBP and enhanced by the addition of Zta. Histone acetylation was also dependent upon the Zta basic DNA binding domain, which could not be substituted with the homologous basic region of c-Fos, indicating specificity in the bZIP domain nucleosome binding function. Finally, we show that Zta and CBP colocalize to viral immediate-early promoters in vivo and that overexpression of Zta leads to a robust increase in H3 and H4 acetylation at various regions of the EBV genome in vivo. Furthermore, deletion of the CBP bromodomain reduced stable CBP-Zta complex formation and histone acetylation at Zta-responsive viral promoters in vivo. These results suggest that activator- and bromodomain-dependent targeting to oligonucleosomal chromatin is required for stable promoter-bound complex formation and transcription activity.
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Affiliation(s)
- Zhong Deng
- The Wistar Institute, Philadelphia, Pennsylvania 19104, USA
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26
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Liao W, Tang Y, Lin SF, Kung HJ, Giam CZ. K-bZIP of Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8 (KSHV/HHV-8) binds KSHV/HHV-8 Rta and represses Rta-mediated transactivation. J Virol 2003; 77:3809-15. [PMID: 12610155 PMCID: PMC149497 DOI: 10.1128/jvi.77.6.3809-3815.2003] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The regulatory circuit for Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8 (KSHV/HHV-8) gene expression bears resemblance to that of Epstein-Barr virus (EBV), but with interesting differences. Based on protein sequence similarities and synteny to their EBV counterparts, two KSHV/HHV-8 viral regulatory factors, HHV-8 Rta and K-bZIP, encoded by open reading frame (ORF) 50 and ORF K8, respectively, have been identified. Rta is an immediate early transcriptional activator that activates lytic viral replication and mediates viral reactivation from latency, while ORF K8 is an early gene activated by Rta. Extensive splicing of ORF K8 mRNA leads to the production of K-bZIP, a protein of the basic domain-leucine zipper (bZIP) family. The role of K-bZIP in viral replication, however, remains unresolved. Here, we report that K-bZIP is a nuclear protein that binds Rta directly both in vivo and in vitro and represses Rta-mediated transactivation of the K-bZIP promoter. We further demonstrate that the leucine zipper domain of K-bZIP is required for Rta binding and a K-bZIP mutant lacking the leucine zipper does not repress Rta activity. Finally, the K-bZIP-mediated repression of Rta transactivation cannot be restored by overexpression of the transcriptional coactivator p300 or the p300-CBP-associated factor, P/CAF. Our results suggest that K-bZIP is involved in a feedback circuit to turn off its own expression and possibly the expression of other early genes activated by Rta.
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Affiliation(s)
- Wei Liao
- Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814, USA
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27
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Mauser A, Holley-Guthrie E, Zanation A, Yarborough W, Kaufmann W, Klingelhutz A, Seaman WT, Kenney S. The Epstein-Barr virus immediate-early protein BZLF1 induces expression of E2F-1 and other proteins involved in cell cycle progression in primary keratinocytes and gastric carcinoma cells. J Virol 2002; 76:12543-52. [PMID: 12438580 PMCID: PMC136734 DOI: 10.1128/jvi.76.24.12543-12552.2002] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Epstein-Barr virus (EBV) immediate-early protein BZLF1 mediates the switch between the latent and lytic forms of EBV infection and has been previously shown to induce a G(1)/S block in cell cycle progression in some cell types. To examine the effect of BZLF1 on cellular gene expression, we performed microarray analysis on telomerase-immortalized human keratinocytes that were mock infected or infected with a control adenovirus vector (AdLacZ) or a vector expressing the EBV BZLF1 protein (AdBZLF1). Cellular genes activated by BZLF1 expression included E2F-1, cyclin E, Cdc25A, and a number of other genes involved in cell cycle progression. Immunoblot analysis confirmed that BZLF1 induced expression of E2F-1, cyclin E, Cdc25A, and stem loop binding protein (a protein known to be primarily expressed during S phase) in telomerase-immortalized keratinocytes. Similarly, BZLF1 increased expression of E2F-1, cyclin E, and stem loop binding protein (SLBP) in primary tonsil keratinocytes. In contrast, BZLF1 did not induce E2F-1 expression in normal human fibroblasts. Cell cycle analysis revealed that while BZLF1 dramatically blocked G(1)/S progression in normal human fibroblasts, it did not significantly affect cell cycle progression in primary human tonsil keratinocytes. Furthermore, in EBV-infected gastric carcinoma cells, the BZLF1-positive cells had an increased number of cells in S phase compared to the BZLF1-negative cells. Thus, in certain cell types (but not others), BZLF1 enhances expression of cellular proteins associated with cell cycle progression, which suggests that an S-phase-like environment may be advantageous for efficient lytic EBV replication in some cell types.
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Affiliation(s)
- Amy Mauser
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7295, USA
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28
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Mauser A, Saito S, Appella E, Anderson CW, Seaman WT, Kenney S. The Epstein-Barr virus immediate-early protein BZLF1 regulates p53 function through multiple mechanisms. J Virol 2002; 76:12503-12. [PMID: 12438576 PMCID: PMC136659 DOI: 10.1128/jvi.76.24.12503-12512.2002] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The Epstein-Barr virus (EBV) immediate-early protein BZLF1 is a transcriptional activator that mediates the switch between the latent and the lytic forms of EBV infection. It was previously reported that BZLF1 inhibits p53 transcriptional function in reporter gene assays. Here we further examined the effects of BZLF1 on p53 function by using a BZLF1-expressing adenovirus vector (AdBZLF1). Infection of cells with the AdBZLF1 vector increased the level of cellular p53 but prevented the induction of p53-dependent cellular target genes, such as p21 and MDM2. BZLF1-expressing cells had increased p53-specific DNA binding activity in electrophoretic mobility shift assays, increased p53 phosphorylation at multiple residues (including serines 6, 9, 15, 33, 46, 315, and 392), and increased acetylation at lysine 320 and lysine 382. Thus, the inhibitory effects of BZLF1 on p53 transcriptional function cannot be explained by its effects on p53 phosphorylation, acetylation, or DNA binding activity. BZLF1 substantially reduced the level of cellular TATA binding protein (TBP) in both normal human fibroblasts and A549 cells, and the inhibitory effects of BZLF1 on p53 transcriptional function could be partially rescued by the overexpression of TBP. Thus, BZLF1 has numerous effects on p53 posttranslational modification but may inhibit p53 transcriptional function in part through an indirect mechanism involving the suppression of TBP expression.
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Affiliation(s)
- Amy Mauser
- Department of Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599, USA
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29
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Deng Z, Chen CJ, Zerby D, Delecluse HJ, Lieberman PM. Identification of acidic and aromatic residues in the Zta activation domain essential for Epstein-Barr virus reactivation. J Virol 2001; 75:10334-47. [PMID: 11581402 PMCID: PMC114608 DOI: 10.1128/jvi.75.21.10334-10347.2001] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Epstein-Barr virus (EBV) lytic cycle transcription and DNA replication require the transcriptional activation function of the viral immediate-early protein Zta. We describe a series of alanine substitution mutations in the Zta activation domain that reveal two functional motifs based on amino acid composition. Alanine substitution of single or paired hydrophobic aromatic amino acid residues resulted in modest transcription activation defects, while combining four substitutions of aromatic residues (F22/F26/W74/F75) led to more severe transcription defects. Substitution of acidic amino acid residue E27, D35, or E54 caused severe transcription defects on most viral promoters. Promoter- and cell-specific defects were observed for some substitution mutants. Aromatic residues were required for Zta interaction with TFIIA-TFIID and the CREB-binding protein (CBP) and for stimulation of CBP histone acetyltransferase activity in vitro. In contrast, acidic amino acid substitution mutants interacted with TFIIA-TFIID and CBP indistinguishably from the wild type. The nuclear domain 10 (ND10) protein SP100 was dispersed by most Zta mutants, but acidic residue mutations led to reduced, while aromatic substitution mutants led to increased SP100 nuclear staining. Acidic residue substitution mutants had more pronounced defects in transcription activation of endogenous viral genes in latently infected cells and for viral replication, as measured by the production of infectious virus. One mutant, K12/F13, was incapable of stimulating EBV lytic replication but had only modest transcription defects. These results indicate that Zta stimulates viral reactivation through two nonredundant structural motifs, one of which interacts with general transcription factors and coactivators, and the other has an essential but as yet not understood function in lytic transcription.
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Affiliation(s)
- Z Deng
- The Wistar Institute, Philadelphia, Pennsylvania 19104, USA
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30
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Morrison TE, Mauser A, Wong A, Ting JP, Kenney SC. Inhibition of IFN-gamma signaling by an Epstein-Barr virus immediate-early protein. Immunity 2001; 15:787-99. [PMID: 11728340 DOI: 10.1016/s1074-7613(01)00226-6] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Viruses have evolved elaborate mechanisms to target many aspects of the host's immune response. The cytokine IFN-gamma plays a central role in resistance of the host to infection via direct antiviral effects as well as modulation of the immune response. In this study, we demonstrate that the Epstein-Barr virus (EBV) immediate-early protein, BZLF1, inhibits the IFN-gamma signaling pathway. BZLF1 decreases the ability of IFN-gamma to activate a variety of important downstream target genes, such as IRF-1, p48, and CIITA, and prevents IFN-gamma-induced class II MHC surface expression. Additionally, BZLF1 inhibits IFN-gamma-induced STAT1 tyrosine phosphorylation and nuclear translocation. Finally, we demonstrate that BZLF1 decreases expression of the IFN-gamma receptor, suggesting a mechanism by which EBV may escape antiviral immune responses during primary infection.
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Affiliation(s)
- T E Morrison
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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31
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Darr CD, Mauser A, Kenney S. Epstein-Barr virus immediate-early protein BRLF1 induces the lytic form of viral replication through a mechanism involving phosphatidylinositol-3 kinase activation. J Virol 2001; 75:6135-42. [PMID: 11390615 PMCID: PMC114329 DOI: 10.1128/jvi.75.13.6135-6142.2001] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Expression of the Epstein-Barr virus (EBV) immediate-early (IE) protein BRLF1 induces the lytic form of viral replication in most EBV-positive cell lines. BRLF1 is a transcriptional activator that binds directly to a GC-rich motif present in some EBV lytic gene promoters. However, BRLF1 activates transcription of the other IE protein, BZLF1, through an indirect mechanism which we previously showed to require activation of the stress mitogen-activated protein kinases. Here we demonstrate that BRLF1 activates phosphatidylinositol-3 (PI3) kinase signaling in host cells. We show that the specific PI3 kinase inhibitor, LY294002, completely abrogates the ability of a BRLF1 adenovirus vector to induce the lytic form of EBV infection, while not affecting lytic infection induced by a BZLF1 adenovirus vector. Furthermore, we demonstrate that the requirement for PI3 kinase activation in BRLF1-induced transcriptional activation is promoter dependent. BRLF1 activation of the SM early promoter (which occurs through a direct binding mechanism) does not require PI3 kinase activation, whereas activation of the IE BZLF1 and early BMRF1 promoters requires PI3 kinase activation. Thus, there are clearly two separate mechanisms by which BRLF1 induces transcriptional activation.
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Affiliation(s)
- C D Darr
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7295, USA
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32
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Adamson AL, Kenney S. Epstein-barr virus immediate-early protein BZLF1 is SUMO-1 modified and disrupts promyelocytic leukemia bodies. J Virol 2001; 75:2388-99. [PMID: 11160742 PMCID: PMC114822 DOI: 10.1128/jvi.75.5.2388-2399.2001] [Citation(s) in RCA: 196] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
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.
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Affiliation(s)
- A L Adamson
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295, USA
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33
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Lu J, Chen SY, Chua HH, Liu YS, Huang YT, Chang Y, Chen JY, Sheen TS, Tsai CH. Upregulation of tyrosine kinase TKT by the Epstein-Barr virus transactivator Zta. J Virol 2000; 74:7391-9. [PMID: 10906192 PMCID: PMC112259 DOI: 10.1128/jvi.74.16.7391-7399.2000] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The Zta protein is a key transactivator involved in initiating the Epstein-Barr virus (EBV) lytic cascade. In addition to transactivating many viral genes, Zta has the capacity to influence host cellular signals by binding to promoter regions or by interacting with several important cellular factors. Based on the observation that tyrosine kinases play central roles in determining the fate of cells, a kinase display assay was used to investigate whether cells expressing Zta have an altered pattern of kinase expression. The assay revealed that TRK-related tyrosine kinase (TKT) is expressed at significant levels in Zta transfectants but not in control cells. Additional evidence was obtained from Northern and Western blotting. Importantly, the upregulation of phosphorylated TKT and TKT downstream effector matrix metalloproteinase 1 in Zta transfectants hinted that TKT might initiate a signaling cascade in Zta-expressing cells. In addition, deletion analysis of the Zta protein revealed that the transactivation and dimerization domains were both essential for the upregulation of TKT transcription. Moreover, correlation of expression levels of Zta and TKT transcripts in nasopharyngeal carcinoma biopsy specimens was clearly demonstrated by quantitative PCR (Q-PCR), which provides the first evidence for an effect of Zta on cellular gene expression in vivo. These findings offer insight into the virus-cell interactions and may help us elucidate the role of EBV in tumorigenesis.
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Affiliation(s)
- J Lu
- Graduate Institute of Microbiology, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan, Republic of China
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34
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Baumann M, Gires O, Kolch W, Mischak H, Zeidler R, Pich D, Hammerschmidt W. The PKC targeting protein RACK1 interacts with the Epstein-Barr virus activator protein BZLF1. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:3891-901. [PMID: 10849009 DOI: 10.1046/j.1432-1327.2000.01430.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Phorbol esters reactivate Epstein-Barr virus (EBV) from latently infected cells via transcriptional activation of the viral immediate-early gene BZLF1. BZLF1 is a member of the extended AP-1 family of transcription factors that binds to specific BZLF1-binding motifs within early EBV promoters and to consensus AP-1 sites. Regulation of BZLF1's activity is achieved at the transcriptional level as well as through post-translational modifications. Recently, we reported that the transcriptional activity of BZLF1 is augmented by TPA [Baumann, M., Mischak, H., Dammeier, S., Kolch, W., Gires, O., Pich, D., Zeidler, R., Delecluse, H. J. & Hammerschmidt, W., (1998) J. Virol. 72, 8105-8114]. The increase of BZLF1's activity depends on a single serine residue (S186) that is phosphorylated by protein kinase C (PKC) in vitro and in vivo after stimulation with 12-O-tetradecanoylphorbol-13-acetate (TPA). Here, we identified RACK1 as a binding partner of BZLF1 in a yeast interaction trap assay. RACK stands for receptor of activated C-kinase and is involved in targeting activated PKCs and other signaling proteins. In vivo, RACK1 binds directly to the transactivation domain of BZLF1. Although a functional relationship between BZLF1 and PKC could be mediated by RACKs, RACK1 did not have a detectable effect on the phosphorylation status of BZLF1 in in vitro or in vivo phosphorylation assays. We suggest that RACK1 may act as a scaffolding protein on BZLF1 independently of activated PKCs.
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Affiliation(s)
- M Baumann
- GSF-National Research Center for Environment and Health, Institute of Clinical Molecular Biology and Tumor Genetics, Department of Gene Vectors, München, Germany
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35
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Rodriguez A, Armstrong M, Dwyer D, Flemington E. Genetic dissection of cell growth arrest functions mediated by the Epstein-Barr virus lytic gene product, Zta. J Virol 1999; 73:9029-38. [PMID: 10516009 PMCID: PMC112935 DOI: 10.1128/jvi.73.11.9029-9038.1999] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Expression of the Epstein-Barr virus (EBV) latency-associated genes activates cell cycle progression and drives immortalization of the infected cell. In contrast, progression of the EBV replication program occurs most efficiently in growth-arrested cells. Previous studies showed that the EBV-encoded immediate-early transcription factor, Zta, can induce expression of the cyclin-dependent kinase inhibitors, p21 and p27, the tumor suppressor, p53, and cell growth arrest. Moreover, Zta-mediated induction of growth arrest occurs independently of its transcriptional transactivation function. Here we show that substitution of Zta's basic DNA binding domain with the analogous region of the Zta homologue, c-Fos, abrogates Zta's ability to induce growth arrest and to induce p21, p27, or p53 expression, suggesting that protein-protein interactions between this region of Zta and key cell cycle control proteins are involved in signaling cell cycle arrest. We also show that despite the crucial role for Zta's basic domain in eliciting cell growth arrest, its amino terminus is required for efficient induction of p27 and it modulates the level of p53 induction. Last, we provide evidence that Zta-mediated inductions of p21, p27, and p53 occur, at least in part, through distinct pathways. Therefore, Zta interacts with multiple growth arrest pathways, a property which may have evolved partly as a means to ensure that lytic replication occurs in a growth-arrested setting in multiple different tissues in various states of differentiation.
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Affiliation(s)
- A Rodriguez
- Harvard University, Boston, Massachusetts 02115, USA
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36
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Seaman WT, Ye D, Wang RX, Hale EE, Weisse M, Quinlivan EB. Gene expression from the ORF50/K8 region of Kaposi's sarcoma-associated herpesvirus. Virology 1999; 263:436-49. [PMID: 10544116 DOI: 10.1006/viro.1999.9963] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The ORF50 gene of Kaposi's sarcoma (KS)-associated herpesvirus, or human herpesvirus 8 (KSHV), activates viral replication and is weakly homologous to the herpesvirus family of R transactivators; therefore, the transcription and translation events from this region of KSHV are key events in viral reactivation. We demonstrate that ORF50 is expressed in a bicistronic message after induction of the viral lytic cycle. ORF50 migrated as a series of polypeptides: the major ones as 119 and 101 kDa, respectively. Using 3' rapid amplification of cDNA ends, RT-PCR, and cDNA library screening, we demonstrate that the major ORF50 transcript also encodes K8. The ORF50/K8 transcript was resistant to cyclohexamide, whereas the K8 transcript was only partially resistant to cyclohexamide at early timepoints. Both transcripts showed partial resistance after 12 h of phorbol ester induction. Using a GAL4-ORF50 fusion protein expression vector, we demonstrate that the transactivation domain of ORF50 resides within a 160-amino-acid region of the carboxyl portion of the ORF. Upstream regions of both ORF50 and K8 have basal promoter activity in KSHV-infected cells. K8, which had sequence homology to Bzip proteins, did not activate either promoter. However, both promoters were activated after cotransfection of ORF50 in BCBL-1 cells.
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MESH Headings
- Alternative Splicing
- Amino Acid Motifs
- Amino Acid Sequence
- Basic-Leucine Zipper Transcription Factors
- Carrier Proteins/chemistry
- Carrier Proteins/genetics
- Carrier Proteins/metabolism
- Cell Line
- Cycloheximide/pharmacology
- Gene Expression Regulation, Viral/drug effects
- Genes, Viral/genetics
- Herpesvirus 4, Human/chemistry
- Herpesvirus 4, Human/genetics
- Herpesvirus 8, Human/drug effects
- Herpesvirus 8, Human/genetics
- Humans
- Molecular Sequence Data
- Open Reading Frames/genetics
- Peptides/chemistry
- Peptides/genetics
- Peptides/metabolism
- Proline/genetics
- Proline/metabolism
- Promoter Regions, Genetic/genetics
- Protein Biosynthesis
- RNA, Messenger/analysis
- RNA, Messenger/genetics
- RNA, Viral/analysis
- RNA, Viral/genetics
- Recombinant Fusion Proteins/chemistry
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Repressor Proteins
- Tetradecanoylphorbol Acetate/pharmacology
- Trans-Activators/chemistry
- Trans-Activators/genetics
- Trans-Activators/metabolism
- Viral Proteins/chemistry
- Viral Proteins/genetics
- Viral Proteins/metabolism
- Virus Activation/drug effects
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Affiliation(s)
- W T Seaman
- Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina, USA
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37
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Adamson AL, Kenney S. The Epstein-Barr virus BZLF1 protein interacts physically and functionally with the histone acetylase CREB-binding protein. J Virol 1999; 73:6551-8. [PMID: 10400751 PMCID: PMC112738 DOI: 10.1128/jvi.73.8.6551-6558.1999] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Epstein-Barr virus (EBV) immediate-early protein BZLF1 (Z) is a key regulator of the EBV latent-to-lytic switch. Z is a transcriptional activator which induces EBV early gene expression. We demonstrate here that Z interacts with CREB-binding protein (CBP), a histone acetylase and transcriptional coactivator. This interaction requires the amino-terminal region of CBP as well as the transactivation and leucine zipper domains of Z. We show that CBP enhances Z-mediated transactivation of EBV early promoters, in reporter gene assays and in the context of the endogenous genome. We also demonstrate that Z decreases CREB transactivation function and that this inhibitory effect is reversed by overexpression of CBP. We show that Z also interacts directly with CREB. However, mutational analysis indicates that Z inhibition of CREB activity requires the direct interaction between Z and CBP but not the direct interaction between Z and CREB. We propose that Z interacts with CBP to enhance viral early gene transcription. In addition, the Z-CBP interaction may control host cellular transcription factor activity through competition for limiting amounts of cellular CBP.
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Affiliation(s)
- A L Adamson
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295, USA
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38
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Swenson JJ, Mauser AE, Kaufmann WK, Kenney SC. The Epstein-Barr virus protein BRLF1 activates S phase entry through E2F1 induction. J Virol 1999; 73:6540-50. [PMID: 10400750 PMCID: PMC112737 DOI: 10.1128/jvi.73.8.6540-6550.1999] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The Epstein-Barr Virus (EBV) immediate-early protein BRLF1 is one of two transactivators which mediate the switch from latent to lytic replication in EBV-infected cells. DNA viruses often modulate the function of critical cell cycle proteins to maximize the efficiency of virus replication. Here we have examined the effect of BRLF1 on cell cycle progression. A replication-deficient adenovirus expressing BRLF1 (AdBRLF1) was used to infect normal human fibroblasts and various epithelial cell lines. BRLF1 expression induced S phase entry in contact-inhibited fibroblasts and in the human osteosarcoma cell line U-2 OS. AdBRLF1 infection produced a dramatic increase in the level of E2F1 but not E2F4. In contrast, the levels of Rb, p107, and p130 were decreased in AdBRLF1-infected cells. Electrophoretic mobility shift assays confirmed an increased level of free E2F1 in the AdBRLF1-infected human fibroblasts. Consistent with the previously described effect of E2F1, AdBRLF1-infected fibroblasts had increased levels of p53 and p21 and died by apoptosis. BRLF1-induced activation of E2F1 may be required for efficient EBV lytic replication, since at least one critical viral replication gene (the viral DNA polymerase) is activated by E2F (C. Liu, N. D. Sista, and J. S. Pagano, J. Virol. 70:2545-2555, 1996).
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Affiliation(s)
- J J Swenson
- Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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39
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Adamson AL, Kenney SC. Rescue of the Epstein-Barr virus BZLF1 mutant, Z(S186A), early gene activation defect by the BRLF1 gene product. Virology 1998; 251:187-97. [PMID: 9813214 DOI: 10.1006/viro.1998.9396] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Expression of the Epstein-Barr virus (EBV) immediate-early protein, BZLF1 (Z), is sufficient to disrupt viral latency. Z transcriptionally activates the EBV early genes by binding to upstream Z-responsive elements (ZREs). Recently, a serine-to-alanine mutation of Z residue 186 (within the basic DNA binding domain) was shown to inhibit the ability of Z to induce lytic infection in latently infected cells, although the Z(S186A) mutant could still bind several known ZREs and activated an early EBV promoter (BMRF1) in transient reporter gene assays (Francis, A. L., Gradoville, L., and Miller, G. (1997). J. Virol. 71, 3054-3061). We now show that a specific deficiency in the ability to bind to ZRE elements in the immediate-early BRLF1 promoter may account for the inability of Z(S186A) to activate BRLF1 expression. Furthermore, we demonstrate that the ability of Z(S186A) to induce early BMRF1 and BHRF1 gene expression is rescued by cotransfection with a BRLF1 expression vector. However, the Z(S186A)/BRLF1 (R) combination cannot induce full lytic replication, suggesting that Z(S186A) may also be deficient in a replication-specific function. These results suggest that in the context of the intact viral genome, both Z and R expression are required for activation of early gene transcription in latently infected cells.
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Affiliation(s)
- A L Adamson
- Lineberger Comprehensive Cancer Center, Departments of Medicine and Microbiology, University of North Carolina at Chapel Hill, North Carolina, Chapel Hill, 27599-7295, USA
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40
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Asković S, Taylor W, Baumann R. The position of the ZEBRA activation domain does not influence its biological activity. Virus Res 1998; 57:125-38. [PMID: 9870581 DOI: 10.1016/s0168-1702(98)00089-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Epstein-Barr virus (EBV) is a human herpesvirus which latently infects B lymphocytes. EBV encodes a unique transcriptional activator, known as ZEBRA, which can disrupt viral latency in B cells and induce lytic viral replication. Furthermore, ZEBRA has been shown to bind at the EBV origin of lytic replication, and is necessary for viral DNA replication to occur. Previously we demonstrated that heterologous activation domains can fully substitute for the ZEBRA activation domain. Here we extend those results by showing that the position of the ZEBRA activation domain or a heterologous replacement domain does not influence its ability to function in the disruption of EBV latency. In this study three novel clones were constructed in which the ZEBRA activation region was repositioned to the carboxy terminus of the protein. These mutants were used to demonstrate that the ability of ZEBRA's wild type domain to function in the complex biological process of virus activation is not compromised by altering its position within the protein.
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Affiliation(s)
- S Asković
- Department of Microbiology, University of Mississippi Medical Center, Jackson 39216, USA
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41
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Baumann M, Mischak H, Dammeier S, Kolch W, Gires O, Pich D, Zeidler R, Delecluse HJ, Hammerschmidt W. Activation of the Epstein-Barr virus transcription factor BZLF1 by 12-O-tetradecanoylphorbol-13-acetate-induced phosphorylation. J Virol 1998; 72:8105-14. [PMID: 9733851 PMCID: PMC110148 DOI: 10.1128/jvi.72.10.8105-8114.1998] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
BZLF1 is a member of the extended AP-1 family of transcription factors which binds to specific BZLF1 sequence motifs within early Epstein-Barr virus (EBV) promoters and to closely related AP-1 motifs. BZLF1's activity is regulated at the transcriptional level as well as through protein interactions and posttranslational modifications. Phorbol esters or immunoglobulin cross-linking both reactivate EBV from latently infected B cells via transactivation of BZLF1. We report here that the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) is capable of inducing BZLF1's activity even further. The induction occurs at the posttranscriptional level and depends on a single serine residue located in the DNA binding domain of BZLF1. This serine residue (S186) is phosphorylated by protein kinase C in vitro and in vivo after stimulation with TPA. Phosphorylation of S186 per se interferes with the DNA binding affinity of BZLF1 in vitro but is mandatory for TPA-induced increase in DNA binding of BZLF1, as shown in gel retardation assays and reconstruction experiments with cellular extracts. In transcriptional reporter assays, S186 is essential for the activation of BZLF1 by TPA. Presumably, a yet-to-be-identified cellular factor restores the DNA binding affinity and enhances the transcriptional activity of S186-phosphorylated BZLF1, which is required to induce the lytic phase of EBV's life cycle.
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Affiliation(s)
- M Baumann
- GSF-National Research Center for Environment and Health, Institut für Klinische Molekularbiologie und Tumorgenetik, Munich, Germany
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42
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Liu P, Liu S, Speck SH. Identification of a negative cis element within the ZII domain of the Epstein-Barr virus lytic switch BZLF1 gene promoter. J Virol 1998; 72:8230-9. [PMID: 9733866 PMCID: PMC110177 DOI: 10.1128/jvi.72.10.8230-8239.1998] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/1998] [Accepted: 07/02/1998] [Indexed: 11/20/2022] Open
Abstract
The Epstein-Barr virus (EBV) lytic switch gene, BZLF1, is tightly regulated in latently infected B cells. The BZLF1 gene promoter (Zp) contains several cis elements that have been previously shown to respond to inducers of the viral lytic cycle. These include four copies of an element referred to as the ZI domains and an element that contains a consensus CRE/AP-1 motif (ZII domain). In addition, Zp is autoregulated through two sites that bind the BZLF1 gene product Zta. The ZI domains have been shown to bind the ubiquitous cellular transcription factors Sp1 and Sp3 and/or the myocyte enhancer factor 2D (Liu et al., EMBO J. 16:143-153, 1997; Liu et al., Virology 228:9-16, 1997). Here we present a functional analysis of the ZII domain and show: (i) ATF-1 and ATF-2 appear to be the predominant cellular factors that bind to the CRE/AP-1 motif present in the ZII domain; and (ii) the region immediately upstream of the CRE/AP-1 motif contains a potent negative cis element, mutation of which results in a >10-fold increase in Zp activity. The negative cis element (ZIIR) in the ZII domain decreases both basal and induced Zp activity and thus is likely to play an important role in regulating reactivation of EBV. In addition, analysis of heterologous promoter constructs indicates that the function of ZIIR is context sensitive. Attempts to demonstrate a cellular factor binding to ZIIR have been unsuccessful, leaving unresolved the mechanism by which repression is mediated.
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Affiliation(s)
- P Liu
- Departments of Pathology and Molecular Microbiology and Division of Molecular Oncology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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43
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Lehman AM, Ellwood KB, Middleton BE, Carey M. Compensatory energetic relationships between upstream activators and the RNA polymerase II general transcription machinery. J Biol Chem 1998; 273:932-9. [PMID: 9422752 DOI: 10.1074/jbc.273.2.932] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Activation of RNA polymerase II transcription in vivo and in vitro is synergistic with respect to increasing numbers of activator binding sites or increasing concentrations of activator. The Epstein-Barr virus ZEBRA protein manifests both forms of synergy during activation of genes involved in the viral lytic cycle. The synergy has an underlying mechanistic basis that we and others have proposed is founded largely on the energetic contributions of (i) upstream ZEBRA binding to its sites, (ii) the general pol II machinery binding to the core promoter, and (iii) interactions between ZEBRA and the general machinery. We hypothesize that these interactions form a network for which a minimum stability must be attained to activate transcription. One prediction of this model is that the energetic contributions should be reciprocal, such that a strong core promoter linked to a weak upstream promoter would be functionally analogous to a weak core linked to a strong upstream promoter. We tested this view by measuring the transcriptional response after systematically altering the upstream and core promoters. Our data provide strong qualitative support for this hypothesis and provide a theoretical basis for analyzing Epstein-Barr virus gene regulation.
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Affiliation(s)
- A M Lehman
- Department of Biological Chemistry, University of California at Los Angeles School of Medicine, Los Angeles, California 90095-1737, USA
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Rodems SM, Pullen SS, Friesen PD. DNA-dependent transregulation by IE1 of Autographa californica nuclear polyhedrosis virus: IE1 domains required for transactivation and DNA binding. J Virol 1997; 71:9270-7. [PMID: 9371585 PMCID: PMC230229 DOI: 10.1128/jvi.71.12.9270-9277.1997] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
IE1 is the principal early transregulator of Autographa californica multicapsid nuclear polyhedrosis virus (AcMNPV). The 582-residue protein stimulates viral transcription and binds as a dimer to 28-bp palindromic repeats (28-mers) comprising the AcMNPV homologous region (hr) transcription enhancers. To define IE1 domains responsible for hr-dependent transactivation, we first constructed a series of IE1 fusions to the DNA binding domain of the yeast GAL4 transactivator. In transfection assays, GAL4-IE1 fusions stimulated transcription from a TATA-containing AcMNPV promoter only upon cis linkage to GAL4 DNA binding sites. IE1 N-terminal residues 8 to 118 were sufficient for GAL4-binding-site-dependent transactivation. To identify IE1 residues required for hr interaction, we tested a series of IE1 mutations for 28-mer binding by using electrophoretic mobility shift assays. Deletion of IE1 residues other than the N-terminal transactivation domain eliminated 28-mer binding. Of 14 insertion mutations, only IE1(I425) and IE1(I553) failed to bind the 28-mer either as homodimers or as heterodimers with functional IE1. In contrast to insertion IE1(I425), IE1(I553) also failed to compete with wild-type IE1 for DNA binding and suggested a defect in oligomerization. Consistent with loss of oligomerization, substitutions within a hydrophobic repeat (residues 543 to 568) at the IE1 C terminus abolished 28-mer binding and demonstrated that this helix-loop-helix-like domain is required for DNA interaction. These data confirm that IE1 contains separable domains for transactivation and oligomerization-dependent DNA binding. Furthermore, they support a model wherein hr-mediated transactivation by IE1 involves sequence-specific DNA binding that contributes to transcriptional stimulation by interaction with components of the basal transcription complex.
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Affiliation(s)
- S M Rodems
- Institute for Molecular Virology and Department of Biochemistry, Graduate School and College of Agricultural and Life Sciences, University of Wisconsin-Madison, 53706, USA
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45
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Asković S, Baumann R. Activation domain requirements for disruption of Epstein-Barr virus latency by ZEBRA. J Virol 1997; 71:6547-54. [PMID: 9261375 PMCID: PMC191931 DOI: 10.1128/jvi.71.9.6547-6554.1997] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Latent infection of B lymphocytes by Epstein-Barr virus (EBV) can be disrupted by expression of the EBV ZEBRA protein. ZEBRA, a transcriptional activator, initiates the EBV lytic cascade by activating viral gene expression. ZEBRA is also indispensable for viral replication and binds directly to the EBV lytic origin of replication. The studies described herein demonstrate that the activation domain. ZEBRA activation can be replaced by a heterologous acidic, proline-rich, or glutamine-rich activation domain. ZEBRA activation domain swap constructs retain ZEBRA's native abilities to activate specific EBV promoters, to disrupt EBV latency, and to stimulate replication at the EBV lytic origin. Additional work, employing sequential and internal deletions of ZEBRA's N-terminal activation domain, indicates that its separate activities are not attributable to specific subdomains but are spread throughout its N terminus and therefore cannot be inactivated by deleting localized regions.
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Affiliation(s)
- S Asković
- Department of Microbiology, University of Mississippi Medical Center, Jackson 39216, USA
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46
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Francis AL, Gradoville L, Miller G. Alteration of a single serine in the basic domain of the Epstein-Barr virus ZEBRA protein separates its functions of transcriptional activation and disruption of latency. J Virol 1997; 71:3054-61. [PMID: 9060666 PMCID: PMC191435 DOI: 10.1128/jvi.71.4.3054-3061.1997] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The ZEBRA protein from Epstein-Barr virus (EBV) activates a switch from the latent to the lytic expression program of the virus. ZEBRA, a member of the bZIP family of DNA-binding proteins, is a transcriptional activator capable of inducing expression from viral lytic cycle promoters. It had previously been thought that ZEBRA's capacity to disrupt EBV latency resided primarily in its ability to activate transcription of genes that encode products required for lytic replication. We generated a point mutant of ZEBRA, Z(S186A), that was not impaired in its ability to activate transcription; however, this mutation abolished its ability to initiate the viral lytic cascade. The mutant, containing a serine-to-alanine substitution in the DNA-binding domain of the protein, bound to several known ZEBRA-binding sites and activated transcription from reporters bearing known ZEBRA-responsive promoters but did not disrupt latency in EBV-infected cell lines. Therefore, initiation of the EBV lytic cycle by the ZEBRA protein requires a function in addition to transcriptional activation; a change of serine 186 to alanine in the DNA-binding domain of ZEBRA abolished this additional function and uncovered a new role for the ZEBRA protein in disruption of EBV latency. The additional function that is required for initiation of the lytic viral life cycle is likely to require phosphorylation of serine 186 of the ZEBRA protein, which may influence either DNA recognition or transcriptional activation of lytic viral promoters in a chromatinized viral episome.
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Affiliation(s)
- A L Francis
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06510, USA
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47
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Liu S, Liu P, Borras A, Chatila T, Speck SH. Cyclosporin A-sensitive induction of the Epstein-Barr virus lytic switch is mediated via a novel pathway involving a MEF2 family member. EMBO J 1997; 16:143-53. [PMID: 9009275 PMCID: PMC1169621 DOI: 10.1093/emboj/16.1.143] [Citation(s) in RCA: 118] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Induction of the Epstein-Barr virus (EBV) lytic cycle by crosslinking surface immunoglobulin is inhibited by the immunosuppressants cyclosporin A (CsA) and FK506. This correlates with the ability of CsA to inhibit Ca2+-dependent transcription of the lytic cycle switch gene BZLF1. It is shown here that CsA sensitivity maps to three sites (ZIA, ZIB and ZID) that bind the serum response factor-related protein MEF2D. A synthetic promoter containing multiple copies of a MEF2D site from Zp, in conjunction with a CREB/AP-1 site (ZII) from Zp, exhibits CsA-sensitive inducibility. Furthermore, the Zp MEF2D sites were functionally interchangeable with MEF2 sites derived from heterologous promoters. While no evidence of a NFAT family member binding to either the MEF2 or CREB/AP-1 sites was obtained, it could be demonstrated that CsA-sensitive induction of Zp was mediated by calcineurin and NFATc2 in synergy with either phorbol ester or especially with the EBV-induced Ca2+/calmodulin-dependent kinase type IV/Gr. These studies identify Zp as prototypic of a novel class of CsA-sensitive and NFAT-dependent promoters defined by the presence of MEF2 sites.
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Affiliation(s)
- S Liu
- Department of Pathology, Children's Hospital, Washington University School of Medicine, St. Louis, MO 63110, USA
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48
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Cayrol C, Flemington E. G0/G1 growth arrest mediated by a region encompassing the basic leucine zipper (bZIP) domain of the Epstein-Barr virus transactivator Zta. J Biol Chem 1996; 271:31799-802. [PMID: 8943219 DOI: 10.1074/jbc.271.50.31799] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The Epstein-Barr virus (EBV) immediate early transactivator Zta is a basic leucine zipper (bZIP) transcription factor that causes G0/G1 cell cycle arrest through induction of the tumor suppressor protein, p53, and the cyclin-dependent kinase inhibitors, p21 and p27 (Cayrol, C., and Flemington, E. K. (1996) EMBO J. 15, 2748-2759). Here, we report a genetic analysis of Zta-mediated G0/G1 growth arrest and p21 induction. The majority of the Zta transactivation domain can be deleted (ZDelta1-128) without significantly affecting the ability of Zta to elicit growth arrest. A larger amino-terminal deletion (ZDelta1-167) abrogates the ability of Zta to inhibit proliferation, mapping the growth-inhibitory domain to a carboxyl-terminal region encompassing the bZIP domain (amino acids 128-245). The integrity of the bZIP domain is required for growth suppression since a two-amino acid mutant which is defective for homodimerization, fails to induce cell cycle arrest. Western blot analysis of p21 expression in cells expressing Zta mutants reveals that the ability of Zta mutants to cause G0/G1 growth arrest is intimately related to their capacity to induce p21 expression. Together, these data demonstrate that a carboxyl-terminal region of Zta that includes the bZIP domain is sufficient to mediate G0/G1 growth arrest and p21 induction.
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Affiliation(s)
- C Cayrol
- Division of Tumor Virology, Division of Neoplastic Disease Mechanisms, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA.
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49
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Sarisky RT, Gao Z, Lieberman PM, Fixman ED, Hayward GS, Hayward SD. A replication function associated with the activation domain of the Epstein-Barr virus Zta transactivator. J Virol 1996; 70:8340-7. [PMID: 8970953 PMCID: PMC190921 DOI: 10.1128/jvi.70.12.8340-8347.1996] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The Zta transactivator is crucial for both Epstein-Barr virus (EBV) lytic gene expression and lytic DNA replication. We have used a cotransfection-replication assay to examine the effect of mutations in the Zta activation domain (amino acids [aa] 1 to 167) on Zta replication activity. Deletion of Zta aa 25 to 86, which are critical for transcriptional activation of ori-Lyt, or aa 93 to 141 did not adversely affect replication of an ori-Lyt-containing target plasmid. However, removal of aa 2 to 25 (delta2-25) abolished replication activity. Within this subdomain, deletion of aa 2 to 10 (delta2-10) or mutation of codons 18 and 19 (m18/19) or 22 and 26 (m22/26) did not affect replication competency, while deletion of codons 13 to 19 (delta13-19) or mutation at codons 12 and 13 (m12/13) impaired Zta replication function. Each of the replication-negative Zta variants was capable of transactivating expression from both BHLF1 promoter-chloramphenicol acetyltransferase constructions and the BMRF1 promoter on endogenous EBV genomes in Raji cells with efficiency comparable to that of the wild-type polypeptide. Thus, a replication contribution of Zta was functionally separable from its transactivation activity and was supplied by the N-terminal region encompassing aa 11 to 25. Replication by a subset of the impaired Zta mutants was partially rescued upon the addition of Rta to the replication assay. The contribution of Rta mapped to domain II of the Rta activation domain and was specific for this region. A chimeric Rta-EBNA-2 transactivation domain fusion, which retains the DNA-binding and transactivation properties associated with wild-type Rta, failed to rescue replication-deficient Zta. Our data suggest that Rta may act as an ancillary replication factor in EBV ori-Lyt DNA synthesis by stabilizing Zta-replisome interactions.
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Affiliation(s)
- R T Sarisky
- Department of Pharmacology and Molecular Sciences, Johns Hopkins School of Medicine, Baltimore, Maryland 21205-2185, USA
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50
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Cayrol C, Flemington EK. The Epstein-Barr virus bZIP transcription factor Zta causes G0/G1 cell cycle arrest through induction of cyclin-dependent kinase inhibitors. EMBO J 1996; 15:2748-59. [PMID: 8654372 PMCID: PMC450210] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
While oncoproteins encoded by small DNA tumor viruses and Epstein-Barr virus (EBV) latent antigens facilitate G1/S progression, the EBV lytic switch transactivator Zta was found to inhibit growth by causing cell cycle arrest in G0/G1 in several epithelial tumor cell lines. Expression of Zta results in induction of the tumor suppressor protein, p53, and the cyclin-dependent kinase inhibitors, p21 and p27, as well as accumulation of hypophosphorylated pRb. Up-regulation of p53 and p27 occurs by post-transcriptional mechanisms while expression of p21 is induced at the RNA level in a p53-dependent manner. Inactivation of pRb by transient overexpression of the human papillomavirus E7 oncoprotein indicates that pRb or pRb-related proteins are key mediators of the growth-inhibitory function of Zta. These findings suggest that EBV plays an active role in redirecting epithelial cell physiology to facilitate the viral replicative program through a Zta-mediated growth arrest function.
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Affiliation(s)
- C Cayrol
- Division of Tumor Virology, Division of Neoplastic Disease Mechanisms, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02115, USA
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