Mechanisms of Gene Regulation by EBV EBNA-1 Protein

EBV EBNA-1蛋白的基因调控机制

• 批准号: 7847575
• 负责人: JEFFERY T SAMPLE
• 金额: $ 38.78万
• 依托单位: PENNSYLVANIA STATE UNIV HERSHEY MED CTR
• 依托单位国家: 美国
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-01 至 2012-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7847575
• 关键词: Acquired Immunodeficiency Syndrome; Acute; Address; Apoptotic; B-Lymphocytes; Binding; Binding Sites; Biological Assay; Biology; Cancer Etiology; Cell division; Cells; Coupled; Cytotoxic T-Lymphocytes; Development; Disease; Down-Regulation; EBNA-1 protein; EBV-associated disease; EBV-associated malignancy; Ensure; Episome; Epitopes; Epstein-Barr Virus Infections; Epstein-Barr Virus latency; Equilibrium; Event; Exons; Foundations; Gene Expression; Gene Expression Regulation; Genetic Transcription; Genome; Growth; Herpesviridae; Homeostasis; Human; Human Herpesvirus 4; Immune; Immune system; Immunologic Surveillance; Individual; Infection; Infectious Mononucleosis; Intervention; Knowledge; Life; Link; Lymphoma; MHC Class I Genes; Maintenance; Malignant Neoplasms; Mediating; Messenger RNA; Molecular; Oncogenic; Pathogenesis; Peptides; Process; Property; Proteins; Publishing; RNA Splicing; Relative (related person); Reporter; Repression; Research; Resistance; Risk; Risk Factors; Role; Screening procedure; Secondary to; Site; T cell response; T-Lymphocyte; Transcript; Transcription Initiation Site; Viral; Viral Genes; Viral Genome; Viral Proteins; Work; base; cell killing; defined contribution; immune function; infected B cell; insight; latent infection; mRNA Precursor; multicatalytic endopeptidase complex; novel; pathogen; prevent; programs; promoter; public health relevance; research study; tumorigenic; viral DNA

DESCRIPTION (provided by applicant): Epstein-Barr virus (EBV) is an extremely successful pathogen, able to persist lifelong as a latent infection within B lymphocytes with little overt disease. However, a breakdown in immune surveillance, e.g., as a consequence of AIDS, remains a significant risk factor for development of EBV-associated lymphoma, underscoring the highly evolved equilibrium that exists between this potentially oncogenic herpesvirus and the host immune system. This equilibrium is dependent on a selective down-regulation of EBV latency-associated gene expression during establishment of persistent infection that ultimately restricts expression to viral genes critical for maintenance of persistence, while precluding those with acute transforming properties and/or which encode dominant epitopes recognized by the EBV-specific T-cell surveillance. A pivotal process in this transition to restricted latency is a promoter switching event that enables exclusive expression of the essential EBV genome-maintenance protein, EBNA-1, from the promoter Qp, which can be negatively autoregulated through two EBNA-1 binding sites immediately downstream of its transcription start site. Our recent efforts to define the mechanism of EBNA-1 repression revealed that it acts not by inhibition of transcription, as originally believed, but by suppression of pre-mRNA processing. The principal significance of this autoregulation, furthermore, has recently become apparent. Although EBNA-1 was earlier thought to be "invisible" to the host immune surveillance as a consequence of its ability to inhibit in cis its degradation by the cell proteasome, thereby preventing presentation of EBNA-1 peptide epitopes in association with HLA class I molecules, subsequent studies indicated that cytotoxic T cells that recognize EBNA-1 not only exist, but that they are directed towards peptides generated during actual synthesis of EBNA-1, not by the degradation of mature EBNA-1. Thus, resistance to proteasomal degradation is secondary to the autoregulated expression of EBNA-1 as the primary mechanism employed by EBV to restrict EBNA-1-specific T-cell killing. Further, recently described anti-apoptotic properties of EBNA-1 suggest that it may have tumorigenic potential. We hypothesize, therefore, that the autoregulatory function of EBNA-1 is highly critical to EBV persistence and its associated pathogenic potential: it ensures sufficient EBNA-1 for genome maintenance, while limiting EBNA-1 synthesis below a threshold that, if exceeded, would subject latently infected B cells to elimination by EBNA-1-specific cytotoxic T cells, and potentially oncogenic transformation. We propose three specific aims to help us reach our long-term objective of defining the contribution of EBNA-1 autoregulation to EBV biology, immune evasion and pathogenesis: 1) Elucidate the influence of EBNA-1 on pre-mRNA processing; 2) Define the molecular mechanism of EBNA-1 autoregulation; and 3) Elucidate the contributions of EBNA-1 autoregulation to the growth and restricted programs of EBV latency. PUBLIC HEALTH RELEVANCE: Epstein-Barr virus (EBV) is a herpesvirus that has significant potential to cause cancer in its human host, particularly within individuals that become immune suppressed as a consequence of AIDS, for example. Through this research we hope to gain a better understanding of how infection by EBV may be prevented or treated. Specifically, we seek to elucidate the mechanism by which a key EBV protein, EBNA-1, regulates its own expression, and to determine the respective importance of this autoregulatory mechanism in the different forms of EBV infection within B lymphocytes. We hypothesize that the autoregulatory function of EBNA-1 ensures that it is expressed at levels necessary to perform its essential role in propagation of the EBV DNA genome, but below levels that would be detected by the host immune system and that might promote malignancy.

描述（由申请方提供）：EB病毒（EBV）是一种非常成功的病原体，能够作为B淋巴细胞内的潜伏感染持续终生，几乎没有明显的疾病。然而，免疫监视的崩溃，例如，作为AIDS的结果，仍然是EBV相关淋巴瘤发展的重要危险因素，强调了这种潜在致癌疱疹病毒和宿主免疫系统之间存在的高度进化平衡。这种平衡依赖于在建立持续性感染期间EBV潜伏相关基因表达的选择性下调，其最终将表达限制于对维持持续性至关重要的病毒基因，同时排除具有急性转化性质和/或编码由EBV特异性T细胞监视识别的显性表位的那些。在这种向限制性潜伏期的转变中的关键过程是启动子转换事件，其使得能够从启动子Qp排他性地表达必需的EBV基因组维持蛋白EBNA-1，其可以通过其转录起始位点下游的两个EBNA-1结合位点进行负性自调节。我们最近的努力，以确定EBNA-1的抑制机制显示，它的作用不是通过抑制转录，如最初认为的，但通过抑制前mRNA的加工。此外，这种自动调节的主要意义最近已经变得明显。尽管早期认为EBNA-1由于其顺式抑制其被细胞蛋白酶体降解的能力而对宿主免疫监视是“不可见的”，从而阻止与HLA I类分子相关的EBNA-1肽表位的呈递，但随后的研究表明识别EBNA-1的细胞毒性T细胞不仅存在，但是它们针对的是在EBNA-1的实际合成过程中产生的肽，而不是通过成熟EBNA-1的降解产生的肽。因此，对蛋白酶体降解的抗性继发于EBNA-1的自身调节表达，作为EBV限制EBNA-1特异性T细胞杀伤的主要机制。此外，最近描述的EBNA-1的抗凋亡特性表明它可能具有致瘤潜力。因此，我们假设EBNA-1的自身调节功能对于EBV的持续存在及其相关的致病潜力是非常关键的：它确保足够的EBNA-1用于基因组维持，同时将EBNA-1合成限制在阈值以下，如果超过该阈值，则潜伏感染的B细胞将被EBNA-1特异性细胞毒性T细胞消除，并可能发生致癌转化。我们提出了三个具体的目标，以帮助我们实现我们的长期目标，定义EBNA-1的自动调节的EBV生物学，免疫逃避和发病机制的贡献：1）阐明EBNA-1前mRNA加工的影响; 2）定义EBNA-1自动调节的分子机制;和3）阐明EBNA-1自动调节的EBV潜伏期的增长和限制程序的贡献。公共卫生关系：EB病毒（EBV）是一种疱疹病毒，其具有在其人类宿主中引起癌症的显著潜力，特别是在例如由于AIDS而变得免疫抑制的个体中。通过这项研究，我们希望更好地了解如何预防或治疗EBV感染。具体而言，我们试图阐明的机制，一个关键的EBV蛋白，EBNA-1，调节其自身的表达，并确定各自的重要性，这种自我调节机制中的不同形式的EBV感染内B淋巴细胞。我们假设EBNA-1的自动调节功能确保其在EBV DNA基因组繁殖中发挥重要作用所需的水平上表达，但低于宿主免疫系统检测到的水平，这可能会促进恶性肿瘤。