Mechanisms of Gene Regulation by EBV EBNA-1 Protein

EBV EBNA-1蛋白的基因调控机制

• 批准号: 7621316
• 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 2011-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7621316
• 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-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; response; 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（由申请人提供）：EB 病毒 (EBV) 是一种极其成功的病原体，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，例如由于艾滋病而导致的，仍然是发生 EBV 相关淋巴瘤的一个重要危险因素，这突显了这种潜在致癌性疱疹病毒与宿主免疫系统之间存在的高度进化的平衡。这种平衡取决于持续感染建立过程中 EBV 潜伏期相关基因表达的选择性下调，最终限制对维持持续性至关重要的病毒基因的表达，同时排除那些具有急性转化特性和/或编码 EBV 特异性 T 细胞监测识别的显性表位的病毒基因。向受限潜伏期转变的一个关键过程是启动子转换事件，该事件使得必需的 EBV 基因组维护蛋白 EBNA-1 从启动子 Qp 独家表达，Qp 可以通过紧邻其转录起始位点下游的两个 EBNA-1 结合位点进行负向自动调节。我们最近对 EBNA-1 抑制机制的研究表明，它并不是像最初认为的那样通过抑制转录来发挥作用，而是通过抑制前 mRNA 加工来发挥作用。此外，这种自动调节的主要意义最近已变得显而易见。尽管 EBNA-1 早期被认为对宿主免疫监视“不可见”，因为它能够顺式抑制细胞蛋白酶体的降解，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，而且针对实际过程中产生的肽。 EBNA-1 的合成，而不是成熟 EBNA-1 的降解。因此，对蛋白酶体降解的抵抗是 EBNA-1 的自动调节表达的继发性，而 EBNA-1 的自动调节表达是 EBV 用于限制 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 的自动调节功能对于 EBV 持久性及其相关的致病潜力非常关键：它确保足够的 EBNA-1 用于基因组维护，同时将 EBNA-1 合成限制在阈值以下，如果超过该阈值，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目标来帮助我们实现确定 EBNA-1 自动调节对 EBV 生物学、免疫逃避和发病机制的贡献的长期目标： 1）阐明 EBNA-1 对前 mRNA 加工的影响； 2）明确EBNA-1自我调节的分子机制； 3) 阐明 EBNA-1 自动调节对 EBV 潜伏期生长和限制程序的贡献。公共卫生相关性：爱泼斯坦-巴尔病毒 (EBV) 是一种疱疹病毒，极有可能在人类宿主中引起癌症，尤其是在因艾滋病等而导致免疫抑制的个体中。通过这项研究，我们希望更好地了解如何预防或治疗 EB 病毒感染。具体来说，我们试图阐明关键 EBV 蛋白 EBNA-1 调节其自身表达的机制，并确定这种自动调节机制在 B 淋巴细胞内不同形式的 EBV 感染中各自的重要性。我们假设 EBNA-1 的自动调节功能确保其表达水平在 EBV DNA 基因组繁殖中发挥其重要作用所必需的水平，但低于宿主免疫系统检测到的水平，并且可能促进恶性肿瘤。