Pathogenesis Mechanism of Geminivirus-Encoded AL2

描述（由申请人提供）：拟建研究的主要目的是在表观遗传水平上阐明宿主先天免疫反应和病毒反防御反应的机制。包括人类和植物在内的多细胞真核生物已经进化出复杂而基本的RNA沉默机制来防御入侵病毒。另一方面，包括感染人类的病毒在内的病毒编码蛋白质，称为病毒抑制因子，以阻断沉默途径以逃避宿主监视。目前世界范围内对宿主-病毒相互作用的研究主要集中在转录后基因沉默（PTGS）的抗病毒作用和病毒对PTGS的抑制上。虽然我们对PTGS水平的病毒抑制的了解已经大大扩展，但我们对转录基因沉默（TGS）水平的病毒抑制的了解仍处于起步阶段。PI小组的初步研究表明，由双链病毒（一种单链DNA病毒）编码的AL2抑制因子，在遗传上干扰异染色质蛋白1 （HP1）和多梳抑制复合体2 （PRC2）的通路，这是负责表观遗传沉默的关键基因。此外，AL2与HP1具有生物化学相互作用。这些结果和其他几个小组的工作导致了一个模型的概念化，即TGS作为一种先天免疫系统来限制侵入性DNA病原体，而病毒抑制因子可以通过直接抑制TGS整合子来打破这种限制。提出的研究将解决这个模型：Aim1将测试假设HP1/PRC2是一个新的宿主防病毒系统，而AL2与这些组件的相互作用代表了一种新的反防御策略。我们将研究HP1/PRC2基因的功能缺失和功能获得突变对双病毒染色质修饰的影响。Aim 2将解决一种猜测，即通过与HP1/PRC2的相互作用，AL2可以重编程宿主基因表达并触发下游发病机制信号级联反应，从而破坏宿主细胞环境导致疾病。共选择了30个al2应答基因，并将研究这些基因是否参与了al2引发的发病过程。本研究将为进一步全面研究DNA病毒抑制因子引发发病的分子机制奠定基础。了解这些机制将阐明在病毒和宿主之间界面发生的基本事件，并将揭示自然抗病毒防御策略，这些策略可能被用于指导治疗或预防措施，以解决哺乳动物宿主中由表观遗传功能障碍引起的健康疾病。

DESCRIPTION (provided by applicant): The primary goal of the proposed research is to elucidate the mechanism of host innate immune responses and viral counter-defense responses at an epigenetic level. Multi-cellular eukaryotes including humans and plants have evolved sophisticated and fundamental mechanisms of RNA silencing to defense invasive viruses. On the other hand, viruses including those infecting humans encode proteins, referred to as viral suppressors, to block silencing pathways to evade host surveillance. The current world-wide study on host-virus interaction focuses on the antivirus role of posttranscriptional gene silencing (PTGS) and viral suppression of PTGS. While our knowledge of viral suppression at the PTGS level has been drastically expanded, our understanding of viral suppression at the level of transcriptional gene silencing (TGS) is still at its infancy. The preliminary studies from the PI's group have illuminated that AL2 suppressor encoded by geminivirus, a family of single-strand DNA viruses, genetically interferes with the pathway of Heterochromatin Protein 1 (HP1) and Polycomb Repressive Complex 2 (PRC2), which are critical genes responsible for epigenetic silencing. Moreover, AL2 biochemically interacts with HP1. These results and work from several other groups led to conceptualization of a model that TGS serves as an innate immune system to restrict invasive DNA pathogens, whereas viral suppressors can break this restriction by directly inhibiting the TGS integrators. The proposed study will address this model: Aim1 will test the hypothesis that HP1/PRC2 is a new line of host antivirus system and AL2 interaction with these components represents a novel counter-defense strategy. Effect of loss-of-function and gain-of-function mutations of HP1/PRC2 genes on modification of geminivirus chromatin will be investigated. Aim 2 will address a speculation that, through interaction with HP1/PRC2, AL2 can reprogram host gene expression and trigger downstream pathogenesis signaling cascades that disrupt host cellular environment leading to disease. A total of 30 AL2-responsive genes have been selected and whether nor not these genes are involved in AL2-elicited pathogenesis processes will be investigated. The proposed study will serve as the starting point for further comprehensive studies on the molecular mechanism of pathogenesis triggered by viral suppressors from the DNA viruses. Understanding these mechanisms will elucidate basic events that occur at the interface between virus and host, and will reveal natural antiviral defense strategies that may be exploited for directed therapies or preventative measures to address health disorders that arise from epigenetic dysfunction in mammalian hosts. PUBLIC HEALTH RELEVANCE: Multi-cellular eukaryotes including humans and plants have evolved sophisticated and conserved epigenetic silencing mechanisms to protect themselves from virus attack. The proposed study is to elucidate the mechanisms by which geminivirus-encoded AL2 protein suppresses epigenetic silencing and triggers downstream pathogenesis signaling cascades that lead to diseases. The proposed study on Arabidopsis immune responses to infection by model DNA viruses and the viral counter- defensive strategies will provide mechanistic insights into the molecular interactions between viruses and mammalian hosts.