Subversion of MHC class I antigen presentation by viral immunomodulatory proteins

描述（由申请方提供）：新生主要组织相容性复合体（MHC）I类分子在细胞内质网（ER）内经历严格的成熟过程，最终在细胞表面呈递内源性和病毒肽至细胞毒性T细胞（CTL）。该途径在控制病毒感染中的重要性通过以下事实强调，即病毒已经进化出许多策略来干扰MHC I成熟和抑制抗原呈递。据认为，这些策略使病毒能够在受感染的宿主细胞中持续存在。因为持久性病毒是临床相关的病原体，我们必须了解它们如何逃避人类免疫系统的检测。这一知识与理解宿主-病原体相互作用有关，并且它还告知我们I类抗原呈递途径对病毒干扰的易感性。我们利用这些信息的能力有助于抗病毒药物的开发。 人类腺病毒（Ads）引起的疾病范围从胃肠道和呼吸道感染到眼部感染。Ad编码E3- 19 K蛋白，其结合并保留受感染细胞的ER内的MHC I类分子。结果表明，E3- 19 K降低了感染细胞上的MHC I表达水平，这是一种保护感染细胞免受CTL裂解的作用。多年来，我们一直有兴趣研究E3- 19 K逃避免疫监视的分子机制。我们最近对E3- 19 K功能进行了一些重要的观察。我们发现，Ad血清型2（Ad 2）E3- 19 K与未成熟（无肽）和成熟（充满肽）的MHC I分子。我们还发现E3- 19 K靶向HLA-A和-B位点的MHC I分子，但不靶向HLA-C和-E位点的MHC I分子。重要的是，我们通过X射线晶体学确定了E3- 19 K/MHC I复合物的第一个三维结构，即与HLA-A2结合的Ad 2 E3- 19 K。迄今为止，E3- 19 K的免疫调节功能的许多重要方面仍不完全清楚。还不知道E3- 19 K是否利用一种以上的策略来干扰ER内的MHC I成熟（目标#1）;也不知道哪些MHC I分子在感染的细胞上被E3- 19 K特异性下调（目标#2）;还没有人研究E3- 19 K/MHC I联合对自然杀伤功能的作用（目标#2）;并且我们仍然缺乏对E3- 19 K/MHC I关联中相互作用的高亲和力和特异性的结构基础的理解（目标#3）。这个项目的目标是建立在我们以前的贡献，并以系统的方式解决这些突出的问题。 我们的研究的重要性突出的关键作用，I类抗原呈递途径在消除入侵的病原体，我们的新奇的Ad 2 E3- 19 K/HLA-A2结构，以及知识，Ad感染可能是致命的儿童和免疫功能低下的患者。我们希望在完成我们的研究后，我们将有一个更深入的了解如何E3- 19 K抵消MHC I限制的细胞免疫防御和影响的过程中，广告感染。

DESCRIPTION (provided by applicant): Nascent major histocompatibility complex (MHC) class I molecules undergo a stringent maturation process within the endoplasmic reticulum (ER) of cells, culminating in the cell-surface presentation of endogenous and viral peptides to cytotoxic T-cells (CTLs). The importance of this pathway in controlling viral infections is underlined by the fact that viruses have evolved numerous strategies to interfere with MHC I maturation and suppress antigen presentation. It is thought that these strategies enable viruses to persist in infected host cells. Because persistent viruses are clinically relevant pathogens, itis essential that we understand how they evade detection by the human immune system. This knowledge is relevant for understanding host-pathogen interaction, and it also informs us on the susceptibility of the class I antigen presentation pathway to viral interferences. Our ability to harness this information can benefit the development of antiviral drugs. Human Adenoviruses (Ads) cause diseases ranging from gastrointestinal and respiratory tract infections to eye infections. Ad encodes the E3-19K protein that binds to and retains MHC class I molecules within the ER of infected cells. It was shown that E3-19K reduces levels of MHC I expression on infected cells, an effect that protects infected cells from lysis by CTLs. We have been interested in studying the molecular mechanism by which E3-19K evades immune surveillance for many years. We have recently made a number of key observations on E3-19K function. We showed that Ad serotype 2 (Ad2) E3-19K associates with immature (peptide-free) and mature (peptide-filled) MHC I molecules. We also showed that E3-19K targets MHC I molecules of the HLA-A and -B loci but not those of the HLA-C and -E loci. Importantly, we determined the first three-dimensional structure of an E3-19K/MHC I complex, namely Ad2 E3-19K bound to HLA-A2, by x-ray crystallography. To date, many important aspects of the immunomodulatory function of E3-19K remains incompletely understood. It is not known if E3-19K utilizes more than one strategy to interfere with MHC I maturation within the ER (Aim #1); it is also not known which MHC I molecules are specifically downregulated by E3-19K on infected cells (Aim #2); no one has yet examined the role of the E3-19K/MHC I association on natural killer functions (Aim #2); and we still lack an understanding of the structural basis for high affinity and specificity of interaction in the E3-19K/MHC I association (Aim #3). The goal of this project is to build on our previous contributions and address these salient questions in a systematic manner. The significance of our studies is highlighted by the critical role that the class I antigen presentatin pathway plays in eliminating invading pathogens, the novelty of our Ad2 E3-19K/HLA-A2 structure, and the knowledge that Ad infections can be fatal in children and immunocompromised patients. We expect that upon completing our studies, we will have a more in depth understanding of how E3-19K counteracts MHC I- restricted cellular immune defenses and influences the course of Ad infection.