Subversion of MHC class I antigen presentation by viral immunomodulatory proteins

描述（由申请人提供）：新生的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，最终在细胞表面向细胞毒性t细胞（ctl）呈递内源性和病毒肽。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，这一事实强调了这一途径在控制病毒感染中的重要性。据认为，这些策略使病毒能够在被感染的宿主细胞中持续存在。因为持续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，它也告诉我们I类抗原递呈途径对病毒干扰的易感性。我们利用这些信息的能力可以促进抗病毒药物的开发。人类腺病毒（Ads）引起从胃肠道和呼吸道感染到眼睛感染的各种疾病。Ad编码E3-19K蛋白，该蛋白结合并保留感染细胞内质网内的MHC I类分子。研究表明，E3-19K降低了感染细胞上MHC I的表达水平，从而保护感染细胞免受ctl的裂解。多年来，我们一直对研究E3-19K逃避免疫监视的分子机制感兴趣。我们最近对E3-19K的功能做了一些重要的观察。我们发现Ad血清型2 (Ad2) E3-19K与未成熟（无肽）和成熟（充满肽）MHC I分子相关。我们还发现E3-19K靶向HLA-A和-B位点的MHC I分子，而不是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E3-19K/MHC I配合物的第一个三维结构，即Ad2 E3-19K与HLA-A2结合。迄今为止，E3-19K免疫调节功能的许多重要方面仍未完全了解。目前尚不清楚E3-19K是否利用多种策略来干扰内质网内MHC I的成熟（Aim #1）；也不知道哪些MHC I分子被感染细胞上的E3-19K特异性下调（Aim #2）；还没有人研究过E3-19K/MHC I关联在自然杀伤功能中的作用（Aim #2）；我们仍然缺乏对E3-19K/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（Aim #3）。该项目的目标是在我们以前的贡献的基础上，以系统的方式解决这些突出的问题。我们研究的重要意义在于，一类抗原呈递蛋白途径在消除入侵病原体中发挥着关键作用，我们的Ad2 E3-19K/HLA-A2结构的新颖性，以及Ad感染在儿童和免疫功能低下患者中可能是致命的知识。我们希望在完成我们的研究后，我们将更深入地了解E3-19K如何抵消MHC I限制的细胞免疫防御并影响Ad感染的过程。

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.