Subversion of MHC class I antigen presentation by viral immunomodulatory proteins

描述(申请人提供)：新生的主要组织相容性复合体(MHC)I类分子在细胞的内质网(ER)内经历严格的成熟过程，最终在细胞表面将内源性和病毒多肽呈递给细胞毒性T细胞(CTL)。病毒已经进化出许多策略来干扰MHC I成熟和抑制抗原递呈，这一事实突显了这一途径在控制病毒感染方面的重要性。人们认为，这些策略使病毒能够在受感染的宿主细胞中持续存在。由于持久性病毒是临床上相关的病原体，我们必须了解它们是如何逃避人类免疫系统的检测的。这一知识对于理解宿主-病原体的相互作用是相关的，它也告诉我们I类抗原提呈途径对病毒干扰的敏感性。我们利用这些信息的能力可以帮助抗病毒药物的开发。人类腺病毒(ADS)会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，该蛋白与感染细胞的内质网结合并保留MHC I类分子。结果表明，E3-19K降低了感染细胞上MHC I的表达水平，这种作用保护感染细胞免受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函数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(充满多肽)的MHC I分子相关。我们还发现，E3-19K针对的是HLA-A和-B基因座的MHC I分子，而不是HLA-C和-E基因座的MHC I分子。重要的是，我们通过X射线结晶学确定了E3-19K/MHC I复合体的第一个三维结构，即与人类白细胞抗原A2结合的AD2 E3-19K。到目前为止，E3-19K免疫调节功能的许多重要方面仍不完全清楚。目前尚不清楚E3-19K是否利用一种以上的策略干扰内质网内MHC I的成熟(目标1)；也不知道E3-19K特异性下调感染细胞上哪些MHC I分子(目标2)；还没有人研究E3-19K/MHC I关联对自然杀伤功能的作用(目标2)；我们仍然缺乏对E3-19K/MHC I关联中高亲和力和特异性相互作用的结构基础(目标3)的了解。该项目的目标是以我们以前的贡献为基础，系统地解决这些突出问题。我们的研究突出了I类抗原提呈蛋白途径在消除入侵病原体方面的关键作用，我们的AD2 E3-19K/HLA-A2结构的新颖性，以及对Ad感染在儿童和免疫功能低下患者中可能致命的认识。我们希望在完成我们的研究后，我们将对E3-19K如何对抗MHC I限制的细胞免疫防御和影响Ad感染的过程有更深入的了解。

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.