Molecular cell biology of MHC class I retention by the gp40 protein of the murine cytomegalovirus

主要组织相容性复合体(MHC)I类分子通过将病毒抗原呈递给细胞表面的细胞毒性T淋巴细胞，从而导致感染细胞的凋亡，从而控制感染，在抗病毒免疫反应中发挥关键作用。因此，许多病毒已经开发出避开MHC I类分子识别的策略来持续存在也就不足为奇了：存在着大量干扰抗原提呈的病毒蛋白，即所谓的免疫转运蛋白。我们一直在研究小鼠巨细胞病毒(MCMV)的免疫eVasin gp40，发现它的作用方式不同于其他免疫eVasin：它与MHC I类分子结合，但与其他直接相互作用的免疫eVasin不同，它不会导致它们的降解，相反，完全成熟的I类分子保留在无法到达细胞表面的分泌途径的早期隔室。我们进一步鉴定了gp40中一个新的序列，连接子，它是保持自身和MHC I类分子之一所必需的。这些数据已经汇总在一份手稿中，不久将提交出版。在这个项目中，我们将研究gp40介导的I类细胞内滞留的先决条件，即gp40本身在细胞内的滞留：我们将描述发生的滞留类型，确定连接序列在保留过程中的功能，并确定gp40可能调节gp40滞留的潜在结合伙伴，从而确定其功能。我们还将详细研究gp40和I类分子在活细胞中的相互作用。对gp40滞留的更深刻理解将有助于阐明病毒免疫逃避策略的多样性，这些策略是导致终生病毒持续存在的原因。

MHC (major histocompatibility complex) class I molecules play a key role in the anti-viral immune response by presenting viral antigens to cytotoxic T lymphocytes at the cell surface, which leads to apoptosis of the infected cell and to the control of infection. It is therefore not astonishing that many viruses have developed strategies to circumvent recognition by MHC class I molecules in order to persist: A vast number of viral proteins exist that interfere with antigen presentation, the so-called immunoevasins. We have been studying the immunoevasin gp40 of the murine cytomegalovirus (MCMV) and found out that its mode of action differs from that one of other immunoevasins: It binds to MHC class I molecules but, unlike other immunoevasins that interact directly, it does not lead to their degradation, instead, fully mature class I molecule are retained in an early compartment of the secretory pathway unable to reach the cell surface. We have further identified a novel sequence in gp40, the linker, which is required for both its own retention and that one of MHC class I molecules. These data are already summarized in a manuscript and will be submitted to publication soon. In this project, we will investigate the prerequisite for gp40-mediated class I intracellular retention, namely, the intracellular retention of gp40 itself: We will describe the kind of retention taking place, determine the function of the linker sequence in the retention process, and identify potential binding partners of gp40 that might regulate gp40 retention and, hence, its function. We will also investigate in detail the interaction between gp40 and class I in live cells. A more profound understanding of gp40 retention will help to shed light on the diversity of viral immune evasion strategies that are responsible for lifelong viral persistence.