Signaling functions of Peli family of E3 ubiquitin ligases

描述(申请人提供)：泛素化已成为免疫系统中调节信号转导的关键机制。去调节的泛素化事件与严重的免疫紊乱有关，如自身免疫和慢性炎症。泛素化系统的一个关键组成部分是E3泛素连接酶，这是一个超家族(超过600个成员)的酶，通过识别底物来赋予泛素化的特异性。由于每个E3都以少量泛素化蛋白质为靶标，因此表征特定E3的生理靶标是一项具有挑战性和非常重要的任务。这些信息对于合理设计治疗方法至关重要。该项目的长期目标是了解新发现的E3泛素连接酶家族Peli(也称为Pellino)的免疫调节功能。Peli蛋白结合两者 赖氨酸(K)63和K48连接的多泛素链，尽管它们在体内的生物学功能仍然知之甚少。通过基因打靶，我们的初步研究和最近发表的工作揭示了Peli1在免疫受体信号和自身免疫调节中的关键和似乎复杂的作用。Peli1负性调节T细胞激活和维持T细胞耐受，Peli1缺乏会引起全身自身免疫症状。矛盾的是，Peli1基因敲除(KO)小鼠对实验性自身免疫性脑脊髓炎(EAE)的诱导是困难的，EAE是中枢神经系统(CNS)的一种器官特异性自身免疫性疾病。有趣的是，尽管Peli1KO小鼠的外周淋巴器官中有大量的炎性T细胞产生，但这些免疫细胞未能迁移到中枢神经系统。我们已经获得了遗传学证据，表明Peli1是先天免疫受体信号传递所必需的，并在中枢神经系统驻留的小胶质细胞中诱导促炎细胞因子和趋化因子。这些创新的发现表明，Peli1在调节T细胞激活和中枢神经系统固有免疫受体信号方面扮演着关键而矛盾的角色。阐明其潜在的机制对于治疗方法是非常重要的。因此，这项赠款申请的总体目标是了解Peli1是如何发挥其免疫调节功能的。我们的假设是，Peli1针对泛素化的不同信号因子，从而调节 先天免疫细胞激活和T细胞耐受。为了实现我们的总体目标，我们将(1)研究Peli1如何调节T细胞的激活和耐受；(2)研究Peli1如何调节先天免疫受体信号和中枢神经系统炎症；以及(3)阐明调节Peli1激活和功能的生化机制。

DESCRIPTION (provided by applicant): Ubiquitination has emerged as a pivotal mechanism that regulates signal transduction in the immune system. Deregulated ubiquitination events are associated with severe immunological disorders, such as autoimmunity and chronic inflammation. A critical component of the ubiquitination system is E3 ubiquitin ligase, a superfamily (more than 600 members) of enzymes that confer specificity of ubiquitination by recognizing substrates. Since each E3 targets a small number of proteins for ubiquitination, characterization of the physiological targets of specific E3s represents a challenging and highly significant task. This information is critical for rational design of therapeutic approaches. The long-range goal of this project is to understand the immunoregulatory functions of a newly identified family of E3 ubiquitin ligases, Peli (also called Pellino). Peli proteins conjugate both lysine (K) 63- and K48-linked polyubiquitin chains, although their in vivo biological functions remains poorly understood. By gene targeting, our preliminary studies and recently published work revealed a critical, and seemingly complex, role for Peli1 in the regulation of immune receptor signaling and autoimmunity. Peli1 negatively regulates T-cell activation and maintains T-cell tolerance, and Peli1 deficiency causes systemic autoimmune symptoms. Paradoxically, the Peli1 knockout (KO) mice are refractory to the induction of experimental autoimmune encephalomyelitis (EAE), an organ-specific autoimmune disease of the central nervous system (CNS). Interestingly, although the Peli1 KO mice have hyper-production of inflammatory T cells in the peripheral lymphoid organs, these immune cells failed to migrate to the CNS. We have obtained genetic evidence that Peli1 is required for innate immune receptor signaling and induction of proinflammatory cytokines and chemokines in the CNS-resident microglial cells. These innovative findings demonstrate a pivotal and paradoxical role for Peli1 in the regulation of T-cell activation and CNS innate immune receptor signaling. Elucidation of the underlying mechanism is highly important for therapeutic approaches. Thus, the overall objective of this grant application is to understand how Peli1 exerts its immunoregulatory functions. Our hypothesis is that Peli1 targets different signaling factors for ubiquitination, thereby regulating both innate immune cell activation and T-cell tolerance. To achieve our overall objective, we will (1) examine how Peli1 regulates T-cell activation and tolerance; (2) examine how Peli1 regulates innate immune receptor signaling and CNS inflammation; and (3) elucidate the biochemical mechanisms regulating the activation and function of Peli1.