Novel lymphocyte-specific Rab GTPase in T cell differentiation

 描述(申请人提供)：T细胞受体(TCR)连接诱导细胞内信号级联反应，包括在T细胞活化和分化中起关键作用的钙-NFAT(活化T细胞核因子)和MAPK(丝裂原活化蛋白激酶)通路。这些通路的缺陷会导致人类和小鼠的免疫缺陷或免疫反应过敏。小分子GTP酶、Ras、Rac和Rho在TCR信号通路的激活中起核心作用，是自身免疫性疾病的治疗靶点。这些小的GTP酶通过与信号适配器的相互作用被招募到免疫突触(IS)，免疫突触是抗原提呈细胞和T细胞之间的界面，并激活下游的MAPK通路。然而，与Ras、Rac和Rho GTP酶相比，Rab GTP酶家族中的60多个成员在T细胞激活中的作用知之甚少。我们的长期目标是揭示Rab GTP酶在TCR信号中的作用，以确定减轻自身免疫的新治疗靶点。我们最近发现了一个新的Rab GTPase，即CRACR2AGTPase，它在TCR信号转导中起关键作用。我们的初步数据表明，CRACR2AGTP酶是一种淋巴细胞特异性的大Rab GTP酶，与小GTP酶不同，它具有许多功能结构域。我们发现CRACR2AGTPase易位到IS中，激活下游的JNK(c-jun N-末端激酶)MAPK通路。此外，它在Th1细胞中高表达，并在干扰素-γ和T-bet的表达中发挥重要作用，从而在自身免疫中发挥重要作用。我们的中心假设是CRACR2AGTP酶通过蛋白质相互作用被招募到IS中，并调节JNK途径来驱动TH1的分化。这项建议的目的是利用高分辨率成像技术、基因组学和条件靶向基因敲除小鼠来确定1)相互作用的伙伴，2)GTP结合和预烯基化介导的调节，以及3)CRACR2AGTP酶在T细胞中的生理作用。CRACR2AGTPase是第一个包含小Rab GTPase结构域的大分子。我们期望揭示迄今为止未知的JNK通路在T细胞分化中的调节机制。我们有信心，我们还将确定Rab GTP酶的独特信号功能，否则已知它只调节细胞内的蛋白质运输。这些机制研究将对这种新型GTP酶治疗自身免疫性疾病的治疗开发具有重要影响。

 DESCRIPTION (provided by applicant): T cell receptor (TCR) ligation induces intracellular signaling cascades including the Ca2+-NFAT (nuclear factor of activated T cells) and MAPK (mitogen-activated protein kinase) pathways that play crucial roles in activation and differentiation of T cells. Defects in these pathways lead to immune deficiency or hypersensitive immune responses in humans and mice. The small GTPases, Ras, Rac and Rho are known to play a central role in activation of TCR signaling pathways and are therapeutic targets in autoimmune diseases. These small GTPases are recruited into the immunological synapse (IS), the interface between an antigen-presenting cell and a T cell via interactions with signaling adaptors and activate the downstream MAPK pathway. However, in contrast to Ras, Rac and Rho GTPases, little is known about the role of more than 60 members of the Rab GTPase family in T cell activation. Our long-term goal is to uncover the role of Rab GTPases in TCR signaling to identify novel therapeutic targets to alleviate autoimmunity. We have recently identified a novel Rab GTPase, "CRACR2A GTPase" that plays a key role in TCR signaling. Our preliminary data show that CRACR2A GTPase is a lymphocyte-specific large Rab GTPase with many functional domains in contrast to small GTPases. We found that CRACR2A GTPase translocates into the IS to activate the downstream JNK (c- Jun N-terminal kinase) MAPK pathway. Furthermore, it is highly expressed in TH1 cells and plays an important role in expression of IFN-γ and T-bet, and thus in autoimmunity. Our central hypothesis is that CRACR2A GTPase is recruited into the IS via protein interactions and regulates the JNK pathway to drive TH1 differentiation. The objective of this proposal is to identify 1) interacting partners, 2) GTP binding and prenylation-mediated regulation, and 3) the physiological role of CRACR2A GTPase in T cells using high resolution imaging techniques, genomics and conditionally targeted knockout mice. CRACR2A GTPase is the first example of a large molecule containing the small Rab GTPase domain. We expect to reveal a hitherto unknown mechanism of regulation of the JNK pathway in T cell differentiation. We are confident that we will also identify a unique signaling function of Rab GTPases, which are otherwise known to mediate only intracellular protein trafficking. These mechanistic studies will have significant impact on therapeutic exploitation of this novel GTPase to treat autoimmune diseases.