Cbl-b in T Cell Activation and Autoimmunity

描述(由申请人提供)：Casitas-B系淋巴瘤蛋白-b(Cbl-b)是一种接头蛋白和环指结构域型E3泛素(Ub)连接酶，已被证明对维持免疫和耐受之间的平衡很重要。先前，我们证明了CD28共刺激增强了TCR诱导的Cbl-b泛素化和降解，而CTLA-4-B7相互作用才能使Cbl-b重新表达。这些观察表明，CD28和CTLA-4严格调控Cbl-b的表达，这对于建立T细胞激活和耐受的阈值是至关重要的。在这一观点的有力支持下，Cbl-b-/-T细胞在体外和体内对无能诱导具有抵抗力。事实上，Cbl-b-/-小鼠对自身免疫非常敏感。进一步的研究表明，Cbl-b不仅下调T细胞的活化，而且选择性地抑制T辅助细胞2(Th2)的分化和过敏性气道炎症。有趣的是，Cbl-b有利于NAOVE CD4？的外周转化。T细胞转化为CD4？Tregs(ITregs)体外培养。虽然Cbl-b-/-CD4？自然产生的树突状细胞(NTregs)在体外表现出正常的抑制活性，Cb1-b-/-CD4？效应T细胞对nTregs的调节具有抵抗力，这可能是由于IL-4的产生增加所致。在分子水平上，Cbl-b在IL-4连接时选择性地与参与Th2细胞分化的重要转录因子Stat-6结合，并可能通过靶向Stat-6的降解来抑制Th2的分化。这些过程在TCR信号中得到加强。此外，Cbl-b通过抑制PI3-K/Akt的激活促进iTreg的生成。基于以上数据，我们假设Cbl-b针对Stat-6泛素化并促进iTreg的产生，从而抑制Th2反应和过敏性呼吸道炎症。为了验证这一假说，我们将研究：1)Cbl-b是否通过靶向Stat-6泛素化来抑制Th2反应，从而抑制全身性呼吸道炎症；以及2)Cbl-b是否以及如何调节体内iTregs的发展，从而调节Th2反应和过敏性气道炎症。这项提案的具体目标将涉及基本问题：Cbl-b如何调节与其生物功能相关的目标底物/途径。更好地了解Cbl-b生物学功能的细胞和分子机制可能会为自身免疫性疾病和过敏性哮喘提供潜在的治疗方法。 与公共卫生相关：CBL-b是一种E3泛素连接酶，负责定位不需要的蛋白质进行降解，从而防止这些不需要的蛋白质积累。缺乏Cbl-b的小鼠表现出T和B淋巴细胞的高活性，并且对自身免疫和哮喘诱发高度敏感。我们有兴趣进一步研究Cbl-b是否以及如何调节其底物蛋白，影响其生物学功能，包括T辅助细胞分化和调节T细胞发育，从而调节对哮喘的易感性。

DESCRIPTION (provided by applicant): Casitas-B-lineage lymphoma protein-b (Cbl-b) is an adaptor protein and RING finger domain-type E3 ubiquitin (Ub) ligase, and has been shown to be important for the maintenance of a balance between immunity and tolerance. Previously, we demonstrated that CD28 costimulation potentiates TCR-induced Cbl-b ubiquitination and degradation, whereas CTLA-4-B7 interaction is required for Cbl-b re-expression. These observations indicate that CD28 and CTLA-4 tightly regulate Cbl-b expression which is critical for establishing the threshold for T cell activation and tolerance. In strong support of this notion, Cbl-b-/- T cells are resistant to anergy induction in vitro and in vivo. Indeed, Cbl-b-/- mice are highly susceptible to autoimmunity. Further studies reveal that Cbl-b not only down- regulates T cell activation, but also selectively inhibits T helper 2 (Th2) differentiation and allergic airway inflammation. Intriguingly, Cbl-b favors peripheral conversion of naove CD4? T cells into CD4???? Tregs (iTregs) in vitro. Although Cbl-b-/- CD4? naturally-occurring Tregs (nTregs) display normal suppressive activity in vitro, Cbl-b-/- CD4? effector T cells (Teffs) are resistant to regulation by nTregs which is possibly due to increased production of IL-4. At the molecular levels, Cbl-b selectively associates with Stat-6, an important transcription factor involved in Th2 cell differentiation, upon IL-4 ligation and may inhibit Th2 differentiation by targeting Stat-6 for degradation. These processes are heightened in the TCR signaling. Furthermore, Cbl-b facilitates iTreg generation by inhibiting PI3-K/Akt activation. Based upon the above data, we hypothesize that Cbl-b targets Stat-6 for ubiquitination and facilitate iTreg generation, thus inhibiting Th2 responses and allergic airway inflammation. To test this hypothesis, we will investigate: 1) whether Cbl-b inhibits Th2 responses by targeting Stat-6 for ubiquitination, thus suppressing alleric airway inflammation; and 2) whether and how Cbl-b regulates the development of iTregs in vivo, therefore modulating Th2 responses and allergic airway inflammation. The specific aims of this proposal will address fundamental question: how does Cbl-b regulate its target substrates/pathways related to its biological functions. A better understanding of cellular and molecular mechanisms of Cbl-b biological functions may lead to potential therapeutic approaches for autoimmune diseases and allergic asthma. PUBLIC HEALTH RELEVANCE: Cbl-b is an E3 ubiquitin ligase which is responsible for targeting unwanted proteins for degradation, and hence prevents the accumulation of these unwanted proteins. Mice lacking Cbl-b display hyper-activity of their T and B lymphocytes and are highly susceptible to autoimmunity and asthma induction. We are interested in further characterizing whether and how Cbl-b regulates its substrate proteins affecting its biological functions including T helper 2 cell differentiation and regulatory T cell development which tune the susceptibility to asthma.