Cbl-b in T Cell Activation and Autoimmunity

描述（申请人提供）：Casitas-B-谱系淋巴瘤蛋白-b (Cbl-b) 是一种接头蛋白和环指结构域型 E3 泛素 (Ub) 连接酶，已被证明对于维持免疫和耐受之间的平衡很重要。此前，我们证明 CD28 共刺激增强了 TCR 诱导的 Cbl-b 泛素化和降解，而 CTLA-4-B7 相互作用是 Cbl-b 重新表达所必需的。这些观察结果表明 CD28 和 CTLA-4 严格调节 Cbl-b 表达，这对于建立 T 细胞激活和耐受的阈值至关重要。 Cbl-b-/- T 细胞在体外和体内均能抵抗无反应性诱导，这有力地支持了这一观点。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细胞活化，还选择性抑制辅助性T细胞2（Th2）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细胞变成CD4？？？ Tregs (iTreg) 体外。虽然Cbl-b-/- CD4？天然存在的 Tregs (nTreg) 在体外表现出正常的抑制活性，Cbl-b-/- CD4?效应 T 细胞 (Teff) 对 nTreg 的调节具有抵抗力，这可能是由于 IL-4 产量增加所致。在分子水平上，Cbl-b 在 IL-4 连接后选择性地与 Stat-6（参与 Th2 细胞分化的重要转录因子）结合，并可能通过靶向 Stat-6 降解来抑制 Th2 分化。这些过程在 TCR 信号传导中得到加强。此外，Cbl-b 通过抑制 PI3-K/Akt 激活来促进 iTreg 生成。基于上述数据，我们假设Cbl-b靶向Stat-6进行泛素化并促进iTreg生成，从而抑制Th2反应和过敏性气道炎症。为了检验这一假设，我们将研究：1) Cbl-b 是否通过靶向 Stat-6 进行泛素化来抑制 Th2 反应，从而抑制过敏性气道炎症； 2) Cbl-b 是否以及如何调节体内 iTreg 的发育，从而调节 Th2 反应和过敏性气道炎症。该提案的具体目标将解决基本问题：Cbl-b如何调节与其生物功能相关的靶底物/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带来潜在的治疗方法。 公共健康相关性：Cbl-b 是一种 E3 泛素连接酶，负责靶向不需要的蛋白质进行降解，从而防止这些不需要的蛋白质的积累。缺乏Cbl-b的小鼠的T和B淋巴细胞表现出过度活跃，并且非常容易受到自身免疫和哮喘诱发的影响。我们有兴趣进一步表征 Cbl-b 是否以及如何调节其底物蛋白，从而影响其生物学功能，包括 T 辅助 2 细胞分化和调节哮喘易感性的调节性 T 细胞发育。

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.