Cbl-b in T Cell Activation and Autoimmunity

描述（由申请人提供）：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，已被证明对维持免疫和耐受之间的平衡很重要。之前，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的表达，这对于建立T细胞激活和耐受的阈值至关重要。在体外和体内实验中，Cbl-b-/- T细胞对能量诱导具有抵抗性，这有力地支持了这一观点。事实上，cb -b-/-小鼠对自身免疫非常敏感。进一步研究发现，Cbl-b不仅下调T细胞活化，而且选择性抑制辅助性T细胞2 （Th2）分化和过敏性气道炎症。有趣的是，Cbl-b有利于幼稚CD4？T细胞进入CD4???？体外培养Tregs （iTregs）。尽管b- b-/- CD4？自然产生的Tregs （nTregs）在体外显示正常的抑制活性，Cbl-b-/- CD4？效应T细胞（Teffs）抵抗nTregs的调节，这可能是由于IL-4的产生增加。在分子水平上，Cbl-b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降解来抑制Th2细胞分化。这些过程在TCR信号传导中得到加强。此外，cb -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靶向Stat-6泛素化，促进iTreg生成，从而抑制Th2反应和过敏性气道炎症。为了验证这一假设，我们将研究：1)Cbl-b是否通过靶向Stat-6泛素化抑制Th2反应，从而抑制过敏性气道炎症；2)体内是否以及如何调节iTregs的发育，从而调节Th2反应和过敏性气道炎症。本提案的具体目的将解决基本问题：Cbl-b如何调节与其生物学功能相关的靶底物/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导致自身免疫性疾病和过敏性哮喘的潜在治疗方法。

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.