Deltex1在T細胞去活化機制調控之探討

Abstract

E3泛素連接酶對於誘發及維持T細胞去活化 (T cell anergy) 扮演重要的角色。誘發T細胞去活化過程中，去活化相關的E3泛素連接酶如Cbl-b, Itch和GRAIL的蛋白質表達量會上升，並透過降解T細胞活化訊息傳遞分子PKCθ和PLCγ1而抑制T細胞再活化。然而這些去活化相關的E3泛素連接酶如何彼此協同，進而維持T細胞去活化卻未完全清楚。 本篇研究中，我們探討Notch相關E3泛素連接酶deltex1 (DTX1) 在維持T細胞去活化的扮演的角色。我們發現，DTX1會結合PKCθ和PLCγ1並抑制其蛋白質表現。進一步的研究顯示，相似Cbl-b和Itch的作用，DTX1催化PKCθ單體泛素化，使得單體泛素化的PKCθ經由核內體-溶小體 (endosome-lysosome) 途徑而分解，處理蛋白酶體抑制劑並不會降低DTX1所調控PKCθ降解。此外，我們也觀察到DTX1會與Cbl-b結合並促進Cbl-b的表現。進一步的實驗證實，DTX1抑制PKCθ主導的Cbl-b降解並增加Cbl-b的蛋白質穩定。本篇的研究闡述了去活化相關的E3泛素連接酶在T細胞去活化中的協同作用：DTX1泛素化PKCθ並經由核內體-溶小體 (endosome-lysosome) 途徑調控PKCθ降解；DTX1透過調控PKCθ降解促進Cbl-b蛋白質穩定；DTX1與Cbl-b共同作用確保PKCθ的活性完全抑制。

Ubiquitin E3 ligases are associated with induction and maintance of T cell anergy. These E3 ligases, including Cbl-b, Itch, and GRAIL, attenuate T cell activation by targeting to signaling molecules such as PKCθ and PLCγ1 for degradetion. How these anergy-associated E3 ligases coordinate during T cell anergy remains incompletely understood. In this study, we found that Notch-related E3 ligase deltex1 (DTX1) also regulated the expression of PKCθ and PLCγ1. DTX1 interacted with PKCθ and PLCγ1 and promoted the degradation of PKCθ and PLCγ1. T cell anergy-induced downregulation of PKCθ was prevented in Dtx1-/- T cells, supporting the essential role of DTX1 in PKCθ downregulation. DTX1 promoted monoubiquitination of PKCθ, similar to Cbl-b and Itch. DTX1-directed PKCθ degradation was not prevented by proteasome inhibitor, but instead DTX1 directed the re-localization of PKCθ into the lysosomal pathway. In addition, DTX1 interacted with Cbl-b and increased the protein levels of Cbl-b. We further demonstrated that, through the downregulation of PKCθ, DTX1 prevented PKCθ-induced Cbl-b degradation and increased Cbl-b protein stability. Our results illustrate the coordination between E3 ligases during T cell anergy; DTX1-mediated PKCθ degradation further stabilizes Cbl-b and DTX1 acts with Cbl-b to assure a more completely silencing of PKCθ.