Cell Signalling Section, Division of Immunology, Department of Pathology, Cambridge University, Cambridge, United Kingdom.
Mol Cell Biol. 2014 Apr;34(8):1486-99. doi: 10.1128/MCB.01331-13. Epub 2014 Feb 10.
Despite playing a central role in tolerance, little is known regarding the mechanism by which intracellular CTLA-4 is shuttled from the trans-Golgi network to the surfaces of T cells. In this context, Ras-related GTPase Rab8 plays an important role in the intracellular transport, while we have previously shown that CTLA-4 binds to the immune cell adaptor TRIM in T cells. In this study, we demonstrate that CTLA-4 forms a multimeric complex comprised of TRIM and related LAX that in turn binds to GTP bound Rab8 for post-Golgi transport to the cell surface. LAX bound via its N terminus to active GTP-Rab8, as well as the cytoplasmic tail of CTLA-4. TRIM required LAX for binding to Rab8 in a complex. Wild-type LAX or its N terminus (residues 1 to 77) increased CTLA-4 surface expression, whereas small interfering RNAs of Rab8 or LAX or disruption of LAX/Rab8 binding reduced numbers of CTLA-4-containing vesicles and its coreceptor surface expression. LAX also promoted the polarization of CTLA-4 and the reorientation of the microtubule-organizing center to the site of T-cell receptor engagement. Our results identify a novel CTLA-4/TRIM/LAX/Rab8 effector complex in the transport of CTLA-4 to the surfaces of T cells.
尽管细胞内 CTLA-4 在耐受中发挥核心作用，但对于其从反式高尔基体网络转运到 T 细胞表面的机制知之甚少。在这种情况下，Ras 相关 GTP 酶 Rab8 在细胞内运输中发挥重要作用，而我们之前已经表明 CTLA-4 与 T 细胞中的免疫细胞衔接蛋白 TRIM 结合。在这项研究中，我们证明 CTLA-4 形成一个由 TRIM 和相关的 LAX 组成的多聚体复合物，该复合物反过来与 GTP 结合的 Rab8 结合，以进行高尔基体后转运到细胞表面。LAX 通过其 N 端与活性 GTP-Rab8 以及 CTLA-4 的细胞质尾巴结合。TRIM 需要 LAX 才能在复合物中与 Rab8 结合。野生型 LAX 或其 N 端（残基 1 至 77）增加了 CTLA-4 的表面表达，而 Rab8 或 LAX 的小干扰 RNA 或 LAX/Rab8 结合的破坏减少了含有 CTLA-4 的囊泡及其共受体的表面表达。LAX 还促进了 CTLA-4 的极化和微管组织中心向 T 细胞受体结合部位的重定向。我们的研究结果确定了一种新型 CTLA-4/TRIM/LAX/Rab8 效应复合物，该复合物在 CTLA-4 向 T 细胞表面的转运中发挥作用。
