Antón Olga, Batista Alicia, Millán Jaime, Andrés-Delgado Laura, Puertollano Rosa, Correas Isabel, Alonso Miguel A
Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Madrid, Spain.
J Exp Med. 2008 Dec 22;205(13):3201-13. doi: 10.1084/jem.20080552. Epub 2008 Dec 8.
The MAL protein is an essential component of the specialized machinery for apical targeting in epithelial cells. The src family kinase Lck plays a pivotal role in T cell signaling. We show that MAL is required in T cells for efficient expression of Lck at the plasma membrane and activation of IL-2 transcription. To investigate the mechanism by which MAL regulates Lck targeting, we analyzed the dynamics of Lck and found that it travels to the plasma membrane in specific transport carriers containing MAL. Coimmunoprecipitation experiments indicated an association of MAL with Lck. Both carrier formation and partitioning of Lck into detergent-insoluble membranes were ablated in the absence of MAL. Polarization of T cell receptor for antigen (TCR) and microtubule-organizing center to immunological synapse (IS) were also defective. Although partial correction of the latter defects was possible by forced expression of Lck at the plasma membrane, their complete correction, formation of transport vesicles, partitioning of Lck, and restoration of signaling pathways, which are required for IL-2 transcription up-regulation, were achieved by exogenous expression of MAL. We concluded that MAL is required for recruitment of Lck to specialized membranes and formation of specific transport carriers for Lck targeting. This novel transport pathway is crucial for TCR-mediated signaling and IS assembly.
MAL蛋白是上皮细胞顶端靶向特定机制的重要组成部分。src家族激酶Lck在T细胞信号传导中起关键作用。我们发现T细胞中MAL对于Lck在质膜上的高效表达以及IL-2转录的激活是必需的。为了研究MAL调节Lck靶向的机制，我们分析了Lck的动力学，发现它通过含有MAL的特定运输载体转运到质膜。免疫共沉淀实验表明MAL与Lck存在关联。在没有MAL的情况下，载体形成以及Lck在去污剂不溶性膜中的分配均被消除。抗原T细胞受体（TCR）和微管组织中心向免疫突触（IS）的极化也存在缺陷。虽然通过在质膜上强制表达Lck可以部分纠正后一种缺陷，但通过外源性表达MAL可以实现对它们的完全纠正，包括运输小泡的形成、Lck的分配以及IL-2转录上调所需的信号通路的恢复。我们得出结论，MAL是将Lck募集到特定膜以及形成用于Lck靶向的特定运输载体所必需的。这种新的运输途径对于TCR介导的信号传导和IS组装至关重要。
