Analysis of TSA-1 that regulates TCR-mediated signal transduction

胸腺共享抗原-1（TSA-1）/干细胞抗原-2（Sca-2）是一种在淋巴细胞上表达的糖基-磷脂酰肌醇（GPI）锚定抗原。我们以前已经证明，通过TSA-1/Sca-2的信号抑制T细胞受体（TCR）介导的T细胞活化和凋亡。为了阐明TSA-1介导的TCR信号通路调节的分子机制，我们在本研究中检测了TSA-1是否与TCR物理偶联。在T细胞杂交瘤、活化T细胞和转染TSA-1和CD 3 zeta cDNA的COS-7细胞中，TSA-1与CD 3 zeta链明显结合，免疫沉淀和共聚焦显微镜证实了TSA-1与T细胞表面的物理结合。使用表达跨膜形式的TSA-1的稳定和瞬时转染子的分析显示，CD 3 ζ的结合不需要TSA-1的GPI锚。最后，在用抗TSA-1刺激后诱导CD 3 ζ链的酪氨酸磷酸化，表明这两种分子之间也存在功能关联。这些结果暗示与CD 3 zeta的物理缔合是TSA-1/Sca-2在TCR信号传导途径中的调节作用的基础。

Thymic shared antigen-1 (TSA-1)/stem cell Ag-2 (Sca-2) is a glycosyl-phosphatidylinositol (GPI) -anchored antigen expressed on lymphocytes. We have previously demonstrated that a signal via TSA-1/Sca-2 inhibits T cell receptor (TCR)-medialted T cell activation and apoptosis. To elucidate a molecular mechanism for TSA-1-mediated modulation of the TCR signaling pathway, we examined whether TSA-1 is physically coupled to the TCR in the present study. TSA-1 was clearly associated with CD3zeta chains in T cell hybridomas, activated T cells, and COS-7 cells transfected with TSA-1 and CD3zeta cDNA.The physical association was confirmed on the surface of T cells in immunoprecipitation and confocal microscopy. The analysis using stable and transient transfectants expressing a transmembrane form of TSA-1 revealed that the association of CD3zeta did not require the GPI anchor of TSA-1. Finally, tyrosine phosphorylation of CD3zeta chains was induced after stimulation with anti-TSA-1, suggesting that a functional association between these two molecules also exists. These results imply that the physical association to CD3zeta underlies a regulatory role of TSA-1/Sca-2 in TCR signaling pathway.