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)是一种表达于淋巴细胞上的糖基磷脂酰肌醇(GPI)锚定抗原。我们先前已经证明，通过TSA-1/SCA-2的信号抑制T细胞受体(TCR)介导的T细胞激活和凋亡。为了阐明TSA-1介导的TCR信号通路的分子机制，我们在本研究中研究了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CD3zeta cDNA的COS-7细胞中，TSA-1明显与CD3zeta链结合，免疫沉淀和共聚焦显微镜观察证实TSA-1与CD3zeta链在T细胞表面发生物理结合。用稳定和瞬时表达TSA-1跨膜形式的转染体进行的分析表明，CD3zeta的结合不需要TSA-1的GPI锚点。最后，在抗TSA-1的刺激下，CD3zeta链的酪氨酸磷酸化被诱导，这表明这两个分子之间也存在功能联系。这些结果表明，TSA-1/SCA-2与CD3zeta的物理结合可能是TCR信号通路中的一种调节作用。

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.