Conroy L A, Jenkinson E J, Owen J J, Michell R H
Centre for Clinical Research in Immunology and Signalling, Medical School, University of Birmingham, GB.
Eur J Immunol. 1995 Jul;25(7):1828-35. doi: 10.1002/eji.1830250706.
Regulation of the development of thymocytes into mature T cells within the thymus is now known to involve antigen-induced deletion, by apoptosis, of potentially autoreactive thymocytes, and it can be mimicked either by stimulating the T cell receptor (TcR) complex by monoclonal antibody (mAb) or by ionophore-induced elevation of cytosolic [Ca2+]. To identify signaling pathways employed by the TcR complex of immature thymocytes, we examined the effects of anti-CD3 and anti-TcR beta constant (c) region mAb, staphylococcal enterotoxin B (SEB) and pharmacological agents on the generation of inositol phosphates through hydrolysis of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] both in cultured fetal mouse thymic lobes and in the CD4+CD8+ immature thymocyte cell line, TM10G. Stimulation of the TcR complex with anti-CD3 mAb provoked an accumulation of inositol phosphates diagnostic of the occurrence of receptor-stimulated phosphoinositidase C (PLC) activation. Anti-TcRC beta mAb and SEB provoked smaller but similar responses. The PLC activation evoked by anti-CD3 mAb was suppressed by inhibitors of receptor tyrosine kinases and was unmodified by protein kinase C activation or elevation of cytosolic [Ca2+]. It thus appears that apoptosis triggered by TcR stimulation is associated with PLC activation by a receptor-regulated tyrosine kinase. Treatment of thymic lobes or TM10G cells with fluoroaluminate provoked apoptosis of a wider range of thymocyte subtypes and such stimulation also provoked an accumulation of inositol phosphates. The responses to fluoroaluminate were not prevented by inhibitors of tyrosine kinases, suggesting that unidentified GTP-binding proteins which couple to PLC activation may also be capable of initiating apoptosis by a route independent of the TcR. These results, when considered alongside previous studies of mature T cells, indicate that stimulation of immature thymocytes or of mature T cells through their TcR complex activates the PLC-catalyzed PtdIns(4,5)P2 hydrolysis signaling pathway, and thus that this signaling pathway may be implicated both in provoking apoptosis in immature T cells and in initiating proliferation in mature T cells.
现在已知胸腺内胸腺细胞发育为成熟T细胞的调节涉及通过凋亡对抗原诱导的潜在自身反应性胸腺细胞的清除，并且可以通过用单克隆抗体（mAb）刺激T细胞受体（TcR）复合物或通过离子载体诱导的胞质[Ca2+]升高来模拟。为了鉴定未成熟胸腺细胞的TcR复合物所采用的信号通路，我们研究了抗CD3和抗TcRβ恒定（c）区mAb、葡萄球菌肠毒素B（SEB）和药理试剂对培养的胎鼠胸腺叶和CD4+CD8+未成熟胸腺细胞系TM10G中通过磷脂酰肌醇4,5-二磷酸[PtdIns(4,5)P2]水解产生肌醇磷酸的影响。用抗CD3 mAb刺激TcR复合物引发了肌醇磷酸的积累，这是受体刺激的磷脂酶C（PLC）激活发生的诊断指标。抗TcRβc mAb和SEB引发了较小但相似的反应。抗CD3 mAb诱发的PLC激活被受体酪氨酸激酶抑制剂抑制，并且不受蛋白激酶C激活或胞质[Ca2+]升高的影响。因此，似乎TcR刺激引发的凋亡与受体调节的酪氨酸激酶介导的PLC激活有关。用氟铝酸盐处理胸腺叶或TM10G细胞会引发更广泛的胸腺细胞亚型的凋亡，并且这种刺激也会引发肌醇磷酸的积累。酪氨酸激酶抑制剂不能阻止对氟铝酸盐的反应，这表明与PLC激活偶联的未鉴定的GTP结合蛋白也可能能够通过独立于TcR的途径引发凋亡。这些结果与先前对成熟T细胞的研究一起考虑时，表明通过其TcR复合物刺激未成熟胸腺细胞或成熟T细胞会激活PLC催化的PtdIns(4,5)P2水解信号通路，因此该信号通路可能既与引发未成熟T细胞的凋亡有关，也与启动成熟T细胞的增殖有关。
