Roifman C M, Wang G
Division of Immunology/Allergy, Hospital for Sick Children, Toronto, Ontario, Canada.
J Immunol. 1992 Aug 15;149(4):1179-84.
The B cell AgR regulates two signal transduction pathways: the tyrosine kinase and the phosphatidylinositol (PtdIns) pathways. Stimulation of B cells with Ag or anti-Ig antibody results in a rapid increase in tyrosine phosphorylation of multiple substrates. The AgR also mediates the activation of phospholipase C-gamma 1 (PLC-gamma 1) thus producing the second messengers, inositol trisphosphate and diacylglycerol. Although the detailed relationship between these two signaling pathways remains unclear, it has recently become apparent that PLC-gamma 1 might be a target for the AgR-associated protein tyrosine kinase. To address the question of whether tyrosine kinase activity is essential for B cell activation, we studied early biochemical changes and later cellular events induced by ligation of the purinoceptor (P2R). Ligation of ATP to its receptor on B cells has been previously shown to elicit increases in cytosolic free Ca2+ and inositol phosphate production as well as induction of c-fos mRNA expression and increased expression of IL-2 and transferrin receptors. We show here that ATP in a wide range of concentrations did not increase protein tyrosine kinase activity. In contrast with the AgR, P2R did not mediate tyrosine phosphorylation of PLC-gamma 1, thus suggesting that it may use another phosphoinositide-specific PLC that does not require phosphorylation on tyrosine residues for its activation. The results were supported by experiments with a specific tyrosine kinase inhibitor, tyrphostin AG-126. Preincubation with this inhibitor blocked AgR but not P2R-mediated inositol phosphate production, cytosolic free Ca2+ changes, and IL-2 and transferrin receptor expression. The results indicate that the PtdIns pathway may be sufficient to induce activation of B cells and that the tyrosine phosphorylation pathway is not necessary for nonantigenic B cell activation.
B细胞抗原受体调节两条信号转导途径：酪氨酸激酶途径和磷脂酰肌醇（PtdIns）途径。用抗原或抗Ig抗体刺激B细胞会导致多种底物的酪氨酸磷酸化迅速增加。抗原受体还介导磷脂酶C-γ1（PLC-γ1）的激活，从而产生第二信使肌醇三磷酸和二酰基甘油。尽管这两条信号通路之间的详细关系仍不清楚，但最近已明显看出PLC-γ1可能是与抗原受体相关的蛋白酪氨酸激酶的作用靶点。为了解决酪氨酸激酶活性对于B细胞激活是否必不可少的问题，我们研究了嘌呤受体（P2R）连接诱导的早期生化变化和后期细胞事件。先前已表明，ATP与其在B细胞上的受体连接会引起胞质游离Ca2+增加、肌醇磷酸生成增加以及c-fos mRNA表达的诱导和IL-2及转铁蛋白受体表达的增加。我们在此表明，广泛浓度范围内的ATP不会增加蛋白酪氨酸激酶活性。与抗原受体相反，P2R不会介导PLC-γ1的酪氨酸磷酸化，因此表明它可能使用另一种磷酸肌醇特异性PLC，其激活不需要酪氨酸残基磷酸化。用特异性酪氨酸激酶抑制剂 tyrphostin AG-126进行的实验支持了这些结果。用该抑制剂预孵育可阻断抗原受体介导的肌醇磷酸生成、胞质游离Ca2+变化以及IL-2和转铁蛋白受体表达，但不影响P2R介导的这些过程。结果表明，磷脂酰肌醇途径可能足以诱导B细胞激活，并且酪氨酸磷酸化途径对于非抗原性B细胞激活不是必需的。
