Regulation of phospholipase C isozymes

磷脂酶C-γ（PLC-γ 2）在B细胞信号传导中起重要作用。PLC-γ 2的各种酪氨酸残基的磷酸化已经涉及其脂肪酶活性的调节。通过使用对每个假定的磷酸化位点特异的抗体，我们现在已经表明PLC γ 2在Y 753、Y 759和Y1217上磷酸化，以响应拉莫斯细胞以及鼠脾B细胞中B细胞受体的接合。在通过这种受体最大限度地刺激的细胞中，Y1217的磷酸化程度是Y 753或Y 759的三倍。通过免疫受体刺激Jurkat T细胞或血小板也引起Y 753和Y 759的磷酸化，但不引起Y1217的磷酸化。在未受刺激的淋巴细胞中，Y 753磷酸化的基础水平明显。Y 753和Y 759的磷酸化程度与PLC-γ 2的脂肪酶活性相关，而Y1217的磷酸化程度与PLC-γ 2的脂肪酶活性无关。在拉莫斯细胞中对各种药理学抑制剂和RNA干扰的作用的检查表明，Btk在很大程度上但不完全负责Y 753和Y 759的磷酸化，而Y1217的磷酸化独立于Btk。最后，Y1217和Y 753和Y 759的磷酸化发生在不同的PLC-γ 2分子上。

Phospholipase C-gamma (PLC-gamma2) plays an important role in B cell signaling. Phosphorylation of various tyrosine residues of PLC-gamma2 has been implicated in regulation of its lipase activity. With the use of antibodies specific for each of the putative phosphorylation sites, we have now shown that PLCgamma2 is phosphorylated on Y753, Y759, and Y1217 in response to engagement of the B cell receptor in Ramos cells, as well as in murine splenic B cells. In cells stimulated maximally via this receptor, the extent of phosphorylation of Y1217 was three times that of Y753 or of Y759. Stimulation of Jurkat T cells or platelets via their immunoreceptors also elicited phosphorylation of Y753 and Y759 but not that of Y1217. A basal level of phosphorylation of Y753 was apparent in unstimulated lymphocytes. The extent of phosphorylation of Y753 and Y759, but not that of Y1217, correlated with the lipase activity of PLC-gamma2. Examination of the effects of various pharmacological inhibitors and of RNA interference in Ramos cells suggested that Btk is largely, but not completely, responsible for phosphorylation of Y753 and Y759, whereas phosphorylation of Y1217 is independent of Btk. Finally, phosphorylation of Y1217 and that of Y753 and Y759 occurred on different PLC-gamma2 molecules.