Regulation of phospholipase C isozymes

磷脂酶c - γ (PLC-gamma2)在B细胞信号传导中起重要作用。PLC-gamma2的各种酪氨酸残基的磷酸化与脂肪酶活性的调节有关。使用针对每个假定磷酸化位点的特异性抗体，我们现在已经证明，在拉莫斯细胞和小鼠脾B细胞中，PLCgamma2在Y753、Y759和Y1217上被磷酸化，以响应B细胞受体的参与。在受该受体刺激最大的细胞中，Y1217的磷酸化程度是Y753或Y759的三倍。通过免疫受体刺激Jurkat T细胞或血小板也会引起Y753和Y759的磷酸化，但不会引起Y1217的磷酸化。在未受刺激的淋巴细胞中，Y753的基础磷酸化水平很明显。Y753和Y759的磷酸化程度与PLC-gamma2的脂肪酶活性相关，而Y1217的磷酸化程度无关。对各种药理学抑制剂和RNA干扰在拉莫斯细胞中的作用的研究表明，Btk在很大程度上（但不是完全）负责Y753和Y759的磷酸化，而Y1217的磷酸化不依赖于Btk。最后，Y1217、Y753和Y759的磷酸化发生在不同的PLC-gamma2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.