Reif K, Gout I, Waterfield M D, Cantrell D A
Lymphocyte Activation Laboratory, Imperial Cancer Research Fund, London, United Kingdom.
J Biol Chem. 1993 May 25;268(15):10780-8.
Phosphatidylinositol (PtdIns) 3-kinase is composed of a catalytic p110 subunit and a regulatory p85 subunit. A synthetic phosphopeptide corresponding to the kinase insert of the human PDGF beta subunit receptor and monoclonal antibodies raised against the two described p85 isoforms, p85 alpha and p85 beta were used to isolate PtdIns 3-kinase from human T lymphocytes. We demonstrate that T cells express both p85 alpha and p85 beta proteins. Both isoforms tightly associate with a p110 protein and with PtdIns 3-kinase activity in T cells. Upon triggering of the T cell antigen receptor (TCR)/CD3 complex or activation of protein kinase C (PKC) the p110 protein complexed to p85 alpha becomes rapidly phosphorylated exclusively on serine residues. p85 alpha does not appear to undergo a change in its basal serine phosphorylation during T cell activation. In contrast, stimulation of the TCR/CD3 complex or PKC, results in a marked and rapid increase in phosphorylation of p85 beta on threonine residues. These data show that PtdIns 3-kinase can be a substrate for serine/threonine kinases in T cells. The differential phosphorylation of p85 alpha and p85 beta reveals the potential for divergent regulation and function of these two PtdIns 3-kinase isoforms during T cell activation.
磷脂酰肌醇（PtdIns）3-激酶由催化性的p110亚基和调节性的p85亚基组成。一种与人血小板衍生生长因子β亚基受体的激酶插入序列相对应的合成磷酸肽，以及针对所描述的两种p85亚型（p85α和p85β）产生的单克隆抗体，被用于从人T淋巴细胞中分离PtdIns 3-激酶。我们证明T细胞表达p85α和p85β两种蛋白。这两种亚型都与T细胞中的一种p110蛋白以及PtdIns 3-激酶活性紧密相关。在触发T细胞抗原受体（TCR）/CD3复合物或激活蛋白激酶C（PKC）后，与p85α复合的p110蛋白会迅速仅在丝氨酸残基上发生磷酸化。在T细胞激活过程中，p85α的基础丝氨酸磷酸化似乎没有变化。相比之下，TCR/CD3复合物或PKC的刺激会导致p85β在苏氨酸残基上的磷酸化显著且迅速增加。这些数据表明PtdIns 3-激酶可能是T细胞中丝氨酸/苏氨酸激酶的底物。p85α和p85β的差异磷酸化揭示了这两种PtdIns 3-激酶亚型在T细胞激活过程中存在不同调节和功能的可能性。
