al-Shami A, Bourgoin S G, Naccache P H
Centre de Recherche en Rhumatologie et Immunologie, Faculty of Medicine, Laval University, Ste-Foy, Québec, Canada.
Blood. 1997 Feb 1;89(3):1035-44.
Phosphatidylinositol 3-kinase (PI3-kinase) is a cytosolic enzyme that plays key roles in mediating signaling through many receptors. The heterodimeric form of PI3-kinase is made up of a regulatory subunit, p85, and a catalytic subunit, p110. Although granulocyte-macrophage colony-stimulating factor (GM-CSF) has been shown to activate PI3-kinase, the mechanisms by which this activation is mediated and regulated are incompletely understood. Here we show that treatment of human neutrophils with GM-CSF induced both time- and concentration-dependent increases in the level of tyrosine phosphorylation of p85. The ability of GM-CSF to activate PI3-kinase was abolished by pretreating the cells with erbstatin, a tyrosine kinase inhibitor. The simultaneous treatment of the cells with GM-CSF and phorbol esters such as phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-dibutyrate (PDBu) significantly inhibited both the tyrosine phosphorylation of p85 and the activation of PI3-kinase. The inhibitory effects of phorbol esters were not induced by their inactive analogues and they were selective to the stimulation of tyrosine phosphorylation of p85 since phorbol esters did not alter the enhancement of the pattern of tyrosine phosphorylation of other cellular proteins, including that of Jak2 induced by GM-CSF. However, PMA significantly inhibited the in situ tyrosine phosphorylation and the activation of lyn observed in response to GM-CSF. The results suggest that the activation of PI3-kinase by GM-CSF is mediated by the tyrosine phosphorylation of p85 and that this activation is downregulated by PKC possibly via the inhibition of lyn.
磷脂酰肌醇3激酶（PI3激酶）是一种胞质酶，在介导多种受体的信号传导中起关键作用。PI3激酶的异二聚体形式由一个调节亚基p85和一个催化亚基p110组成。虽然粒细胞巨噬细胞集落刺激因子（GM-CSF）已被证明可激活PI3激酶，但这种激活的介导和调节机制尚不完全清楚。在此我们表明，用GM-CSF处理人中性粒细胞会导致p85酪氨酸磷酸化水平出现时间和浓度依赖性增加。用酪氨酸激酶抑制剂埃伯司他预处理细胞可消除GM-CSF激活PI3激酶的能力。同时用GM-CSF和佛波酯如佛波醇12-肉豆蔻酸酯13-乙酸酯（PMA）和佛波醇12,13-二丁酸酯（PDBu）处理细胞，可显著抑制p85的酪氨酸磷酸化和PI3激酶的激活。佛波酯的抑制作用不是由其无活性类似物诱导的，并且它们对p85酪氨酸磷酸化的刺激具有选择性，因为佛波酯不会改变其他细胞蛋白酪氨酸磷酸化模式的增强，包括GM-CSF诱导的Jak2的酪氨酸磷酸化模式增强。然而，PMA显著抑制了GM-CSF诱导的原位酪氨酸磷酸化和Lyn的激活。结果表明，GM-CSF对PI3激酶的激活是由p85的酪氨酸磷酸化介导的，并且这种激活可能通过抑制Lyn而被蛋白激酶C下调。
