Xu Jianfeng, Weng Yu-I, Simonyi Agnes, Krugh Brent W, Liao Zhongji, Weisman Gary A, Sun Grace Y
Department of Biochemistry, University of Missouri-Columbia, Columbia, Missouri, USA.
J Neurochem. 2002 Oct;83(2):259-70. doi: 10.1046/j.1471-4159.2002.01145.x.
Although Group IV cytosolic phospholipase A2 (cPLA2) in astrocytes has been implicated in a number of neurodegenerative diseases, mechanisms leading to its activation and release of arachidonic acid (AA) have not been clearly elucidated. In primary murine astrocytes, phorbol myristate acetate (PMA) and ATP stimulated phosphorylation of ERK1/2 and cPLA2 as well as evoked AA release. However, complete inhibition of phospho-ERK by U0126, an inhibitor of mitogen-activated protein kinase kinase (MEK), did not completely inhibit PMA-stimulated cPLA2 and AA release. Epidermal growth factor (EGF) also stimulated phosphorylation of ERK1/2 and cPLA2[largely through a protein kinase C (PKC)-independent pathway], but EGF did not evoke AA release. These results suggest that phosphorylation of cPLA2 due to phospho-ERK is not sufficient to evoke AA release. However, complete inhibition of ATP-induced cPLA2 phosphorylation and AA release was observed when astrocytes were treated with GF109203x, a general PKC inhibitor, together with U0126, indicating the important role for both PKC and ERK in mediating the ATP-induced AA response. There is evidence that PMA and ATP stimulated AA release through different PKC isoforms in astrocytes. In agreement with the sensitivity of PMA-induced responses to PKC down-regulation, prolonged treatment with PMA resulted in down-regulation of PKCalpha and epsilon in these cells. Furthermore, PMA but not ATP stimulated rapid translocation of PKCalpha from cytosol to membranes. Together, our results provided evidence for an important role of PKC in mediating cPLA2 phosphorylation and AA release in astrocytes through both ERK1/2-dependent and ERK1/2-independent pathways.
虽然星形胶质细胞中的IV型胞质磷脂酶A2（cPLA2）与多种神经退行性疾病有关，但其激活及花生四烯酸（AA）释放的机制尚未完全阐明。在原代小鼠星形胶质细胞中，佛波酯肉豆蔻酸乙酸酯（PMA）和ATP可刺激细胞外信号调节激酶1/2（ERK1/2）和cPLA2的磷酸化，并引发AA释放。然而，丝裂原活化蛋白激酶激酶（MEK）抑制剂U0126对磷酸化ERK的完全抑制并未完全抑制PMA刺激的cPLA2和AA释放。表皮生长因子（EGF）也可刺激ERK1/2和cPLA2的磷酸化（主要通过不依赖蛋白激酶C（PKC）的途径），但EGF不会引发AA释放。这些结果表明，磷酸化ERK导致的cPLA2磷酸化不足以引发AA释放。然而，当星形胶质细胞用通用PKC抑制剂GF109203x和U0126共同处理时，可观察到ATP诱导的cPLA2磷酸化和AA释放被完全抑制，这表明PKC和ERK在介导ATP诱导的AA反应中均起重要作用。有证据表明，PMA和ATP通过星形胶质细胞中不同的PKC亚型刺激AA释放。与PMA诱导的反应对PKC下调的敏感性一致，用PMA长期处理导致这些细胞中PKCα和ε下调。此外，PMA而非ATP刺激PKCα从胞质迅速转位至细胞膜。总之，我们的结果为PKC在通过ERK1/2依赖性和ERK1/2非依赖性途径介导星形胶质细胞中cPLA2磷酸化和AA释放中起重要作用提供了证据。
