Higashi K, Hoshino M, Nomura T, Saso K, Ito M, Hoek J B
First Department of Internal Medicine, Nagoya City University Medical School, Japan.
Alcohol Clin Exp Res. 1996 Dec;20(9 Suppl):320A-324A.
Phospholipase C (PLC)-mediated signal transduction processes in rat hepatocytes are subject to modulation by protein phosphatases (PPases) and protein kinases, including protein kinase A (PKA) and protein kinase C. Ethanol (EtOH) stimulates PLC activity in liver cells in the absence of hormones, and EtOH pretreatment inhibits the subsequent stimulation of PLC by hormonal stimuli. There is evidence that protein kinase activities are involved in these actions of EtOH. We investigated the effects of okadaic acid (OKA), a PPase inhibitor, and 8-(4-chlorophenylthio)adenosine 3':5'-cyclic monophosphate (cpt-cAMP), a cell permeant cAMP analog that activates PKA, on EtOH-induced PLC activation. In addition, we studied the combined effects of cpt-cAMP and EtOH/OKA on vasopressin-induced PLC activation. PLC activation (cytosolic Ca2+ mobilization and inositol trisphosphate accumulation) induced by EtOH and vasopressin was inhibited by treatment with OKA, and was potentiated by cpt-cAMP. OKA treatment prevented the effect of cpt-cAMP. Pretreatment with EtOH caused inhibition of vasopressin-induced PLC activation. EtOH also decreased the enhancing effect of cpt-cAMP on the responses to vasopressin. The susceptibility to enhancement by cpt-cAMP plotted as a function of the initial rate of vasopressin-induced Ca2+ mobilization in EtOH-treated cells was similar to the pattern observed in OKA-treated cells. These data suggest that interactions of OKA and PKA on EtOH-induced PLC activation occurred at the level of G-protein, and indicate that EtOH may act as an inhibitory agent of PPase.
大鼠肝细胞中磷脂酶C（PLC）介导的信号转导过程受蛋白磷酸酶（PPases）和蛋白激酶调节，包括蛋白激酶A（PKA）和蛋白激酶C。在无激素情况下，乙醇（EtOH）刺激肝细胞中的PLC活性，且乙醇预处理可抑制随后激素刺激对PLC的激活作用。有证据表明蛋白激酶活性参与了乙醇的这些作用。我们研究了蛋白磷酸酶抑制剂冈田酸（OKA）和可激活PKA的细胞渗透性环磷酸腺苷类似物8 -（4 - 氯苯硫基）腺苷3':5'-环一磷酸（cpt - cAMP）对乙醇诱导的PLC激活的影响。此外，我们研究了cpt - cAMP与乙醇/OKA联合对血管加压素诱导的PLC激活的影响。用OKA处理可抑制乙醇和血管加压素诱导的PLC激活（胞质Ca2+动员和肌醇三磷酸积累），而cpt - cAMP可增强这种激活。OKA处理可阻断cpt - cAMP的作用。乙醇预处理可抑制血管加压素诱导的PLC激活。乙醇还降低了cpt - cAMP对血管加压素反应的增强作用。以乙醇处理细胞中血管加压素诱导的Ca2+动员初始速率为函数绘制的cpt - cAMP增强敏感性与OKA处理细胞中观察到的模式相似。这些数据表明OKA和PKA在乙醇诱导的PLC激活上的相互作用发生在G蛋白水平，并表明乙醇可能作为蛋白磷酸酶的抑制剂。
