Epidermal growth factor (EGF) and hormones stimulate phosphoinositide hydrolysis and increase EGF receptor protein synthesis and mRNA levels in rat liver epithelial cells. Evidence for protein kinase C-dependent and -independent pathways.
Epidermal growth factor (EGF) and hormones stimulate phosphoinositide hydrolysis and increase EGF receptor protein synthesis and mRNA levels in rat liver epithelial cells. Evidence for protein kinase C-dependent and -independent pathways.
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DOI：
10.1016/s0021-9258(18)68324-3
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发表时间：
1988-09
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影响因子：
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通讯作者：
H. Earp;J. Hepler;L. Petch;A. Miller;A. Berry;J. Harris;V. Raymond;B. McCune;L. Lee;J. Grisham
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文献类型：
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作者：
H. Earp;J. Hepler;L. Petch;A. Miller;A. Berry;J. Harris;V. Raymond;B. McCune;L. Lee;J. Grisham
表皮生长因子（EGF）刺激WB细胞，大鼠肝上皮细胞的连续线的三磷酸肌醇的快速积累。由于我们之前已经表明EGF刺激这些细胞中的EGF受体合成，我们测试了刺激PtdIns（4，5）P2水解的激素是否会增加EGF受体蛋白合成和mRNA水平。肾上腺素、血管紧张素II和[Arg 8]加压素激活WB细胞中的磷脂酶C，如肌醇磷酸、肌醇单磷酸、肌醇二磷酸和肌醇三磷酸的积累所证明的。每种激素处理3-4小时也可使EGF受体蛋白合成速率增加3-6倍，如通过[35 S]甲硫氨酸标记细胞的EGF受体的免疫沉淀所评估的。WB细胞EGF受体mRNA水平的北方印迹分析显示，与磷酸肌醇信号系统连接的试剂在1-2小时内增加受体mRNA含量。在暴露于EGF和激素3小时后观察到3-7倍的最大增加。佛波酯，12-O-十四酰基佛波13-乙酸酯（TPA），它激活蛋白激酶C也刺激EGF受体的合成。用高浓度TPA预处理WB细胞18 h，可“下调”蛋白激酶C，并阻断TPA指导的EGF受体mRNA合成。与此相反，TPA预处理对EGF受体mRNA水平的影响并没有显着降低。肾上腺素诱导的EGF受体mRNA的增加从4倍减少到2倍。同样，TPA预处理18小时取消TPA对EGF受体蛋白合成的影响，但不影响EGF依赖的EGF受体蛋白合成。18小时TPA预处理减少了30-50%的肾上腺素或血管紧张素II的受体蛋白合成的诱导。我们的结论是，在WB细胞EGF受体的合成可以调节EGF和其他激素刺激PtdIns（4，5）P2水解。在这些细胞中，EGF受体的合成似乎受到几种机制的调节：一种途径依赖于EGF受体的激活，并可以独立于蛋白激酶C的激活;另一种途径与PtdIns（4，5）P2水解相关，并至少部分依赖于蛋白激酶C的激活。
Epidermal growth factor (EGF) stimulated the rapid accumulation of inositol trisphosphate in WB cells, a continuous line of rat hepatic epithelial cells. Since we previously had shown that EGF stimulates EGF receptor synthesis in these cells, we tested whether hormones that stimulate PtdIns(4,5)P2 hydrolysis would increase EGF receptor protein synthesis and mRNA levels. Epinephrine, angiotensin II, and [Arg8]vasopressin activate phospholipase C in WB cells as evidenced by the accumulation of the inositol phosphates, inositol monophosphate, inositol bisphosphate, and inositol trisphosphate. A 3-4-h treatment with each hormone also increased the rate of EGF receptor protein synthesis by 3-6-fold as assessed by immunoprecipitation of EGF receptor from [35S]methionine-labeled cells. Northern blot analyses of WB cell EGF receptor mRNA levels revealed that agents linked to the phosphoinositide signaling system increased receptor mRNA content within 1-2 h. A maximal increase of 3-7-fold was observed after a 3-h exposure to EGF and hormones. The phorbol ester, 12-O-tetradecanoylphorbol 13-acetate (TPA), which activates protein kinase C also stimulated EGF receptor synthesis. Pretreatment of WB cells for 18 h with high concentrations of TPA “down-regulated” protein kinase C and blocked TPA-directed EGF receptor mRNA synthesis. In contrast, the effect of EGF on EGF receptor mRNA levels was not significantly decreased by TPA pretreatment. Epinephrine-induced increases in EGF receptor mRNA were reduced from 4- to 2-fold. Similarly, 18 h TPA pretreatment abolished the effect of TPA on EGF receptor protein synthesis but did not affect EGF-dependent EGF receptor protein synthesis. The 18-h TPA pretreatment diminished by 30-50% the induction of receptor protein synthesis by epinephrine or angiotensin II. We conclude that in WB cells EGF receptor synthesis can be regulated by EGF and other hormones that stimulate PtdIns(4,5)P2 hydrolysis. In these cells, EGF receptor synthesis appears to be regulated by several mechanism: one pathway is dependent upon EGF receptor activation and can operate independently of protein kinase C activation; another pathway is correlated with PtdIns(4,5)P2 hydrolysis and is dependent, at least in part, upon protein kinase C activation.