Morrison M D, Bate A J, Harding H L, Whatmore A J, Dickson A J
Department of Biochemistry and Molecular Biology, University of Manchester, UK.
Biochim Biophys Acta. 1993 Aug 18;1178(2):135-40. doi: 10.1016/0167-4889(93)90003-8.
In normal rat hepatocytes in primary culture the level of mRNA encoding the key gluconeogenic enzyme phospho enol pyruvate carboxykinase (PEPCK) is increased by the cyclic AMP analogue, chlorophenylthio cyclic AMP (cpt cAMP), and this response is reversed by insulin. The protein-phosphatase inhibitor okadaic acid diminished the stimulatory effects of cpt cAMP on PEPCK mRNA. Protein kinase A remained fully active in the presence of okadaic acid, therefore, the insulin-mimetic actions of okadaic acid were localised to a site subsequent to initial protein kinase A activation. Insulin produced a decrease in PEPCK mRNA expression which was similar to that of okadaic acid both in extent and mechanism (i.e., lack of change in protein kinase A activation). The effects of okadaic acid on PEPCK mRNA amount were not additive with those of insulin and the effects of insulin were not abolished by okadaic acid. These data suggest that okadaic acid and insulin may interact with the cAMP regulation of the PEPCK gene expression at a common site. The mechanisms by which this may be attained are discussed in relation to what is known about the control of specific protein kinases and protein phosphatases by insulin and okadaic acid and of the importance of protein phosphorylation state to regulation of gene-transcriptional processes.
在原代培养的正常大鼠肝细胞中，编码关键糖异生酶磷酸烯醇丙酮酸羧激酶（PEPCK）的mRNA水平会被环磷酸腺苷类似物氯苯硫基环磷酸腺苷（cpt cAMP）升高，而这种反应会被胰岛素逆转。蛋白磷酸酶抑制剂冈田酸减弱了cpt cAMP对PEPCK mRNA的刺激作用。在冈田酸存在的情况下蛋白激酶A仍保持完全活性，因此，冈田酸的胰岛素模拟作用定位于初始蛋白激酶A激活之后的位点。胰岛素使PEPCK mRNA表达降低，其程度和机制与冈田酸相似（即蛋白激酶A激活无变化）。冈田酸对PEPCK mRNA量的影响与胰岛素的影响并非相加关系，且胰岛素的作用未被冈田酸消除。这些数据表明，冈田酸和胰岛素可能在一个共同位点与PEPCK基因表达的cAMP调节相互作用。结合已知的胰岛素和冈田酸对特定蛋白激酶和蛋白磷酸酶的控制以及蛋白磷酸化状态对基因转录过程调节的重要性，讨论了实现这一点的可能机制。
