van Roon M A, Zonneveld D, Charles R, Lamers W H
Department of Anatomy and Embryology, University of Amsterdam, The Netherlands.
Eur J Biochem. 1988 Dec 1;178(1):191-6. doi: 10.1111/j.1432-1033.1988.tb14443.x.
The aim of this study was to establish whether the initial accumulation of hepatocyte-specific proteins after hormone induction is regulated at the pretranslational and/or the translational level. To this end, mRNA molar concentrations were determined and compared with rates of protein synthesis from previous studies [van Roon, M.A., Charles, R. & Lamers, W.H. (1987) Eur. J. Biochem. 165, 229-234]. In vivo, carbamoylphosphate-synthetase mRNA starts to accumulate at day 17 of pregnancy. Phosphoenolpyruvate-carboxykinase mRNA starts to accumulate only just prior to birth. Embryonic day 14 (i.e. 8 days before the expected day of birth), livers were chosen to study the regulation of the initiation of hepatocyte-specific mRNA accumulation in vitro. Accumulation of carbamoylphosphate-synthetase and phosphoenolpyruvate-carboxykinase mRNA is regulated by the same hormones as accumulation of the respective proteins. The rate at which carbamoylphosphate-synthetase and phosphoenolpyruvate-carboxykinase mRNA molecules accumulate in cultured embryonic hepatocytes is relatively low, compared to that of postnatal hepatocytes. However, the increase of the rate of synthesis of carbamoylphosphate-synthetase and phosphoenolpyruvate-carboxykinase protein is even 3-6-fold slower than that of mRNA. This shows that initially mRNAs accumulate intracellularly to a relatively high concentration without being efficiently translated or translatable. Only after the mRNA concentration reaches a plateau of 72 h and 48 h respectively, the cellular capacity to synthesize the respective proteins increases. Therefore, the translational efficiency is certainly one of the major rate-limiting factors of the initial phases of expression of the hepatocyte-specific genes for carbamoylphosphate synthetase and phosphoenolpyruvate carboxykinase.
本研究的目的是确定激素诱导后肝细胞特异性蛋白质的初始积累是否在转录前和/或翻译水平受到调控。为此，测定了mRNA的摩尔浓度，并与先前研究[van Roon, M.A., Charles, R. & Lamers, W.H. (1987) Eur. J. Biochem. 165, 229 - 234]中的蛋白质合成速率进行了比较。在体内，氨甲酰磷酸合成酶mRNA在妊娠第17天开始积累。磷酸烯醇式丙酮酸羧激酶mRNA仅在出生前才开始积累。选择胚胎第14天（即预期出生日的前8天）的肝脏来研究体外肝细胞特异性mRNA积累起始的调控。氨甲酰磷酸合成酶和磷酸烯醇式丙酮酸羧激酶mRNA的积累与各自蛋白质的积累受相同激素调控。与出生后肝细胞相比，氨甲酰磷酸合成酶和磷酸烯醇式丙酮酸羧激酶mRNA分子在培养的胚胎肝细胞中的积累速率相对较低。然而，氨甲酰磷酸合成酶和磷酸烯醇式丙酮酸羧激酶蛋白质合成速率的增加甚至比mRNA慢3 - 6倍。这表明最初mRNA在细胞内积累到相对较高的浓度，但没有被有效翻译或可翻译。只有在mRNA浓度分别达到72小时和48小时的平台期后，细胞合成各自蛋白质的能力才会增加。因此，翻译效率肯定是氨甲酰磷酸合成酶和磷酸烯醇式丙酮酸羧激酶肝细胞特异性基因表达初始阶段的主要限速因素之一。
