In vivo induction of hepatic P4502E1 by ethanol: role of increased enzyme synthesis.
In vivo induction of hepatic P4502E1 by ethanol: role of increased enzyme synthesis.
复制标题
DOI：
10.1006/abbi.1993.1341
复制
发表时间：
1993-07
影响因子：
3.9
通讯作者：
M. Tsutsumi;J. Lasker;T. Takahashi;Charles S. Lieber
中科院分区：
文献类型：
--
作者：
M. Tsutsumi;J. Lasker;T. Takahashi;Charles S. Lieber
P4502 E1（2 E1）是一种乙醇诱导的P450酶，在某些肝毒素和化学致癌物的生物活化中起重要作用。乙醇和其他试剂（例如，丙酮），范围从由2 E1 mRNA的增加和/或其被翻译的效率引起的增强的从头酶合成到由底物稳定引起的降低的酶降解。为了评估这些机制，我们首先研究了肝脏2 E1蛋白诱导的时间过程中，大鼠对喂液体饮食含有36%的总热量，无论是乙醇或糊精麦芽糖（对照）28天。用抗2 E1免疫球蛋白进行的Western印迹分析显示，在乙醇喂养10天后，2 E1达到了一个新的稳态水平（比对照组高8倍），并在治疗期间保持升高。微粒体对硝基苯酚羟基化（2 E1催化的反应）表现出相似的诱导时程，在乙醇给药第10天也观察到酶活性的最大增加。然后，我们确定了稳态2 E1蛋白质周转乙醇喂养和对照动物给予[35 S]蛋氨酸加[3 H]氨基乙酰丙酸放射性标记2 E1脱辅基蛋白和假体血红素组，分别。单相指数衰减曲线显示，治疗组之间的肝脏2 E1蛋白和血红素半衰期（分别为27-28 h和17 h）无差异。然而，2 E1的合成率，通过测量的初始速率纳入[35 S]蛋氨酸和[3 H]aminolevulinate到2 E1脱辅基蛋白和血红素，增加了动物饲养乙醇。我们的研究结果表明，在体内诱导肝2 E1蛋白的乙醇涉及增加酶的合成，而不是减少酶的降解。这种从头2 E1合成的增强很可能需要乙醇介导的2 E1 mRNA稳态水平的增加和/或其翻译效率的刺激。
P4502E1 (2E1), an ethanol-inducible P450 enzyme, plays an important role in the bioactivation of certain hepatotoxins and chemical carcinogens. Different mechanisms of 2E1 induction by ethanol and other agents (e.g., acetone) have been proposed, ranging from enhanced de novo enzyme synthesis caused by an increase in 2E1 mRNA and/or the efficiency with which it is translated to decreased enzyme degradation stemming from substrate stabilization. To evaluate these mechanisms, we first examined the time course of hepatic 2E1 protein induction in rats pair-fed liquid diets containing 36% of total calories as either ethanol or dextrin-maltose (controls) for 28 days. Western blot analysis with anti-2E1 immunoglobulins revealed that 2E1 reached a new steady-state level (eightfold greater than that found with controls) after ethanol feeding for 10 days and remained elevated for the duration of treatment. Microsomal p-nitrophenol hydroxylation, a 2E1-catalyzed reaction, exhibited a similar induction time course, with the maximal increase in enzyme activity also observed on Day 10 of ethanol administration. We then determined steady-state 2E1 protein turnover in ethanol-fed and control animals that were given [35S]methionine plus[3H]aminolevulinate to radiolabel 2E1 apoprotein and the prosthetic heme group, respectively. Monophasic exponential decay curves showed that hepatic 2E1 protein and heme half-lives (27-28 h and 17 h, respectively) did not differ between the treatment groups. However, rates of 2E1 synthesis, assessed by measuring initial rates of incorporation of [35S]methionine and [3H]aminolevulinate into 2E1 apoprotein and heme, were increased in animals fed ethanol. Our results indicate that the in vivo induction of hepatic 2E1 protein by ethanol involves increased enzyme synthesis rather than decreased enzyme degradation. This enhancement of de novo 2E1 synthesis most likely entails the ethanol-mediated increase of steady-state levels of 2E1 mRNA and/or the stimulation of its translational efficiency.