Rosser D S, Ashby M N, Ellis J L, Edwards P A
Department of Biological Chemistry, UCLA School of Medicine 90024.
J Biol Chem. 1989 Jul 25;264(21):12653-6.
Human hepatoma HepG2 cells were used to demonstrate coordinate regulation of three enzymes of cholesterol synthesis under a variety of conditions. Addition of either delipidized serum and mevinolin or low density lipoprotein, 25-hydroxycholesterol, or mevalonic acid to HepG2 cells resulted in rapid changes both in the levels of the mRNAs and in the rates of synthesis of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) synthase, HMG-CoA reductase, and farnesyl pyrophosphate synthetase (prenyltranferase). In all cases, the changes in mRNA levels were paralleled by changes in the rates of specific protein synthesis. Pulse-chase techniques were used to determine the half-lives of all three proteins. Addition of low density lipoprotein to the media during the chase increased the rate of degradation of HMG-CoA reductase 4.6-fold but had no affect on the half-lives of HMG-CoA synthase or prenyltransferase. Therefore, we conclude that the coordinate regulation of these three enzymes under a variety of conditions occurs at the level of enzyme synthesis and not at the level of protein stability.
利用人肝癌HepG2细胞来证明在多种条件下胆固醇合成的三种酶的协同调节作用。向HepG2细胞中添加脱脂血清和洛伐他汀、或低密度脂蛋白、25-羟基胆固醇、或甲羟戊酸，会导致3-羟基-3-甲基戊二酰辅酶A（HMG-CoA）合酶、HMG-CoA还原酶和法尼基焦磷酸合成酶（异戊二烯转移酶）的mRNA水平和合成速率迅速发生变化。在所有情况下，mRNA水平的变化与特定蛋白质合成速率的变化同步。采用脉冲追踪技术来测定这三种蛋白质的半衰期。在追踪期间向培养基中添加低密度脂蛋白，会使HMG-CoA还原酶的降解速率提高4.6倍，但对HMG-CoA合酶或异戊二烯转移酶的半衰期没有影响。因此，我们得出结论，在多种条件下这三种酶的协同调节作用发生在酶合成水平，而非蛋白质稳定性水平。
