Horman Sandrine, Beauloye Christophe, Vertommen Didier, Vanoverschelde Jean-Louis, Hue Louis, Rider Mark H
Hormone and Metabolic Research Unit, Christian de Duve Institute of Cellular Pathology, University of Louvain Medical School, Avenue Hippocrate 75, ICP-UCL 7529, B-1200 Brussels, Belgium.
J Biol Chem. 2003 Oct 24;278(43):41970-6. doi: 10.1074/jbc.M302403200. Epub 2003 Aug 14.
Protein synthesis, in particular peptide chain elongation, is an energy-consuming biosynthetic process. AMP-activated protein kinase (AMPK) is a key regulatory enzyme involved in cellular energy homeostasis. Therefore, we tested the hypothesis that, as in liver, it could mediate the inhibition of protein synthesis by oxygen deprivation in heart by modulating the phosphorylation of eukaryotic elongation factor-2 (eEF2), which becomes inactive in its phosphorylated form. In anoxic cardiomyocytes, AMPK activation was associated with an inhibition of protein synthesis and an increase in phosphorylation of eEF2. Rapamycin, an inhibitor of the mammalian target of rapamycin (mTOR), did not mimic the effect of oxygen deprivation to inhibit protein synthesis in cardiomyocytes or lead to eEF2 phosphorylation in perfused hearts, suggesting that AMPK activation did not inhibit mTOR/p70 ribosomal protein S6 kinase (p70S6K) signaling. Human recombinant eEF2 kinase (eEF2K) was phosphorylated by AMPK in a time- and AMP-dependent fashion, and phosphorylation led to eEF2K activation, similar to that observed in extracts from ischemic hearts. In contrast, increasing the workload resulted in a dephosphorylation of eEF2, which was rapamycin-insensitive, thus excluding a role for mTOR in this effect. eEF2K activity was unchanged by increasing the workload, suggesting that the decrease in eEF2 phosphorylation could result from the activation of an eEF2 phosphatase.
蛋白质合成，尤其是肽链延伸，是一个耗能的生物合成过程。AMP激活的蛋白激酶（AMPK）是参与细胞能量稳态的关键调节酶。因此，我们检验了这样一个假设：与肝脏中一样，它可能通过调节真核延伸因子2（eEF2）的磷酸化来介导缺氧对心脏蛋白质合成的抑制，eEF2磷酸化形式会失活。在缺氧心肌细胞中，AMPK激活与蛋白质合成抑制及eEF2磷酸化增加相关。雷帕霉素是哺乳动物雷帕霉素靶蛋白（mTOR）的抑制剂，它不能模拟缺氧对心肌细胞蛋白质合成的抑制作用，也不能导致灌注心脏中eEF2磷酸化，这表明AMPK激活并未抑制mTOR/p70核糖体蛋白S6激酶（p70S6K）信号通路。人重组eEF2激酶（eEF2K）被AMPK以时间和AMP依赖的方式磷酸化，磷酸化导致eEF2K激活，这与在缺血心脏提取物中观察到的情况相似。相反，增加工作负荷导致eEF2去磷酸化，这对雷帕霉素不敏感，因此排除了mTOR在此效应中的作用。增加工作负荷时eEF2K活性不变，这表明eEF2磷酸化减少可能是由eEF2磷酸酶激活所致。
