Diggle T A, Redpath N T, Heesom K J, Denton R M
Department of Biochemistry, University of Leicester, University Road, Leicester LE1 7RH, U.K.
Biochem J. 1998 Dec 15;336 ( Pt 3)(Pt 3):525-9. doi: 10.1042/bj3360525.
Treatment of primary rat epididymal adipocytes or 3T3-L1 adipocytes with various agents which increase cAMP led to the phosphorylation of eukaryotic translation elongation factor-2 (eEF-2). The increase in eEF-2 phosphorylation was a consequence of the activation of eEF-2 kinase (eEF-2K), which is a Ca2+/calmodulin-dependent kinase. eEF-2K was shown to be essentially inactive at less than 0.1 microM free Ca2+ when measured in cell-free extracts. Treatment of adipocytes with isoproterenol induced Ca2+-independent eEF-2K activity, and an 8-10-fold activation of eEF-2K was observed at Ca2+ concentrations of less than 0.1 microM. Increased cAMP in 3T3-L1 adipocytes led to the inhibition of total protein synthesis and decreased the rate of polypeptide-chain elongation. We also show that the phosphorylation of eEF-2 and the activity of eEF-2K are insulin-regulated in adipocytes. These results demonstrate a novel mechanism for the control of protein synthesis by hormones which act by increasing cytoplasmic cAMP.
用各种能增加环磷酸腺苷（cAMP）的试剂处理原代大鼠附睾脂肪细胞或3T3-L1脂肪细胞，会导致真核生物翻译延伸因子2（eEF-2）磷酸化。eEF-2磷酸化的增加是eEF-2激酶（eEF-2K）激活的结果，eEF-2K是一种钙/钙调蛋白依赖性激酶。当在无细胞提取物中测量时，eEF-2K在游离钙浓度低于0.1微摩尔时基本无活性。用异丙肾上腺素处理脂肪细胞可诱导不依赖钙的eEF-2K活性，在钙浓度低于0.1微摩尔时观察到eEF-2K有8至10倍的激活。3T3-L1脂肪细胞中环磷酸腺苷增加导致总蛋白质合成受到抑制，并降低多肽链延伸速率。我们还表明，脂肪细胞中eEF-2的磷酸化和eEF-2K的活性受胰岛素调节。这些结果证明了激素通过增加细胞质中环磷酸腺苷来控制蛋白质合成的一种新机制。
