Liao J, Barthel A, Nakatani K, Roth R A
Department of Molecular Pharmacology, Stanford University School of Medicine, Stanford, California 94305, USA.
J Biol Chem. 1998 Oct 16;273(42):27320-4. doi: 10.1074/jbc.273.42.27320.
A rat hepatoma cell line, H4IIE, was stably transfected with a tamoxifen regulatable Akt-1 construct. Treatment of these cells with tamoxifen caused a rapid stimulation of Akt enzymatic activity that was comparable with the activity observed with the endogenous Akt after insulin stimulation. Prior studies have extensively documented that insulin can repress the glucocorticoid and cAMP-stimulated increase in phosphoenolpyruvate carboxykinase (PEPCK) gene transcription. Activation of this regulatable Akt with tamoxifen was found to mimic the dominant inhibitory effect of insulin on PEPCK gene transcription. Dose response curves to insulin and tamoxifen demonstrated that this response was very sensitive to Akt activation although the maximal response observed with tamoxifen activation was slightly less than that observed with insulin, indicating that the response to insulin may also involve other signaling cascades. The regulation of PEPCK transcription via Akt was, like that previously described for insulin, not dependent upon 70 kDa S6 kinase activity in that it was not inhibited by rapamycin. Finally, the expression of a kinase dead Akt was able to partially inhibit the ability of insulin to stimulate this response. In summary, the present results indicate that activation of Akt alone is sufficient to repress the glucocorticoid and cAMP-stimulated increase in PEPCK gene transcription.
将一种他莫昔芬可调节的Akt-1构建体稳定转染到大鼠肝癌细胞系H4IIE中。用他莫昔芬处理这些细胞会迅速刺激Akt酶活性，该活性与胰岛素刺激后内源性Akt所观察到的活性相当。先前的研究已广泛证明，胰岛素可抑制糖皮质激素和cAMP刺激的磷酸烯醇式丙酮酸羧激酶（PEPCK）基因转录增加。发现用他莫昔芬激活这种可调节的Akt可模拟胰岛素对PEPCK基因转录的显性抑制作用。胰岛素和他莫昔芬的剂量反应曲线表明，尽管他莫昔芬激活所观察到的最大反应略小于胰岛素激活所观察到的反应，但这种反应对Akt激活非常敏感，这表明对胰岛素的反应可能还涉及其他信号级联反应。通过Akt对PEPCK转录的调节，与先前对胰岛素的描述一样，不依赖于70 kDa S6激酶活性，因为它不受雷帕霉素抑制。最后，一种激酶失活的Akt的表达能够部分抑制胰岛素刺激这种反应的能力。总之，目前的结果表明，单独激活Akt足以抑制糖皮质激素和cAMP刺激的PEPCK基因转录增加。
