Nakae J, Barr V, Accili D
Department of Medicine, College of Physicians and Surgeons of Columbia University, New York, NY 10032, USA.
EMBO J. 2000 Mar 1;19(5):989-96. doi: 10.1093/emboj/19.5.989.
The transcription factor FKHR is inhibited by phosphorylation in response to insulin and IGF-1 through Akt kinase. Here we show that FKHR phosphorylation in hepatocytes conforms to a hierarchical pattern in which phosphorylation of the Akt site at S(253), in the forkhead DNA binding domain, is a prerequisite for the phosphorylation of two additional potential Akt sites, T(24) and S(316). Using insulin receptor-deficient hepatocytes, we show that T(24) fails to be phosphorylated by IGF-1 receptors, suggesting that this residue is targeted by a kinase specifically activated by insulin receptors. Lack of T(24) phosphorylation is associated with the failure of IGF-1 to induce nuclear export of FKHR, and to inhibit expression of a reporter gene under the transcriptional control of the IGF binding protein-1 insulin response element. We propose that site-specific phosphorylation of FKHR is one of the mechanisms by which insulin and IGF-1 receptors exert different effects on gene expression.
转录因子FKHR在胰岛素和IGF-1的作用下通过Akt激酶磷酸化而受到抑制。在此我们表明，肝细胞中FKHR的磷酸化符合一种层级模式，即叉头DNA结合域中S(253)处的Akt位点磷酸化是另外两个潜在Akt位点T(24)和S(316)磷酸化的先决条件。利用胰岛素受体缺陷型肝细胞，我们发现T(24)不能被IGF-1受体磷酸化，这表明该残基是由胰岛素受体特异性激活的激酶作用的靶点。T(24)磷酸化的缺失与IGF-1不能诱导FKHR核输出以及不能抑制IGF结合蛋白-1胰岛素反应元件转录控制下的报告基因表达有关。我们提出，FKHR的位点特异性磷酸化是胰岛素和IGF-1受体对基因表达产生不同作用的机制之一。
