Bernal-Mizrachi E, Wen W, Srinivasan S, Klenk A, Cohen D, Permutt M A
Division of Endocrinology, Diabetes, and Metabolism, Washington University School Of Medicine, St. Louis, Missouri 63110, USA.
Am J Physiol Endocrinol Metab. 2001 Dec;281(6):E1286-99. doi: 10.1152/ajpendo.2001.281.6.E1286.
Elk-1, a member of the ternary complex factor family of Ets domain proteins that bind serum response elements, is activated by phosphorylation in a cell-specific manner in response to growth factors and other agents. The purpose of the current study was to determine whether Elk-1 activation contributes to glucose-/depolarization-induced Ca(2+)-dependent induction of immediate early response genes in pancreatic islet beta-cells. The results of experiments in insulinoma (MIN6) cells demonstrated that Elk-1-binding sites (Ets elements) in the Egr-1 gene promoter contribute to transcriptional activation of the gene. Treatment with either epidermal growth factor (EGF), a known inducer of beta-cell hyperplasia, glucose, or KCl-induced depolarization resulted in Ser(383) phosphorylation and transcriptional activation of Elk-1 (4 +/- 0.3-, P = 0.003, 2.3 +/- 0.19-, P = 0.002, and 2.2 +/- 0.1- fold, P = 0.001 respectively). The depolarization response was inhibited by the Ca(2+) channel blocker verapamil and by the MEK inhibitor PD98059 (53 +/- 6 and 55 +/- 0.5%, respectively). EGF-induced activation of Elk-1 was also inhibited by PD98059 (60 +/- 5%). A dominant negative Ras produced partial inhibition (42%) of the depolarization-induced Elk-1 transcriptional activation. Transfection with a constitutively active Ca(2+)/calmodulin kinase IV plasmid also resulted in Elk-1 transcriptional activation. Experiments with p38, phosphatidylinositol 3-kinase, and protein kinase A inhibitors indicated that these pathways are not involved. We conclude that Elk-1 activation contributes to glucose-/depolarization-induced Ca(2+)-dependent induction of immediate early growth response genes in pancreatic islet beta-cells. Furthermore, the results demonstrated a convergence of nutrient- and growth factor-mediated signaling pathways on Elk-1 activation through induction of Ras/mitogen-activated protein kinase ERK-1 and -2. The role of these pathways in the glucose-induced proliferation of islet beta-cells can now be assessed.
Elk-1是Ets结构域蛋白三元复合因子家族的成员，可结合血清反应元件，它在细胞中会因生长因子和其他因子的刺激而以细胞特异性方式通过磷酸化被激活。本研究的目的是确定Elk-1的激活是否有助于葡萄糖/去极化诱导的胰岛β细胞中早期即刻反应基因的钙依赖性诱导。胰岛素瘤（MIN6）细胞的实验结果表明，Egr-1基因启动子中的Elk-1结合位点（Ets元件）有助于该基因的转录激活。用表皮生长因子（EGF，一种已知的β细胞增生诱导剂）、葡萄糖或氯化钾诱导的去极化处理，均导致Elk-1的Ser(383)磷酸化和转录激活（分别为4±0.3倍，P = 0.003；2.3±0.19倍，P = 0.002；2.2±0.1倍，P = 0.001）。去极化反应受到钙通道阻滞剂维拉帕米和MEK抑制剂PD98059的抑制（分别为53±6%和55±0.5%）。PD98059也抑制了EGF诱导的Elk-1激活（60±5%）。显性负性Ras对去极化诱导的Elk-1转录激活产生部分抑制（42%）。转染组成型活性钙/钙调蛋白激酶IV质粒也导致Elk-1转录激活。使用p38、磷脂酰肌醇3激酶和蛋白激酶A抑制剂的实验表明这些途径不参与其中。我们得出结论，Elk-1激活有助于葡萄糖/去极化诱导的胰岛β细胞中早期即刻生长反应基因的钙依赖性诱导。此外，结果表明营养物质和生长因子介导的信号通路通过诱导Ras/丝裂原活化蛋白激酶ERK-1和-2在Elk-1激活上存在汇聚。现在可以评估这些途径在葡萄糖诱导的胰岛β细胞增殖中的作用。
