Song Woo-Jin, Schreiber Weston E, Zhong Enhong, Liu Fei-Fei, Kornfeld Benjamin D, Wondisford Fredric E, Hussain Mehboob A
Metabolism Division, Departments of Pediatrics and Medicine, Johns Hopkins University, Baltimore, Maryland, USA.
Diabetes. 2008 Sep;57(9):2371-81. doi: 10.2337/db07-1541. Epub 2008 Jun 10.
Beta-cell proliferation is an important mechanism underlying beta-cell mass adaptation to metabolic demands. We have examined effects, in particular those mediated through intracellular cAMP signaling, of the incretin hormone analog exendin-4 on cell cycle regulation in beta-cells.
Changes in islet protein levels of cyclins and of two critical cell cycle regulators cyclin kinase inhibitor p27 and S-phase kinase-associated protein 2 (Skp2) were assessed in mice treated with exendin-4 and in a mouse model with specific upregulation of nuclear cAMP signaling exhibiting increased beta-cell proliferation (CBP-S436A mouse). Because cyclin A2 was stimulated by cAMP, we assessed the role of cylcin A2 in cell cycle progression in Min6 and isolated islet beta-cells.
Mice treated with exendin-4 showed increased beta-cell proliferation, elevated islet protein levels of cyclin A2 with unchanged D-type cyclins, elevated PDX-1 and Skp2 levels, and reduced p27 levels. Exendin-4 stimulated cyclin A2 promoter activity via the cAMP-cAMP response element binding protein pathway. CBP-S436A islets exhibited elevated cyclin A2, reduced p27, and no changes in D-type cyclins, PDX-1, or Skp2. In cultured islets, exendin-4 increased cyclin A2 and Skp2 and reduced p27. Cyclin A2 overexpression in primary islets increased proliferation and reduced p27. In Min6 cells, cyclin A2 knockdown prevented exendin-4-stimulated proliferation. PDX-1 knockdown reduced exendin-4-stimulated cAMP synthesis and cyclin A2 transcription.
Cyclin A2 is required for beta-cell proliferation, exendin-4 stimulates cyclin A2 expression via the cAMP pathway, and exendin-4 stimulation of cAMP requires PDX-1.
β细胞增殖是β细胞质量适应代谢需求的重要机制。我们研究了肠促胰岛素激素类似物艾塞那肽-4对β细胞周期调控的影响，特别是通过细胞内cAMP信号介导的影响。
在接受艾塞那肽-4治疗的小鼠以及核cAMP信号特异性上调且β细胞增殖增加的小鼠模型（CBP-S436A小鼠）中，评估细胞周期蛋白以及两种关键细胞周期调节因子细胞周期蛋白激酶抑制剂p27和S期激酶相关蛋白2（Skp2）的胰岛蛋白水平变化。由于细胞周期蛋白A2受cAMP刺激，我们评估了细胞周期蛋白A2在Min6细胞和分离的胰岛β细胞周期进程中的作用。
接受艾塞那肽-4治疗的小鼠β细胞增殖增加，细胞周期蛋白A2的胰岛蛋白水平升高，D型细胞周期蛋白水平不变，PDX-1和Skp2水平升高，p27水平降低。艾塞那肽-4通过cAMP - cAMP反应元件结合蛋白途径刺激细胞周期蛋白A2启动子活性。CBP-S436A胰岛细胞周期蛋白A2升高，p27降低，D型细胞周期蛋白、PDX-1或Skp2无变化。在培养的胰岛中，艾塞那肽-4增加细胞周期蛋白A2和Skp2并降低p27。原代胰岛中细胞周期蛋白A2过表达增加增殖并降低p27。在Min6细胞中，细胞周期蛋白A2敲低可阻止艾塞那肽-4刺激的增殖。PDX-1敲低可降低艾塞那肽-4刺激的cAMP合成和细胞周期蛋白A2转录。
细胞周期蛋白A2是β细胞增殖所必需的，艾塞那肽-4通过cAMP途径刺激细胞周期蛋白A2表达，且艾塞那肽-4对cAMP的刺激需要PDX-1。
