Division of Endocrinology and Metabolism, Department of Internal Medicine, Faculty of Medicine, Kagawa University, Ikenobe Miki-CHO, Kita-gun, Kagawa, Japan.
J Cell Mol Med. 2010 May;14(5):1083-7. doi: 10.1111/j.1582-4934.2009.00955.x. Epub 2009 Oct 29.
ATP-binding cassette transporter A1 (ABCA1) in pancreatic beta cells influences insulin secretion and glucose homeostasis. This study investigates whether the long-acting agonist of the glucagon-like peptide 1, namely exendin-4, which mediates stimulatory effects on ABCA1 gene expression, could interfere with the Ca(2+)/calmodulin (CaM)-dependent protein kinase (CaMK) cascade. ABCA1 promoter activity was examined by reporter gene assay in rat insulin-secreting INS-1 cells incubated with exendin-4. CaMKIV activity was assessed by detection of activation-loop phosphorylation (Thr(196)) of CaMKIV. We investigated the influence of the constitutively active form (CaMKIVc) or CaMKIV knockdown on ABCA1 expression. Increased abundance of ABCA1 protein was noted in response to rising concentrations of exendin-4 with maximum induction at 10 nM. Exendin-4 also stimulated ABCA1 promoter activity, but failed to do so in the presence of STO-609, a CaMKK inhibitor. Up-regulation of CaMKIV phosphorylation (at Thr(196)) peaked after 10 min. of exposure to exendin-4. CaMKIVc enhanced or up-regulated ABCA1 promoter activity in INS-1 cells. Furthermore, exendin-4 induction of ABCA1 protein expression was significantly suppressed in cells treated with CaMKIV-siRNA. Activation of the CaMKK/CaMKIV cascade by exendin-4 stimulated ABCA1 gene transcription, indicating that exendin-4 plays an important role in insulin secretion and cholesterol ester content in pancreatic beta cells.
三磷酸腺苷结合盒转运体 A1（ABCA1）在胰腺β细胞中影响胰岛素分泌和葡萄糖稳态。本研究旨在探讨胰高血糖素样肽 1 的长效激动剂，即 exendin-4，是否能通过刺激 ABCA1 基因表达来干预 Ca（2+）/钙调蛋白（CaM）依赖性蛋白激酶（CaMK）级联。在孵育 exendin-4 的大鼠胰岛素分泌细胞 INS-1 中，通过报告基因检测 ABCA1 启动子活性。通过检测 CaMKIV 激活环磷酸化（Thr（196））来评估 CaMKIV 活性。我们研究了组成型激活形式（CaMKIVc）或 CaMKIV 敲低对 ABCA1 表达的影响。随着 exendin-4 浓度的升高，ABCA1 蛋白的丰度增加，最大诱导浓度为 10 nM。exendin-4 还刺激 ABCA1 启动子活性，但在 CaMKK 抑制剂 STO-609 存在下则无此作用。暴露于 exendin-4 10 分钟后，CaMKIV 磷酸化（Thr（196））达到峰值。CaMKIVc 增强或上调 INS-1 细胞中 ABCA1 启动子活性。此外，在经 CaMKIV-siRNA 处理的细胞中，exendin-4 诱导的 ABCA1 蛋白表达显著受到抑制。exendin-4 通过激活 CaMKK/CaMKIV 级联刺激 ABCA1 基因转录，表明 exendin-4 在胰岛素分泌和胰腺β细胞胆固醇酯含量中发挥重要作用。
