Sayo Y, Hosokawa H, Imachi H, Murao K, Sato M, Wong N C, Ishida T, Takahara J
First Department of Internal Medicine, Kagawa Medical University, Kagawa, Japan.
Eur J Biochem. 2000 Feb;267(4):971-8. doi: 10.1046/j.1432-1327.2000.01080.x.
Although transforming growth factor-beta (TGF-beta) stimulates pancreatic islet cells to synthesize and secret insulin, the mechanism underlying this effect is not known. To investigate this question, we examined the insulin promoter activity focusing on a transcription factor, pancreatic and duodenal homeobox gene-1 (PDX-1) that binds to the A3 element of the rat insulin promoter. Studies performed using the rat insulinoma cell line, INS-1 showed that TGF-beta stimulation of endogenous insulin mRNA expression correlated with increased activity of a reporter construct containing the insulin promoter. A potential mechanism for this increase arose from, electrophoretic mobility shift assay showing that the nuclear extract from TGF-beta treated cells contained higher levels of A3 binding activity. Western blot analysis confirmed that PDX-1 was increased in the nuclear extract from INS-1 cells treated with TGF-beta. As expected, a mutant insulin promoter that lacked the PDX-1 binding site was not stimulated by TGF-beta. In summary, the results of these studies show that TGF-beta stimulates the transcription of insulin gene and this action is mediated by the transcription factor, PDX-1.
尽管转化生长因子-β（TGF-β）能刺激胰岛细胞合成并分泌胰岛素，但其作用机制尚不清楚。为研究该问题，我们聚焦于一种转录因子——胰腺和十二指肠同源盒基因-1（PDX-1），它可与大鼠胰岛素启动子的A3元件结合，对胰岛素启动子活性进行了检测。利用大鼠胰岛素瘤细胞系INS-1进行的研究表明，TGF-β刺激内源性胰岛素mRNA表达与含有胰岛素启动子的报告基因构建体活性增加相关。这种增加的潜在机制源于电泳迁移率变动分析，结果显示经TGF-β处理的细胞的核提取物中A3结合活性水平更高。蛋白质印迹分析证实，经TGF-β处理的INS-1细胞核提取物中PDX-1增加。正如预期的那样，缺乏PDX-1结合位点的突变胰岛素启动子不受TGF-β刺激。总之，这些研究结果表明，TGF-β刺激胰岛素基因转录，且这一作用由转录因子PDX-1介导。
