Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-8657, Japan.
Biochem J. 2013 Feb 15;450(1):221-9. doi: 10.1042/BJ20121393.
FGF19 (fibroblast growth factor 19), expressed in the small intestine, acts as an enterohepatic hormone by mediating inhibitory effects on the bile acid synthetic pathway and regulating carbohydrate and lipid metabolism. In an attempt to identify novel agents other than bile acids that induce increased FGF19 expression, we found that some ER (endoplasmic reticulum) stress inducers were effective. When intestinal epithelial Caco-2 cells were incubated with thapsigargin, marked increases were observed in the mRNA and secreted protein levels of FGF19. This was not associated with the farnesoid X receptor. Reporter gene analyses using the 5'-promoter region of FGF19 revealed that a functional AARE (amino-acid-response element) was localized in this region, and this site was responsible for inducing its transcription through ATF4 (activating transcription factor 4), which is activated in response to ER stress. EMSAs (electrophoretic mobility-shift assays) and ChIP (chromatin immunoprecipitation) assays showed that ATF4 bound to this site and enhanced FGF19 expression. Overexpression of ATF4 in Caco-2 cells induced increased FGF19 mRNA expression, whereas shRNA (short hairpin RNA)-mediated depletion of ATF4 significantly attenuated a thapsigargin-induced increase in FGF19 mRNA.
成纤维细胞生长因子 19（fibroblast growth factor 19，FGF19）在小肠中表达，作为一种肠肝激素，通过介导对胆汁酸合成途径的抑制作用，并调节碳水化合物和脂质代谢。为了寻找除胆汁酸以外能诱导 FGF19 表达增加的新型药物，我们发现一些内质网（endoplasmic reticulum，ER）应激诱导剂是有效的。当将肠上皮细胞 Caco-2 与他普西龙（thapsigargin）孵育时，观察到 FGF19 的 mRNA 和分泌蛋白水平明显增加。这与法尼醇 X 受体无关。使用 FGF19 的 5'-启动子区域进行报告基因分析表明，该区域存在功能性 AARE（氨基酸反应元件），该位点通过激活转录因子 4（activating transcription factor 4，ATF4）负责诱导其转录，ATF4 是对 ER 应激做出反应而被激活的。电泳迁移率变动分析（electrophoretic mobility-shift assays，EMSA）和染色质免疫沉淀（chromatin immunoprecipitation，ChIP）分析表明，ATF4 与该位点结合并增强 FGF19 的表达。在 Caco-2 细胞中过表达 ATF4 可诱导 FGF19 mRNA 表达增加，而 shRNA（短发夹 RNA）介导的 ATF4 耗竭则显著减弱了他普西龙诱导的 FGF19 mRNA 增加。
