Liu Ning-Chun, Lin Wen-Jye, Kim Eungseok, Collins Loretta L, Lin Hung-Yun, Yu I-Chen, Sparks Janet D, Chen Lu-Min, Lee Yi-Fen, Chang Chawnshang
Department of Pathology, Cancer Center, University of Rochester, Rochester, NY 14642, USA.
Diabetes. 2007 Dec;56(12):2901-9. doi: 10.2337/db07-0359. Epub 2007 Sep 7.
Regulation of phosphoenolpyruvate carboxykinase (PEPCK), the key gene in gluconeogenesis, is critical for glucose homeostasis in response to quick nutritional depletion and/or hormonal alteration.
RESEARCH DESIGN/METHODS AND RESULTS: Here, we identified the testicular orphan nuclear receptor 4 (TR4) as a key PEPCK regulator modulating PEPCK gene via a transcriptional mechanism. TR4 transactivates the 490-bp PEPCK promoter-containing luciferase reporter gene activity by direct binding to the TR4 responsive element (TR4RE) located at -451 to -439 in the promoter region. Binding to TR4RE was confirmed by electrophoretic mobility shift and chromatin immunoprecipitation assays. Eliminating TR4 via knockout and RNA interference (RNAi) in hepatocytes significantly reduced the PEPCK gene expression and glucose production in response to glucose depletion. In contrast, ectopic expression of TR4 increased PEPCK gene expression and hepatic glucose production in human and mouse hepatoma cells. Mice lacking TR4 also display reduction of PEPCK expression with impaired gluconeogenesis.
Together, both in vitro and in vivo data demonstrate the identification of a new pathway, TR4 --> PEPCK --> gluconeogenesis --> blood glucose, which may allow us to modulate metabolic programs via the control of a new key player, TR4, a member of the nuclear receptor superfamily.
磷酸烯醇式丙酮酸羧激酶（PEPCK）是糖异生作用中的关键基因，其调节作用对于机体在快速营养消耗和/或激素改变时维持葡萄糖稳态至关重要。
研究设计/方法与结果：在此，我们确定睾丸孤儿核受体4（TR4）是通过转录机制调节PEPCK基因的关键因子。TR4通过直接结合位于启动子区域-451至-439处的TR4反应元件（TR4RE），反式激活含490 bp PEPCK启动子的荧光素酶报告基因活性。通过电泳迁移率变动分析和染色质免疫沉淀试验证实了TR4与TR4RE的结合。在肝细胞中通过基因敲除和RNA干扰（RNAi）消除TR4，可显著降低葡萄糖消耗时的PEPCK基因表达和葡萄糖生成。相反，在人和小鼠肝癌细胞中异位表达TR4可增加PEPCK基因表达和肝葡萄糖生成。缺乏TR4的小鼠也表现出PEPCK表达降低及糖异生受损。
总之，体外和体内数据均表明确定了一条新途径，即TR4→PEPCK→糖异生→血糖，这可能使我们能够通过控制核受体超家族成员TR4这一新的关键因子来调节代谢程序。
