Laboratory of Molecular and Cellular Pathophysiology, Showa Pharmaceutical University, Tokyo, Japan.
Thromb Haemost. 2009 Dec;102(6):1204-11. doi: 10.1160/TH09-03-0194.
Thrombin-activatable fibrinolysis inhibitor (TAFI), a carboxypeptidase B-like proenzyme, is predominantly biosynthesised in the liver and released into circulating plasma. Activated TAFI has a role in maintaining the balance between blood coagulation and fibrinolysis. We investigated the regulation of TAFI expression in cultured human hepatoma HepG2 cells. Stimulation of the cells with forskolin and dibutyryl cyclic AMP (DBcAMP) increased TAFI antigen levels in the cells in parallel with TAFI mRNA levels and antigen release from the cells into the conditioned medium. The elevated TAFI expression was abolished by pretreatment of the cells with KT5720, a protein kinase A (PKA) inhibitor. The promoter activity of the TAFI gene and the half-life of the TAFI transcript in DBcAMP-stimulated HepG2 cells increased to 1.5-fold and 2.0-fold, respectively, of those in the control cells. The increased promoter activity and the prolonged half-life were abolished by pretreatment of the cells with KT5720. These results suggest that an increase in intracellular cAMP levels up-regulates TAFI expression in the cells in accompaniment with an elevation of TAFI mRNA levels, and that the elevated mRNA levels are derived from both transcriptional and post-transcriptional regulations of the TAFI gene mediated by activation of the AMP/PKA signaling pathway.
凝血酶激活的纤溶抑制物（TAFI），一种羧肽酶 B 样酶原，主要在肝脏中生物合成并释放到循环血浆中。活化的 TAFI 在维持血液凝固和纤维蛋白溶解之间的平衡中起作用。我们研究了培养的人肝癌 HepG2 细胞中 TAFI 表达的调节。用 forskolin 和二丁酰环 AMP（DBcAMP）刺激细胞，与 TAFI mRNA 水平平行地增加 TAFI 抗原水平，并将 TAFI 抗原从细胞释放到条件培养基中。用蛋白激酶 A（PKA）抑制剂 KT5720 预处理细胞可消除升高的 TAFI 表达。DBcAMP 刺激的 HepG2 细胞中 TAFI 基因的启动子活性和 TAFI 转录本的半衰期分别增加到对照细胞的 1.5 倍和 2.0 倍。用 KT5720 预处理细胞可消除增加的启动子活性和延长的半衰期。这些结果表明，细胞内 cAMP 水平的升高伴随着 TAFI mRNA 水平的升高而上调细胞中 TAFI 的表达，并且升高的 mRNA 水平源自 AMP/PKA 信号通路激活介导的 TAFI 基因的转录和转录后调节。
