Beuers U, Throckmorton D C, Anderson M S, Isales C M, Thasler W, Kullak-Ublick G A, Sauter G, Koebe H G, Paumgartner G, Boyer J L
Department of Internal Medicne, Yale University School of Medicine, New Haven Connecticut, USA.
Gastroenterology. 1996 May;110(5):1553-63. doi: 10.1053/gast.1996.v110.pm8613063.
BACKGROUND & AIMS: Ursodeoxycholic acid (UDCA) improves liver function in patients with chronic cholestatic liver diseases by an unknown mechanism. UDCA is conjugated to taurine in vivo, and tauroursodeoxycholic acid (TUDCA) is a potent hepatocellular Ca2+ agonist and stimulates biliary exocytosis and hepatocellular Ca2+ influx, both of which are defective in experimental cholestasis. Protein kinase C (PKC) mediates stimulation of exocytosis in the liver. The aim of this study was to determine the effects of TUDCA on PKC in isolated hepatocytes.
The effect of TUDCA on the distribution of PKC isoenzymes within the hepatocyte was studied using immunoblotting and immunofluorescence techniques. In addition, the effect of TUDCA on the accummulation of sn-1,2-diacylglycerol (DAG), the intracellular activator of PKC, and hepatocellular PKC activity was studied using radioenzymatic techniques.
Immunoblotting studies showed the presence of four isoenzymes (alpha, delta, epsilon, and zeta). The phorbol ester phorbol 12-myristate 13-acetate (1 mumol/L) induced translocation of alpha-PKC, delta-PKC, and epsilon-PKC from cytosol to a particulate membrane fraction, a key step for activation of PKC. TUDCA, but not taurocholic acid, selectively induced translocation of the alpha-PKC isoenzyme from cytosol to the membranes. In addition, TUDCA induced a significant increase in hepatocellular DAG mass and stimulated membrane-associated PKC activity.
TUDCA might stimulate Ca(2+)-dependent hepatocellular exocytosis into bile in part by activation of alpha-PKC.
熊去氧胆酸（UDCA）可改善慢性胆汁淤积性肝病患者的肝功能，但其机制尚不明确。UDCA在体内与牛磺酸结合，牛磺熊去氧胆酸（TUDCA）是一种有效的肝细胞Ca2+激动剂，可刺激胆汁分泌和肝细胞Ca2+内流，而这两者在实验性胆汁淤积中均存在缺陷。蛋白激酶C（PKC）介导肝脏中的分泌刺激作用。本研究旨在确定TUDCA对分离的肝细胞中PKC的影响。
采用免疫印迹和免疫荧光技术研究TUDCA对肝细胞内PKC同工酶分布的影响。此外，采用放射酶法研究TUDCA对PKC的细胞内激活剂sn-1,2-二酰甘油（DAG）积累及肝细胞PKC活性的影响。
免疫印迹研究显示存在四种同工酶（α、δ、ε和ζ）。佛波酯佛波醇12-肉豆蔻酸酯13-乙酸酯（1 μmol/L）诱导α-PKC、δ-PKC和ε-PKC从细胞质向颗粒膜部分转位，这是PKC激活的关键步骤。TUDCA而非牛磺胆酸选择性地诱导α-PKC同工酶从细胞质向膜转位。此外，TUDCA导致肝细胞DAG含量显著增加，并刺激膜相关PKC活性。
TUDCA可能部分通过激活α-PKC刺激Ca(2+)依赖性肝细胞向胆汁的分泌。
