Hirano Fuminori, Haneda Masakazu, Makino Isao
Second Department of Internal Medicine, Asahikawa Medical College, Asahikawa, Japan.
J Gastroenterol Hepatol. 2006 Dec;21(12):1807-13. doi: 10.1111/j.1440-1746.2006.04363.x.
Increased concentration of endogenous bile acids in the liver correlates with clinical features of cholestatic liver diseases. Recently, it was reported that non-toxic hydrophobic bile acid activated a survival signaling pathway via phosphatidylinositol 3 (PI3) kinase in hepatocytes. However, whether bile acid induces inhibitors of apoptosis protein (IAPs) directly in human hepatocytes remains unknown. This study investigated effects of bile acids on cIAP-1, cIAP-2 and XIAP expression in hepatocytes.
Human fetal hepatocytes and HepG2 cells were treated with free or conjugated chenodeoxycholic acid (CDCA) or ursodeoxycholic acid in the presence or absence of several inhibitors. Reverse transcriptase-polymerase chain reaction and Western blot analyses were performed for mRNA and protein expressions, respectively, of IAPs. Luciferase assay was used to investigate transcriptional activity of nuclear factor (NF)-kappaB.
Chenodeoxycholic acid up-regulated both mRNA and protein expressions of cIAP-1. In particular, taurochenodeoxycholic acid (TCDCA), but not glycochenodeoxycholic acid (GCDCA), induced cIAP-1 mRNA expression. In contrast, cIAP-2 and XIAP mRNA expressions were not influenced by CDCA. Moreover, CDCA-induced cIAP-1 mRNA expression was inhibited completely by calphostin C and SB203580, but not by wortmannin. Luciferase assay showed that CDCA and TCDCA activated NF-kappaB-driven transcriptional activity.
It was shown that CDCA induced cIAP-1 expression in hepatocytes through protein kinase C- and p38 mitogen-activated protein kinase-mediated pathway. Especially, TCDCA, but not GCDCA, increased cIAP-1 mRNA expression and NF-kappaB-regulated transcriptional activity. Therefore, it is suggested that CDCA and TCDCA themselves have an inhibitory potential against apoptosis through the cIAP-1-survival signaling pathway, in addition to PI3 kinase-dependent pathway.
肝脏内源性胆汁酸浓度升高与胆汁淤积性肝病的临床特征相关。最近，有报道称无毒疏水胆汁酸通过磷脂酰肌醇3（PI3）激酶在肝细胞中激活了生存信号通路。然而，胆汁酸是否直接在人肝细胞中诱导凋亡抑制蛋白（IAPs）仍不清楚。本研究调查了胆汁酸对肝细胞中cIAP-1、cIAP-2和XIAP表达的影响。
在有或没有几种抑制剂的情况下，用人胎儿肝细胞和HepG2细胞分别用游离或结合型鹅去氧胆酸（CDCA）或熊去氧胆酸处理。分别对IAPs的mRNA和蛋白表达进行逆转录聚合酶链反应和蛋白质印迹分析。使用荧光素酶测定法研究核因子（NF）-κB的转录活性。
鹅去氧胆酸上调了cIAP-1的mRNA和蛋白表达。特别是，牛磺鹅去氧胆酸（TCDCA）而非甘氨鹅去氧胆酸（GCDCA）诱导了cIAP-1 mRNA表达。相反，cIAP-2和XIAP mRNA表达不受CDCA影响。此外，CDCA诱导的cIAP-1 mRNA表达被钙泊三醇C和SB203580完全抑制，但不被渥曼青霉素抑制。荧光素酶测定表明CDCA和TCDCA激活了NF-κB驱动的转录活性。
结果表明，CDCA通过蛋白激酶C和p38丝裂原活化蛋白激酶介导的途径在肝细胞中诱导cIAP-1表达。特别是，TCDCA而非GCDCA增加了cIAP-1 mRNA表达和NF-κB调节的转录活性。因此，除了PI3激酶依赖性途径外，提示CDCA和TCDCA自身通过cIAP-1生存信号通路具有抗凋亡的潜在作用。
