Rust Christian, Wild Nadine, Bernt Carina, Vennegeerts Timo, Wimmer Ralf, Beuers Ulrich
Department of Medicine 2, Grosshadern, University of Munich, 81377 Munich, Germany.
Department of Medicine 2, Grosshadern, University of Munich, 81377 Munich, Germany.
J Biol Chem. 2009 Jan 30;284(5):2908-2916. doi: 10.1074/jbc.M804585200. Epub 2008 Nov 18.
Apoptosis induced by hydrophobic bile acids is thought to contribute to liver injury during cholestasis. Caspase-6 is an executioner caspase that also appears to have regulatory functions in hematopoetic cell lines. We aimed to elucidate the role of caspase-6 in bile acid-induced apoptosis. The major human hydrophobic bile acid, glycochenodeoxycholic acid (GCDCA, 75 micromol/liter), rapidly induced caspase-6 cleavage in HepG2-Ntcp human hepatoma cells. GCDCA-induced, but not tumor necrosis factor alpha- or etoposide-induced activation of effector caspases-3 and -7 was significantly reduced by 50% in caspase-6-deficient HepG2-Ntcp cells as well as in primary rat hepatocytes pretreated with a caspase-6 inhibitor. Inhibition of caspase-9 reduced GCDCA-induced activation of caspase-6, whereas inhibition of caspase-6 reduced activation of caspase-8 placing caspase-6 between caspase-9 and caspase-8. GCDCA also induced apoptosis in Fas-deficient Hep3B-Ntcp and HuH7-Ntcp hepatoma cells. In addition, GCDCA-induced apoptosis was reduced by 50% in FADD-deficient HepG2-Ntcp cells, whereas apoptosis induced by tumor necrosis factor alpha was reduced by 90%. Collectively, these observations suggest that GCDCA can induce hepatocyte apoptosis in the absence of death receptor signaling, presumably by a compensatory mitochondrial pathway. In conclusion, caspase-6 appears to play an important regulatory role in the promotion of bile acid-induced apoptosis as part of a feedback loop.
疏水性胆汁酸诱导的细胞凋亡被认为与胆汁淤积时的肝损伤有关。半胱天冬酶-6是一种执行性半胱天冬酶，在造血细胞系中似乎也具有调节功能。我们旨在阐明半胱天冬酶-6在胆汁酸诱导的细胞凋亡中的作用。主要的人疏水性胆汁酸甘氨鹅脱氧胆酸（GCDCA，75微摩尔/升）可迅速诱导HepG2-Ntcp人肝癌细胞中的半胱天冬酶-6裂解。在半胱天冬酶-6缺陷的HepG2-Ntcp细胞以及用半胱天冬酶-6抑制剂预处理的原代大鼠肝细胞中，GCDCA诱导的效应半胱天冬酶-3和-7的激活（而非肿瘤坏死因子α或依托泊苷诱导的激活）显著降低了50%。半胱天冬酶-9的抑制降低了GCDCA诱导的半胱天冬酶-6的激活，而半胱天冬酶-6的抑制降低了半胱天冬酶-8的激活，使半胱天冬酶-6处于半胱天冬酶-9和半胱天冬酶-8之间。GCDCA还可诱导Fas缺陷的Hep3B-Ntcp和HuH7-Ntcp肝癌细胞凋亡。此外，在FADD缺陷的HepG2-Ntcp细胞中，GCDCA诱导的凋亡减少了50%，而肿瘤坏死因子α诱导的凋亡减少了90%。总体而言，这些观察结果表明，GCDCA可能通过一条代偿性线粒体途径在无死亡受体信号传导的情况下诱导肝细胞凋亡。总之，半胱天冬酶-6似乎作为反馈环的一部分，在促进胆汁酸诱导的细胞凋亡中发挥重要的调节作用。
