Chou Ai-Hsiang, Tsai Hwei-Fang, Wu Yi-Ying, Hu Chung-Yi, Hwang Lih-Hwa, Hsu Ping-I, Hsu Ping-Ning
Graduate Institute of Immunology, College of Medicine, National Taiwan University, Taipei, Taiwan.
J Immunol. 2005 Feb 15;174(4):2160-6. doi: 10.4049/jimmunol.174.4.2160.
Hepatitis C virus (HCV) is a major human pathogen causing chronic liver disease, which leads to cirrhosis of liver and hepatocellular carcinoma. The HCV core protein, a viral nucleocapsid, has been shown to affect various intracellular events, including cell proliferation and apoptosis. However, the precise mechanisms of the effects are not fully understood. In this study, we show that HCV core protein sensitizes human hepatocellular carcinoma cell line, Huh7, conferred sensitivity to TRAIL-, but not Fas ligand-mediated apoptosis. Huh7 cells are resistant to TRAIL, despite the induction of caspase-8 after TRAIL engagement. However, HCV core protein induces TRAIL apoptosis signaling via sequential induction of caspase-8, Bid cleavage, activation of mitochondrial pathway, and effector caspase-3. HCV core protein also induces activation of caspase-9 after TRAIL engagement, and the induction of TRAIL sensitivity by HCV core protein could be reversed by caspase-9 inhibitor. Therefore, the HCV core protein-induced TRAIL-mediated apoptosis is dependent upon activation of caspase-8 downstream pathway to convey the death signal to mitochondria, leading to activation of mitochondrial signaling pathway and breaking the apoptosis resistance. These results combined indicate that the HCV core protein enhances TRAIL-, but not Fas ligand-mediated apoptotic cell death in Huh7 cells via a mechanism dependent on the activation of mitochondria apoptosis signaling pathway. These results suggest that HCV core protein may have a role in immune-mediated liver cell injury by modulation of TRAIL-induced apoptosis.
丙型肝炎病毒（HCV）是导致慢性肝病的主要人类病原体，可引发肝硬化和肝细胞癌。HCV核心蛋白作为一种病毒核衣壳蛋白，已被证明会影响多种细胞内事件，包括细胞增殖和凋亡。然而，其作用的精确机制尚未完全明确。在本研究中，我们发现HCV核心蛋白使人类肝癌细胞系Huh7对TRAIL介导的凋亡敏感，但对Fas配体介导的凋亡不敏感。Huh7细胞对TRAIL具有抗性，尽管TRAIL作用后会诱导半胱天冬酶-8的产生。然而，HCV核心蛋白通过依次诱导半胱天冬酶-8、Bid裂解、激活线粒体途径以及效应半胱天冬酶-3来诱导TRAIL凋亡信号。HCV核心蛋白在TRAIL作用后还会诱导半胱天冬酶-9的激活，并且HCV核心蛋白诱导的TRAIL敏感性可被半胱天冬酶-9抑制剂逆转。因此，HCV核心蛋白诱导的TRAIL介导的凋亡依赖于半胱天冬酶-8下游途径的激活，从而将死亡信号传递至线粒体，导致线粒体信号途径的激活并打破凋亡抗性。综合这些结果表明，HCV核心蛋白通过依赖线粒体凋亡信号途径激活的机制增强了Huh7细胞中TRAIL介导的凋亡细胞死亡，但不增强Fas配体介导的凋亡细胞死亡。这些结果提示，HCV核心蛋白可能通过调节TRAIL诱导的凋亡在免疫介导的肝细胞损伤中发挥作用。
