慢性肝炎及肝硬化一直是影響國人健康及造成死亡的主要原因之一。除了酒精及藥物之外，病毒感染也是重要肇因，其中B型肝炎已有疫苗可以有效預防，而C型肝炎病毒尚未有疫苗或有效治療方式來控制，因此C型肝炎病毒感染所導致的慢性肝炎或肝癌在台灣將是越來越重要的醫療議題。當宿主細胞受到C型肝炎病毒感染的時候，可藉由C型肝炎病毒本身外套膜蛋白的高度變異來躲避宿主免疫系統的攻擊；另外一種方式則是透過病毒蛋白的作用來抑制宿主免疫系統的產生或是促使細胞凋亡來幫助病毒繁殖擴散，導致組織產生持續性的發炎反應，進而引起慢性肝炎、肝硬化以及肝癌。之前的研究指出C型肝炎病毒套膜蛋白E2會導致細胞凋亡，但是確實的相關機制卻還不是很清楚。因此我們先探討C型肝炎病毒的套膜蛋白E2是否有導致Huh-7人類肝癌細胞株發生細胞凋亡的能力，再進一步研究探討其相關的分子機制。經由MTT assay、DNA fragmentation以及western blot等分析方式，我們發現套膜蛋白E2確實會導致Huh-7細胞產生細胞凋亡，並且促進procaspase 8、procaspase 9及procaspase 3的活化以及使得PARP蛋白受到切割，細胞色素C、Bax及tBid蛋白表現量也因而增加，同時Bid及Bcl-2蛋白表現量減少。根據上述結果可以發現，套膜蛋白E2會使細胞凋亡抑制蛋白(Bcl-2)的蛋白表現量減少，並且藉由透過切割活化procaspase 8，將Bid的C端切除而形成tBid蛋白，tBid蛋白移動到粒線體細胞膜上使得Bax蛋白的活化，導致粒線體膜電位改變，而將細胞色素C釋放至細胞質當中，促使procaspase 9蛋白活化，並繼續活化下游的procaspase 3蛋白，並導致procaspase 3的受質PARP蛋白受到切割而進行細胞凋亡。
Hepatitis C virus (HCV) is the major causative agent for hepatitis and hepatocellular carcinoma. Epidemiological studies have suggested that ~80% of acute HCV infection cases would develop into chronic infection. Such persistent infection may be mild, or sometimes even asymptomatic, in early phases of the disease, however, after a decade or two, may cause liver cirrhosis and eventually hepatocellular carcinoma, which then have a great social and economical impact. Although the mechanism for virus persistence is poorly understood, the high mutation rate of viral envelope proteins and the suppression of the host immune system are believed to involve in the chronic infection. Previous studies suggested that the envelope protein E2 could induce apoptosis in cultured mammalian cell lines, but the mechanism involved in the development of persistent infection and the pathogenesis is not fully understood. Therefore, in this study we first studied if E2 may induce apoptosis in Huh-7 cells to confirm the impact of HCV E2 protein on apoptosis. Our results showed that E2 indeed could induce apoptosis of Huh-7 cells by promoting the activation of procaspase 8, procaspase 9 and procaspase 3 and cleaveage of PARP, while protein expression levels of cytochrome c, Bax and tBid were up-regulated in a time-dependent fashion, at the same time and that of Bid and Bcl-2 protein were down-regulated. In summary, E2 may induce apoptosis of Huh-7 cells through a mitochondria-dependent pathway.
