Mohd-Ismail Nur Khairiah, Deng Lin, Sukumaran Sunil Kumar, Yu Victor C, Hotta Hak, Tan Yee-Joo
Collaborative Anti-Viral Research Group, Institute of Molecular and Cell Biology, Singapore.
J Virol. 2009 Oct;83(19):9993-10006. doi: 10.1128/JVI.00509-09. Epub 2009 Jul 15.
The hepatitis C virus (HCV) core protein is known to modulate apoptosis and contribute to viral replication and pathogenesis. In this study, we have identified a Bcl-2 homology 3 (BH3) domain in the core protein that is essential for its proapoptotic property. Coimmunoprecipitation experiments showed that the core protein interacts specifically with the human myeloid cell factor 1 (Mcl-1), a prosurvival member of the Bcl-2 family, but not with other prosurvival members (Bcl-X(L) and Bcl-w). Moreover, the overexpression of Mcl-1 protects against core-induced apoptosis. By using peptide mimetics, core was found to release cytochrome c from isolated mitochondria when complemented with Bad. Thus, core is a bona fide BH3-only protein having properties similar to those of Noxa, a BH3-only member of the Bcl-2 family that binds preferentially to Mcl-1. There are three critical hydrophobic residues in the BH3 domain of the core protein, and they are essential for the proapoptotic property of the core protein. Furthermore, the genotype 1b core protein is more effective than the genotype 2a core protein in inducing apoptosis due to a single-amino-acid difference at one of these hydrophobic residues (residue 119). Replacing this residue in the J6/JFH-1 infectious clone (genotype 2a) with the corresponding amino acid in the genotype 1b core protein produced a mutant virus, J6/JFH-1(V119L), which induced significantly higher levels of apoptosis in the infected cells than the parental J6/JFH-1 virus. Furthermore, the core protein of J6/JFH-1(V119L), but not that of J6/JFH-1, interacted with Mcl-1 in virus-infected cells. Taken together, the core protein is a novel BH3-only viral homologue that contributes to the induction of apoptosis during HCV infection.
已知丙型肝炎病毒（HCV）核心蛋白可调节细胞凋亡，并有助于病毒复制和发病机制。在本研究中，我们在核心蛋白中鉴定出一个Bcl-2同源3（BH3）结构域，该结构域对其促凋亡特性至关重要。免疫共沉淀实验表明，核心蛋白与人髓样细胞因子1（Mcl-1）特异性相互作用，Mcl-1是Bcl-2家族的一个促生存成员，但不与其他促生存成员（Bcl-X(L)和Bcl-w）相互作用。此外，Mcl-1的过表达可保护细胞免受核心蛋白诱导的凋亡。通过使用肽模拟物，发现核心蛋白在与Bad互补时可从分离的线粒体中释放细胞色素c。因此，核心蛋白是一种真正的仅含BH3的蛋白，其特性与Noxa相似，Noxa是Bcl-2家族中仅含BH3的成员，优先与Mcl-1结合。核心蛋白的BH3结构域中有三个关键的疏水残基，它们对核心蛋白的促凋亡特性至关重要。此外，由于这些疏水残基之一（第119位残基）存在单氨基酸差异，基因型1b核心蛋白比基因型2a核心蛋白在诱导凋亡方面更有效。用基因型1b核心蛋白中的相应氨基酸替换J6/JFH-1感染性克隆（基因型2a）中的该残基，产生了一种突变病毒J6/JFH-1(V119L)，该病毒在感染细胞中诱导的凋亡水平明显高于亲本J6/JFH-1病毒。此外，J6/JFH-1(V119L)的核心蛋白，而不是J6/JFH-1的核心蛋白，在病毒感染细胞中与Mcl-1相互作用。综上所述，核心蛋白是一种新型的仅含BH3的病毒同源物，在HCV感染期间有助于诱导细胞凋亡。
