Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309, USA.
Proc Natl Acad Sci U S A. 2012 Nov 6;109(45):18471-6. doi: 10.1073/pnas.1204668109. Epub 2012 Oct 22.
Infection with the hepatitis B virus (HBV) promotes the development of hepatitis, cirrhosis, and hepatocellular carcinoma (HCC) and is a leading cause of morbidity and mortality worldwide. HBV X protein (HBx) is an important effector for HBV pathogenesis, but its cellular targets and acting mechanisms remain elusive. We show here that HBx interacts with the anti-apoptotic proteins Bcl-2 and Bcl-xL through a Bcl-2 homology 3 (BH3)-like motif in mammalian cells. Importantly, mutations in the BH3-like motif that prevent HBx binding to Bcl-2 and Bcl-xL abrogate cytosolic calcium elevation and cell death induced by HBx expression in hepatocytes and severely impair HBV viral replication, which can be substantially rescued by restoring cytosolic calcium. These results suggest that HBx binding to Bcl-2 family members and subsequent elevation of cytosolic calcium are important for HBV viral replication. Consistently, RNAi knockdown of Bcl-2 or Bcl-xL results in reduced calcium elevation by HBx and decreased viral replication in hepatocytes. Our results suggest that HBx targets Bcl-2 proteins through its BH3-like motif to promote cytosolic calcium elevation, cell death, and viral replication during HBV pathogenesis, which presents an excellent therapeutic intervention point in treating patients with chronic HBV.
乙型肝炎病毒 (HBV) 感染可促进肝炎、肝硬化和肝细胞癌 (HCC) 的发展，是全球发病率和死亡率的主要原因。HBV X 蛋白 (HBx) 是 HBV 发病机制的重要效应因子，但它的细胞靶标和作用机制仍不清楚。我们在这里显示，HBx 通过哺乳动物细胞中的 Bcl-2 同源结构域 3 (BH3) 样结构域与抗凋亡蛋白 Bcl-2 和 Bcl-xL 相互作用。重要的是，在 BH3 样结构域中发生突变，阻止 HBx 与 Bcl-2 和 Bcl-xL 结合，可消除 HBx 在肝细胞中表达引起的细胞质钙离子升高和细胞死亡，并严重损害 HBV 病毒复制，而通过恢复细胞质钙离子可显著挽救。这些结果表明，HBx 与 Bcl-2 家族成员的结合以及随后细胞质钙离子的升高对 HBV 病毒复制很重要。一致地，通过 RNAi 敲低 Bcl-2 或 Bcl-xL 可导致 HBx 引起的钙离子升高减少和肝细胞中病毒复制减少。我们的结果表明，HBx 通过其 BH3 样结构域靶向 Bcl-2 蛋白，以促进 HBV 发病机制中的细胞质钙离子升高、细胞死亡和病毒复制，这为治疗慢性 HBV 患者提供了一个极好的治疗干预点。
