Department of Biochemistry and Molecular Biology, Ajou University School of Medicine and the Graduate School of Molecular Science and Technology, Ajou University, Suwon, South Korea.
Carcinogenesis. 2013 Jul;34(7):1680-8. doi: 10.1093/carcin/bgt105. Epub 2013 Mar 27.
Hepatitis B virus (HBV) X protein (HBx), encoded by the HBV genome, is involved in the development of HBV-mediated liver cancer, whose frequency is highly correlated with chromosomal instability (CIN). We reported previously that HBx induces mitotic checkpoint dysfunction by targeting the human serine/threonine kinase BubR1 (hBubR1). However, the underlying mechanism remained unresolved. Here, we show that HBx protein-associated protein α (HBxAPα)/Rsf-1 associates with hBubR1 and HBx in the chromatin fraction during mitosis. Depletion of HBxAPα/Rsf-1 abolished the interaction between HBx and hBubR1, indicating that HBxAPα/Rsf-1 mediates these interactions. Knockdown of HBxAPα/Rsf-1 with small interfering RNA did not affect the recruitment of hBubR1 to kinetochores; however, it did significantly impair HBx targeting to kinetochores. A deletion mutant analysis revealed that two Kunitz domains of HBx, the Cdc20-binding domain of hBubR1 and full-length of HBxAPα/Rsf-1 were essential for these interactions. Thus, binding of HBx to hBubR1, stabilized by HBxAPα/Rsf-1, significantly attenuated hBubR1 binding to Cdc20 and consequently increased the rate of mitotic aberrations. Collectively, our data show that the HBx impairs hBubR1 function and induces CIN through HBxAPα/Rsf-1, providing a novel mechanism for induction of genomic instability by a viral pathogen in hepatocarcinogenesis.
乙型肝炎病毒（HBV）X 蛋白（HBx）由 HBV 基因组编码，参与 HBV 介导的肝癌的发展，其频率与染色体不稳定性（CIN）高度相关。我们之前报道过，HBx 通过靶向人类丝氨酸/苏氨酸激酶 BubR1（hBubR1）导致有丝分裂检查点功能障碍。然而，其潜在机制仍未解决。在这里，我们显示 HBx 蛋白相关蛋白α（HBxAPα）/Rsf-1 在有丝分裂期间与 hBubR1 和 HBx 一起定位于染色质部分。HBxAPα/Rsf-1 的耗竭消除了 HBx 和 hBubR1 之间的相互作用，表明 HBxAPα/Rsf-1 介导了这些相互作用。用小干扰 RNA 敲低 HBxAPα/Rsf-1 不会影响 hBubR1 向动粒的募集；然而，它显著损害了 HBx 向动粒的靶向。缺失突变分析显示，HBx 的两个 Kunitz 结构域、hBubR1 的 Cdc20 结合结构域和全长的 HBxAPα/Rsf-1 对于这些相互作用是必需的。因此，HBx 与 hBubR1 的结合，通过 HBxAPα/Rsf-1 稳定，显著削弱了 hBubR1 与 Cdc20 的结合，从而增加了有丝分裂异常的速度。总之，我们的数据表明，HBx 通过 HBxAPα/Rsf-1 损害 hBubR1 的功能并诱导 CIN，为病毒病原体在肝癌发生中诱导基因组不稳定性提供了一种新的机制。
