Terada Yasuhiko, Yasuda Yuko
Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455, USA.
Mol Cell Biol. 2006 Nov;26(21):8149-58. doi: 10.1128/MCB.01170-06. Epub 2006 Aug 21.
Vpr, the viral protein R of human immunodeficiency virus type 1, induces G(2) cell cycle arrest and apoptosis in mammalian cells via ATR (for "ataxia-telangiectasia-mediated and Rad3-related") checkpoint activation. The expression of Vpr induces the formation of the gamma-histone 2A variant X (H2AX) and breast cancer susceptibility protein 1 (BRCA1) nuclear foci, and a C-terminal domain is required for Vpr-induced ATR activation and its nuclear localization. However, the cellular target of Vpr, as well as the mechanism of G(2) checkpoint activation, was unknown. Here we report that Vpr induces checkpoint activation and G(2) arrest by binding to the CUS1 domain of SAP145 and interfering with the functions of the SAP145 and SAP49 proteins, two subunits of the multimeric splicing factor 3b (SF3b). Vpr interacts with and colocalizes with SAP145 through its C-terminal domain in a speckled distribution. The depletion of either SAP145 or SAP49 leads to checkpoint-mediated G(2) cell cycle arrest through the induction of nuclear foci containing gamma-H2AX and BRCA1. In addition, the expression of Vpr excludes SAP49 from the nuclear speckles and inhibits the formation of the SAP145-SAP49 complex. To conclude, these results point out the unexpected roles of the SAP145-SAP49 splicing factors in cell cycle progression and suggest that cellular expression of Vpr induces checkpoint activation and G(2) arrest by interfering with the function of SAP145-SAP49 complex in host cells.
Vpr是1型人类免疫缺陷病毒的病毒蛋白R，它通过激活ATR（共济失调毛细血管扩张症相关和Rad3相关蛋白）检查点，在哺乳动物细胞中诱导G2期细胞周期停滞和凋亡。Vpr的表达诱导γ-组蛋白2A变体X（H2AX）和乳腺癌易感蛋白1（BRCA1）核灶的形成，并且Vpr诱导的ATR激活及其核定位需要一个C末端结构域。然而，Vpr的细胞靶点以及G2检查点激活的机制尚不清楚。在此我们报告，Vpr通过与SAP145的CUS1结构域结合并干扰多聚体剪接因子3b（SF3b）的两个亚基SAP145和SAP49的功能，从而诱导检查点激活和G2期停滞。Vpr通过其C末端结构域与SAP145相互作用并共定位，呈斑点状分布。SAP145或SAP49的缺失通过诱导含有γ-H2AX和BRCA1的核灶，导致检查点介导的G2期细胞周期停滞。此外，Vpr的表达使SAP49从核斑点中排除，并抑制SAP145-SAP49复合物的形成。总之，这些结果指出了SAP145-SAP49剪接因子在细胞周期进程中的意外作用，并表明Vpr的细胞表达通过干扰宿主细胞中SAP145-SAP49复合物的功能来诱导检查点激活和G(2)停滞。
