Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232-8240 Department of Biochemistry and Molecular Biology, University of Texas Medical School at Houston, Houston, TX 77030 Institute of Medical Biology, A*STAR, Singapore 138648 Department of Pediatrics, National University of Singapore, Singapore 119228.
Mol Biol Cell. 2013 Sep;24(18):2954-65. doi: 10.1091/mbc.E13-05-0254. Epub 2013 Jul 31.
We previously reported that Asunder (ASUN) is essential for recruitment of dynein motors to the nuclear envelope (NE) and nucleus-centrosome coupling at the onset of cell division in cultured human cells and Drosophila spermatocytes, although the mechanisms underlying this regulation remain unknown. We also identified ASUN as a functional component of Integrator (INT), a multisubunit complex required for 3'-end processing of small nuclear RNAs. We now provide evidence that ASUN acts in the nucleus in concert with other INT components to mediate recruitment of dynein to the NE. Knockdown of other individual INT subunits in HeLa cells recapitulates the loss of perinuclear dynein in ASUN-small interfering RNA cells. Forced localization of ASUN to the cytoplasm via mutation of its nuclear localization sequence blocks its capacity to restore perinuclear dynein in both cultured human cells lacking ASUN and Drosophila asun spermatocytes. In addition, the levels of several INT subunits are reduced at G2/M when dynein is recruited to the NE, suggesting that INT does not directly mediate this step. Taken together, our data support a model in which a nuclear INT complex promotes recruitment of cytoplasmic dynein to the NE, possibly via a mechanism involving RNA processing.
我们之前报道过，Asunder（ASUN）对于培养的人类细胞和果蝇精母细胞在细胞分裂开始时将动力蛋白招募到核膜（NE）和核-中心体连接中是必需的，尽管这种调节的机制尚不清楚。我们还将 ASUN 鉴定为 Integrator（INT）的一个功能组件，INT 是一种多亚基复合物，对于小核 RNA 的 3'端加工是必需的。我们现在提供的证据表明，ASUN 与其他 INT 组件一起在核内发挥作用，以介导动力蛋白向 NE 的募集。在 HeLa 细胞中敲低其他单个 INT 亚基可重现 ASUN-siRNA 细胞中围绕核的动力蛋白缺失。通过突变其核定位序列将 ASUN 强制定位到细胞质中，会阻止其在缺乏 ASUN 的培养的人类细胞和 Drosophila asun 精母细胞中恢复围绕核的动力蛋白的能力。此外，当动力蛋白被招募到 NE 时，几种 INT 亚基的水平在 G2/M 降低，这表明 INT 不会直接介导这一步骤。综上所述，我们的数据支持这样一种模型，即核 INT 复合物促进细胞质动力蛋白向 NE 的募集，可能通过涉及 RNA 加工的机制。
