Division of Molecular and Cellular Biology, National Institute for Child Health and Human Development, National Institutes of Health , Bethesda, MD 20892, USA.
Cell Cycle. 2020 Aug;19(15):1899-1916. doi: 10.1080/15384101.2020.1782036. Epub 2020 Jun 28.
The Ran GTPase plays critical roles in multiple cellular processes including interphase nucleocytoplasmic transport and mitotic spindle assembly. During mitosis in mammalian cells, GTP-bound Ran (Ran-GTP) is concentrated near mitotic chromatin while GDP-bound Ran (Ran-GDP) is more abundant distal to chromosomes. This pattern spatially controls spindle formation because Ran-GTP locally releases spindle assembly factors (SAFs), such as Hepatoma Up-Regulated Protein (HURP), from inhibitory interactions near chromosomes. Regulator of Chromatin Condensation 1 (RCC1) is Ran's chromatin-bound exchange factor, and RanBP1 is a conserved Ran-GTP-binding protein that has been implicated as a mitotic regulator of RCC1 in embryonic systems. Here, we show that RanBP1 controls mitotic RCC1 dynamics in human somatic tissue culture cells. In addition, we observed the re-localization of HURP in metaphase cells after RanBP1 degradation, consistent with the idea that altered RCC1 dynamics functionally modulate SAF activities. Together, our findings reveal an important mitotic role for RanBP1 in human somatic cells, controlling the spatial distribution and magnitude of mitotic Ran-GTP production and thereby ensuring the accurate execution of Ran-dependent mitotic events.
AID: Auxin-induced degron; FLIP: Fluorescence loss in photobleaching; FRAP: Fluorescence recovery after photobleaching; GDP: guanosine diphosphate; GTP: guanosine triphosphate; HURP: Hepatoma Up-Regulated Protein; NE: nuclear envelope; NEBD: Nuclear Envelope Breakdown; RanBP1: Ran-binding protein 1; RanGAP1: Ran GTPase-Activating Protein 1; RCC1: Regulator of Chromatin Condensation 1; RRR complex: RCC1/Ran/RanBP1 heterotrimeric complex; SAF: Spindle Assembly Factor; TIR1: Transport Inhibitor Response 1 protein; XEE: Xenopus egg extract.
Ran GTPase 在包括核质间运输和有丝分裂纺锤体组装在内的多种细胞过程中发挥关键作用。在哺乳动物细胞的有丝分裂过程中，GTP 结合的 Ran（Ran-GTP）在有丝分裂染色质附近浓缩，而 GDP 结合的 Ran（Ran-GDP）在染色体远端更丰富。这种模式通过空间控制纺锤体的形成，因为 Ran-GTP 局部从染色体附近的抑制性相互作用中释放出纺锤体组装因子（SAF），如肝癌上调蛋白（HURP）。染色质结合的 Ran 交换因子是 RCC1，而 RanBP1 是一种保守的 Ran-GTP 结合蛋白，在胚胎系统中被认为是 RCC1 的有丝分裂调节剂。在这里，我们表明 RanBP1 控制人类体细胞培养细胞中的有丝分裂 RCC1 动力学。此外，我们观察到在 RanBP1 降解后中期细胞中 HURP 的重新定位，这与改变的 RCC1 动力学在功能上调节 SAF 活性的想法一致。总之，我们的发现揭示了 RanBP1 在人类体细胞中有丝分裂中的重要作用，控制有丝分裂 Ran-GTP 产生的空间分布和幅度，从而确保 Ran 依赖性有丝分裂事件的准确执行。
AID：Auxin-induced degron；FLIP：Fluorescence loss in photobleaching；FRAP：Fluorescence recovery after photobleaching；GDP：鸟苷二磷酸；GTP：鸟苷三磷酸；HURP：肝癌上调蛋白；NE：核膜；NEBD：核膜破裂；RanBP1：Ran 结合蛋白 1；RanGAP1：Ran GTPase 激活蛋白 1；RCC1：染色质凝聚调节剂 1；RRR 复合物：RCC1/Ran/RanBP1 异三聚体复合物；SAF：纺锤体组装因子；TIR1：转运抑制剂反应 1 蛋白；XEE：非洲爪蟾卵提取物。
