Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
Mol Biol Cell. 2011 Dec;22(23):4539-48. doi: 10.1091/mbc.E11-03-0267. Epub 2011 Oct 12.
The small GTPase Ran and the importin proteins regulate nucleocytoplasmic transport. New evidence suggests that Ran GTP and the importins are also involved in conveying proteins into cilia. In this study, we find that Ran GTP accumulation at the basal bodies is coordinated with the initiation of ciliogenesis. The Ran-binding protein 1 (RanBP1), which indirectly accelerates Ran GTP → Ran GDP hydrolysis and promotes the dissociation of the Ran/importin complex, also localizes to basal bodies and cilia. To confirm the crucial link between Ran GTP and ciliogenesis, we manipulated the levels of RanBP1 and determined the effects on Ran GTP and primary cilia formation. We discovered that RanBP1 knockdown results in an increased concentration of Ran GTP at basal bodies, leading to ciliogenesis. In contrast, overexpression of RanBP1 antagonizes primary cilia formation. Furthermore, we demonstrate that RanBP1 knockdown disrupts the proper localization of KIF17, a kinesin-2 motor, at the distal tips of primary cilia in Madin-Darby canine kidney cells. Our studies illuminate a new function for Ran GTP in stimulating cilia formation and reinforce the notion that Ran GTP and the importins play key roles in ciliogenesis and ciliary protein transport.
小分子 GTP 酶 Ran 和输入蛋白调节核质转运。新的证据表明，Ran GTP 和输入蛋白也参与将蛋白质输送到纤毛中。在这项研究中，我们发现 Ran GTP 在基体处的积累与纤毛发生的起始相协调。Ran 结合蛋白 1（RanBP1）间接加速 Ran GTP→Ran GDP 水解，并促进 Ran/输入蛋白复合物的解离，也定位于基体和纤毛。为了确认 Ran GTP 和纤毛发生之间的关键联系，我们操纵了 RanBP1 的水平，并确定了对 Ran GTP 和初级纤毛形成的影响。我们发现，RanBP1 敲低导致基体处 Ran GTP 浓度增加，从而导致纤毛发生。相比之下，RanBP1 的过表达会拮抗初级纤毛的形成。此外，我们证明 RanBP1 敲低会破坏 Madin-Darby 犬肾细胞中初级纤毛远端尖端 KIF17（一种驱动蛋白-2 马达）的正确定位。我们的研究阐明了 Ran GTP 在刺激纤毛发生中的新功能，并强化了 Ran GTP 和输入蛋白在纤毛发生和纤毛蛋白运输中发挥关键作用的观点。
