Brownawell Amy M, Macara Ian G
Center for Cell Signaling, University of Virginia, Charlottesville, VA 22908, USA.
J Cell Biol. 2002 Jan 7;156(1):53-64. doi: 10.1083/jcb.200110082. Epub 2002 Jan 3.
We have identified a novel human karyopherin (Kap) beta family member that is related to human Crm1 and the Saccharomyces cerevisiae protein, Msn5p/Kap142p. Like other known transport receptors, this Kap binds specifically to RanGTP, interacts with nucleoporins, and shuttles between the nuclear and cytoplasmic compartments. We report that interleukin enhancer binding factor (ILF)3, a double-stranded RNA binding protein, associates with this Kap in a RanGTP-dependent manner and that its double-stranded RNA binding domain (dsRBD) is the limiting sequence required for this interaction. Importantly, the Kap interacts with dsRBDs found in several other proteins and binding is blocked by double-stranded RNA. We find that the dsRBD of ILF3 functions as a novel nuclear export sequence (NES) in intact cells, and its ability to serve as an NES is dependent on the expression of the Kap. In digitonin-permeabilized cells, the Kap but not Crm1 stimulated nuclear export of ILF3. Based on the ability of this Kap to mediate the export of dsRNA binding proteins, we named the protein exportin-5. We propose that exportin-5 is not an RNA export factor but instead participates in the regulated translocation of dsRBD proteins to the cytoplasm where they interact with target mRNAs.
我们鉴定出了一种新的人类核转运蛋白（Kap）β家族成员，它与人类Crm1及酿酒酵母蛋白Msn5p/Kap142p相关。与其他已知的转运受体一样，这种Kap特异性结合RanGTP，与核孔蛋白相互作用，并在核质区室之间穿梭。我们报告称，双链RNA结合蛋白白细胞介素增强子结合因子（ILF）3以RanGTP依赖的方式与这种Kap结合，其双链RNA结合结构域（dsRBD）是这种相互作用所需的关键序列。重要的是，该Kap与其他几种蛋白质中的dsRBD相互作用，且双链RNA会阻断这种结合。我们发现，在完整细胞中，ILF3的dsRBD作为一种新的核输出序列（NES）发挥作用，其作为NES的能力取决于Kap的表达。在洋地黄皂苷通透的细胞中，是Kap而非Crm1刺激了ILF3的核输出。基于这种Kap介导双链RNA结合蛋白输出的能力，我们将该蛋白命名为输出蛋白-5。我们提出，输出蛋白-5不是一种RNA输出因子，而是参与双链RNA结合结构域蛋白向细胞质的调控转运，在细胞质中它们与靶mRNA相互作用。
