The Nup358-RanGAP complex is required for efficient importin alpha/beta-dependent nuclear import

Mol Biol Cell. 2008 May;19(5):2300-10. doi: 10.1091/mbc.e07-12-1279. Epub 2008 Feb 27.


In vertebrate cells, the nucleoporin Nup358/RanBP2 is a major component of the filaments that emanate from the nuclear pore complex into the cytoplasm. Nup358 forms a complex with SUMOylated RanGAP1, the GTPase activating protein for Ran. RanGAP1 plays a pivotal role in the establishment of a RanGTP gradient across the nuclear envelope and, hence, in the majority of nucleocytoplasmic transport pathways. Here, we investigate the roles of the Nup358-RanGAP1 complex and of soluble RanGAP1 in nuclear protein transport, combining in vivo and in vitro approaches. Depletion of Nup358 by RNA interference led to a clear reduction of importin alpha/beta-dependent nuclear import of various reporter proteins. In vitro, transport could be partially restored by the addition of importin beta, RanBP1, and/or RanGAP1 to the transport reaction. In intact Nup358-depleted cells, overexpression of importin beta strongly stimulated nuclear import, demonstrating that the transport receptor is the most rate-limiting factor at reduced Nup358-concentrations. As an alternative approach, we used antibody-inhibition experiments. Antibodies against RanGAP1 inhibited the enzymatic activity of soluble and nuclear pore-associated RanGAP1, as well as nuclear import and export. Although export could be fully restored by soluble RanGAP, import was only partially rescued. Together, these data suggest a dual function of the Nup358-RanGAP1 complex as a coordinator of importin beta recycling and reformation of novel import complexes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Active Transport, Cell Nucleus
  • Animals
  • Antibody Specificity
  • Cell Nucleus / metabolism*
  • Cell Survival
  • GTPase-Activating Proteins / metabolism*
  • HeLa Cells
  • Humans
  • Mice
  • Models, Biological
  • Molecular Chaperones / metabolism*
  • Nuclear Localization Signals / metabolism
  • Nuclear Pore
  • Nuclear Pore Complex Proteins / deficiency
  • Nuclear Pore Complex Proteins / metabolism*
  • RNA Interference
  • Recombinant Fusion Proteins / metabolism
  • Solubility
  • alpha Karyopherins / metabolism*
  • beta Karyopherins / metabolism*


  • GTPase-Activating Proteins
  • Molecular Chaperones
  • Nuclear Localization Signals
  • Nuclear Pore Complex Proteins
  • Rangap1 protein, mouse
  • Recombinant Fusion Proteins
  • alpha Karyopherins
  • beta Karyopherins
  • ran-binding protein 2