Importin α-importin β complex mediated nuclear translocation of insulin-like growth factor binding protein-5

Endocr J. 2017 Oct 28;64(10):963-975. doi: 10.1507/endocrj.EJ17-0156. Epub 2017 Aug 23.


Insulin-like growth factor-binding protein (IGFBP)-5 is a secreted protein that binds to IGFs and modulates IGF actions, as well as regulates cell proliferation, migration, and apoptosis independent of IGF. Proper cellular localization is critical for the effective function of most signaling molecules. In previous studies, we have shown that the nuclear IGFBP-5 comes from ER-cytosol retro-translocation. In this study, we further investigated the pathway mediating IGFBP-5 nuclear import after it retro-translocation. Importin-α5 was identified as an IGFBP-5-interacting protein with a yeast two-hybrid system, and its interaction with IGFBP-5 was further confirmed by GST pull down and co-immunoprecipitation. Binding affinity of IGFBP-5 and importins were determined by surface plasmon resonance (IGFBP-5/importin-β: KD=2.44e-7, IGFBP-5/importin-α5: KD=3.4e-7). Blocking the importin-α5/importin-β nuclear import pathway using SiRNA or dominant negative impotin-β dramatically inhibited IGFBP-5-EGFP nuclear import, though importin-α5 overexpress does not affect IGFBP-5 nuclear import. Furthermore, nuclear IGFBP-5 was quantified using luciferase report assay. When deleted the IGFBP-5 nuclear localization sequence (NLS), IGFBP-5ΔNLS loss the ability to translocate into the nucleus and accumulation of IGFBP-5ΔNLS was visualized in the cytosol. Altogether, our findings provide a substantially evidence showed that the IGFBP-5 nuclear import is mediated by importin-α/importin-β complex, and NLS is critical domain in IGFBP-5 nuclear translocation.

Keywords: Importin; Insulin-like growth factor-binding protein; Nuclear localization signal; Nuclear translocation.

MeSH terms

  • Active Transport, Cell Nucleus
  • Gene Deletion
  • Genes, Reporter
  • Green Fluorescent Proteins / chemistry
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • HEK293 Cells
  • HeLa Cells
  • Humans
  • Immunoprecipitation
  • Insulin-Like Growth Factor Binding Protein 5 / chemistry
  • Insulin-Like Growth Factor Binding Protein 5 / genetics
  • Insulin-Like Growth Factor Binding Protein 5 / metabolism*
  • Kinetics
  • Microscopy, Confocal
  • Microscopy, Fluorescence
  • Mutation
  • Nuclear Localization Signals / antagonists & inhibitors
  • Nuclear Localization Signals / genetics
  • Nuclear Localization Signals / metabolism
  • Peptide Fragments / antagonists & inhibitors
  • Peptide Fragments / chemistry
  • Peptide Fragments / genetics
  • Peptide Fragments / metabolism
  • Protein Multimerization
  • RNA Interference
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism
  • Surface Plasmon Resonance
  • Two-Hybrid System Techniques
  • alpha Karyopherins / antagonists & inhibitors
  • alpha Karyopherins / chemistry
  • alpha Karyopherins / genetics
  • alpha Karyopherins / metabolism*
  • beta Karyopherins / antagonists & inhibitors
  • beta Karyopherins / chemistry
  • beta Karyopherins / genetics
  • beta Karyopherins / metabolism*


  • IGFBP5 protein, human
  • Insulin-Like Growth Factor Binding Protein 5
  • KPNB1 protein, human
  • Nuclear Localization Signals
  • Peptide Fragments
  • Recombinant Fusion Proteins
  • alpha Karyopherins
  • beta Karyopherins
  • enhanced green fluorescent protein
  • Green Fluorescent Proteins