Identification of importin alpha 7 specific transport cargoes using a proteomic screening approach


  • S. Hügel
  • R. Depping
  • G. Dittmar
  • F. Rother
  • R. Cabot
  • M.D. Sury
  • E. Hartmann
  • M. Bader


  • Molecular & Cellular Proteomics


  • Mol Cell Proteomics 13 (5): 1286-1298


  • The importin alpha:beta complex is responsible for the nuclear import of proteins bearing classical nuclear localization signals. In mammals several importin alpha subtypes are known to exist which are suggested to have individual functions. Importin alpha 7 was shown to play a crucial role in early embryo development in mice. Embryos from importin alpha 7 depleted females stop at the two-cell stage and show disturbed zygotic genome activation. Since there is evidence that individual importin alpha subtypes possess cargo specificities, we hypothesized that importin alpha 7 binds a unique set of intracellular proteins. By using a collection of in vitro and in vivo binding assays, importin alpha 7 interaction partners were identified that differed from proteins found to bind to importin alpha 2 and 3. One of the proteins preferentially binding importin alpha 7 was the maternal effect protein Brg1. However, Brg1 was localized in oocyte nuclei in importin alpha 7 deficient embryos, albeit in reduced amounts, suggesting additional modes of nuclear translocation of this factor. An additional SILAC based screening approach identified Ash2l, Chd3, Mcm3, and Smarcc1 whose nuclear import seems to be disturbed in importin alpha 7 deficient fibroblasts.