In vivo analysis of importin alpha proteins reveals cellular proliferation inhibition and substrate specificity


  • C. Quensel
  • B. Friedrich
  • T. Sommer
  • E. Hartmann
  • M. Koehler


  • Molecular and Cellular Biology


  • Mol Cell Biol 24 (23): 10246-10255


  • The "classical" nuclear import pathway depends on importins {alpha} and {beta}. Humans have only one importin {beta}, while six {alpha} importins have been described. Whether or not distinct {alpha} importins are essential for specific import pathways in living human cells is unclear, We used RNA interference technology to specifically down-regulate the expression of ubiquitously expressed human {alpha} importins in HeLa cells. Down-regulation of importins {alpha}3, {alpha}5, {alpha}7, and {beta} strongly inhibited HeLa cell proliferation, while down-regulation of importins {alpha}1 and {alpha}4 had only a minor effect or no effect. Nucleoplasmin import was not prevented by down-regulation of any {alpha} importin, indicating that the importin {alpha}/{beta} pathway was generally not affected. In contrast, importin {alpha}3 or {alpha}5 down-regulation specifically inhibited the nuclear import of the Ran guanine nucleotide exchange factor, RCC1. Coinjection of recombinant {alpha} importins and RCC1 into down-regulated cells demonstrated that these transport defects were specifically caused by the limited availability of importin {alpha}3 in both cases. Thus, importin {alpha}3 is the only {alpha} importin responsible for the classical nuclear import of RCC1 in living cells.