Importins belong to the karyopherin family of nuclear transport proteins and are divided into two subgroups: importin alpha and importin beta. Importins function mainly in the import and export of nuclear proteins. KPNA2, a member of the importin alpha family, contains an N-terminal importin beta binding motif followed by a hydrophobic region consisting of 10 armadillo repeats that function in binding to the nuclear localization signal sites of cargo proteins. A trimeric complex forms, translocates into the nucleus, and then dissociates upon binding of RanGTP to importin beta. The dissociated importin alpha is recycled back to the cytoplasm with the help of export factor CAS. KPNA2 can differentially regulate target localization by binding to different cargo proteins, either actively transporting them to the nucleus or retaining them in the cytoplasm by formation of incompetent complexes. Research studies indicate that KPNA2 promotes cell proliferation and tumorigenesis. Research studies have also shown that up-regulation of KPNA2 is associated with cancer progression. Therefore, it has become a focus of biomarker research.
[1] Chook, Y.M. and Blobel, G. (2001) Curr Opin Struct Biol 11, 703-15.
[2] Pemberton, L.F. and Paschal, B.M. (2005) Traffic 6, 187-98.
[3] Kelley, J.B. et al. (2010) BMC Cell Biol 11, 63.
[4] Weis, K. et al. (1995) Science 268, 1049-53.
[5] Fontes, M.R. et al. (2003) J Biol Chem 278, 27981-7.
[6] Görlich, D. (1998) EMBO J 17, 2721-7.
[7] Goldfarb, D.S. et al. (2004) Trends Cell Biol 14, 505-14.
[8] Yasuhara, N. et al. (2013) Dev Cell 26, 123-35.
[9] Huang, L. et al. (2013) Cell Death Dis 4, e745.
[10] Grupp, K. et al. (2014) Mod Pathol 27, 96-106.
