title: Importin KPNA2 is required for proper nuclear localization and multiple functions of NBS1.
abstract: Nijmegen breakage syndrome (NBS) is a chromosomal-instability syndrome associated with cancer predisposition, radiosensitivity, microcephaly, and growth retardation. The NBS gene product, NBS1, is a component of the MRE11-RAD50-NBS1 (MRN) complex, a central player associated with double strand break (DSB) repair. In response to radiation, NBS1 is phosphorylated by ATM, and the MRN complex relocalizes to form punctate nuclear foci for DNA repair. NBS1 controls both the nuclear localization of the MRN complexes and radiation-induced focus formation. We report here that the KPNA2 (importin alpha1) is important for the normal nuclear localization of the MRN complex and its proper formation of the nuclear foci. KPNA2 is the only member of the importin alpha family that physically interacts with NBS1, and the KPNA2-mediated nucleus localization sequence (NLS) is mapped to amino acid residues 461-467 of NBS1 that is sufficient for both the interaction with KPNA2 and the proper nuclear localization. Inhibition of KPNA2 or blockage of the KPNA2 interaction with NBS1 results in a reduction of radiation-induced nuclear focus accumulation, DSB repair, and cell cycle checkpoint signaling of NBS1. Collectively, our results strongly suggest that an interaction with KPNA2 contributes to nuclear localization and multiple tumor suppression functions of the NBS1 complex.
authors.affiliation: Department of Microbiology, College of Medicine, National Taiwan University, No. 1, Section 1, Jen-Ai Road, Taipei 10018, Taiwan.
authors.forename: Shun-Fu
authors.initials: SF
authors.lastname: Tseng
authors.forename: Chun-Yu
authors.initials: CY
authors.lastname: Chang
authors.forename: Kou-Juey
authors.initials: KJ
authors.lastname: Wu
authors.forename: Shu-Chun
authors.initials: SC
authors.lastname: Teng
mesh_terms: D001483:Base Sequence; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism / Q000528:radiation effects; D004260:DNA Repair; D018076:DNA, Complementary / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D049932:Nijmegen Breakage Syndrome / Q000209:etiology / Q000235:genetics / Q000378:metabolism; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D034622:RNA Interference; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020798:Two-Hybrid System Techniques; D028901:alpha Karyopherins
chemical_list: D018797:Cell Cycle Proteins; D018076:DNA, Complementary; C490630:KPNA2 protein, human; C112156:NBN protein, human; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D011994:Recombinant Proteins; D028901:alpha Karyopherins