title: UV-induced nuclear import of XPA is mediated by importin-α4 in an ATR-dependent manner.
abstract: Xeroderma pigmentosum Group A (XPA) is a crucial factor in mammalian nucleotide excision repair (NER) and nuclear import of XPA from the cytoplasm for NER is regulated in cellular DNA damage responses in S-phase. In this study, experiments were carried out to determine the transport mechanisms that are responsible for the UV (ultraviolet)-induced nuclear import of XPA. We found that, in addition to the nuclear localization signal (NLS) of XPA, importin-α4 or/and importin-α7 are required for the XPA nuclear import. Further investigation indicated that, importin-α4 and importin-α7 directly interacted with XPA in cells. Interestingly, the binding of importin-α4 to XPA was dependent on UV-irradiation, while the binding of importin-α7 was not, suggesting a role for importin-α7 in nuclear translocation of XPA in the absence of DNA damage, perhaps with specificity to certain non-S-phases of the cell-cycle. Consistent with the previous report of a dependence of UV-induced XPA nuclear import on ataxia telangiectasia and Rad3-related protein (ATR) in S-phase, knockdown of ATR reduced the amount of XPA interacting with importin-α4. In contrast, the GTPase XPA binding protein 1 (XAB1), previously proposed to be required for XPA nuclear import, showed no effect on the nuclear import of XPA in our siRNA knockdown analysis. In conclusion, our results suggest that upon DNA damage transport adaptor importin-α4 imports XPA into the nucleus in an ATR-dependent manner, while XAB1 has no role in this process. In addition, these findings reveal a potential new therapeutic target for the sensitization of cancer cells to chemotherapy.
authors.affiliation: Department of Biomedical Sciences, East Tennessee State University, J.H. Quillen College of Medicine, Johnson City, Tennessee, USA.
authors.forename: Zhengke
authors.initials: Z
authors.lastname: Li
authors.forename: Phillip R
authors.initials: PR
authors.lastname: Musich
authors.forename: Brian M
authors.initials: BM
authors.lastname: Cartwright
authors.forename: Hui
authors.initials: H
authors.lastname: Wang
authors.forename: Yue
authors.initials: Y
authors.lastname: Zou
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000528:radiation effects; D064007:Ataxia Telangiectasia Mutated Proteins / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism* / Q000528:radiation effects*; D019204:GTP-Binding Proteins / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006801:Humans; D008954:Models, Biological; D019913:Nuclear Localization Signals / Q000378:metabolism; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D014466:Ultraviolet Rays; D051760:Xeroderma Pigmentosum Group A Protein / Q000737:chemistry / Q000378:metabolism*; D028901:alpha Karyopherins / Q000378:metabolism*
chemical_list: C106306:KPNA3 protein, human; C494630:KPNA6 protein, human; D019913:Nuclear Localization Signals; D011994:Recombinant Proteins; C497314:XPA protein, human; D051760:Xeroderma Pigmentosum Group A Protein; D028901:alpha Karyopherins; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C472669:GPN1 protein, human; D019204:GTP-Binding Proteins