title: Reduction of exportin 6 activity leads to actin accumulation via failure of RanGTP restoration and NTF2 sequestration in the nuclei of senescent cells.
abstract: We have previously reported that G-actin accumulation in nuclei is a universal phenomenon of cellular senescence. By employing primary culture of human diploid fibroblast (HDF) and stress-induced premature senescence (SIPS), we explored whether the failure of actin export to cytoplasm is responsible for actin accumulation in nuclei of senescent cells. Expression of exportin 6 (Exp6) and small G-protein, Ran, was significantly reduced in the replicative senescence, but not yet in SIPS, whereas nuclear import of actin by cofilin was already increased in SIPS. After treatment of young HDF cells with H(2)O(2), rapid reduction of nuclear RanGTP was observed along with cytoplasmic increase of RanGDP. Furthermore, significantly reduced interaction of Exp6 with RanGTP was found by GST-Exp6 pull-down analysis. Failure of RanGTP restoration was accompanied with inhibition of ATP synthesis and NTF2 sequestration in the nuclei along with accordant change of senescence morphology. Indeed, knockdown of Exp6 expression significantly increased actin molecule in the nuclei of young HDF cells. Therefore, actin accumulation in nuclei of senescent cells is most likely due to the failure of RanGTP restoration with ATP deficiency and NTF2 accumulation in nuclei, which result in the decrease of actin export via Exp6 inactivation, in addition to actin import by cofilin activation.
authors.affiliation: Department of Biochemistry and Molecular Biology, BK21 Division of Cell Transformation and Restoration, Ajou University School of Medicine, Suwon 443-721, Republic of Korea.
authors.forename: Su Hyun
authors.initials: SH
authors.lastname: Park
authors.forename: Tae Jun
authors.initials: TJ
authors.lastname: Park
authors.forename: In Kyoung
authors.initials: IK
authors.lastname: Lim
mesh_terms: D051339:Actin Depolymerizing Factors / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000187:drug effects / Q000502:physiology*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism*; D029543:Nucleocytoplasmic Transport Proteins / Q000235:genetics / Q000378:metabolism*; D016877:Oxidants / Q000494:pharmacology; D011257:Pregnancy Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020931:ran GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D051339:Actin Depolymerizing Factors; D000199:Actins; D028884:Karyopherins; C038965:NUTF2 protein, human; D029543:Nucleocytoplasmic Transport Proteins; D016877:Oxidants; D011257:Pregnancy Proteins; D011993:Recombinant Fusion Proteins; C558183:XPO6 protein, human; D000255:Adenosine Triphosphate; D006861:Hydrogen Peroxide; D020931:ran GTP-Binding Protein