title: Part of Ran is associated with AKAP450 at the centrosome: involvement in microtubule-organizing activity.
abstract: The small Ran GTPase, a key regulator of nucleocytoplasmic transport, is also involved in microtubule assembly and nuclear membrane formation. Herein, we show by immunofluorescence, immunoelectron microscopy, and biochemical analysis that a fraction of Ran is tightly associated with the centrosome throughout the cell cycle. Ran interaction with the centrosome is mediated by the centrosomal matrix A kinase anchoring protein (AKAP450). Accordingly, when AKAP450 is delocalized from the centrosome, Ran is also delocalized, and as a consequence, microtubule regrowth or anchoring is altered, despite the persisting association of gamma-tubulin with the centrosome. Moreover, Ran is recruited to Xenopus sperm centrosome during its activation for microtubule nucleation. We also demonstrate that centrosomal proteins such as centrin and pericentrin, but not gamma-tubulin, AKAP450, or ninein, undertake a nucleocytoplasmic exchange as they concentrate in the nucleus upon export inhibition by leptomycin B. Together, these results suggest a challenging possibility, namely, that centrosome activity could depend upon nucleocytoplasmic exchange of centrosomal proteins and local Ran-dependent concentration at the centrosome.
mesh_terms: D054758:A Kinase Anchor Proteins; D048868:Adaptor Proteins, Signal Transducing; D000941:Antigens / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002453:Cell Cycle / Q000502:physiology*; D002458:Cell Fractionation; D018385:Centrosome / Q000378:metabolism*; D003001:Cloning, Molecular; D003598:Cytoskeletal Proteins; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D019204:GTP-Binding Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D016253:Microscopy, Immunoelectron; D008870:Microtubules / Q000378:metabolism*; D008958:Models, Molecular; D009687:Nuclear Proteins / Q000378:metabolism*; D021381:Protein Transport; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000378:metabolism; D014404:Tubulin / Q000378:metabolism; D014407:Tumor Cells, Cultured; D020931:ran GTP-Binding Protein / Q000378:metabolism*
chemical_list: D054758:A Kinase Anchor Proteins; C119719:AKAP9 protein, human; D048868:Adaptor Proteins, Signal Transducing; D000941:Antigens; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D005231:Fatty Acids, Unsaturated; C512806:NIN protein, human; D009687:Nuclear Proteins; C120587:RAN protein, human; D014404:Tubulin; C086178:pericentrin; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; D019204:GTP-Binding Proteins; D020931:ran GTP-Binding Protein; C038753:leptomycin B