title: RanBP10 is a cytoplasmic guanine nucleotide exchange factor that modulates noncentrosomal microtubules.
abstract: Microtubule spindle assembly in mitosis is stimulated by Ran.GTP, which is generated along condensed chromosomes by the guanine nucleotide exchange factor (GEF) RCC1. This relationship suggests that similar activities might modulate other microtubule structures. Interphase microtubules usually extend from the centrosome, although noncentrosomal microtubules function in some differentiated cells, including megakaryocytes. In these cells, platelet biogenesis requires massive mobilization of microtubules in the cell periphery, where they form proplatelets, the immediate precursors of platelets, in the apparent absence of centrioles. Here we identify a cytoplasmic Ran-binding protein, RanBP10, as a factor that binds beta-tubulin and associates with megakaryocyte microtubules. Unexpectedly, RanBP10 harbors GEF activity toward Ran. A point mutation in the candidate GEF domain abolishes exchange activity, and our results implicate RanBP10 as a localized cytoplasmic Ran-GEF. RNA interference-mediated loss of RanBP10 in cultured megakaryocytes disrupts microtubule organization. These results lead us to propose that spatiotemporally restricted generation of cytoplasmic Ran.GTP may influence organization of the specialized microtubules required in thrombopoiesis and that RanBP10 might serve as a molecular link between Ran and noncentrosomal microtubules.
authors.affiliation: Dana-Farber Cancer Institute, Boston, MA 02115, USA. harald.schulze@charite.de
authors.forename: Harald
authors.initials: H
authors.lastname: Schulze
authors.forename: Marei
authors.initials: M
authors.lastname: Dose
authors.forename: Manav
authors.initials: M
authors.lastname: Korpal
authors.forename: Imke
authors.initials: I
authors.lastname: Meyer
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Italiano
authors.forename: Ramesh A
authors.initials: RA
authors.lastname: Shivdasani
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism; D002454:Cell Differentiation; D018385:Centrosome / Q000737:chemistry / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D008533:Megakaryocytes / Q000378:metabolism; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000502:physiology*; D008870:Microtubules / Q000378:metabolism*; D008954:Models, Biological; D034622:RNA Interference; D034061:Thrombopoiesis; D020798:Two-Hybrid System Techniques; D020931:ran GTP-Binding Protein / Q000378:metabolism*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D008869:Microtubule-Associated Proteins; C529801:RANBP10 protein, human; D020931:ran GTP-Binding Protein