title: Protein 4.1R, a microtubule-associated protein involved in microtubule aster assembly in mammalian mitotic extract.
abstract: Non-erythroid protein 4.1R (4.1R) consists of a complex family of isoforms. We have shown that 4.1R isoforms localize at the mitotic spindle/spindle poles and associate in a complex with the mitotic-spindle organization proteins Nuclear Mitotic Apparatus protein (NuMA), dynein, and dynactin. We addressed the mitotic function of 4.1R by investigating its association with microtubules, the main component of the mitotic spindles, and its role in mitotic aster assembly in vitro. 4.1R appears to partially co-localize with microtubules throughout the mitotic stages of the cell cycle. In vitro sedimentation assays showed that 4.1R isoforms directly interact with microtubules. Glutathione S-transferase (GST) pull-down assays using GST-4.1R fusions and mitotic cell extracts further showed that the association of 4.1R with tubulin results from both the membrane-binding domain and C-terminal domain of 4.1R. Moreover, 4.1R, but not actin, is a mitotic microtubule-associated protein; 4.1R associates with microtubules in the microtubule pellet of the mitotic asters assembled in mammalian cell-free mitotic extract. The organization of microtubules into asters depends on 4.1R in that immunodepletion of 4.1R from the extract resulted in randomly dispersed microtubules. Furthermore, adding a 135-kDa recombinant 4.1R reconstituted the mitotic asters. Finally, we demonstrated that a mitotic 4.1R isoform appears to form a complex in vivo with tubulin and NuMA in highly synchronized mitotic HeLa extracts. Our results suggest that a 135-kDa non-erythroid 4.1R is important to cell division, because it participates in the formation of mitotic spindles and spindle poles through its interaction with mitotic microtubules.
authors.affiliation: Department of Medical Oncology, Dana Farber Cancer Institute, 44 Binney Street, Boston, MA 02115, USA. shu-ching_huang@dfci.harvard.edu
authors.forename: Shu-Ching
authors.initials: SC
authors.lastname: Huang
authors.forename: Ramasamy
authors.initials: R
authors.lastname: Jagadeeswaran
authors.forename: Eva S
authors.initials: ES
authors.lastname: Liu
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Benz
mesh_terms: D001798:Blood Proteins / Q000737:chemistry* / Q000378:metabolism; D002453:Cell Cycle; D002467:Cell Nucleus / Q000378:metabolism; D003598:Cytoskeletal Proteins; D018076:DNA, Complementary / Q000378:metabolism; D000072159:Dynactin Complex; D004398:Dyneins / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins; D008856:Microscopy, Fluorescence; D008869:Microtubule-Associated Proteins / Q000737:chemistry* / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism*; D008938:Mitosis; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D008941:Spindle Apparatus; D014404:Tubulin / Q000378:metabolism
chemical_list: D001798:Blood Proteins; D003598:Cytoskeletal Proteins; D018076:DNA, Complementary; D000072159:Dynactin Complex; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D014404:Tubulin; C028841:erythrocyte membrane band 4.1 protein; D005982:Glutathione Transferase; D004398:Dyneins