title: Minor alteration of microtubule dynamics causes loss of tension across kinetochore pairs and activates the spindle checkpoint.
abstract: We have previously identified the opium alkaloid noscapine as a microtubule interacting agent that binds stoichiometrically to tubulin and alters its conformation. Here we show that, unlike many other microtubule inhibitors, noscapine does not significantly promote or inhibit microtubule polymerization. Instead, it alters the steady-state dynamics of microtubule assembly, primarily by increasing the amount of time that the microtubules spend in an attenuated (pause) state. Further studies reveal that even at high concentrations, noscapine does not alter the tubulin polymer/monomer ratio in HeLa cells. Cells treated with noscapine arrest at mitosis with nearly normal bipolar spindles. Strikingly, although most of the chromosomes in these cells are aligned at the metaphase plate, the rest remain near the spindle poles, both of which exhibit loss of tension across kinetochore pairs. Furthermore, levels of the spindle checkpoint proteins Mad2, Bub1, and BubR1 decrease by 138-, 3.7-, and 3.9-fold, respectively, at the kinetochore region upon chromosome alignment. Our results thus suggest that an exquisite control of microtubule dynamics is required for kinetochore tension generation and chromosome alignment during mitosis. Our data also support the idea that Mad2 and Bub1/BubR1 respond to kinetochore-microtubule attachment and/or tension to different degrees.
authors.affiliation: Graduate Program in Biochemistry, Cell and Developmental Biology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhou
authors.forename: Dulal
authors.initials: D
authors.lastname: Panda
authors.forename: Jaren W
authors.initials: JW
authors.lastname: Landen
authors.forename: Leslie
authors.initials: L
authors.lastname: Wilson
authors.forename: Harish C
authors.initials: HC
authors.lastname: Joshi
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002352:Carrier Proteins; D002417:Cattle; D018797:Cell Cycle Proteins; D004247:DNA / Q000378:metabolism; D005434:Flow Cytometry; D005656:Fungal Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D018386:Kinetochores / Q000737:chemistry* / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008870:Microtubules / Q000378:metabolism*; D009665:Noscapine / Q000494:pharmacology; D009687:Nuclear Proteins; D008941:Spindle Apparatus / Q000378:metabolism; D013997:Time Factors; D014404:Tubulin / Q000378:metabolism
chemical_list: D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D005656:Fungal Proteins; D009687:Nuclear Proteins; D014404:Tubulin; D009665:Noscapine; D004247:DNA