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Aurora B kinase and protein phosphatase 1 have opposing roles in modulating kinetochore assembly.

Emanuele MJ, Lan W, Jwa M, Miller SA, Chan CS, Stukenberg PT - J. Cell Biol. (2008)

Bottom Line: PP1 is necessary for kinetochores to disassemble at the exit from M phase, and purified enzyme is sufficient to cause disassembly on isolated mitotic nuclei.These data demonstrate that Aurora B activity is required for kinetochore maintenance and that PP1 is necessary and sufficient to disassemble kinetochores.We suggest that Aurora B and PP1 coordinate cell cycle-dependent changes in kinetochore assembly though phosphorylation of kinetochore substrates.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908, USA.

ABSTRACT
The outer kinetochore binds microtubules to control chromosome movement. Outer kinetochore assembly is restricted to mitosis, whereas the inner kinetochore remains tethered to centromeres throughout the cell cycle. The cues that regulate this transient assembly are unknown. We find that inhibition of Aurora B kinase significantly reduces outer kinetochore assembly in Xenopus laevis and human tissue culture cells, frog egg extracts, and budding yeast. In X. leavis M phase extracts, preassembled kinetochores disassemble after inhibiting Aurora B activity with either drugs or antibodies. Kinetochore disassembly, induced by Aurora B inhibition, is rescued by restraining protein phosphatase 1 (PP1) activity. PP1 is necessary for kinetochores to disassemble at the exit from M phase, and purified enzyme is sufficient to cause disassembly on isolated mitotic nuclei. These data demonstrate that Aurora B activity is required for kinetochore maintenance and that PP1 is necessary and sufficient to disassemble kinetochores. We suggest that Aurora B and PP1 coordinate cell cycle-dependent changes in kinetochore assembly though phosphorylation of kinetochore substrates.

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Model of Aurora B and PP1 activity relative to kinetochore assembly in the mitosis. G2 and the mitotic phases (prophase, prometaphase, metaphase, anaphases A and B, and telophase) are depicted. Microtubules are displayed in green, chromosomes in blue, kinetochores in yellow, and active Aurora B kinase in red. The times at which Aurora B (red lines) and PP1 (green lines) are activated are shown relative to the morphological changes of mitosis. In prophase, Aurora B is activated and begins to move from chromosome arms to centromeres. By prometaphase, activated Aurora B is fully localized to the inner centromere and outer kinetochore proteins are assembled. Complete chromosome alignment occurs in metaphase, at which point the spindle checkpoint signal is extinguished and sister chromatids separate and begin poleward anaphase movements. Aurora B dissociates from the inner centromere in anaphase and relocalizes to overlapping spindle midzone microtubules, where it remains active in a gradient of kinase activity that spreads from out from the spindle midzone (fading red). Kinetochores disassemble as they move outside of the zone of Aurora B activity in anaphase B. PP1 is initially activated in anaphase, and its small protein inhibitor I-2 is further degraded in anaphase B and telophase. Active PP1, in the absence of Aurora B, leads to outer kinetochores disassembly in telophase before the ensuing G1.
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fig8: Model of Aurora B and PP1 activity relative to kinetochore assembly in the mitosis. G2 and the mitotic phases (prophase, prometaphase, metaphase, anaphases A and B, and telophase) are depicted. Microtubules are displayed in green, chromosomes in blue, kinetochores in yellow, and active Aurora B kinase in red. The times at which Aurora B (red lines) and PP1 (green lines) are activated are shown relative to the morphological changes of mitosis. In prophase, Aurora B is activated and begins to move from chromosome arms to centromeres. By prometaphase, activated Aurora B is fully localized to the inner centromere and outer kinetochore proteins are assembled. Complete chromosome alignment occurs in metaphase, at which point the spindle checkpoint signal is extinguished and sister chromatids separate and begin poleward anaphase movements. Aurora B dissociates from the inner centromere in anaphase and relocalizes to overlapping spindle midzone microtubules, where it remains active in a gradient of kinase activity that spreads from out from the spindle midzone (fading red). Kinetochores disassemble as they move outside of the zone of Aurora B activity in anaphase B. PP1 is initially activated in anaphase, and its small protein inhibitor I-2 is further degraded in anaphase B and telophase. Active PP1, in the absence of Aurora B, leads to outer kinetochores disassembly in telophase before the ensuing G1.

Mentions: A model depicting the activities of Aurora B and PP1 during the somatic cell cycle relative to the times of kinetochore assembly and disassembly is depicted in Fig. 8. The various steps of the mitotic cell cycle, starting in late G2 and proceeding through telophase, are shown relative to Aurora B and PP1 activity. In prophase, Aurora B becomes activated and, by prometaphase, Aurora B is localized to inner centromere. At this time, the outer kinetochore proteins are recruited and assembled onto centromeres. At the metaphase-to-anaphase transition, Aurora B is released from the inner centromere but remains catalytically active in a gradient of activity concentrated on the spindle midzone and diffuses throughout the cell (unpublished data). We hypothesize that one role for the gradient of Aurora B activity is to keep kinetochores assembled in anaphase A. By anaphase B, kinetochores pass beyond the periphery of Aurora B's zone of activity, and outer kinetochore proteins are displaced from the centromere. Recent work has demonstrated that Ncd80 levels are reduced 5–10-fold at kinetochores in anaphase B (McAinsh et al., 2006). In late anaphase B and telophase, I-2 levels, which remain high throughout mitosis, begin to decrease, which is concomitant with the complete loss of outer kinetochore proteins at centromeres, a decrease in Aurora B activity, and, finally, mitotic exit.


Aurora B kinase and protein phosphatase 1 have opposing roles in modulating kinetochore assembly.

Emanuele MJ, Lan W, Jwa M, Miller SA, Chan CS, Stukenberg PT - J. Cell Biol. (2008)

Model of Aurora B and PP1 activity relative to kinetochore assembly in the mitosis. G2 and the mitotic phases (prophase, prometaphase, metaphase, anaphases A and B, and telophase) are depicted. Microtubules are displayed in green, chromosomes in blue, kinetochores in yellow, and active Aurora B kinase in red. The times at which Aurora B (red lines) and PP1 (green lines) are activated are shown relative to the morphological changes of mitosis. In prophase, Aurora B is activated and begins to move from chromosome arms to centromeres. By prometaphase, activated Aurora B is fully localized to the inner centromere and outer kinetochore proteins are assembled. Complete chromosome alignment occurs in metaphase, at which point the spindle checkpoint signal is extinguished and sister chromatids separate and begin poleward anaphase movements. Aurora B dissociates from the inner centromere in anaphase and relocalizes to overlapping spindle midzone microtubules, where it remains active in a gradient of kinase activity that spreads from out from the spindle midzone (fading red). Kinetochores disassemble as they move outside of the zone of Aurora B activity in anaphase B. PP1 is initially activated in anaphase, and its small protein inhibitor I-2 is further degraded in anaphase B and telophase. Active PP1, in the absence of Aurora B, leads to outer kinetochores disassembly in telophase before the ensuing G1.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2315672&req=5

fig8: Model of Aurora B and PP1 activity relative to kinetochore assembly in the mitosis. G2 and the mitotic phases (prophase, prometaphase, metaphase, anaphases A and B, and telophase) are depicted. Microtubules are displayed in green, chromosomes in blue, kinetochores in yellow, and active Aurora B kinase in red. The times at which Aurora B (red lines) and PP1 (green lines) are activated are shown relative to the morphological changes of mitosis. In prophase, Aurora B is activated and begins to move from chromosome arms to centromeres. By prometaphase, activated Aurora B is fully localized to the inner centromere and outer kinetochore proteins are assembled. Complete chromosome alignment occurs in metaphase, at which point the spindle checkpoint signal is extinguished and sister chromatids separate and begin poleward anaphase movements. Aurora B dissociates from the inner centromere in anaphase and relocalizes to overlapping spindle midzone microtubules, where it remains active in a gradient of kinase activity that spreads from out from the spindle midzone (fading red). Kinetochores disassemble as they move outside of the zone of Aurora B activity in anaphase B. PP1 is initially activated in anaphase, and its small protein inhibitor I-2 is further degraded in anaphase B and telophase. Active PP1, in the absence of Aurora B, leads to outer kinetochores disassembly in telophase before the ensuing G1.
Mentions: A model depicting the activities of Aurora B and PP1 during the somatic cell cycle relative to the times of kinetochore assembly and disassembly is depicted in Fig. 8. The various steps of the mitotic cell cycle, starting in late G2 and proceeding through telophase, are shown relative to Aurora B and PP1 activity. In prophase, Aurora B becomes activated and, by prometaphase, Aurora B is localized to inner centromere. At this time, the outer kinetochore proteins are recruited and assembled onto centromeres. At the metaphase-to-anaphase transition, Aurora B is released from the inner centromere but remains catalytically active in a gradient of activity concentrated on the spindle midzone and diffuses throughout the cell (unpublished data). We hypothesize that one role for the gradient of Aurora B activity is to keep kinetochores assembled in anaphase A. By anaphase B, kinetochores pass beyond the periphery of Aurora B's zone of activity, and outer kinetochore proteins are displaced from the centromere. Recent work has demonstrated that Ncd80 levels are reduced 5–10-fold at kinetochores in anaphase B (McAinsh et al., 2006). In late anaphase B and telophase, I-2 levels, which remain high throughout mitosis, begin to decrease, which is concomitant with the complete loss of outer kinetochore proteins at centromeres, a decrease in Aurora B activity, and, finally, mitotic exit.

Bottom Line: PP1 is necessary for kinetochores to disassemble at the exit from M phase, and purified enzyme is sufficient to cause disassembly on isolated mitotic nuclei.These data demonstrate that Aurora B activity is required for kinetochore maintenance and that PP1 is necessary and sufficient to disassemble kinetochores.We suggest that Aurora B and PP1 coordinate cell cycle-dependent changes in kinetochore assembly though phosphorylation of kinetochore substrates.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908, USA.

ABSTRACT
The outer kinetochore binds microtubules to control chromosome movement. Outer kinetochore assembly is restricted to mitosis, whereas the inner kinetochore remains tethered to centromeres throughout the cell cycle. The cues that regulate this transient assembly are unknown. We find that inhibition of Aurora B kinase significantly reduces outer kinetochore assembly in Xenopus laevis and human tissue culture cells, frog egg extracts, and budding yeast. In X. leavis M phase extracts, preassembled kinetochores disassemble after inhibiting Aurora B activity with either drugs or antibodies. Kinetochore disassembly, induced by Aurora B inhibition, is rescued by restraining protein phosphatase 1 (PP1) activity. PP1 is necessary for kinetochores to disassemble at the exit from M phase, and purified enzyme is sufficient to cause disassembly on isolated mitotic nuclei. These data demonstrate that Aurora B activity is required for kinetochore maintenance and that PP1 is necessary and sufficient to disassemble kinetochores. We suggest that Aurora B and PP1 coordinate cell cycle-dependent changes in kinetochore assembly though phosphorylation of kinetochore substrates.

Show MeSH
Related in: MedlinePlus