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First published online 11 November 2008
doi: 10.1242/jcs.035360

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The NIMA-family kinase Nek6 phosphorylates the kinesin Eg5 at a novel site necessary for mitotic spindle formation

Joseph Rapley¹, Marta Nicolàs², Aaron Groen³, Laura Regué², M. Teresa Bertran², Carme Caelles^2,4, Joseph Avruch^1,* and Joan Roig^2,*,

¹ Department of Molecular Biology and Medical Services, Massachusetts General Hospital and Department of Medicine, Harvard Medical School, Boston, MA 02114, USA
² Cell Signaling Group, Molecular Medicine Program, Institute for Research in Biomedicine (IRB Barcelona), 08028 Barcelona, Spain
³ Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
⁴ Department of Biochemistry and Molecular Biology (Pharmacy), Universitat de Barcelona, 08028 Barcelona, Spain

Author for correspondence (e-mail: joan.roig{at}irbbarcelona.org)

Accepted 3 September 2008

Nek6 and Nercc1 (also known as Nek9) belong to the NIMA family of protein kinases. Nercc1 is activated in mitosis, whereupon it binds, phosphorylates and activates Nek6. Interference with Nek6 or Nercc1 in mammalian cells causes prometaphase-metaphase arrest, and depletion of Nercc1 from Xenopus egg extracts prevents normal spindle assembly. Herein we show that Nek6 is constitutively associated with Eg5 (also known as Kinesin-5 and Kif11), a kinesin that is necessary for spindle bipolarity. Nek6 phosphorylated Eg5 at several sites in vitro and one of these sites, Ser1033, is phosphorylated in vivo during mitosis. Whereas CDK1 phosphorylates nearly all Eg5 at Thr926 during mitosis, Nek6 phosphorylates 3% of Eg5, primarily at the spindle poles. Eg5 depletion caused mitotic arrest, resulting in cells with a monopolar spindle. This arrest could be rescued by wild-type Eg5 but not by Eg5[Thr926Ala]. Despite substantial overexpression, Eg5[Ser1033Ala] rescued 50% of cells compared with wild-type Eg5, whereas an Eg5[Ser1033Asp] mutant was nearly as effective as wild type. Thus, during mitosis Nek6 phosphorylates a subset of Eg5 polypeptides at a conserved site, the phosphorylation of which is crucial for the mitotic function of Eg5.

Key words: NIMA, Nek, Nercc1, Nek9, Nek6, Kinesin, Eg5, Kinesin-5, Spindle, Mitosis

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