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Vol. 17, Issue 3, 1041-1050, March 2006

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Microtubule Regulation in Mitosis: Tubulin Phosphorylation by the Cyclin-dependent Kinase Cdk1

Anne Fourest-Lieuvin ^*, Leticia Peris ^*, Vincent Gache ^*, Isabel Garcia-Saez , Céline Juillan-Binard ^*, Violaine Lantez ^*, and Didier Job ^*

^* Laboratoire du Cytosquelette, INSERM Unité 366, CEA, 38054 Grenoble Cedex 9, France; Laboratoire des Moteurs Moléculaires, Institut de Biologie Structurale J-P Ebel, CEA-CNRS-UJF, 38027 Grenoble Cedex 1, France

Submitted July 13, 2005; Revised November 15, 2005; Accepted December 2, 2005
Monitoring Editor: J. Richard McIntosh

The activation of the cyclin-depdndent kinase Cdk1 at the transition from interphase to mitosis induces important changes in microtubule dynamics. Cdk1 phosphorylates a number of microtubule- or tubulin-binding proteins but, hitherto, tubulin itself has not been detected as a Cdk1 substrate. Here we show that Cdk1 phosphorylates -tubulin both in vitro and in vivo. Phosphorylation occurs on Ser172 of -tubulin, a site that is well conserved in evolution. Using a phosphopeptide antibody, we find that a fraction of the cell tubulin is phosphorylated during mitosis, and this tubulin phosphorylation is inhibited by the Cdk1 inhibitor roscovitine. In mitotic cells, phosphorylated tubulin is excluded from microtubules, being present in the soluble tubulin fraction. Consistent with this distribution in cells, the incorporation of Cdk1-phosphorylated tubulin into growing microtubules is impaired in vitro. Additionally, EGFP-3-tubulin^S172D/E mutants that mimic phosphorylated tubulin are unable to incorporate into microtubules when expressed in cells. Modeling shows that the presence of a phosphoserine at position 172 may impair both GTP binding to -tubulin and interactions between tubulin dimers. These data indicate that phosphorylation of tubulin by Cdk1 could be involved in the regulation of microtubule dynamics during mitosis.

Abbreviations used: Cdk1, cyclin-dependent kinase 1; CK2, casein kinase 2; EGFP, enhanced green fluorescent protein; MAP, microtubule-associated protein; PI, phosphorimager; WT, wild-type.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Address correspondence to: Anne Fourest-Lieuvin (anne.fourestlieuvin{at}cea.fr).

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