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Vol. 18, Issue 11, 4457-4469, November 2007
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*Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210-1292; and Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309
Submitted March 27, 2007;
Revised July 13, 2007;
Accepted August 24, 2007
Monitoring Editor: Stephen Doxsey
Supernumerary centrosomes promote the assembly of abnormal mitotic spindles in many human tumors. In human cells, overexpression of the cyclin-dependent kinase (Cdk)2 partner cyclin A during a prolonged S phase produces extra centrosomes, called centrosome reduplication. Cdk2 activity protects the Mps1 protein kinase from proteasome-mediated degradation, and we demonstrate here that Mps1 mediates cyclin A-dependent centrosome reduplication. Overexpression of cyclin A or a brief proteasome inhibition increases the centrosomal levels of Mps1, whereas depletion of Cdk2 leads to the proteasome-dependent loss of Mps1 from centrosomes only. When a Cdk2 phosphorylation site within Mps1 (T468) is mutated to alanine, Mps1 cannot accumulate at centrosomes or participate in centrosome duplication. In contrast, phosphomimetic mutations at T468 or deletion of the region surrounding T468 prevent the proteasome-dependent removal of Mps1 from centrosomes in the absence of Cdk2 activity. Moreover, cyclin A-dependent centrosome reduplication requires Mps1, and these stabilizing Mps1 mutations cause centrosome reduplication, bypassing cyclin A. Together, our data demonstrate that the region surrounding T468 contains a motif that regulates the accumulation of Mps1 at centrosomes. We suggest that phosphorylation of T468 attenuates the degradation of Mps1 at centrosomes and that preventing this degradation is necessary and sufficient to cause centrosome reduplication in human cells.
The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).
These authors contributed equally to this work.
Address correspondence to: Harold A. Fisk (fisk.13{at}osu.edu)
Abbreviations used: Cdk2/A, cyclin A-associated Cdk2; Cdk2/E, cyclin E-associated Cdk2; HU, hydroxyurea; IIF, indirect immunofluorescence; siRNA, small interfering RNA.
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