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The mechanism regulating the dissociation of the centrosomal protein C-Nap1 from mitotic spindle poles

MPG-Autoren
http://pubman.mpdl.mpg.de/cone/persons/resource/persons78378

Mayor,  T.
Former Research Groups, Max Planck Institute of Biochemistry, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons78060

Hacker,  U.
Former Research Groups, Max Planck Institute of Biochemistry, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons78459

Nigg,  E. A.
Former Research Groups, Max Planck Institute of Biochemistry, Max Planck Society;

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Zitation

Mayor, T., Hacker, U., Stierhof, Y. D., & Nigg, E. A. (2002). The mechanism regulating the dissociation of the centrosomal protein C-Nap1 from mitotic spindle poles. Journal of Cell Science, 115(16), 3275-3284.


Zitierlink: http://hdl.handle.net/11858/00-001M-0000-0010-6E84-6
Zusammenfassung
The centrosomal protein C-Nap1 is thought to play an important role in centrosome cohesion during interphase of the cell cycle. At the onset of mitosis, when centrosomes separate for bipolar spindle formation, C-Nap1 dissociates from centrosomes. Here we report the results of experiments aimed at determining whether the dissociation of C-Nap1 from mitotic centrosomes is triggered by proteolysis or phosphorylation. Specifically, we analyzed both the cell cycle regulation of endogenous C-Nap1 and the fate of exogenously expressed full-length C-Nap1. Western blot analyses suggested a reduction in the endogenous C-Nap1 level during M phase, but studies using proteasome inhibitors and destruction assays performed in Xenopus extracts argue against ubiquitin-dependent degradation of C-Nap1. Instead, our data indicate that the mitotic C-Nap1 signal is reduced as a consequence of M-phase-specific phosphorylation. Overexpression of full-length C-Nap1 in human U2OS cells caused the formation of large structures that embedded the centrosome and impaired its microtubule nucleation activity. Remarkably, however, these centrosome-associated structures did not interfere with cell division. Instead, centrosomes were found to separate from these structures at the onset of mitosis, indicating that a localized and cell-cycle-regulated activity can dissociate C-Nap1 from centrosomes. A prime candidate for this activity is the centrosomal protein kinase Nek2, as the formation of large C-Nap1 structures was substantially reduced upon co-expression of active Nek2. We conclude that the dissociation of C-Nap1 from mitotic centrosomes is regulated by localized phosphorylation rather than generalized proteolysis.