Regis Giet

Study of the Xenopus laevis centrosomal protein kinase pEg2

Abstract :
Mitosis is a fundamental stage of the cell cycle that should result in the equal distribution of chromosomes to each of the daughter cells. The structure that contributes to the equal distribution of chromosomes is made up of microtubules and is called the mitotic spindle. In recent years, a new family of protein kinases has been highlighted. The members of this family are associated with the mitotic spindle. These protein kinases control the segregation of chromosomes. Human kinases are overexpressed in many cancerous lines and one of them induces tumors. We studied the protein kinase pEg2 of Xenopus laevis, a member of this new family. This protein kinase is localized on the centrosomes and microtubules of the mitotic spindle. The pEg2 protein kinase is composed of two domains: a catalytic domain and an N-terminal domain. The role of this domain is to ensure the subcellular localization of protein kinase. In vitro, using cell-free extracts of Xenopus eggs, we showed that the protein kinase pEg2 controls the separation of centrosomes at the beginning of mitosis and the stability of the mitotic spindle. It phosphorylates in vivo a motor protein of the kinesin family (XlEg5) also associated with mitotic spindles. This motor protein also controls the separation of centrosomes and the stability of the mitotic spindle. These results suggest that pEg2 might regulate microtubule binding activity of XlEg5. Analysis of the expression and activity of the protein kinase pEg2 in cultured Xenopus cells has shown that the Eg2 mRNA, the pEg2 protein, and its kinase activity are regulated during the cell cycle with a maximum of during G2 phase and Mitosis. In these cells, pEg2 is degraded at the end of mitosis by the ubiquitin pathway. pEg2 protein kinase is also activated by phosphorylation.

Financial support :

Committee : October 29, 1999
Michel Bornens
Bruno Goud
Bernard Maro
Nathalie Morin
Claude Prigent (PhD co-director)
Michel Philippe (PhD co-director)

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