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Abstract : Ordered activation of cyclin-dependent kinases (CDK), associated to their regulatory cyclin subunit, controls the progression of eukaryotic cells within the cell cycle. The activity of CDK/cyclin is notably regulated by a balance between inhibitory phosphorylation (Wee, Myt) and activating dephosphorylation by CDC25 phosphatases. In human cells, three dual specificity phosphatases, CDC25A, B and C, are involved in the regulation of these complexes at various stages of the cell cycle. CDC25A is active in G1/S transition while CDC25C controls entry into mitosis. In contrast, CDC25B would operate in S phase as well as at the G2/M transition. The existence of three versions of CDC25B (B1, B2 and B3) resulting from alternative splicing might explain this controversy. In order to study the functions and involvements of each variant of CDC25B, we first studied their regulation by kinase CK2, a kinase which may play a role in G2/M transition. Our in vitro studies indicated that CK2 phosphorylates the three variants of CDC25B, but not CDC25C. Mass spectrometry analysis of CDC25B indicated that at least two residues, serine 186 and 187, are phosphorylated by CK2 in vitro. In addition, CDC25B interacts with CK2 in vivo and in vitro in human and insect cells. Finally, phosphorylation of CDC25B by CK2 increases its phosphatase activity both in vitro and in vivo. Thus CK2 is a positive regulator of the catalytic activity of CDC25B. In the course of the cell cycle or during checkpoint response, CDC25B is also regulated at the level of intracellular location. Indeed, the phosphatase shuttles between cytoplasm and nucleus, and the shuttle may be regulated notably by phosphorylation. We have shown that protein kinase AKT/PKB phosphorylates CDC25B in vitro on serine 353 and leads to cytoplasmic storage. Activation of AKT/PKB by hydrogen peroxide induces the cytoplasmic localization of CDC25B. Mutating serine 353 abolishes CDC25B phosphorylation by ATK/PKB but causes only a delay in cytoplasmic stockpiling of CDC25B, suggesting that other mechanisms participate to this phenomenon. In summary, our studies allowed the identification of two new regulators of CDC25B, CK2 which regulates its catalytic activity, and AKT/PKB which participates to the control of its intracellular location, and have provided a better understanding of the regulation of this phosphatase, even though many other partners still await identification.
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Contributor : Jean-Pierre Bouché <>
Submitted on : Tuesday, September 6, 2005 - 6:44:17 PM
Last modification on : Wednesday, October 14, 2020 - 4:04:27 AM
Long-term archiving on: : Friday, April 2, 2010 - 10:23:58 PM


  • HAL Id : tel-00010054, version 1



Nathalie Theis-Febvre. REGULATION DE L'ACTIVITE ET DE LA LOCALISATION DES PHOSPHATASES CDC25B. Biologie cellulaire. Université Paul Sabatier - Toulouse III, 2003. Français. ⟨tel-00010054⟩



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