Biomedical subjects

Véronique Baldin

Publications and source records attributed to Véronique Baldin.

7 recordsLinked to original sources

PubMed2004

A novel synthetic inhibitor of CDC25 phosphatases: BN82002.

CDC25 dual-specificity phosphatases are essential regulators that dephosphorylate and activate cyclin-dependent kinase/cyclin complexes at key transitions of the cell cycle. CDC25 activity is currently considered to be an interesting target for the development of new antiproliferative agents. Here we report the identification of a new CDC25 inhibitor and the characterization of its effects at the molecular and cellular levels, and in animal models. BN82002 inhibits the phosphatase activity of recombinant human CDC25A, B, and C in vitro. It impairs the proliferation of tumoral cell lines and increases cyclin-dependent kinase 1 inhibitory tyrosine phosphorylation. In synchronized HeLa cells, BN82002 delays cell cycle progression at G1-S, in S phase and at the G2-M transition. In contrast, BN82002 arrests U2OS cell cycle mostly in the G1 phase. Selectivity of this inhibitor is demonstrated: (a) by the reversion of the mitotic-inducing effect observed in HeLa cells upon CDC25B overexpression; and (b) by the partial reversion of cell cycle arrest in U2OS expressing CDC25. We also show that BN82002 reduces growth rate of human tumor xenografts in athymic nude mice. BN82002 is a original CDC25 inhibitor that is active both in cell and animal models. This greatly reinforces the interest in CDC25 as an anticancer target.

Animals↗

PubMed2004

[Death-tag].

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Cells↗

PubMed2003

LIM-only protein FHL3 interacts with CDC25B2 phosphatase.

LIM domain proteins are important regulators of the growth, determination, and differentiation of cells. In this report, FHL3 (human four-and-a-half LIM-only protein 3) is shown to interact with human phosphatase CDC25B, a cell cycle regulator involved in the control of G2/M. We found that this interaction was specific to the CDC25B2 isoform. Deletion and point mutation studies indicated that the second LIM domain of FHL3 was essential for this interaction. FRET experiments in C2C12 cells showed that, although both proteins were colocated in the cytoplasm and the nucleus, they interacted only in the nucleus. Finally, we showed that FHL3 binding impaired neither CDC25B2 phosphatase activity nor its localization. Further work is now needed to elucidate the consequences of this interaction on myoblast fate decision and cycle control.

Animals↗

PubMed2003

Protein kinase CK2 regulates CDC25B phosphatase activity.

Human dual-specificity phosphatases CDC25 (A, B and C) play an important role in the control of cell cycle progression by activating the cyclin-dependent kinases (CDKs). Regulation of these phosphatases during the cell cycle involves post-translational modifications such as phosphorylation and protein-protein interactions. Given the suspected involvement of the protein kinase CK2 at the G2/M transition, we have investigated its effects on the CDC25B phosphatase. We show that in vitro CK2 phosphorylates CDC25B, but not CDC25C. Mass spectrometry analysis demonstrates that at least two serine residues, Ser-186 and Ser-187, are phosphorylated in vivo. We also report that CDC25B interacts with CK2, and this interaction, mediated by the CK2beta regulatory subunit, involves domains that are located within the first 55 amino acids of CK2beta and between amino acids 122 and 200 on CDC25B. This association was confirmed in vivo, in Sf9 insect cells and in U(2)OS human cells expressing an HA epitope-tagged CDC25B. Finally, we demonstrate that phosphorylation of CDC25B by protein kinase CK2 increases the catalytic activity of the phosphatase in vitro as well as in vivo. We discuss the possibility that CDC25B phosphorylation by CK2 could play a role in the regulation of the activity of CDC25B as a starter of mitosis.

Amino Acid Sequence↗

PubMed2003

PKB/Akt phosphorylates the CDC25B phosphatase and regulates its intracellular localisation.

Regulation of the intracellular localisation of its actors is one of the key mechanisms underlying cell cycle control. CDC25 phosphatases are activators of Cyclin-Dependent Kinases (CDK) that undergo nucleo-cytoplasmic shuttling during the cell cycle and in response to checkpoint activation. Here we report that the protein kinase PKB/Akt phosphorylates CDC25B on serine 353, resulting in a nuclear export-dependent cytoplasmic accumulation of the phosphatase. Oxidative stress activates PKB/Akt and reproduces the effect on CDC25B phosphorylation and localisation. However, inhibition of PKB/Akt activity only partially reverted the effect of oxidative stress on CDC25B localisation and mutation of serine 353 abolishes phosphorylation but only delays nuclear exclusion. These results indicate that additional mechanisms are also involved in preventing nuclear import of CDC25B. Our findings identify CDC25B as a target of PKB/Akt and provide new insight into the regulation of its localisation in response to stress-activated signalling pathways.

3-Phosphoinositide-Dependent Protein Kinases↗

PubMed2002

Human pEg3 kinase associates with and phosphorylates CDC25B phosphatase: a potential role for pEg3 in cell cycle regulation.

The pEg3 protein is a member of the evolutionarily conserved KIN1/PAR-1/MARK kinase family which is involved in cell polarity and microtubule dynamics. In Xenopus, pEg3 has been shown to be a cell cycle dependent kinase whose activity increases to a maximum level during mitosis of the first embryonic cell division. CDC25B is one of the three CDC25 phosphatase genes identified in human. It is thought to regulate the G2/M progression by dephosphorylating and activating the CDK/cyclin complexes. In the present study we show that the human pEg3 kinase is able to specifically phosphorylate CDC25B in vitro. One phosphorylation site was identified and corresponded to serine 323. This residue is equivalent to serine 216 in human CDC25C which plays an important role in the regulation of phosphatase during the cell cycle and at the G2 checkpoint. pEg3 is also able to specifically associate with CDC25B in vitro and in vivo. We show that the ectopic expression of active pEg3 in human U2OS cells induces an accumulation of cells in G2. This effect is counteracted by overexpression of CDC25B. Taken together these results suggest that pEg3 is a potential regulator of the G2/M progression and may act antagonistically to the CDC25B phosphatase.

Animals↗

PubMed2002

Nuclear localization of CDC25B1 and serine 146 integrity are required for induction of mitosis.

CDC25B phosphatases are essential regulators that control cyclin-dependent kinases activities at the entry into mitosis. In this study, we demonstrate that serine 146 is required for two crucial features of CDC25B1. It is essential for CDC25B1 to function as a mitotic inducer and to prevent CDC25B1 export from the nucleus. We also show that serine 146 is phosphorylated in vitro by CDK1-cyclin B. However, phosphorylation of CDC25B does not stimulate its phosphatase activity, and mutation of serine 146 had no effect on its catalytic activity. Serine 146 phosphorylation is proposed to be a key event in the regulation of the CDC25B function in the initiation of mammalian mitosis.

Cell Cycle Proteins↗