CDC25B Involvement in the Centrosome Duplication Cycle and in Microtubule Nucleation

Abstract

Centrosome amplification is frequently reported in human cancers, although the molecular mechanisms that are responsible for this remain unclear. There is significant evidence to support a role for cyclin-dependent kinase (CDK)-cyclin complexes in centrosome duplication. The activities of CDKcyclin complexes are, in turn, regulated by the CDC25 family of phosphatases in a strict spatiotemporal manner, and we have recently reported that CDC25B localizes to the centrosomes from early S phase. In the present study, we have investigated the role of centrosomally localized CDC25B in centrosome duplication. We first observed that overexpression of CDC25B under an inducible promoter in S phase results in centrosome overduplication. We found that forced expression of wild-type but not phosphatase-inactive CDC25B at the centrosomes results in centrosome amplification, aberrant microtubule organization, and abnormal accumulation of ;-tubulin. In contrast, inhibition of CDC25B phosphatase activity inhibits the assembly of interphase microtubules and the centrosomal localization of ;-tubulin. We propose that CDC25B is part of the pathway that controls the localization of ;-tubulin to the centrosomes, thereby regulating centrosome duplication during S phase and the nucleation of microtubules. We speculate that abnormal expression of CDC25B in numerous human tumors might therefore have a critical role in centrosome amplification and genomic instability. [Cancer Res 2007;67(24):11557-64]

Asymmetric localization of the CDC25B phosphatase to the mother centrosome during interphase

“…[10][11][12][13] We have also recently demonstrated that overexpression of the CDC25B phosphatase causes centrosome overduplication, while overexpression of a catalytically inactive form has no effect on centrosome duplication. 14 In the present study, we report that CDC25B, along with other key cell cycle regulators, localise asymmetrically around the mother centrosome throughout interphase, and demonstrate a requirement for CDC25B in the normal centriole duplication cycle.…”

“…The observation that CDC25B localises to the mother centriole (Fig. 3B), which provides a platform for daughter centriole assembly, 28 and our recent evidence for CDC25B's involvement in centrosome overduplication, 14 suggested that CDC25B may also be involved in regulating early centrosome cycle events. We therefore studied the consequences of CDC25B loss of function on centriole duplication.…”

“…CDC25B preferentially localizes to the mother centrosome during interphase. Since we have previously reported a role for CDC25B in microtubule nucleation during interphase 14,24 and microtubules are often found to originate from the sub-distal appendages of the mother centriole, 25 we sought to determine whether CDC25B localises to the mother centrosome during interphase. To this end, we performed co-immunofluorescence analyses between ninein, a specific marker of mature centrosomes 26 and CHK1 (since the polyclonal antibody against ninein was not compatible with any of the currently available CDC25B antibodies).…”

Constitutive Activation of the DNA Damage Signaling Pathway in Acute Myeloid Leukemia with Complex Karyotype: Potential Importance for Checkpoint Targeting Therapy

“…Immunofluorescence studies were performed as previously described (26). Cellular DNA was counterstained with 4′,6-diamidino-2-phenylindole.…”

Kizuna is a novel mitotic substrate for CDC25B phosphatase

“…[7][8][9] At the G2/M transition, a pool of CDC25B is phosphorylated and activated by Aurora-A kinase at centrosomes, 10 where the initial activation of CDK1/Cyclin B complexes takes place, 11 suggesting that CDC25B might locally participate in the control of the onset of mitosis. Furthermore, CDC25B also participates in the control of g-Tubulin localization to the centrosomes, is involved in the centrosome duplication cycle, 12 and regulates proteasome-mediated degradation of centrin 2. 13 Centrosomes are the major microtubule organizing centers.…”