CDC25B involvement in the centrosome duplication cycle and in microtubule nucleation

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 CDK-cyclin 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 gamma-tubulin. In contrast, inhibition of CDC25B phosphatase activity inhibits the assembly of interphase microtubules and the centrosomal localization of gamma-tubulin. We propose that CDC25B is part of the pathway that controls the localization of gamma-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.