Molecular Dissection of the Centrosome Overduplication Pathway in S-phase-arrested Cells

Cancer cells frequently exhibit overduplicated centrosomes that lead to formation of multipolar spindles, chromosome missegregation, and aneuploidy. However, the molecular events involved in centrosome overdu-plication remain largely unknown. Experimentally, centrosome overduplication is observed in p53-deficient cells arrested in S phase with hydroxyurea. Using this assay, we have identified distinct roles for Cdk2, microtubules, dynein, and Hsp90 in the overduplication of functional centrosomes in mammalian cells and show that Cdk2 is also required for the generation of centriolar satellites. Moreover, we demonstrate that nuclear export is required for centriolar satellite formation and centrosome overduplication, with export inhibitors causing a Cdk-dependent accumulation of nuclear centrin granules. Hence, we propose that cen-trosome precursors may arise in the nucleus, providing a novel mechanistic explanation for how nuclear Cdk2 can promote centrosome overduplication in the cytoplasm. Furthermore, this study defines a molecular pathway that may be targeted to prevent centrosome overduplication in S-phase-arrested cancer cells. Equal segregation of genetic material between daughter cells requires the mitotic spindle to be bipolar, with monopolar or multipolar spindles leading to abnormal segregation. Because spindle poles are organized by centrosomes, maintaining the righ