Centrosomal proteins Nde1 and Su48 form a complex regulated by phosphorylation

The centrosome modulates spindle formation and plays a critical role in guiding proper segregation of chromosomes during cell division. Centrosome aberrations, frequently seen in human tumors, may cause abnormal chromosome segregation and contribute to malignant transformation. To explore the components of the centrosomes, we previously identified a novel centrosomal protein called Su48. To further characterize the Su48-containing protein ensemble in the centrosome, we performed yeast two-hybrid screens and isolated a number of Su48- interacting molecules, including the centrosomal protein Nde1. Here, we demonstrate that Su48 can associate with Nde1. Moreover, we found that Nde1 is subjected to phosphorylation in vivo. In particular, we identified six putative Cdc2 phosphorylation sites in Nde1 and found that alteration of these sites diminishes phosphorylation by Cdc2 in vitro and affects the stability of Su48- Nde1 interactions and the centrosomal localization of Nde1. Ablation of Nde1 by gene specific small interfering RNA causes mitotic delay and cell death, coupled with a modest decrease in the incidence of the cells that harbor excessive centrosomes. Collectively, our findings indicate that Nde1 can form a protein complex with Su48 in the centrosome and plays an important role for successful mitosis.