Centrosomal Protein 55 (Cep55) Stability Is Negatively Regulated by p53 Protein through Polo-like Kinase 1 (Plk1)

Centrosomal protein 55 (Cep55), which is localized to the centrosome in interphase cells and recruited to the midbody during cytokinesis, is a regulator required for the completion of cell abscission. Up-regulation of Cep55 and inactivation of p53 occur in the majority of human cancers, raising the possibility of a link between these two genes. In this study we evaluated the role of p53 in Cep55 regulation. We demonstrated that Cep55 expression levels are well correlated with cancer cell growth rate and that p53 is able to negatively regulate Cep55 protein and promoter activity. Down-regulation of expression of Cep55 was accompanied by repression of polo-like kinase 1 (Plk1) levels due to p53 induction. Overexpression of Plk1 and knockdown of p53 expression both enhanced the post-translational protein stability of Cep55. BI 2356, a selective Plk1 inhibitor, however, prevented Cep55 accumulation in p53 knockdown cells while persistently keeping Plk1 levels elevated. Our results, therefore, indicate the existence of a p53-Plk1-Cep55 axis in which p53 negatively regulates expression of Cep55, through Plk1 which, in turn, is a positive regulator of Cep55 protein stability.