Functional Dissection of Cep55 through p53-Mediated Enhanced Protein Stability and Conditional Gene Targeting

Cell cycle regulation plays a pivotal role in controlling cell proliferation and survival. Aberrant expression of cell cycle- associated genes generally afflicts cells with tumor-prone characteristics and promotes chromosome instability. Cep55 (centrosome protein 55kDa) was identified recently as an important regulator of cytokinesis involved in cell growth and proliferation. Upregulation of Cep55 and inactivation of p53 occur in the majority of human cancer, raising the possibility of a link between these two genes. To decipher the relationship between Cep55 and p53, we recently demonstrated 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 (Chang et al., J. Biol. Chem. 2011). As an extension to our ongoing projects relating to functional regulation of Cep55 in vitro, we would like to propose that enhanced Cep55 protein stability may be attributed to its high expression levels in tumors due to diminished p53 expression. To demonstrate whether Cep55 plays a causal role in tumor development in vivo we will produce mice with enhanced Cep55 protein stability/expression through gene engineered mouse model. Compound mouse with p53 insufficiency (p53+/-) will be generated by mating mouse expressing ectopic Cep55 with p53 null mouse. Specifically we will perform knock-in gene targeting to produce mouse with ectopically high Cep55 expression levels throughout whole body, in which a constitutive phosphorylation mutant E436 will replace its endogenous allele S436. Furthermore we will set up experiments to generate conditional knockout mice deficient for Cep55 to address the role of this protein in cell-autonomous control of cell proliferation in testis, one of the tissues with most prominent Cep55 expression. Finally with these mouse models we can assay for cooperating molecules associated with Cep55 in tumorigenesis and testis development by genome-wide expression analysis. Functional characterization of Cep55 in vivo will provide us with insight into as yet unrecognized role of a centrosomal protein in development and tumorigenesis.

Project ID:PC10301-0919
External Project ID:NSC101-2320-B182-003-MY3