Interaction between [p12.sup.CDK2AP1] and a novel unnamed protein product inhibits cell proliferation by regulating the cell cycle

Human [p12.sup.CDK2AP1] protein is encoded by the cyclin-dependent kinase 2-associated protein 1 (CDK2AP1) gene. This protein suppresses cell growth, differentiation and angiogenesis in numerous types of carcinoma by interacting with certain cell cycle proteins, including CDK2 and DNA polymerase a/primase. [p12.sup.CDK2AP1] exerts its functions predominantly through protein-protein interactions. Therefore, the identification of other [p12.sup.CDK2AP1]-interacting proteins may clarify its role in cell cycle regulation and carcinogenesis. The aim of this study was to identify additional [p12.sup.CDK2AP1]-interacting proteins. A novel unnamed protein product (UPP, BC006130) was identified through using a yeast two-hybrid system. The interaction of [p12.sup.CDK2AP1] with the UPP was further verified by glutathione S-transferase pull-down and co-immunoprecipitation experiments in vitro. The qPCR results following overexpression and siRNA assays demonstrated that the expression levels of the UPP were mediated by the CDK2AP1 gene. Furthermore, overexpression of the UPP gene was shown to shorten the length of the G2/M phase of the cell cycle in normal and tumor cell lines in a flow cytometry assay. The results of human tumor xenografts experiments in Balb/c nude mice indicated that stable transfection with the UPP gene was able to inhibit tumor cell proliferation in vivo. Overall, this study identified and characterized a novel interactive protein of [p12.sup.CDK2AP1], which may inhibit cell proliferation by mediating the cell cycle. It expands the understanding of the mechanisms of [p12.sup.CDK2AP1] and its potential as a cancer therapeutic target. Key words: P12CDK2AP1, protein-protein interaction, cell cycle, cell proliferation