Effects of Deregulated Cyclin Expression in Mitosis. A Role in Breast Tumorigenesis

摘要

The purpose of this project is to study the effects of constitutive cyclin E expression on mitotic division and to better understand the mechanisms through which cyclin E leads to chromosome instability. Cyclin E functions to promote the G1/S phase transition and centrosome duplication; however, deregulation of cyclin E expression in cell culture results in premature entry into S phase and induces a moderate level of chromosome instability. We show that deregulated cyclin E can directly interfere with mitotic division leading to chromosome instability. Cells delay in late stages of prometaphase prior to complete alignment of chromosomes at the metaphase plate. In some cases, cells fail to divide chromosomes and instead return to interphase, resulting in polyploidy. In this third year of funding, I have completed the final goal of the project to determine the mechanism by which cyclin E delays mitosis. Cyclin E was found to inhibit the anaphase promoting complex (APC) ubiquitin ligase by inhibiting the specificity subunit, Cdh1, through a kinase-dependent mechanism. This inhibition led to significant accumulation of APC-Cdh1 substrates, cyclin B1, Cdc20, and securin. Furthermore, reducing Cdh1 in cells by RNAi mimics the protein accumulation and mitotic delay phenotypes observed upon cyclin E deregulation.