Changes in Protein Abundance are Essential for Proper Cell Cycle Regulation

In order for a cell to successfully complete the cell cycle, the cell must accurately duplicate its DNA in a timely and precise manner. One way the cell controls this process is by regulating the formation of the pre-replication complex (pre-RC) and S phase entry through fluctuations in protein abundance. Two proteins essential for pre-RC formation, Cdc6 and Cdt1, peak at different phases of the cell cycle; this results in two small windows when pre-RC formation can occur. While this regulation of the cell cycle has been very well studied, how other processes are regulated during the cell cycle are not well known. We used SILAC mass spectrometry to identify biological processes whose regulation may have a cell cycle component. We showed that RNA processing, in particular alternative splicing, is regulated during S phase. Additionally, we looked for genes whose transcription is altered when cells undergo re-replication, as regulation of these proteins may play a role in transformation, genome stability, or tumorigenesis. By identifying a re-replication gene expression signature, we can identify tumor types that are undergoing re-replication. Identification of this signature in human tumors may enhance diagnostics and prognosis, as these tumor types may benefit from a particular type of chemotherapeutic. Because a successful division involves the cooperation of many biological processes, the identification of proteins that are regulated in a cell cycle manner or in response to a particular form of DNA damage, re-replication, could result in novel targets for chemotherapeutics and biomarkers.