Loss of a FOX03A-dependent cell cycle checkpoint for DNA replication origins sensitises cancer cells to CDC7 inhibitors
Session type: Parallel sessions
University College London, UK
Proffered paper presentation
Small molecule targeting of Cdc7 kinase reversibly arrests primary cells in G1 phase, triggering a putative checkpoint that monitors the formation of a critical number of DNA replication-competent origins to ensure complete duplication of the genome. This essential cell cycle checkpoint is lost in cancer, resulting in an abortive S phase and cancer cell specific killing after treatment with Cdc7 inhibitors. We have used RNA interference against CDC7 to dissect the molecular nature of this checkpoint in primary cells and its deregulation in cancer.
We demonstrate that cell cycle arrest in G1 is dependent on nuclear accumulation of the Forkhead transcription factor FoxO3a. FoxO3a activates the ARF┤Mdm2┤p53→p21 pathway and mediates p15 upregulation. P53 in turn activates the expression of Dkk3, a known antagonist of the Wnt/β-catenin signalling pathway, leading to Myc and cyclin D1 downregulation. The resulting loss of CDK activity inactivates the Rb-E2F pathway, thus overriding the regular G1/S transcriptional programme. Primary somatic cells concomitantly depleted of Cdc7/FoxO3a, Cdc7/p15, Cdc7/p53 or Cdc7/Dkk3 are all able to bypass the cell cycle blockade and proceed into an abortive S phase followed by apoptosis.
Our results establish that checkpoint control of DNA replication origins is critically dependent on a number of tumour suppressor proteins commonly inactivated in cancer, raising the prospect of pharmacological Cdc7 inhibitors as powerful anti-cancer agents with broad tumour spectrum activity. Knowledge of the tripartite regulatory network underlying the checkpoint may help predicting individual patient response to Cdc7 inhibitors in the future. Knowledge of the regulatory network underlying the checkpoint may help predicting individual patient response to Cdc7 inhibitors in the future.