Abstract
The circadian timing system orchestrates most of mammalian physiology and behavior in synchrony with the external light/dark cycle. This regulation is achieved through endogenous clocks present in virtually all body cells, where they control key cellular processes, including metabolism, transport, and the cell cycle. Consistently, it has been observed in preclinical cancer models that both the efficacy and toxicity of most chemotherapeutic drugs depend on their time of administration. To further explore the molecular basis underlying the link between the circadian timing system and the cellular response to anticancer drugs, we investigated the circadian transcriptome and CDK inhibitor toxicity in colon mucosa cells. We first show here that among 181 circadian transcripts, approximately 30% of them drive the cell cycle in the healthy mouse colon mucosa, with a majority peaking during the early resting phase. The identification of 26 mitotic genes within this cluster further indicated that the transcriptional coordination of mitosis by the circadian clock participates in the gating of cell division in this tissue. Subsequent selective siRNA-mediated silencing of these 26 targets revealed that low expression levels of the mitotic and anti-apoptotic gene Birc5/survivin significantly and specifically increased the sensitivity of colon epithelial cells to CDK inhibitors. By identifying Birc5/survivin as a potential determinant for the circadian modulation of CDK inhibitor toxicity, these data provide a mechanistic basis for the preclinical development of future CDK inhibitor-based chronotherapeutic strategies.