Abstract B34: Investigating disruptions in the circadian clock in cancer cells

Abstract

Abstract The circadian clock is man's internal time-keeping mechanism; it synchronizes human physiology with the external cycle of day and night. At the molecular level, all cells display a circadian clock driven by core clock proteins that constitute transcription-translation feedback loops, generating oscillating patterns of circadian clock gene expression over time. It is becoming increasingly apparent that disruptions in the circadian clock may contribute to cancer development. This study aimed to investigate the molecular components of the circadian clock in two cancer types prevalent in South Africa: cervical and oesophageal cancer. To our knowledge the circadian clock has not previously been investigated in these cancer types. Microarray and real-time RT-PCR analyses revealed significantly decreased expression of Period 2 (Per2) mRNA in cervical and oesophageal cancer patient tissue compared to normal tissue. Cervical and oesophageal cancer cell lines similarly displayed significantly reduced mRNA and protein levels of certain circadian clock genes, including positive and negative regulators of the circadian clock. Nuclear transport of circadian clock proteins was investigated, since cancer cells display increased nuclear transport rates and circadian clock proteins rely on nucleocytoplasmic shuttling to maintain the correct pace of the circadian clock. Fluorescence recovery after photobleaching (FRAP) analysis was performed and revealed increased nuclear import rates of Bmal1 in cancer compared to normal cells. Altered expression and nuclear import rates of circadian clock proteins in cancer cells suggest these cells might harbor an impaired circadian clock. Luminescence assays are thus currently being employed to determine whether cancer cells display rhythmic expression of core clock genes, as an indication of a functioning circadian clock. A real-time bioluminescence imager is being used to measure Bmal1 and Per2 promoter-luciferase activities in cancer cells over time, after synchronization of circadian oscillators with the glucocorticoid analogue, Dexamethasone. This type of study is relevant to the field of chronotherapy, where elucidating differences in circadian clock functioning in normal and cancer cells could yield better insights into the timing of administration of chemotherapy, ultimately ensuring a better patient response. Citation Format: Waldo Lexow, Sian-Ailin Da Silva, Virna D. Leaner, Pauline J. van der Watt. Investigating disruptions in the circadian clock in cancer cells [abstract]. In: Proceedings of the AACR International Conference: New Frontiers in Cancer Research; 2017 Jan 18-22; Cape Town, South Africa. Philadelphia (PA): AACR; Cancer Res 2017;77(22 Suppl):Abstract nr B34.