Abstract 2168: Per2 (PERIOD 2) mediates low-dose radiation-induced adaptive response in human mammary epithelial cells
Authors: Alexandrou Aris T. , Menaa Cheikh , Fan Ming , Woloschak Gayle E. , Grdina David J. , Li Jian-Jian 
Published: August 2012

Abstract
Introduction Central and peripheral clocks generate self-sustained circadian rhythms that are intimately involved in metabolic and physiological processes. Circadian deregulation is associated with many human diseases including cancer, diabetes, and neurological disorders. Epidemiological studies have shown that disruption in circadian rhythms, such as nocturnal workers, is linked to an increased cancer risk including breast carcinoma. This effect is likely related to the perturbation of hormonal and cytokine circulation caused by deregulated circadian genes affecting cell survival and proliferation. Mice with gene deletion of Per2, a core component of the circadian rhythm, show higher incidence of lymphoma. Moreover, the absence of Per2 altered the levels of c-Myc and Cyclin D, two genes involved in the homeostasis of cell proliferation. Recent work demonstrates that Cyr, a partner of Per2, regulates cell death in response to chemotherapy agents. However, the exact function of Per2 signaling pathway in maintaining cell homeostasis against environmental stress conditions, such as low dose ionizing radiation, has not been elucidated. Methods and Results Our current studies aim to elucidate the contribution of PER2 in the low-dose radiation-induced radioadaptive response of human mammary epithelial cells (MCF10A). MCF10A and breast cancer cells (MCF7) treated with LDIR at 4-hour intervals (i.e., 0, 4, 8, 12, 16, 20, 24) showed highest PER2 expression at 8 hours in contrast to the absence of PER2 in MCF7 cells. To examine whether LDIR-induced Per2 expression is responsible for the cell death adaptation, MCF10 cells transfected with either Per2 siRNA or scramble were exposed to different doses of IR (i.e., 10cGy, 10cGy + 5Gy, and 5Gy). We found that knockdown of Per2 gene expression caused ablation of the LDIR-induced radioadaptive response with a significant increase in apoptosis of irradiated samples compared to controls. This finding was translated by reduced clonogenic survival and increased apoptosis assessed by flow cytometry analysis. Furthermore, mechanistic analysis showed that phospho-glycogen synthase kinase-3ß (p-GSK3ß) activation mediated LDIR-induced PER2 expression, and subsequently the adaptive protection of human mammary epithelial cells. Therefore, an enhanced interaction between p-GSK3ß and PER2 plays an active role in LDIR-induced radiation protection. This data represents the first experimental evidence that Per2 plays a critical role in protecting human epithelial cells in environmental stress conditions. Conclusion Induction of Per2 by LDIR treatment protects human breast epithelial cells against subsequential exposure to high dose radiation-induced genotoxic effects. Per2-mediated radioprotection requires p-GSK3ß activation.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2168. doi:1538-7445.AM2012-2168