Disrupting Circadian Homeostasis of Sympathetic Signaling Promotes Tumor Development in Mice Susie Lee 1 , Lawrence A. Donehower 2,3,5 , Alan J. Herron 4 , David D. Moore 3,5 , Loning Fu 1,3,5 * 1 Department of Pediatrics/U.S. Department of Agriculture/Agricultural Research Service/Children’s Nutrition Research Center, Baylor College of Medicine, Houston, Texas, United States of America, 2 Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, United States of America, 3 Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas, United States of America, 4 Department of Pathology, Center for Comparative Medicine, Baylor College of Medicine, Houston, Texas, United States of America, 5 Dan L. Duncan Cancer Center, Baylor College of Medicine, Houston, Texas, United States of America Abstract Background: Cell proliferation in all rapidly renewing mammalian tissues follows a circadian rhythm that is often disrupted in advanced-stage tumors. Epidemiologic studies have revealed a clear link between disruption of circadian rhythms and cancer development in humans. Mice lacking the circadian genes Period1 and 2 (Per) or Cryptochrome1 and 2 (Cry) are deficient in cell cycle regulation and Per2 mutant mice are cancer-prone. However, it remains unclear how circadian rhythm in cell proliferation is generated in vivo and why disruption of circadian rhythm may lead to tumorigenesis. Methodology/Principal Findings: Mice lacking Per1 and 2, Cry1 and 2, or one copy of Bmal1, all show increased spontaneous and radiation-induced tumor development. The neoplastic growth of Per-mutant somatic cells is not controlled cell-autonomously but is dependent upon extracellular mitogenic signals. Among the circadian output pathways, the rhythmic sympathetic signaling plays a key role in the central-peripheral timing mechanism that simultaneously activates the cell cycle clock via AP1-controlled Myc induction and p53 via peripheral clock-controlled ATM activation. Jet- lag promptly desynchronizes the central clock-SNS-peripheral clock axis, abolishes the peripheral clock-dependent ATM activation, and activates myc oncogenic potential, leading to tumor development in the same organ systems in wild-type and circadian gene-mutant mice. Conclusions/Significance: Tumor suppression in vivo is a clock-controlled physiological function. The central circadian clock paces extracellular mitogenic signals that drive peripheral clock-controlled expression of key cell cycle and tumor suppressor genes to generate a circadian rhythm in cell proliferation. Frequent disruption of circadian rhythm is an important tumor promoting factor. Citation: Lee S, Donehower LA, Herron AJ, Moore DD, Fu L (2010) Disrupting Circadian Homeostasis of Sympathetic Signaling Promotes Tumor Development in Mice. PLoS ONE 5(6): e10995. doi:10.1371/journal.pone.0010995 Editor: Frank Beier, University of Western Ontario, Canada Received December 7, 2009; Accepted May 11, 2010; Published June 7, 2010 Copyright: ß 2010 Lee et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by National Institutes of Health (NIH) grant CA107821-01A1, and United States Department of Agriculture (USDA) grants CRIS 6250- 51000-049 and CRIS 6250-51000-055 to L.F. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: loningf@bcm.edu Introduction Disruption of circadian rhythm increases spontaneous and carcinogen-induced mammary tumors in rodents [1,2,3,4,5,6]. Epidemiological studies have revealed that human night-shift workers show an increased risk of breast, colon, lung, endometrial and prostate cancer, hepatocellular carcinoma and non-Hodg- kin’s lymphoma [7,8,9,10,11,12]. Loss of circadian rhythm is also associated with accelerated tumor growth in both rodents and human cancer patients [13,14,15]. These findings raise the question of how circadian dysfunction increases the risk of cancers. Circadian rhythms in mammals are generated by an endoge- nous clock composed of a central clock located in the hypothalamic suprachiasmatic nucleus (SCN) and subordinate clocks in all peripheral tissues. The SCN clock responds to external cues and drives peripheral clocks via circadian output pathways. Both the central and peripheral clocks are operated by feedback loops of circadian genes, including Bmal1, Clock, Period (Per1-3) and Cryptochrome (Cry1 and 2). Bmal1 and Clock encode bHLH-PAS transcription factors that heterodimerize and bind to E-boxes in gene promoters to activate Per and Cry transcription, whereas Per and Cry encode repressors of BMAL1/CLOCK. The alternating activation and suppression of the BMAL1-driven positive loop and the PER/CRY-controlled negative loop result in a circadian oscillation of the molecular clock [16,17,18]. The molecular clock regulates clock-controlled genes (CCGs) to control tissue/organ function. Most CCGs follow tissue-specific expression patterns. Only a small group of CCGs, which include key cell cycle regulators and tumor suppressors, are expressed in all tissues studied. Such circadian control leads to the coupling of cell proliferation with key tissue functions in vivo [19,20,21,22,23,24]. Disruption of circadian rhythm in cell proliferation is frequently associated with tumor development and progression in mammals [4,5,12,25,26,27,28]. Both positive and negative loops of the molecular clock are involved in cell cycle control. For example, BMAL1 suppresses proto-oncogene c-myc but stimulates the tumor suppressor Wee1 PLoS ONE | www.plosone.org 1 June 2010 | Volume 5 | Issue 6 | e10995