title: Effects of light and food schedules on liver and tumor molecular clocks in mice.
abstract: BACKGROUND
  Disrupted circadian coordination accelerates malignant growth, but the molecular mechanism is unclear.
  
  
  METHODS
  Healthy or Glasgow osteosarcoma-bearing mice (n = 162) were synchronized with light and darkness over 2-3 weeks, submitted to an 8-hour advance onset of light every 2 days (chronic jet lag) to disrupt circadian coordination, or submitted to chronic jet lag and meal timing to prevent molecular clock alteration. The expression of molecular clock genes and of the cell cycle genes c-Myc and p53 in liver and tumor was determined with quantitative reverse transcription-polymerase chain reaction at six circadian times over a 24-hour period of light and darkness and analyzed with analysis of variance and cosinor. Tumor weight was measured daily over the course of the experiment. All statistical tests were two-sided.
  
  
  RESULTS
  In synchronized mice, mean mRNA levels of clock genes Rev-erbalpha, Per2, and Bmal1 varied by 206-, four-, and 26-fold, respectively, over the 24 hours in healthy mouse liver; by 36-, 35-, and 32-fold in the livers of tumor-bearing mice; and by 9.4-, 5.5-, and sixfold in tumor tissue (P = .046 to <.001). In mice subjected to chronic jet lag, the periodic changes were dampened and the clock gene rhythms were temporally shifted in liver and ablated in tumor, and tumor growth was accelerated. Meal timing reversed the chronic jet lag-induced alterations in Rev-erbalpha and Per2 expression in liver and of all three clock genes in tumor and slowed tumor growth. Tumor growth differed as a function of light and feeding schedules (P = .04). No obvious rhythm was detected for p53 or c-Myc in liver or tumor tissues of synchronized mice. In healthy mice subjected to chronic jet lag, the mean level of p53 expression was cut in half (P = .002), and a 12-fold circadian variation in c-Myc mRNA level (P = .03) was induced in the liver of healthy mice, whereas complex expression patterns were found in the liver and tumor of tumor-bearing mice.
  
  
  CONCLUSIONS
  Altered light-dark or feeding schedules modified the expression of molecular clock genes and genes involved in carcinogenesis and tumor progression.
authors.affiliation: INSERM E 0354 Chronothérapeutique des cancers, Hôpital P. Brousse and Université Paris XI, 94807 Villejuif Cedex, France.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Filipski
authors.forename: Pasquale F
authors.initials: PF
authors.lastname: Innominato
authors.forename: MingWei
authors.initials: M
authors.lastname: Wu
authors.forename: Xiao-Mei
authors.initials: XM
authors.lastname: Li
authors.forename: Stefano
authors.initials: S
authors.lastname: Iacobelli
authors.forename: Li-Jian
authors.initials: LJ
authors.lastname: Xian
authors.forename: Francis
authors.initials: F
authors.lastname: Lévi
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D018797:Cell Cycle Proteins; D002940:Circadian Rhythm; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005502:Food; D015972:Gene Expression Regulation, Neoplastic; D008027:Light; D008099:Liver / Q000378:metabolism*; D008297:Male; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D056953:Nuclear Receptor Subfamily 1, Group D, Member 1; D056950:Period Circadian Proteins; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C498262:Nr1d1 protein, mouse; D009687:Nuclear Proteins; D056953:Nuclear Receptor Subfamily 1, Group D, Member 1; C513312:Per2 protein, mouse; D056950:Period Circadian Proteins; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53