title: CLOCK in breast tumorigenesis: genetic, epigenetic, and transcriptional profiling analyses.
abstract: The transcription factors responsible for maintaining circadian rhythm influence a variety of biological processes. Recently, it has been suggested that the core circadian genes may play a role in breast tumorigenesis, possibly by influencing hormone regulation or other pathways relevant to cancer. To evaluate this hypothesis, we conducted a genetic and epigenetic association study, as well as a transcriptional profiling array and a pathway-based network analysis. We report significant correlations between single nucleotide polymorphisms associated with the central circadian regulator CLOCK and breast cancer risk, with apparent effect modification by estrogen receptor/progesterone receptor status. We also found that hypermethylation in the CLOCK promoter reduced the risk of breast cancer, and lower levels of CLOCK expression were documented in healthy controls relative to normal or tumor tissue from patients with breast cancer. Finally, we silenced CLOCK in vitro and performed a whole-genome expression microarray and pathway analysis, which identified a cancer-relevant network of transcripts with altered expression following CLOCK gene knockdown. Our findings support the hypothesis that circadian genes influence tumorigenesis, and identify a set of circadian gene variants as candidate breast cancer susceptibility biomarkers.
authors.affiliation: Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
authors.forename: Aaron E
authors.initials: AE
authors.lastname: Hoffman
authors.forename: Chun-Hui
authors.initials: CH
authors.lastname: Yi
authors.forename: Tongzhang
authors.initials: T
authors.lastname: Zheng
authors.forename: Richard G
authors.initials: RG
authors.lastname: Stevens
authors.forename: Derek
authors.initials: D
authors.lastname: Leaderer
authors.forename: Yawei
authors.initials: Y
authors.lastname: Zhang
authors.forename: Theodore R
authors.initials: TR
authors.lastname: Holford
authors.forename: Johnni
authors.initials: J
authors.lastname: Hansen
authors.forename: Jennifer
authors.initials: J
authors.lastname: Paulson
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhu
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000235:genetics*; D056926:CLOCK Proteins / Q000235:genetics* / Q000502:physiology; D016022:Case-Control Studies; D044127:Epigenesis, Genetic / Q000502:physiology; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D020022:Genetic Predisposition to Disease; D006801:Humans; D008875:Middle Aged; D020641:Polymorphism, Single Nucleotide; D012307:Risk Factors; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D056926:CLOCK Proteins; C538943:CLOCK protein, human