title: Mutations in the circadian gene CLOCK in colorectal cancer.
abstract: The circadian clock regulates daily variations in physiologic processes. CLOCK acts as a regulator in the circadian apparatus controlling the expression of other clock genes, including PER1. Clock genes have been implicated in cancer-related functions; in this work, we investigated CLOCK as a possible target of somatic mutations in microsatellite unstable colorectal cancers. Combining microarray gene expression data and public gene sequence information, we identified CLOCK as 1 of 790 putative novel microsatellite instability (MSI) target genes. A total of 101 MSI colorectal carcinomas (CRC) were sequenced for a coding microsatellite in CLOCK. The effect of restoring CLOCK expression was studied in LS180 cells lacking wild-type CLOCK by stably expressing GST-CLOCK or glutathione S-transferase empty vector and testing the effects of UV-induced apoptosis and radiation by DNA content analysis using flow cytometry. Putative novel CLOCK target genes were searched by using ChIP-seq. CLOCK mutations occurred in 53% of MSI CRCs. Restoring CLOCK expression in cells with biallelic CLOCK inactivation resulted in protection against UV-induced apoptosis and decreased G(2)-M arrest in response to ionizing radiation. Using ChIP-Seq, novel CLOCK-binding elements were identified near DNA damage genes p21, NBR1, BRCA1, and RAD50. CLOCK is shown to be mutated in cancer, and altered response to DNA damage provides one plausible mechanism of tumorigenesis.
authors.affiliation: Genome-Scale Biology Research Program and Department of Medical Genetics, University of Helsinki, Helsinki, Finland.
authors.forename: Pia
authors.initials: P
authors.lastname: Alhopuro
authors.forename: Mikael
authors.initials: M
authors.lastname: Björklund
authors.forename: Heli
authors.initials: H
authors.lastname: Sammalkorpi
authors.forename: Mikko
authors.initials: M
authors.lastname: Turunen
authors.forename: Sari
authors.initials: S
authors.lastname: Tuupanen
authors.forename: Mia
authors.initials: M
authors.lastname: Biström
authors.forename: Iina
authors.initials: I
authors.lastname: Niittymäki
authors.forename: Heli J
authors.initials: HJ
authors.lastname: Lehtonen
authors.forename: Teemu
authors.initials: T
authors.lastname: Kivioja
authors.forename: Virpi
authors.initials: V
authors.lastname: Launonen
authors.forename: Juha
authors.initials: J
authors.lastname: Saharinen
authors.forename: Kari
authors.initials: K
authors.lastname: Nousiainen
authors.forename: Sampsa
authors.initials: S
authors.lastname: Hautaniemi
authors.forename: Kyösti
authors.initials: K
authors.lastname: Nuorva
authors.forename: Jukka-Pekka
authors.initials: JP
authors.lastname: Mecklin
authors.forename: Heikki
authors.initials: H
authors.lastname: Järvinen
authors.forename: Torben
authors.initials: T
authors.lastname: Orntoft
authors.forename: Diego
authors.initials: D
authors.lastname: Arango
authors.forename: Rainer
authors.initials: R
authors.lastname: Lehtonen
authors.forename: Auli
authors.initials: A
authors.lastname: Karhu
authors.forename: Jussi
authors.initials: J
authors.lastname: Taipale
authors.forename: Lauri A
authors.initials: LA
authors.lastname: Aaltonen
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics*; D000595:Amino Acid Sequence; D001483:Base Sequence; D056926:CLOCK Proteins / Q000235:genetics*; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics*; D016368:Frameshift Mutation; D020869:Gene Expression Profiling; D045325:HCT116 Cells; D006801:Humans; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D009154:Mutation
chemical_list: D056926:CLOCK Proteins; C538943:CLOCK protein, human