Mutations in the circadian gene CLOCK in colorectal cancer.
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.
Alhopuro
Pia
P
Genome-Scale Biology Research Program and Department of Medical Genetics, University of Helsinki, Helsinki, Finland.
Björklund
Mikael
M
Sammalkorpi
Heli
H
Turunen
Mikko
M
Tuupanen
Sari
S
Biström
Mia
M
Niittymäki
Iina
I
Lehtonen
Heli J
HJ
Kivioja
Teemu
T
Launonen
Virpi
V
Saharinen
Juha
J
Nousiainen
Kari
K
Hautaniemi
Sampsa
S
Nuorva
Kyösti
K
Mecklin
Jukka-Pekka
JP
Järvinen
Heikki
H
Orntoft
Torben
T
Arango
Diego
D
Lehtonen
Rainer
R
Karhu
Auli
A
Taipale
Jussi
J
Aaltonen
Lauri A
LA
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
D056926:CLOCK Proteins; C538943:CLOCK protein, human