Mutations in the circadian gene CLOCK in colorectal cancer

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• The circadian clock regulates physiological processes, with CLOCK gene expression controlling other clock genes.
• Clock genes are implicated in cancer development.
• Microsatellite instability (MSI) is a hallmark of certain colorectal cancers (CRCs).

Purpose of the Study:

• To investigate CLOCK as a potential target of somatic mutations in MSI colorectal cancers.
• To understand the functional consequences of CLOCK mutations in CRC.
• To identify novel CLOCK target genes involved in DNA damage response.

Main Methods:

• Analysis of microarray gene expression data and public gene sequence information.
• Sequencing of CLOCK gene coding microsatellites in 101 MSI CRCs.
• Functional studies in LS180 cells with restored CLOCK expression, assessing UV-induced apoptosis and radiation response via flow cytometry.
• Chromatin immunoprecipitation sequencing (ChIP-seq) to identify CLOCK-binding elements.

Main Results:

• CLOCK was identified as a putative novel MSI target gene.
• CLOCK mutations were found in 53% of MSI CRCs.
• Restoring CLOCK expression in cells with biallelic inactivation conferred protection against UV-induced apoptosis and reduced G(2)-M arrest after ionizing radiation.
• Novel CLOCK-binding elements were identified near DNA damage response genes (p21, NBR1, BRCA1, RAD50).

Conclusions:

• CLOCK is frequently mutated in MSI colorectal cancers.
• Altered response to DNA damage due to CLOCK mutations is a plausible mechanism in CRC tumorigenesis.
• CLOCK plays a significant role in DNA damage response pathways relevant to colorectal cancer.