Circadian Clock Disruption Drives Cancer Risk Through Multiple Cellular Pathways

This extensive review by Fortin and colleagues provides crucial insights into how circadian rhythm disruption contributes to cancer development and progression. The research matters because growing portions of the population experience circadian misalignment due to modern lifestyle factors including shift work, artificial light exposure, and irregular eating patterns.

The authors systematically examined how the circadian clock—the body's internal 24-hour timing system—regulates four critical cellular processes. First, they found extensive crosstalk between circadian proteins and cell cycle checkpoints, with clock disruption leading to altered proliferation rates and increased cancer susceptibility. Second, they documented how circadian proteins modulate DNA damage response pathways, including the tumor suppressor p53 and checkpoint kinases ATR/ATM, with clock disruption impairing the cell's ability to repair DNA damage.

The review reveals that multiple DNA repair mechanisms operate under circadian control. Nucleotide excision repair, which removes UV-induced DNA damage, shows strong circadian rhythmicity that disappears in clock-deficient mice. Base excision repair and double-strand break repair pathways also exhibit time-of-day dependent activity, suggesting the clock synchronizes DNA repair with environmental damage patterns.

Metabolic regulation represents another key connection, with circadian clock genes orchestrating glucose metabolism, lipid storage, and mitochondrial function. High-fat diets and irregular feeding patterns disrupt these rhythms, while time-restricted feeding can restore metabolic synchronization. The immune system also operates under circadian control, with cytokine release, immune cell trafficking, and inflammatory responses all showing daily rhythms that are lost when the clock is disrupted.

The clinical implications are significant. The authors discuss potential links between circadian disruption and rising early-onset colorectal cancer rates, suggesting that modern lifestyle factors may be contributing to cancer in younger populations. They also outline opportunities for chronotherapy—timing cancer treatments to align with circadian rhythms for enhanced efficacy and reduced toxicity. However, the authors note that circadian effects can be tissue-specific and context-dependent, requiring further research to fully understand therapeutic applications.