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Circadian rhythms are patterns of behavior, physiology, and metabolism that occur within a period of approximately 24 h. These rhythms are generated endogenously, but synchronize to external cues, thus enabling organisms to beneficially align physiological processes to the inherently dynamic, yet predictable, seasonal changes in the day–night cycle. The cell autonomous circadian oscillator temporally coordinates cellular processes, including metabolism, proliferation, cell signaling, organelle function, proteostasis, and DNA damage repair to sustain cellular homeostasis. It is hypothesized that the circadian oscillators evolved as a “flight from light” mechanism to minimize UV damage to single stranded DNA by restricting DNA replication to the nighttime. Support for this hypothesis is accumulating with the recent observation that the circadian rhythm and cell cycle are intimately coupled to each other, so that specific phases of cell cycle occur at a defined phase of the circadian oscillator at single-cell level [1]. Furthermore, chronic circadian disruption perturbs cellular homeostasis and predisposes to cancer. Conversely, numerous cancer cell lines display severe circadian alterations, which likely contribute to aggressive proliferation of the tumor. Hence, it is becoming increasingly important to understand the relevance of circadian rhythm for optimizing fitness under natural conditions and its utility and adaptability in the modern world so that the knowledge can be better leveraged for the prevention and treatment of cancer. |
