Researchers have found that shifting work schedules inactivate tumor suppressor genes, which promotes cancer development.
More than 3.5 million French people work staggered hours. This work organization disrupts the sleep-wake biological cycle. Desynchronization that affects the body’s cells and increases the risk of cancer, reveals a study published in Cell Metabolism. This work by the Koch Institute of the Massachusetts Institute of Technology (MIT) is the first to describe the mechanisms responsible for the excess risk of cancer already described in workers with atypical hours.
In humans and many living organisms, it is the day-night alternation that synchronizes the sleep-wake cycle. Many cellular mechanisms, including division, are controlled by circadian rhythms. However, by working at night and sleeping during the day, workers’ cells are out of sync. “The cells need a light marker, this acts as a reset button,” explains Thales Papagiannakopoulos, works manager. When you lose this landmark, you lose your natural rhythm in all the cells of your body ”
Inactivation of tumor suppressor genes
While studying mice, the researchers discovered that shifting schedules cause the inactivation of two genes involved in circadian rhythms that are also tumor suppressor genes. Their role is to regulate cell proliferation. When they are inactive, the cells are no longer controlled and can multiply in an anarchic way, with a risk of tumor formation.
To study this effect on these genes, scientists looked at mice genetically engineered to develop non-small cell lung cancer (NSCLC), the most common form of lung cancer. One group of rodents lived at their usual pace (exposed for 12 hours to light then 12 hours of sleep), while the others stayed awake 8 hours longer than usual every 2-3 days. The researchers then observed that the tumors of mice exposed to staggered hours grew faster, and that their cancer was more aggressive than in other mice.
In another experiment, the mice followed their biological rhythm, but scientists turned off tumor suppressor genes in some guinea pigs. As a result, the tumors grew much faster in these mice, as they did when exposed to the staggered hours, than the others.
Same effect in humans
After observing these harmful effects in animals, the researchers studied lung cancer cells taken from patients. Here again, they noted that the tumor suppressor genes were inactive, as were several genes regulating circadian rhythms, in these cells, especially in the most aggressive tumors.
MIT researchers are now trying to find out whether this desynchronization can lead to the appearance of other cancers. Several studies have notably suggested that women working at nighttime have an increased risk of developing breast cancer. Their work will also focus on the development of drugs targeting tumor suppressor genes.
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