The "cancer clock" is ticking in our cells
Cancer-predicting "death clock" found in cells
The probability of developing cancer in humans can be predetermined by two "hours" of DNA mutations found in almost all cells of the human body. The discovery is reported on the pages of the journal Nature Genetics (Alexandrov et al., Clock-like mutational processes in human somatic cells), and a New Scientist briefly told about it (‘Death clock’ in cells could tell you when you'll get cancer).
We are talking about mutations in DNA (changes in individual genes) that occur at different rates. In the case of accumulation of some mutations, it is permanent, which leads to DNA damage and eventually to cancer.
Michael Stratton from the Sanger Institute (Cambridge) found two types of "clocks" that mark the rate of mutations in almost all cells of the human body. Scientists have also determined the speed of their "course" in various tissues.
First, the researchers studied the DNA sequences of tumors in 10,000 patients suffering from cancer (36 types of disease). A special algorithm made it possible to identify certain mutation structures, so-called signatures, in the "cancer" genomes. Then, among these signatures, we found those that differ in the regular nature of mutations, the rate of increase of which is associated with the age of a person. There were two of them, and both types of "clocks" begin to "tick" even in healthy tissues, scientists emphasize.
Stratton called the first "clock" mitotic – they mark mutations resulting from cell division. "The rate of mutations correlates with the rate of cell turnover in tissues. In the future, we will be able to use this number to understand how many times a cell has divided," the scientist noted. Almost nothing is known about the second "clock" to science. They probably have something to do with DNA repair, more precisely, with errors in the repair mechanisms.
Knowing the age of the patient, the scientists were also able to determine the speed of the "clock" in various tissues. Thus, the fastest mutations accumulated in the cells of the stomach and intestines (about 23 mutations per cell per year), and the slowest – in the cells of the mammary glands and ovaries (3-4 mutations per year).
Since the course of this clock does not stop when a healthy cell turns into a cancerous one, it can be a valuable indicator of the rate of metastasis or the growth of resistance of cancer cells to drugs. Scientists even hope to predict by the clock the beginning of the transformation of cells into malignant.
"All our lives we accumulate mutations, and in some people a certain combination of the latter leads to cancer. It remains to be seen whether the rate of mutations varies in individual individuals: if so, then by its indicators we will be able to predict how much time is left before the appearance of cancer," Stratton notes.
Moreover, according to the scientist, changing the rate of these mutations can slow down the occurrence of cancer. "I'm not saying that this will definitely be possible – DNA mutations are a fundamental process for our biological device, but our discovery makes us think in this direction. As soon as we find a new phenomenon that causes cancer, we think about how to remove it," the scientist summarizes.
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11.11.2015