The oldest tumor
Scientists have found cancer cells with an 11,000-year history
Cancer cells of transmissible sarcoma of dogs have been transmitted among animals for 11 thousand years, that is, they represent the oldest cell line on Earth. This conclusion was reached by scientists who read the genome of cancer cells isolated from two dogs from Brazil and Australia. The study was published in Science (Murchison et al., Transmissable Dog Cancer Genome Reveals the Origin and History of an Ancient Cell Lineage, you can read about it briefly on the journal's website (An 11,000-Year-Old Dog Tumor).
Cells of transmissible venereal sarcoma of dogs. Photo: Joel Mills / Wikipedia
DNA sequencing of sarcoma has shown that cells have accumulated almost two million mutations since their malignant degeneration. Proteins encoded by 10 thousand genes had changes in amino acid composition; 646 genes were lost. At the same time, the cancer cells isolated from the two animals almost did not differ from each other.
When comparing the DNA of cancer cells with the normal canine genome, scientists came to the conclusion that this cell line originated about 11 thousand years ago, and began to spread widely about 500 years ago. In the initial period, the authors believe, sarcoma existed in a closed small population, where it "learned" to be transmitted from one animal to another. The fact is that cancer transmission is usually impossible due to genetic differences that lead to the rapid destruction of foreign cells. However, it is possible to avoid an immune reaction in a closed population, where animals, thanks to closely related crossing, are genetically very similar. Persisting in such a population, sarcoma gradually acquired mutations that made it possible to avoid an immune response from distant relatives of its original host.
It should be noted that estimates of the lifetime of a cell line are based solely on the sum of accumulated mutations and the accepted rate of their occurrence. This rate, however, strongly depends on the work of the cellular repair system, which is usually severely damaged in cancer cells. Changes in the rate of mutations can lead to orders of magnitude different estimates of the lifetime of cells and organisms.
Three types of cell-borne cancers are now known among mammals. In addition to sarcoma of dogs, these include cancer of Tasmanian devils and sarcoma of Syrian hamsters. The disease of dogs is transmitted sexually, and the facial tumor of Tasmanian devils is transmitted through bites. The spread of the incurable disease has led to a 70 percent drop in the number of Australian marsupials in recent years.
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24.01.2014