Endogenous retroviruses and cancer
How fragments of ancient viruses in the human genome affect the body
Andrey Zhukov, Hi-News.ru
Our DNA contains genes not only of our direct ancestors. Every modern person contains the genes of Neanderthals, but, as it turned out, this is not all. Our DNA also contains traces of viruses that once attacked the body of ancient people. The search for these very traces helps scientists to understand what diseases people had thousands of years ago. But most importantly, ancient viruses in our bodies may well play a role in modern diseases such as cancer. And recently, scientists have been finding more and more evidence for this.
What role do ancient viruses play in the genome
A few decades ago, it was believed that endogenous viral elements, that is, traces of ancient viruses, of which there are thousands in the human body, are in a dormant state in the human body, and do not manifest themselves in any way. They were classified as so-called "junk DNA", that is, a part of the genome that does not perform any function, but simply exists.
However, in the last few years, this assumption has become questionable. The fact is that science has made a big step forward in terms of studying genes. New, more sensitive methods make it possible to determine much more precisely the influence of genes on certain processes in the body, as well as to determine when they are active and when they are really in a dormant state.
Ancient viruses and cancerous tumors
In a recent study, a group of scientists focused their attention on the activation of one of the ancient viruses in healthy tissues of people with cancer. They were especially interested in the tissues around the tumors. Recall that healthy cells, which are located around malignant cells, play an important role in the development of oncology. In fact, cancer makes them work for themselves.
In their study, the scientists used tissue samples taken after death from almost 950 people. They included 54 types of healthy tissues found throughout the body, including in such key organs as the brain, heart, kidneys, liver, etc. The authors analyzed which of the genes were "included". Scientists were able to identify them by specific strands of RNA.
The authors tried to find evidence of the existence of active "human endogenous retroviruses" (HERV) present in the genome. One of these viruses is HML-2. It appeared in the human genome several hundred thousand years ago. Moreover, it was found only in the human genome. Other primates, the closest relatives of humans, do not have it.
In all 54 samples of healthy tissues, scientists found active HML-2. Moreover, the virus was most active in the pituitary gland and thyroid gland, as well as in healthy tissues around tumors. Scientists report this in the publication PLOS Biology (Burn et al., Widespread expression of the ancient HERV-K (HML-2) virus group in normal human tissues).
How ancient viruses affect cancerous tumors
The main question remains open — what does HERV do in healthy cells, and how does it affect a cancerous tumor? According to scientists, when HERV is activated, viral fragments do not give full-fledged viruses that can infect cells. Most likely, as a result of their activation, cells begin to build certain RNA molecules, which subsequently encourage cells to build certain proteins.
Scientists have no evidence that HERV in any way affects the course of the disease and, moreover, provokes the appearance of cancer. However, according to the researchers, HERV can be used as potential biomarkers of cancer. That is, by the presence of HERV in certain tissues, theoretically, it is possible to diagnose the disease.
In the near future, scientists want to find out how HERV behave in malignant cells. Moreover, the team plans to pay attention not only to HML-2, but also to other endogenous retroviruses. It is possible that the new study will provide more answers to the questions. However, even the current study is a clear confirmation that the genome of ancient viruses in our body is not at all in a dormant state, as previously thought.
I must say that this is not the first time when it turns out that "junk DNA" is not really "junk", but performs a certain function in the body. It follows that further study of HERV may help to better understand the nature of some diseases and find new, more effective methods of treatment and diagnosis.
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