Transport RNA against nonsense mutations

Genetic diseases will be treated by helping cells ignore mutations in DNA

Evgenia Efimova, Vesti

Imagine a situation where the instructions for what a person collects (for example, a set of furniture) are incorrect. What should I do in this case? Sometimes this situation also occurs in the human body: for example, when DNA mutations in people with genetic diseases lead to the production of defective proteins. The researchers tried to solve the problem and created a new technology that helps cells bypass such an incorrect "instruction".

Most human genes generate a kind of recipe for how a protein should be created. Each subsequent three-letter sequence in DNA (known as a codon) determines which amino acid should be added next in the growing chain of amino acids in order to create a protein. This process continues until the protein creation mechanism reaches a codon that "calls" to stop. It's called a stop codon.

But sometimes mutations create stop codons in the wrong places. A single mutation can stop the construction of a protein at around 15 amino acids, although in reality it should have hundreds of such "bricks". This "cutting" makes the protein absolutely useless. This phenomenon is known as nonsense mutation (or meaningless mutation), and it is precisely such "breakdowns" that cause about one tenth of all genetic diseases.

But in nature, there are probably still ways to avoid the appearance of "premature" stop codons. For the first time, one such method was proposed in the 1980s, but it took more than a decade for people to be able to make it work in human cells. The method focuses on transport RNA (tRNA) – molecules that, during the production of proteins, recognize stop codons and select the necessary amino acids.

After a while, it became possible to create an artificial tRNA that would also recognize "premature" stop codons, and instead of stopping the process of protein creation, add the amino acid necessary to obtain a useful protein.

So, in 2014, Carla Oliveira and her colleagues from the University of Porto (Universidade do Porto) restored the production of healthy protein in cells carrying a special mutation. It leads to congenital stomach and breast cancer. The only solution for such patients is organ removal.

Now Christopher Ahern and his research team from the University of Iowa have used artificial tRNA to restore the production of a protein that is usually missing or spoiled in people diagnosed with cystic fibrosis (also known as cystic fibrosis).

Just like Oliveira's team, American specialists applied the technique to "treat" the cells in the Petri dish. But after further experiments, the technique can become an excellent alternative to medications in the treatment of cystic fibrosis, scientists believe.

According to Ahern, one day it will be possible to cure cystic fibrosis by repairing or even replacing the damaged gene. However, obtaining long gene sequences for gene therapy or editing genes in lung cells is a huge challenge.

The artificial tRNA molecule is much smaller, so it will help solve the genetic problem and carry out treatment at a faster pace.

Once inside the cells, the artificial tRNA seems to compete with proteins, which usually bind to stop codons and stop the production of proteins. This means that artificial tRNAs do not "fix" every protein created by a defective gene, but they are able to fix enough proteins to significantly change the situation for the better in many genetic diseases. Let's explain that even a low content of the right proteins can fundamentally change the course of the disease.

"The results of the study are really interesting," says Malcolm Brodlie from Newcastle University (in an article by Michael Le Page Making cells ignore mutations could treat genetic diseases, published in the journal New Scientist – VM). But he notes that although scientists have obtained cells that produce proteins with the correct sequence of amino acids, they still have not shown that these proteins are fully functional.

Now let's add a small fly in the ointment: there is a possibility that artificial tRNAs can interfere with the work of correct (timely) stop codons by spoiling them with other proteins. This can happen completely randomly. But there is still such a possibility.

Meanwhile, the results of other studies suggest that artificial tRNAs will be safe. "It is known that the embedded tRNA, which is designed to block stop codons, behaves quite tolerant in the animal's body," says Jason Chin from the University of Cambridge. Chin's research group uses artificial tRNAs to "expand" the arsenal of genetic code in animals – worms or fruit flies.

The researchers add that the development of any treatment method based on the new technology is still far away. For the reason that artificial tRNAs are more difficult to deliver to cells than conventional drugs. But the researchers hope that this will become possible in the foreseeable future.

The results of the study (Lueck et al., Engineered tRNA suppression of a CFTR nonsense mutation) are published on the bioRxiv preprint site, that is, they have not yet been verified by an expert group of fellow scientists.

Portal "Eternal youth" http://vechnayamolodost.ru  29.11.2016