Researchers from the Institut Jacques Monod (CNRS/University of Paris Diderot), the Institute of Biology of the Ecole Normale Supérieure (ENS/CNRS/Inserm), and the University of Bristol, have described for the first time in its totality the mechanisms by which DNA damaged by UV radiation is repaired, and how the proteins involved in this process cooperate to ensure its efficiency.
This work opens new perspectives not only in the fight against cancer but also in combating certain bacterial infections, and is published in Nature on August 3rd 2016.
The DNA of our cells is continuously damaged by numerous external agents, such as carcinogens contained in tobacco smoke or UV radiation emitted by the sun. If left unrepaired, this damage leads to mutations which ultimately favor the emergence of cancerous cells, which is why the cell must rapidly and efficiently repair its DNA. To do so, the cell employs a battery of enzymes which must act in a synchronous fashion to identify and repair the damaged parts of its genome. The complexity of this process has long stumped researchers trying to understand the mechanisms at play.
Thanks to new nanotechnologies, a team of scientists which brings together both physicists and biologists has been able to film, in real-time, the enzymes that repair DNA damage. This work started in 2012, when the team focused on the initial steps of the DNA repair mechanism. Today the team has revealed, for the first time, the repair process in its entirety.
A special type of microscope, which makes it possible to both manipulate and observe single molecules of DNA and proteins, has enabled the team to observe a single DNA molecule, damaged by UV. They added to it the RNA polymerase enzyme, the one naturally responsible for “reading” the lengths of the DNA code and initiating production of protein from this DNA code, but which can get “stalled” if it reads a segment of damaged DNA. It is thanks to this “stalling” that the cell recognizes that the DNA has been damaged and launches its repair. In practical terms, the team of scientists was able to observe a series of four proteins (named Mfd, UvrA, UvrB and UvrC) successively interacting with the RNA polymerase and coordinating among themselves and the UV-damaged DNA to enact the latter’s repair.
By determining the order in which these components acted and by characterizing the manner in which they “handed off” to each other in a kind of molecular relay-race, the team was able to define the critical steps of this process.
This work will ultimately lead to new applications, both in the fight against cancer and in efforts to treat pathogenic bacteria. Indeed, when cancer cells become resistant to chemotherapy or radiation therapy – the purpose of which is to damage the DNA of cancer cells – it is because these cancer cells have activated DNA repair and undone clinically-generated DNA damage. One can thus work towards preventing DNA repair during cancer therapy so as to prevent tumor resistance to therapy. It also turns out that some pathogenic bacteria, including those responsible for tuberculosis, use proteins very similar to Mfd to proliferate. Thus, identifying how these proteins work together to enact DNA repair could also be useful in fighting pathogenic bacteria.
Researchers from the Lomonosov Moscow State University discovered a new mechanism of DNA repair, which will help to treat and to prevent diseases in the future
The DNA molecule is chemically unstable giving rise to DNA lesions of different nature. That is why DNA damage detection, signaling and repair, collectively known as the DNA damage response, are needed.
A group of researchers, lead by Vasily M. Studitsky, professor at the Lomonosov Moscow State University, discovered a new mechanism of DNA repair, which opens up new perspectives for the treatment and prevention of neurodegenerative diseases. The article describing their discovery is published in AAAS’ first open access online-only journal Science Advances.
“In higher organisms DNA is bound with proteins in complexes called the nucleosome. Every ~200 base pairs are organized in nucleosomes, consisting of eight histone proteins, which, like the thread on the bobbin, wound double helix of DNA, which is coiled into two supercoiled loops. Part of the surface of the DNA helix is hidden, because it interacts with histones. Our entire genome is packed this way, except for the areas, from which the information is being currently read”, — says Vasily M. Studitsky , who is the leading researcher and the head of the Laboratory of Regulation of Transcription and Replication at the Biological Faculty of the Lomonosov Moscow State University.
The dense packing allows DNA molecule with a length of about two meters to fit into a microscopic cell nucleus, but it makes significant surfaces of the DNA inaccessible for the repair enzymes — the proteins that manage the “repair” of damaged DNA regions. The damage of the DNA, if not repaired, leads to accumulation of mutations, cell death, and to the development of various diseases, including neurodegenerative, e.g. Alzheimer’s disease.
A group of researchers, lead by Vasily M. Studitsky, studied the mechanism of detection of single-stranded DNA breaks at which the connection is lost between nucleotides on one strand in the places where the DNA is associated with histones.
Scientists know quite a lot about the mechanism of the repair. It is known that for the synthesis of a protein, information written in the genetic code, which could be imagined as the manual for its assembly where triples of nucleotides match certain amino acids, should be taken out of the nucleus into the cytoplasm of the cell.
Thin and long strand of the DNA is packed in the nucleus and can tear at the exit to the outside. Moreover, it cannot be sacrificed as the cell’s nuclear DNA is is only present in two copies. Therefore, when it is necessary to synthesize specific protein, small region of DNA is unwound, the two strands are disconnected, and the information on the protein structure with one of the DNA strands is written in form of RNA, single-stranded molecule. The mRNA molecule, which serves as the template for making a protein, is synthesized by the principle of complementarity: each nucleotide pair corresponds to another one.
During the transcription of information (its rewriting into RNA) the RNA polymerase enzyme “rides” on the DNA chain, and stops when it finds the break. Like a proofreader of a text, RNA polymerase after it is stalled, triggers a cascade of reactions, resulting in the repair enzymes fixing the damaged area. At the same time, the RNA polymerase cannot detect discontinuities present in the other DNA strand.
There’s a good reason people over 60 are not donor candidates for bone marrow transplantation. The immune system ages and weakens with time, making the elderly prone to life-threatening infection and other maladies, and a UC San Francisco research team now has discovered a reason why.
“We have found the cellular mechanism responsible for the inability of blood-forming cells to maintain blood production over time in an old organism, and have identified molecular defects that could be restored for rejuvenation therapies,” said Emmanuelle Passegué, PhD, a professor of medicine and a member of the Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research at UCSF. Passegué, an expert on the stem cells that give rise to the blood and immune system, led a team that published the new findings online July 30, 2014 in the journal Nature.
Blood and immune cells are short-lived, and unlike most tissues, must be constantly replenished. The cells that must keep producing them throughout a lifetime are called “hematopoietic stem cells.” Through cycles of cell division these stem cells preserve their own numbers and generate the daughter cells that give rise to replacement blood and immune cells. But the hematopoietic stem cells falter with age, because they lose the ability to replicate their DNA accurately and efficiently during cell division, Passegué’s lab team determined.