UVA light can harm directly your DNA!

To begin with

Scientists have discovered that UVA radiation, a part of the sunlight radiation, can be directly absorbed by a DNA double helix and provoke chemical alterations known to induce carcinogenic mutations.

Keywords

Skin cancer, UVA radiation, Cyclobutane dimer, Photochemistry, Antioxidant, Absorption spectrum, DNA molecule

About

UVA radiation, as well as UVB and UVC are constituent radiations of light and are responsible for damaging the DNA molecule, which is the carrier of the genetic code within the cell of an organism. UVA has attracted scientists attention since the solar light reaching the earth contains many more UVA photons than UVB or UVC. Moreover, UVA radiation exists in the light of the lamps used in solaria tanning beds. (watch Dr. Markovitsi talking about the UVA radiation)

The scientific data obtained by the researchers of the Francis Perrin Laboratory (FPL) and the Laboratory of Nucleic Acid Lesions (LAN) provided clear evidence that UVA radiation can be absorbed directly by DNA, which then undergoes damage. This mechanism is called ‘direct damage’ because it is enacted without the mediation of any other molecule within the cell, as it was thought previously, such as molecules coming from medication, pollution, or food intake etc.

In other words, the DNA damage induced by UVA radiation is an intrinsic property of the DNA molecule and it will always happen under similar circumstances. Therefore, this should be considered seriously when protective measures are to be taken, especially when we have to be exposed to the sun. (watch Dr. Banyasz talking about the efficiency of photochemical reactions of DNA)

(Press here to watch a series of animated drawings on the interaction between UVA radiation and DNA created by FUB)

Links with society

Do you dream of a nice suntan?

If you try to get a nice suntan lying all day on a beautiful beach or by going to a solarium, don’t forget that the UVA radiation, while helping you bronzing, affects badly your genetic material. Such damage may eventually lead to skin cancer. In case you think that the famous chemical substances known as ‘antioxidants’ (e.g. vitamin E, vitamin C, or beta carotene) are capable of protecting you against skin cancer, you’ll be disappointed by the results of recent research carried out by the Francis Perrin Laboratory (FPL) and the Laboratory of Nucleic Acid Lesions (LAN). The antioxidants alone are not enough to protect us from DNA damages induced by UVA. Our protection against UVA radiation necessitates the use of high index sunscreens or, even better, the avoidance of overexposure to the sun. (watch Dr. Markovitsi talking about the dangers of tanning)

Research innovation

What’s new?

What was known so far within the research community was that the formation of cyclobutane dimers induced by UVA radiation proceeds via an indirect mechanism. The process was thought as follows: UVA photons get absorbed by another molecule present within the cell, which is called 'photosensitizer'. The photosensitizer in turn, would transfer its energy to the DNA molecule where chemical reactions would take place, leading to the formation of the cyclobutane dimers.
However, new scientific data coming from the Francis Perrin Laboratory (FPL) and the Laboratory of Nucleic Acid Lesions (LAN) provided evidence for the existence of a direct mechanism. This means that UVA radiation is directly absorbed by the DNA molecule, without the intermediation of another chemical substance. (watch Dr. Markovitsi talking about the research results)

Relevant scientific publications

-- UVA-induced cyclobutane pyrimidine dimers in DNA: a direct photochemical mechanism? S Mouret, C Philippe, J Gracia-Chantegrel, A Banyasz, S Karpati, D Markovitsi, T Douki, Organic Chemical Biology, 2010, volume 8, pages 1706-1711.

Description of the method

In order to see how UVA light interferes with DNA, researchers from the FPL and LAN tested two hypotheses:

A. Is the DNA double helix capable of absorbing UVA photons?

The researchers from the FPL proved in a clear and unambiguous way that the DNA double helix is indeed capable of directly absorbing UVA radiation.

Scientists used a ‘simplified’ form of the DNA double helix made of one strand of ‘thymines’ and one strand of the complementary base ‘adenine’ whereas natural DNA is composed of combinations of two base pairs: adenine – thymine and guanine - cytosine. Thymines were selected as they are known to form cyclobutane dimers, an entity associated with carcinogenic mutations. (watch Dr. Markovitsi talking about the experiments and their results)

Then, the scientists focused on the way this ‘simplified’ DNA absorbs light, with special focus on the UVA spectral region. A scientific diagram called 'absorption spectrum' depicts how the DNA helix absorbs different radiations, e.g. UVA, UVB and UVC. The scientists observed that indeed this model DNA helix does absorb UVA, even though weakly, which is why it was difficult to notice until that time and required extremely delicate handling. (watch Dr. Vaya demonstrating how an absorption spectrum is obtained) The UVA absorption phenomenon is depicted in the figure as a long tail.
This research effort was inspired by similar investigations in the UVC spectral region. The scientists from the FPL by use of special equipment and sophisticated experiments with femtosecond lasers as well as theoretical calculations have shown that when DNA bases are arranged in a double helix they are coupled and behave in a collective way. This results in, amongst others, a different way that light is absorbed. (watch Dr. Banyasz describing the research methodology)

B. Does such absorption provoke the formation of cyclobutane dimers, an entity associated with carcinogenic mutations?
The scientists investigated whether the UVA radiation absorbed by the DNA helix provokes the formation of cyclobutane dimers. (watch Dr. Markovitsi talking about the formation of cyclobutane dimers)
To this end, water solutions containing both samples of DNA as found in nature and ‘simplified’ DNA double helices were first irradiated with UVA light, at the Francis Perrin Laboratory. Then, the solutions were sent for analysis to another laboratory at Grenoble, headed by Thierry Douki.
Thierry analyzed the DNA damages induced by the irradiation, using sophisticated techniques developed in his laboratory. He found that cyclobutane dimers were indeed formed. The researchers repeated the same experiment with natural DNA samples to see that cyclobutane dimers had been formed again after the irradiation with UVA light. (watch Dr. Banyasz describing the research methodology)

The"face" of Science: Let's meet the scientists!

Who are the people working behind the scenes?

A research group does not work alone. This particular research project was part of the results obtained in the frame of a collaborative effort funded by the French National Research Agency.

Editing Team

Editing team of the Digital Exhibit "UVA light can harm directly your DNA!"

Scientific editors: Akos Banyasz (CNRS research scientist), Dimitra Markovitsi (leader of this research project), Ignacio Vaya Perez (post-doctoral fellow), Marion Perron (CNRS technician)

Content Coordination: Glykeria Anyfandi
Science Communication Editors: Glykeria Anyfandi, Evlalia Amygdalaki
Content Administration: Christina Troumpetari, John Stoitsis
Technical Development: John Stoitsis
Animation and ICT material: CediS, Free University of Berlin
Photographs, videos & web material: Evlalia Amygdalaki
e-Knownet Live experiments: Interactive Science & Technology Exhibition, Eugenides Foundation