No matter how careful we are, at some point in all of our lives we will develop sunburn. Despite all of the NHS campaigns and warnings that sun damage can cause skin cancer, many of us will know at least one person who forgoes using suncream and lets themselves bake in the sun in the quest for the perfect summer glow. But what is sunburn? And why is it so dangerous? First we need to take a look at our skin.
All of us have a pigment called Melanin in our skin- some of you will already know it as the protein that determines skin colour. But Melanin also acts to absorb UV light, releasing it as heat, protecting our cells from these damaging rays. When radiation gets through this barrier and starts to damage our cells, the body senses this and floods the area with blood, also inducing inflammation that causes those damaged cells to be shed, helping to stop the accumulation of damage that can lead to the formation of cancers.
Noncoding RNA (RNA molecules that don’t code for proteins) have been shown to play a part in the recognition of this damage to our cells. It has been shown that these RNA are released from keratinocytes after UV radiation, stimulating the release of the inflammatory cytokines TNF-alpha and IL-6, which can also induce apoptosis in cells. UVB radiation was shown to alter double stranded regions of certain noncoding RNAs such as U1, and this change was enough to induce cytokine production as well as inducing production of NF-kB. This UV response was mediated by the RNA binding to Toll-like receptor 3 (TLR3).
If you’ve ever read the back of a bottle of sunscreen you’ll already know that UV radiation exists in a number of different forms, the most damaging and carcinogenic being UVB rays. UVB is responsible for the formation of DNA lesions, most notably pyrimidine dimers and pyrimidine-pyrimidone photoproducts. Both of these historically would have been repaired by proteins called photolyases which recognise the damage through the distortion of the DNA helix by the lesions. However, placental mammals (like us!) have lost this capability over time and now must use other repair pathways (such as nucleotide excision repair) to fix the lesions. There is a huge amount of interplay between our DNA repair pathways and the proteins involved in this, and it’s really important that the DNA that codes for these proteins aren’t themselves damaged by UV and other damaging agents or these mechanisms can fail.
With Cancer Research UK stating that around 86% of of malignant melanomas are linked to our lifestyle, it’s really important that we take care of our skin!
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Bernard JJ, Cowing-Zitron C, Nakatsuji T, Muehleisen B, Muto J, Borkowski AW, Martinez L, Greidinger EL, Yu BD, & Gallo RL (2012). Ultraviolet radiation damages self noncoding RNA and is detected by TLR3. Nature medicine, 18 (8), 1286-90 PMID: 22772463
Lima-Bessa, K., & Menck, C. (2005). Skin Cancer: Lights on Genome Lesions Current Biology, 15 (2) DOI: 10.1016/j.cub.2004.12.056
Image from- https://www.flickr.com/photos/esther-/1791843722/