Sun and skin

Abstract

Ultraviolet (UV) radiation within sunlight is the prime cause of skin cancer in humans. It is a complete carcinogen, being muta-genic and immunosuppressive. UV also disrupts the cell cycle. Both UVB and UVA wavebands cause genetic damage, leading to mutations if the cell divides prior to DNA repair. Our group has shown that UVA is the dominant mutagen in the basal layer of the epidermis, which contains the dividing cells that give rise to skin cancer. This appears to be due to lower levels of DNA repair in these basal keratinocytes and deeper penetrance of UVA than UVB to these cells. We have recently discovered a novel hotspot mutation in the chromatin remodeling gene Brm in human skin cancers which is consistent with being caused by UVA. Both the UVB and UVA wavebands within sunlight are potently immuno-suppressive in humans, enabling mutated cells to grow unchecked. Our recent action spectrum shows two immunosuppressive peaks, one in the UVB range at 300 nm and a second in the high wavelength UVA at 370 nm with wavelengths between these peaks being less effective. There is now accumulating evidence that the role of UVA in causing skin cancer in humans has been underestimated.