MEDIA RELEASE
11 March 2012
Study sheds new light on role of UVA causing skin cancer
While it was once thought that UVB was the prime culprit of skin cancers, a new
study undertaken by Professor Gary Halliday’s research team at the Sydney Cancer
Centre at Royal Prince Alfred Hospital and the University of Sydney suggests that
the role of UVA in causing skin damage leading to skin cancer has been severely
underestimated.
Speaking at The Royal College of Pathologists of Australasia’s (RCPA) 11th annual
Pathology Update conference at the Sydney Convention Centre in Darling Harbour
on the weekend, Prof Halliday says his research team has proven that UVA is not
just a contributing factor, but is in fact, the dominant mutagen in the basal layer of the
epidermis, which contains the dividing cells that cause skin cancer.
Ultraviolet (UV) radiation within sunlight is the prime cause of skin cancer in humans.
Both mutagenic and immunosuppressive, they also cause severe disruption to cell
cycles, causing widespread genetic damage.
However, of the major kinds of UV radiation, UVA and UVB are the only ones able to
penetrate the atmosphere, causing conditions such as premature aging, skin cancers
and eye damage.
While UVB is directly absorbed by DNA causing photolesions such as pyrimydine
dimers (CPD), UVA is absorbed by unknown chromophores, causes reactive oxygen
species and inflicts oxidative damage to DNA, proteins and lipids.
"The reason why UVA is so effective in causing cancer appears to be due to lower
levels of DNA repair in these basal keratinocytes and deeper penetrance of UVA
than UVB to these cells.
According to Prof Halliday, the basal layer of the human skin is especially susceptible
to UVA-induced genetic damage as it has low expressions of hOGG1, a major
enzyme which repairs oxidised guanine (8-oxoG), the main photodamage caused by
UVA.
The average penetration of UVA into the skin is also much deeper than that of UVB
at 320-400mm and 290-320nm respectively.
“We have recently discovered a novel hotspot mutation in the chromatin remodelling
gene, the exon-4 of BRM in human skin tumours, which is consistent with that being
caused by UVA," says Prof Halliday.
"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. This adds to the
accumulating evidence that the role of UVA in causing skin cancer in humans has
been underestimated."
In high erythemal doses of sunlight, for example during recreational activities, it is
UVB that suppresses immunity, not UVA. However in low dose sunlight, for example
during normal day activities, it is quite evident that UVA is causing the most damage
to the skin’s immune system.
The Royal College of Pathologists of Australasia
The RCPA is the leading organisation representing pathologists in Australasia. Its
mission is to train and support pathologists and to improve the use of pathology
testing to achieve better healthcare.
For more information on Pathology Update, visit
http://www.rcpa.edu.au/Continuing/PathologyUpdate/PathologyUpdate2012
END
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