"Ginger" mice are found to be more susceptible to melanoma even without any exposure to ultraviolet radiation.
Fair-skinned, red-haired people know — sometimes through painful experience — that they are more susceptible to the damaging effects of the Sun’s ultraviolet (UV) rays, including sunburn, skin ageing and a higher risk of skin cancers. But a study suggests that in mice, the pigment responsible for reddish coloring has a role in the development of melanoma.
“There is something about the redhead genetic background that is behaving in a carcinogenic fashion, independent of UV,” says David Fisher, a cancer biologist at Massachusetts General Hospital in Boston, who led the study. “It means that shielding from UV would not be enough.”
Compared to people with darker skin, those with fair, freckly skin and red hair produce a different form of the pigment melanin. This red–yellow form, called pheomelanin, is less effective at protecting the skin from UV damage than the darker form, eumelanin. The difference is caused by a mutation in the gene MC1R.
But for a number of years there have been hints that UV exposure alone might not account entirely for the risk of melanoma in redheads. Fisher and his team wanted to investigate the molecular backdrop for this increased risk. The researchers looked at how melanomas develop in mouse models of olive-skinned, ginger and albino colouring. The last group had the same genetic background as the dark-skinned mice but lacked the enzyme needed to synthesize melanin. The researchers also tweaked each group’s genes to be more susceptible to developing benign moles, which Fisher says is a probable first step in the development of melanoma.
The researchers planned to expose the mice to UV light and monitor differences in melanoma development. But before they got to that part of the experiment, about half the ginger mice had developed melanomas. Fisher says that he and his team were shocked. “The first thing we needed to do was bring a UV meter into the animal room to be sure there wasn’t some inadvertent UV being radiated out of the light bulbs or something,” he says. “And it turned out there was not.” The result suggested that the pigment itself was a cause of melanoma. The researchers suggest that the increased melanoma risk could have something to do with the pigment-production process, or a by-product of it, in melanin-containing cells called melanocytes.
Via Dr. Stefan Gruenwald