Sunless Suntan Proves Possible



Sun seekers and tanning-bed junkies take note: Researchers have induced honest-to-goodness suntans in mice without exposing them to ultraviolet (UV) rays. Instead, they rubbed a lotion into the critters' skin that activated their tanning machinery, which then protected the mice from UV's cancer-causing effects. The animals carried a mutation making them fair skinned and unable to tan otherwise, like human redheads, suggesting that a similar tanning trick might help even the pastiest of us bask in the sun without worry.

True redheads are famous for having fair skin that tends to burn, not tan. These individuals often have an abnormality in pigment-producing skin cells called melanocytes. Normally, when ultraviolet radiation strikes the skin, a receptor protein on the surface of melanocytes known as MC1R kicks into gear, causing the cells to produce the pigment melanin. In many redheads, MC1R has an altered shape that hampers its response to the usual biochemical signals initiated by UV light. Researchers wondered, though, could the melanin machinery be turned on in these individuals anyway?

In mice at least, the answer is yes. A team studied rodents carrying a mutated Mc1r gene and bred to have melanocytes in their skin, as opposed to their fur. As might be expected, under increasingly strong UV irradiation, the animals skipped the tanning stage and went directly to burn. Then the researchers applied the plant compound forskolin, which is known to promote cellular production of a molecule called cyclic AMP, a chemical that the normal MC1R also targets. When anointed daily with forskolin, the mice developed a rich caramel hue, report David Fisher of the Dana-Farber Cancer Institute and colleagues in the September 21 Nature. "After a couple of weeks they were virtually black," Fisher says. These bronzed rodents were nearly as resistant to UV-induced sunburn as naturally black-colored mice, and even animals especially prone to skin cancer saw fewer and slower-developing tumors when slathered with forskolin. Fisher says his group is working to identify a compound that would offer similar protection to people and is safe to apply.

"It's a very elegant study," says skin cancer researcher Meenhard Herlyn of the University of Pennsylvania. "We can now test new compounds to induce pigmentation, and that has major ramifications for the future prevention of skin cancer. It makes me quite optimistic." Others note the value added by studying the right mouse. "This is an incredibly good example of how mouse models can be used to gain insight into human disease or prevention," says Glenn Merlino of the National Cancer Institute.

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