Tanning may protect against melanoma By Ben Wasserman - foodconsumer.org Mar 9, 2007 - 2:46:31 PM
 | 100 Questions and Answers about Melanoma & Other Skin Cancers by Edward F. McClay |
Tanning may protect against melanoma
There is a reason for the skin to become dark brown after it’s exposed to the sunshine. Tanning induced by ultraviolet rays plays a role in protecting against the development of skin cancer, namely melanoma, the fastest growing form of cancer in the world, according to a new study.
Early studies have linked exposure to sunshine rays to increased risk of skin cancer. But the new study suggests that when the skin is exposed to sun rays, a protein known as the “master watchman of the genome” is triggered to guard against cancer-causing DNA damage, which would otherwise lead to the development of skin cancer.
In addition, the study reported in the March 9 issue of the journal Cell by researchers from Dana-Farber Cancer Institute suggested that the protein, p53 also may play a role in people’s desire to be exposed to the sunshine, which can reduce one’s risk of melanoma by promoting tanning.
A scientist with foodconsumer.org said that the role of the sunshine or Ultraviolet rays may be more than just protecting against melanoma as early studies have associated sun exposure to reduced risk of a number of other cancers although some researchers attribute such a protective effect to the increased level of vitamin D.
“The number one risk factor for melanoma is an inability to tan; people who tan easily or have dark pigmentation are far less likely to develop the disease,” says the study’s senior author, David E. Fisher, MD, PhD, director of the Melanoma Program at Dana-Farber and a professor in pediatrics at Children's Hospital Boston.
“This study suggests that p53, one of the best-known tumor-suppressor proteins in our body, has a powerful role in protecting us against sun damage in the skin.”
Earlier last year, Fisher and his colleagues published a study revealing that ultraviolet (UV) radiation from the sun triggers the secretion of a hormone called α-MSH in skin cells, which attaches to nearby skin cells called melanocytes, promoting the production of a skin-darkening pigment called melanin.
But it has been unknown how production of α-MSH is increased although investigators knew it is created when another protein known as opiomelanocortin or POMC was split apart. They also knew sun rays increase POMC in cells. But what causes the increase in POMC remained unclear.
The answer might be protein P53, according to Fisher and colleagues. A gene analysis showed that PMOC proteins meshed well with p53, leading the researchers to speculate that there was a possibility that when p53 docks well, POMC production increases.
Studies of human and mouse keratinocytes showed that 6-hour exposure of the cells to UV radiation drastically increased both POMC and p53, leading to an increase in α-MSH by a factor of 30 times compared to the cells unexposed.
Further evidence supported the p53's role in tanning. When p53 was inserted into keratinocytes, POMC increased drastically. In contrast, mice without p53 in the cells did not experience POMC increase and the mice did not tan.
The p53 theory may also explain the common skin condition or the development of small dark spots, which is caused by stress or irritation of the skin, but not ultraviolet rays and is common among elderly people. The condition is not dangerous, but renders a negative cosmetic effect.
“Our research offers a potential explanation of how this condition – known as post-inflammatory hyper-pigmentation, or age spots – occurs,” Fisher says.
“We know that it occurs as a result of stress, and p53 is a classic ‘stress’ protein, going into action when cells experience stress-related DNA damage. What we’ve learned about p53 suggests that it may trigger the hyperpigmentation process.”
The researchers also said that the same process that causes PMOC to increase production of α-MSH, which leads to the protection against melanoma, may also causes the production of β-endorphin, which binds to the body's opiate receptor associated with perception of feelings of pleasure.
This theory explains why people often get additive to exposure to sunshine.
“Even as p53 is causing skin to tan during sunlight exposure, it may also affect neuronal circuits,” Fisher says.
“These proteins may provide an explicit link between the regulation of tanning and of mood. It raises the question of whether p53-mediated induction of β-endorphin is involved in sun-seeking behavior, which often increases skin cancer risk.”
| 100 Questions and Answers about Melanoma & Other Skin Cancers by Edward F. McClay |