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As we enter the darkest days of the year, we may start to long for the warmth of the sun’s rays. But it’s important to remember how damaging UV radiation can be. In particular, exposure to the sun is well known to increase the risk of skin cancer, although researchers have not had a full understanding of exactly how UV rays cause cancer.
A new study from a team of researchers in New York and California helps to explain the biological reasons behind how the sun’s rays can lead to melanoma.
Melanoma starts in specialized cells that produce skin pigment
There are a few different forms of skin cancer, but melanoma is the deadliest type. If undetected, it can become aggressive and spread around the body. An estimated 7,200 Canadians will be diagnosed with melanoma this year.
The skin has several different types of cells. One type, called a melanocyte, produces melanin, the pigment that gives skin its colour. Melanocytes produce extra melanin when they are exposed to the sun, giving skin the tanned look, and they can also give rise to melanoma.
Melanocytes, like many cells, arise from stem cells, unspecialized cells that can develop into many different types of cells depending on the cues they get from the body. Stem cells are important for replacing cells that die naturally, but they can also be the cells that transform into cancer cells. In this study, the researchers wanted to know whether melanocyte stem cells could develop into melanoma, and if so, how.
UV radiation triggers cancer-causing immune response
When the researchers studied melanocyte stem cells, they found that these cells could accumulate genetic changes that lead to cancer, but could stay in a dormant state. They needed an external prompt to make the leap into becoming cancer cells. UV radiation acted as the trigger that caused the altered stem cells to start growing into a melanoma tumour.
The researchers also studied the processes involved in this switch. When they triggered an immune system response by applying a chemical to the skin, the melanocyte stem cells became cancerous. Since UV radiation triggers the same type of immune response on the skin, this may be the process by which UV rays lead to cancer.
The researchers found that a gene called Hmga2 may play a role in melanoma development. When melanocyte stem cells had the Hmga2 gene, the cells became cancerous after UV exposure, but melanocyte stem cells without the gene did not develop melanoma, even if they had other cancer-causing genetic changes. This result needs to be studied in more detail, but it provides a potential genetic target for preventing melanoma.
Blocking UV radiation is critical to preventing melanoma
Melanocyte stem cells with genetic changes linked to cancer still need the external prompt of UV radiation to start growing a tumour. Knowing how important UV rays are in melanoma development illustrates that nobody is safe from UV exposure. Practicing sun safety such as checking the daily UV index, covering up, and wearing sunscreen is critical to preventing skin cancer.
Researchers can also look to the biological processes involved in cells’ transformation to cancer, such as the immune response and the role of the Hmga2 gene in melanocyte stem cells, for more ideas of new ways to prevent this disease.
Eileen Hoftyzer, BSc, and Carolyn Goard, PhD