Sun and skin – a dangerous combination
Box 3 | The molecular mechanisms of skin cancer
The body kills skin cells that have been exposed to too much ultraviolet radiation. Bringing about cell death is the function of a protein called p53. When an ultraviolet ray hits the DNA within a gene that codes for p53, basal cell and squamous cell cancer can result.
When present in a high enough concentration, the p53 protein causes a cell to ‘self-destruct’. This protein is normally produced in greater amounts after exposure to ultraviolet radiation. But after the radiation damages the gene for p53, the p53 protein that the gene makes is slightly altered and doesn’t function correctly. The defective version of the protein cannot make a damaged cell die.
The gene for p53 only needs a very small change for a defective protein to be produced. This tiny error will be perpetuated whenever the cell divides. Eventually, many cells with the incorrect gene will exist.
The cells with the incorrect gene won’t die when exposed to too much ultraviolet radiation. Instead they will reproduce, stimulated to do so because they find the normal cells around them dead. With each subsequent heavy exposure to too much sunlight, more normal cells will commit suicide, and the colony of cells with the damaged gene will multiply all the more. This is the beginning of a tumour.
So, by inducing cells carrying the normal p53 gene to kill themselves off, sunlight favours the proliferation of p53-mutated cells. Ultraviolet radiation is thus responsible for the two key steps in cancer generation: mutation and tumour promotion. The p53 gene and its protein are involved in the development of basal cell carcinoma and squamous cell carcinoma, but not melanoma. A similar gene, p16, and its protein are thought to be involved in the development of melanoma, but these studies are preliminary.
Boxes
Box 1. The ultraviolet family
Box 2. Types of skin cancer
Box 4. Diagnosing skin cancer
Box 5. Australian research
Box 6. Sunblocks and sunscreens
Related sites
p53: The guardian of the genome (Howard Hughes Medical Institute, USA)
DNA and genes (Back to basics, Australian Academy of Science)
Page updated March 2006.