Elephants have a much higher resistance to cancer than humans
Biologists have long been puzzled by elephants’ remarkable resistance to cancer. Their malignancy rate is about a quarter that of humans, even though they live almost as long as us and have far more cells where tumours could start.
Now researchers at the University of Utah have solved the mystery: elephants have many copies of a powerful tumour-suppressing gene called p53.
The study, published in the Journal of the American Medical Association, compared the genomes of captive African and Asian elephants (in Salt Lake City’s Hogle Zoo and Ringling Bros Centre for Elephant Conservation) with the human genome. The researchers found that most elephants carry 40 copies of p53, which causes cells with damaged DNA to self-destruct, while humans have just two copies.
Senior author Joshua Schiffman says the research has implications for human medicine: “Nature has already figured out how to prevent cancer. It’s up to us to learn how different animals tackle the problem so we can adapt those strategies to prevent cancer in people.”
Elephants have a normal lifespan of 50 to 75 years — and 100 times more cells than humans, each of which could potentially trigger a tumour if its DNA goes wrong. Yet analysis of a database of 644 elephant autopsies suggests that their lifetime cancer mortality is below 5 per cent, while humans have between 11 and 25 per cent cancer mortality.
To test whether all those p53 genes protect against cancer, the team irradiated white blood cells extracted from elephants and people, to damage their DNA. In response the elephant cells were more ready than their human counterparts to commit suicide (a process known as apoptosis).
“It’s as if the elephants said, ‘It’s so important that we don’t get cancer, we’re going to kill this cell and start over fresh’,” says Schiffman. “If you kill the damaged cell, it’s gone and it can’t turn into cancer. This may be a more effective approach to cancer prevention than trying to stop a mutated cell from dividing and not being able to completely repair itself.”
People suffering from Li-Fraumeni syndrome, who have only one active copy of p53, are almost certain to develop cancer at least once during their life. Their DNA-damaged cells are very reluctant to commit suicide.
“By all logical reasoning, elephants should be developing a tremendous amount of cancer and in fact should be extinct by now due to such a high risk for cancer,” concludes Schiffman. “We think that making more p53 is nature’s way of keeping this species alive.”
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