Why Elephants beat the cancer odds
Theory doesn’t always play out in practice. Theoretically politicians are servants of the people. Theoretically children respect parents and parents deserve children’s respect. Theoretically you can’t make false claims in advertising. Theoretically the kind of heat generated by the sun would burn anything approaching it to a cinder and yet the space around the sun is not even singed. There are many instances where the theory meets a hiccup on the way to reality and a new study has come up with an answer to this hiccup that occurs in the case of elephants and cancer.
Theoretically, an animals cancer risk should increase with their size and lifespan; the bigger an animal, the more cells they have, which should increase the rate of cell division and susceptibility to gene mutations. However, despite being significantly bigger and having 100 times more cells than humans, the cancer mortality rate for elephants is only 4.8 per cent, compared with an 11-25 per cent cancer mortality rate in humans. Now researchers believe they have an answer as to why the theory in this instance goes astray.
Elephants possess at least 20 copies of a major tumour-suppressor gene called TP53, while healthy humans only have one copy.
For the new study, researchers have assessed information on disease and cause of death for 36 mammalian species, including African and Asian elephants. The genomes of all species were assessed and based on their data the researchers believe the reason for the elephants protection against cancer is that elephants possess at least 20 copies of a major tumour-suppressor gene called TP53, while healthy humans only have one copy, with two alleles (gene variants) inherited from each parent.
The TP53 gene plays a crucial role in dealing with damage to DNA by triggering a form of cell death in damaged cells called apoptosis via the p53 protein. The researchers found that compared to human white blood cells elephant white blood cells produced an increased apoptotic response after DNA was damaged.
This is all good news for elephants but what it means for humans is not necessarily clear. It certainly does remind us that relatively recent lifestyle factors like smoking and exposure to pollutants exceed the capacity of our cancer suppressing mechanisms. In the case of elephants it seems that having multiple copies of TP53 genes has evolved as a way of protecting against cancer. Perhaps the TP53 genes could be a focus for future investigation in humans but for now at least we have possibly solved the riddle of cancer and the elephants.
