Why elephants donâ€™t get cancer: extra tumor-suppressors
J Thoendell stashed this in Science
Since elephants have 100 times the number of cells that human beings do, they should have 100 times the risk of getting cancer. That's a lot of mistakes waiting to happen.
In reality, given their size and prodigious lifespans, elephants have one of the lowest cancer mortality rates in the animal kingdom: 4.8 percent, compared to a range of 11 to 25 percent for humans. How can this be?
Scientists at the Huntsman Cancer Institute, University of Utah School of Medicine, and Primary Childrenâ€™s Hospital helped figure out the answer,Â published ThursdayÂ in theÂ Journal of the American Medical Association. Another team, at the University of Chicago and their colleagues,Â posted a related paperÂ this week. As it turns out, elephants have developed some ingenious safeguards against developing cancer. Understanding their cellular protections might help us learn more about how to suppress cancer in humans.
There are countless ways that cell division can go wrong. Thatâ€™s whyâ€”as we learned from the winners of this weekâ€™sÂ Chemistry Nobel Prizeâ€”your cells come equipped with a host of repair enzymes whose sole purpose is to prevent or repair genetic mistakes. These cellular copy-editors proofread each strand of newly-divided DNA, identifying errors and repairing the faulty bits to ensure that your DNA stays fresh and clean and functional. In humans, just one of those enzymes can fix a thousand different kinds of errors. Not too shabby! Â
But elephants have one-upped us. For theÂ JAMAÂ study, researchers first compared cancer rates across the animal kingdom to find out that elephants were remarkably cancer-free given their size. (Other animals fared well, too. For comparison, rock hyraxes have a 1 percent cancer mortality rate, African wild dogs have an 8 percent rate, and lions have a 2 percent rate.) Then, they scoured the elephant genome to find out why.
The answer resided in a key tumor-suppressing protein called p53, known as the "guardian of the genome." Compared to humans, elephants had far more genes for this protein: 38 versions versus just two. The result was a superior genetic safety net for correcting errors and ensuring that damaged, tumor-prone cells get nipped in the bud.Â "The enormous mass, extended life-span, and reproductive advantage of older elephants would have selected for an efficient and fail-safe method for cancer suppression," the authors write.
What an astounding finding.
More about the master tumor suppressor that stops cancer in elephants:
Top Reddit comment:
They did not find a 'Master Tumor Suppressor.' They found multiple copies of ONE tumor suppressing gene - which is well known to exist in most animals. Having more copies of p53, the gene, means it's less likely to have them all be destroyed in the event of DNA damage - leading to lower cancer incidence.
Keep in mind that elephants still get cancer - in fact, it's the same rate as humans. The only thing interesting is that the rate should theoretically be much higher - given how many more cells are in an elephant.
The trade-off they're talking about? I wouldn't say there's necessarily a bad thing about the p53 gene. It's a gene that suppresses cancer - I doubt multiple instances of the gene would help or hinder genetic fitness in most animals. Most of us used to die before we got cancer. In elephants, however - who have many more cells, having more p53 IS a benefit. Without so many copies, cancer would be a serious restricting factor on how long they can survive.
TLDRÂ Title again exaggerates what we actually found.
ELI5Â Imagine cancer is a lake flowing into many dams. The dams prevent cancer from becoming an unstoppable torrent of destruction. Environmental damage (radiation, etc) destroys dams. We've got many dams, so that if one of these dams are destroyed the flow is still steady at the base. If they're all destroyed (from extreme conditions), then the water will flow forever.
Elephants live longer (in the eyes of natural selection). They also have more cells = more potential cancer cells. They have more dams, because more dams are likely to break due to their unique conditions.