Let’s consider a paradox of probabilities. If all cells have the same risk of becoming cancerous, then the likelihood of developing cancer is proportional to the number of cells in an animal. This argument generally holds true for the incidence of cancer and body size for individuals within a given species. However, when comparing across different animal species, there is no constant proportionality between body size and cancer rate. For example, elephants are 100 times larger than humans and live to a similar age, but they are actually three times less likely to die of cancer. Part of this paradox, “Peto’s Paradox,” was answered three years ago by researchers at the University of Chicago and the University of Utah. They found that elephants had 20 times more copies of the tumor suppressor genes than humans.
However, this month in Cell Reports, the University of Chicago team found a second and even more bizarre process in elephants: a gene that returns from the dead to kill cancerous cells. A pseudogene, colloquially called a “dead” gene, is a non-functional version of a normal gene that was mistakenly produced by a cell. The pseudogene “leukemia inhibitory factor 6” (LIF6) in elephants becomes functional when the cell senses damaged DNA. The animated “zombie gene” then produces proteins that quickly locate and destroy the cell’s mitochondria, the cell’s main energy source, resulting in the cell’s death.
While this discovery doesn’t completely answer how large-bodied animals can experience such longevity, it is certainly a step bringing us closer to understanding the original paradox. The researchers hope that by continuing to learn about how elephants live mostly cancer-free, they can translate these findings into cancer prevention strategies for humans as well.
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