Posts Tagged ‘elephant’

by Laura Elizabeth Mason

Elephants have developed a way to resist cancer, by resurrecting a ‘zombie’ gene known as leukemia inhibitory factor 6 (LIF6). Activated LIF6 responds to damaged DNA and efficiently kills cells that are destined to become cancer cells.

Cancer is a complex genetic disease that is caused by specific changes to the genes in one cell or group of cells. These genetic alterations cause the cell to divide uncontrollably. If all mammalian cells were equally susceptible to the genetic mutations that cause cancer, then theoretically the risk of developing cancer should be greater in larger animals – due to them having more cells and a longer life-span. However, previous studies have demonstrated that elephants have a lower-than-expected rate of cancer, compared to other mammals.

“Elephants get cancer far less than we’d expect based on their size, so we want to understand the genetic basis for this cancer resistance,” said senior author Vincent Lynch from the University of Chicago, in a recent press release.

“We found that elephants and their relatives have many non-functioning copies of the LIF gene, but that elephants themselves evolved a way to turn one of these copies, LIF6, back on.”

p53 wakes up LIF6

The TP53 gene is found in all animals, it codes for the protein p53, a tumor suppressor, that stops cells with damaged DNA from dividing. Unlike humans, who only have one copy of TP53, elephants have 20. An increased number of TP53 genes enhances the DNA-damage response, providing elephants with a distinct advantage – they are able to either repair the damaged cells or ‘kill off’ irreparable cells more efficiently.

In their latest study the researchers found that in response to DNA damage, LIF6 is transcriptionally upregulated by p53. LIF6 codes for a protein that rapidly translocates to the cell’s mitochondria. Once it reaches the mitochondrion it causes the outer mitochondrial membrane pore to open – leading to mitochondrial dysfunction, causing the cell to die.

The researchers plan to conduct additional studies to further define the molecular mechanisms by which LIF6 induces cell death.

The team hope their findings will aid efforts to therapeutically target cancer. “Maybe we can find ways of developing drugs that mimic the behaviors of the elephant’s LIF6 or of getting cancerous cells to turn on their existing zombie copies of the LIF gene,” concluded Lynch.

Reference
Vazquez et al. A zombie LIF gene in elephants is up-regulated by TP53 to induce apoptosis in response to DNA damage. Cell Reports. 2018. http://dx.doi.org/10.1016/j.celrep.2018.07.042

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Elephants’ secret to their low rates of cancer might be explained in part by a so-called zombie gene—one that was revived during evolution from a defunct duplicate of another gene. In the face of DNA damage, elephant cells fire up the activity of the zombie gene LIF6 to kill cells, thereby destroying any cancer-causing genetic defects, researchers reported in Cell Reports.

“From an evolutionary biology perspective, it’s completely fascinating,” Joshua Schiffman, a pediatric oncologist at the University of Utah who was not involved in the work, tells National Geographic.

The better-known LIF gene has a number of functions in mammals, including as an extracellular cytokine. In elephants, LIF is duplicated numerous times as pseudogenes, which don’t have the proper sequence to produce functioning transcripts. For the latest study, the researchers wanted to see whether the duplications might have anything to do with elephant cells’ unusual response to DNA damage: indiscriminant destruction.

The team found that one of the pseudogenes, LIF6, evolved after LIF was duplicated in a way that produces a transcript, and that the gene product is controlled by TP53, a tumor suppressor. When the researchers overexpressed LIF6 in elephant cells, the cells underwent apoptosis. The same thing happened with they introduced the gene to Chinese hamster ovary cells, indicating that LIF6 has a role in elephants’ defense against DNA damage.

More work needs to be done to determine whether the LIF6 revival is responsible for elephants’ low cancer rates. There are likely to be other contributors, says coauthor Vincent Lynch, an evolutionary biologist at the University of Chicago, in an interview with The New York Times. “There are lots of stories like LIF6 in the elephant genome, and I want to know them all.”

https://www.the-scientist.com/news-opinion/elephants-revived-a-zombie-gene-that-perhaps-fends-off-cancer-64643