Apoptosis

Here’s how fast cell death can strike

Scientists have clocked the speed of a form of cellular suicide called apoptosis

BY 

TINA HESMAN SAEY 

3:17PM, AUGUST 9, 2018

DYING BY THE NUMBERS  In this electron micrograph, prostate tumor cells dying from a type of programmed cell death called apoptosis are shown (purple) alongside healthy cancer cells (yellow). Scientists are learning more about how apoptosis spreads through cells.

Scientists now know how long it takes for a cell to tell itself it’s time to die.

Signals triggering a type of cell suicide called apoptosis move through a cell like a wave, traveling at a rate of 30 micrometers per minute, Stanford University systems biologists Xianrui Cheng and James Ferrell Jr. report in the Aug. 10 Science.

These findings resolve a debate over whether these death signals spread by diffusion, with signaling molecules working their own way across a cell, or as self-regenerating trigger waves, like toppling dominoes. The apoptosis process starts with damage that causes the release of death signal chemicals. One example is cytochrome c leaking from damaged mitochondria, the cell’s power plant. Once cytochrome c concentrations get high enough, the chemicals signal proteins called caspases to go to work. Caspases trigger other proteins to poke holes in neighboring mitochondria, releasing more cytochrome c and moving the death wave across the cell. That chain reaction happens more quickly than diffusion can, Ferrell says. In an African clawed frog egg, a trigger wave takes about a half-hour to spread across the 1.2 millimeter cell, whereas diffusion would take five hours, he says.

Like forest fires, trigger waves will keep going as long as there is fuel to feed them — in this case, the death signal chemicals and proteins, Ferrell says. He predicts that many other biological signals may move as trigger waves.

“We biologists are just waking to this idea that trigger waves are a recurring theme in biological communication,” Ferrell says.

Discovering that apoptosis travels as trigger waves in cells may give scientists clues about how to persuade cancer cells to kill themselves (SN: 1/21/17, p. 10). Or researchers may learn how to prevent cells from dying in conditions such as Alzheimer’s disease or muscular dystrophy.