In the June 30 issue of the journal Cell, the research team found that a natural "brake" exists in a cell to prevent it from undergoing apoptosis, or programmed cell death, and they say that optimal anti-cancer therapies should take a two-pronged approach to overriding this brake in order to force a tumor cell to die. Very few drugs do this now, they say.
cytochrome c (CC) from a cell's mitochondria, the organelle's energy storehouse. These molecules then bind to another protein called Apaf-1 in the cell cytoplasm, and together they form a scaffolding "death wheel" to activate enzymes called caspases that shred a cell apart.
But what they also believed is that a cell needs extra energy from ATP to undergo apoptosis, and that this extra energy was produced from the "pools" of free nucleotides that exist in the cell cytoplasm. Nucleotides are the primary structural chemical units that make up DNA, RNA and proteins, and they combine to play a variety of roles in the cell, such as formation of ATP.
However, through a series of biological and biochemical experiments, Tang and his research team found that adding ATP to a cancer cell could potentially impede apoptosis. They discovered that these nucleotide pools, in fact, act not to promote apoptosis through production of ATP, but to hinder it. They are "pro-survival factors" that prevent CC, when released from the mitochondria, from "seeing" Apaf-1 in the cytoplasm, Tang says.
"When we induced some cell stress and damage, the low levels of CC that came out from the mitochondria were ineffective because they are sequestered by an ocean of free nucleotides and ATP," he says. "No one had ever realized this kind of barrier existed to impede apoptosis."