A study undertaken by biologists at the University of California, Berkeley, has found that damage to a cell's DNA sets off a chain reaction that leads to the increased expression of a marker recognized by the body's immune system.
The new findings, published in an advanced online issue of Nature, shed light on a long-standing question of how the natural killer (NK) cells - which are able to attack tumors - can differentiate cells that are cancerous from those that are healthy.
"Our study is the first to show that there are mechanisms in place for the immune system to identify cancer cells," said Stephan Gasser, UC Berkeley post-doctoral researcher in molecular and cell biology and lead author of the paper. "It reveals how natural killer cells distinguish something they're supposed to get rid of versus something they're supposed to keep."
The researchers explain that the immune system is designed to detect and attack foreign invaders, but cancer cells present a special challenge because they are still the bodies own cells, albeit ones in which the genes have gone awry.
"Many scientists question the importance of the immune system in stemming the development of cancer," said David H. Raulet, professor of immunology at UC Berkeley's Department of Molecular and Cell Biology and senior investigator of the study. "Our research adds to recent evidence that the immune system plays a significant role."
The researchers put cultures of ovarian epithelial cells and fibroblasts from mice through a battery of abuse, including heat shock, pH changes, oxygen deprivation and starvation. However, the only type of stress that set off the sequence of events associated with impairment of a cell's genetic material -- the DNA damage pathway -- was exposure to radiation and chemotherapy drugs.
They found that cells in which the DNA damage pathway was triggered were the ones that exhibited an increase in the expression of special proteins on the cell surface. These "ligands" on the membrane are specific to the NKG2D receptor on natural killer cells and are used to flag damaged cells for destruction. There are several types of NKG2D ligands, but the best known is called Rae1.