HOUSTON - ATM, a protein that reacts to DNA damage by ordering repairs or the suicide of the defective cell, plays a similar, previously unknown role in response to oxidative damage outside of the nucleus, researchers report this week in the online version of the Proceedings of the National Academy of Sciences.
"This tumor-suppressor that works in the nucleus to prevent replication of defective cells also has a second life out in the cytoplasm, which was totally unexpected," said senior author Cheryl Walker, Ph.D., professor in The University of Texas M. D. Anderson Cancer Center Department of Carcinogenesis.
"ATM recognizes damage caused by reactive oxygen species (ROS) and tells the cell to stop growing by suppressing the protein-synthesizing pathway mTORC1 or orders the cell to consume itself, a process called autophagy," Walker said. This pathway parallels the protein's role of damage recognition and response in the nucleus.
Reactive oxygen species are a byproduct of cellular metabolism and in small amounts play a role in cell signaling. Their ability to react with other molecules makes them toxic, and they are kept in check by antioxidant enzymes. When that natural balance is disrupted, elevated levels of these volatile molecules damage proteins, lipids and DNA, Walker said.
The authors note that elevated ROS has been linked to more than 150 diseases, including diabetes, cancer, neurodegenerative diseases and atherosclerosis.
In its previously known role, ATM (short for Ataxia-Telangiectasia Mutated) senses DNA damage, orders the cell to repair the damage and halts cell division pending repair via the tumor suppressor p53. If repair is not possible, ATM sets off apoptosis - programmed cell death. ATM is commonly mutated in cancer.
The added protective role discovered by the researchers also points to a potential way to activate the tumor-suppressor without damaging DNA.
|Contact: Scott Merville|
University of Texas M. D. Anderson Cancer Center