Scientists at the University of Texas Southwestern Medical Center say they have identified a gene called NORAD that helps maintain the proper number of chromosomes in cells. They add that when the gene is inactivated, the number of chromosomes in a cell becomes unstable, a key feature of cancer cells.
Previously, genes that encode the recipe for making proteins have been implicated in maintaining the proper number of chromosomes in a cell. The NORAD gene, however, does not encode a protein. Instead, NORAD produces a long noncoding RNA (lncRNA), which was not previously known to be important in chromosome maintenance. The researchers published their study (“Noncoding RNA NORAD Regulates Genomic Stability by Sequestering PUMILIO Proteins”) in Cell.
“In the absence of the NORAD RNA, the number of chromosomes in cells becomes highly abnormal,” explains Joshua Mendell, M.D., Ph.D., professor of molecular biology at UT Southwestern and a Howard Hughes Medical Institute Investigator. “This is an entirely new function for a noncoding RNA and may have implications in cancer biology since genomic instability is a hallmark of tumor cells.”
Investigators began studying this particular molecule because the RNA kicks into action after DNA is damaged; they therefore termed it Noncoding RNA Activated by DNA Damage, or NORAD. The team unexpectedly found that NORAD plays a critical role in keeping the genome stable, and conducted experiments showing that when NORAD is absent, cells frequently lose or gain whole chromosomes.
Microscopic imaging revealed that cells lacking NORAD are unable to properly pass on chromosomes as they divide. NORAD controls chromosome segregation during cell division by regulating the activity of a family of PUMILIO proteins. In cells lacking NORAD, overactivity of PUMILIO leads to an unstable genome. Since most cancer cells also exhibit genomic instability, Dr. Mendell and his collaborators are now exploring whether abnormal function of NORAD or PUMILIO proteins contribute to human tumors. By investigating the roles of microRNAs and other noncoding RNAs, the Mendell lab is hoping to eventually develop new therapies that have the potential to treat cancer and other diseases.