The enzyme is known as PTPRO (for "protein tyrosine phosphatase receptor-type O"). When the gene responsible for producing PTPRO is silenced, as can happen in lung cancer, for example, the amount of the enzyme drops, allowing the cells to grow when they shouldn't.
The research, led by investigators at The Ohio State University Comprehensive Cancer Center Arthur G. James Cancer Hospital and Richard J. Solove Research Institute, may offer a new target for cancer therapy and may lead to new ways to diagnose some cancers and determine a patient's prognosis and response to treatment.
The findings were published in a recent issue of the Proceedings of the National Academy of Sciences.
"This appears to be the first report of an enzyme also serving as a tumor suppressor," says study leader Samson T. Jacob, William C. and Joan E. Davis Professor in cancer research and professor of molecular and cellular biochemistry and internal medicine. "It shouldn't come as a surprise, however, because of the nature of this enzyme."
PTPRO removes phosphate groups from the amino-acid tyrosine found in specific proteins. Some proteins become activated and some become inactivated when phosphate groups are removed. It is likely that the silencing of PTPRO alters the phosphate levels of some of these proteins and helps initiate processes that lead to cancer.
In this study, Jacob and his colleagues show that the PTPRO gene is silenced gradually by a process known as methylation. Methylation causes the addition of small chemical units known as methyl groups to a gene. As methyl units accumulate on a gene, the gene become less active and fewer copies of its protein are made.