The protein tyrosine phosphatase gamma (PTPG) gene appearsto be a tumor suppressor gene.
Researchers led by S. LaForgia of Temple University inPhiladelphia reported in the June issue of the Proceedings ofthe National Academy of Sciences that PTPG is located in aregion of human chromosome 3 that is frequently deleted inpatients with kidney or lung cancer. Three of five kidneycancer lines and five of 10 lung cancer lines lacked at leastone copy of PTPG.
PTPG encodes an enzyme that removes phosphate groups fromproteins. Since the addition of phosphate groups to proteins byprotein kinases appears to be the key to stimulating cellgrowth and since many kinases are oncogenes, scientistsbelieve that phosphatases act as the brakes to suppress cellgrowth. Loss of phosphatase activity could lead to cancer.
Three additional PNAS articles further characterize tumorsuppressor gene p53, which is associated with a wide varietyof cancers, including colon, breast, lung and brain cancer.
Researchers at the University of Maryland and Johns HopkinsOncology Center, both in Baltimore, reported that deletions ofp53 are also associated with cancer of the esophagus.
Duke University researchers showed that mutant forms of thep53 gene are overexpressed in breast cancer. The mutated p53proteins apparently bind to normal p53 proteins and inactivatethem.
Scientists at the Fred Hutchinson Cancer Research Center andthe University of Washington, both in Seattle, have identified aDNA sequence with which p53 interacts to enhance expression.Identification of this site in the muscle-specific creatinekinase gene may shed light on how p53 controls cell growth. Itis not yet known whether p53 binds directly to the DNA or ifp53 binds to other proteins that bind to the DNA.
-- Carol Talkington Verser, Ph.D. Special to BioWorld
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