Phosphotyrosyl protein phosphatases: potential regulators of cell proliferation and differentiation.

Tyrosyl phosphorylated proteins have been associated with the regulation of cellular activities, including proliferation, differentiation, and transformation. The overall cellular levels of tyrosyl phosphorylated proteins are regulated by the balance of the activities of both tyrosyl protein kinases and phosphotyrosyl protein phosphatases. Until recently, it was generally assumed that the kinase reaction was the key regulatory process for determining the level of tyrosyl phosphorylated proteins and that the dephosphorylation reaction was an unregulated event. However, recent evidence strongly suggest a regulatory role for phosphotyrosyl protein phosphatases for determination of the overall level of tyrosyl phosphorylated proteins. This review focuses on the discussion of the properties, the regulation, and the primary structure of phosphotyrosyl protein phosphatases. Evidence that supports an important role for phosphotyrosyl protein phosphatases on cell proliferation and differentiation also is presented.