Protein tyrosine phosphatases in signaling.

During the past few years, molecular cloning has established the existence of a structurally diverse family of intracellular and transmembrane protein tyrosine phosphatases (PTPases). The importance of PTPases in signaling is best understood in three model systems: the mammalian transmembrane CD45 PTPase, the Drosophila Src homology (SH)2 domain containing corkscrew PTPase and its vertebrate homolog SH-PTP2, and the mouse SH2-domain-containing hematopoietic cell PTPase. Whereas CD45, corkscrew and SH-PTP2 positively regulate tyrosine phosphorylation, the hematopoietic cell PTPase negatively regulates or terminates signaling. Recent data indicate that several transmembrane PTPases mediate cell adhesion, suggesting that they effect adhesion-specific signaling events.