PROTEIN-TYROSINE PHOSPHATASES IN SIGNALING

During the past few years, molecular cloning has established the exist ence of a structurally diverse family of intracellular and transmembra ne 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 co ntaining corkscrew PTPase and its vertebrate homolog SH-PTP2, and the mouse SH2-domain-containing hematopoietic cell PTPase. Whereas CD45, c orkscrew and SH-PTP2 positively regulate tyrosine phosphorylation, the hematopoietic cell PTPase negatively regulates or terminates signalin g. Recent data indicate that several transmembrane PTPases mediate cel l adhesion, suggesting that they effect adhesion-specific signaling ev ents.