THE SYK FAMILY OF PROTEIN-TYROSINE KINASES IN T-CELL ACTIVATION AND DEVELOPMENT

The processes of T-cell development and activation employ similar imma ture and mature receptors as well as similar signal transduction pathw ays to achieve different outcomes. Many signaling molecules are shared between the receptor signaling pathways, including two families of cy toplasmic protein tyrosine kinases, the Src family and the Syk family The two Syk family members expressed in T cells, Syk and ZAP-70, are s tructurally similar but are expressed at different times during thymic development and during T-cell activation. These two kinases, although they share many physical features, differ in terms oi biochemical act ivity and regulation. We discuss the overlapping and distinct characte ristics of Syk and ZAP-70 in T-cell signaling and the potential biolog ical importance of their differences.