DIFFERENTIAL REGULATION OF ACTIVATION-INDUCED TYROSINE PHOSPHORYLATION AND RECRUITMENT OF SLP-76 TO VAV BY DISTINCT ISOFORMS OF THE CD45 PROTEIN-TYROSINE-PHOSPHATASE

The CD45 family of transmembrane protein-tyrosine phosphatases plays a critical role in T cell activation signaling by regulating the tyrosi ne phosphorylation of protein-tyrosine kinases and their substrates. M ultiple alternatively spliced CD45 isoforms, differing only in their e xtracellular domains, are differentially expressed by subsets of T cel ls with distinct functional repertoires. However, the physiological fu nction of the various iso forms remains elusive, Using a novel panel o f Jurkat T cell clones that uniquely express either the smallest (CD45 (0)) or the largest (CD45(ABC)) isoform, we previously demonstrated CD 45 isoform-specific differences in interleukin-a secretion and tyrosin e phosphorylation of Vav. We now demonstrate differential activation-i nduced tyrosine phosphorylation of a 76-kDa Vav-associated protein (pp 76) by cells expressing distinct CD45 isoforms. The tyrosine phosphory lation of Vav and associated pp76 follow parallel kinetics. pp76 inter acts with the SH2 and SH3 domains of Vav. We have identified pp76 as S LP-76, a recently cloned Grb2-binding protein. After activation with a nti-CD3, CD45(ABC) transfectants demonstrate increased tyrosine phosph orylation and physical association of SLP-76 with Vav compared to tran sfectants expressing CD45(0). These results establish a novel physical link between Vav and SLP-76 that is differentially regulated by CD45 isoform expression.