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 tyrosine phosphorylation of protein-tyrosine kinases and their substrates. Multiple alternatively spliced CD45 isoforms, differing only in their extracellular domains, are differentially expressed by subsets of T cells with distinct functional repertoires. However, the physiological function of the various isoforms remains elusive. Using a novel panel of Jurkat T cell clones that uniquely express either the smallest (CD45(0)) or the largest (CD45(ABC)) isoform, we previously demonstrated CD45 isoform-specific differences in interleukin-2 secretion and tyrosine phosphorylation of Vav. We now demonstrate differential activation-induced tyrosine phosphorylation of a 76-kDa Vav-associated protein (pp76) by cells expressing distinct CD45 isoforms. The tyrosine phosphorylation of Vav and associated pp76 follow parallel kinetics. pp76 interacts with the SH2 and SH3 domains of Vav. We have identified pp76 as SLP-76, a recently cloned Grb2-binding protein. After activation with anti-CD3, CD45(ABC) transfectants demonstrate increased tyrosine phosphorylation and physical association of SLP-76 with Vav compared to transfectants expressing CD45(0). These results establish a novel physical link between Vav and SLP-76 that is differentially regulated by CD45 isoform expression.