THE PROTEIN INTERACTIONS OF THE IMMUNOGLOBULIN RECEPTOR FAMILY TYROSINE-BASED ACTIVATION MOTIFS PRESENT IN THE T-CELL RECEPTOR ZETA-SUBUNITAND THE CD3 GAMMA-CHAIN, DELTA-CHAIN AND EPSILON-CHAIN

Immunoglobulin family tyrosine-based activation motifs (ITAM), which d efine the conserved signaling sequence EX(2)YX(2)L/IX(7)YX(2)L/I, coup le the T cell antigen receptor (TCR) to cellular proteins including pr otein tyrosine kinases (PTK) and adapter molecules. The TCR is a multi chain complex with four invariant chains CD3 gamma, delta and epsilon that each contain a single ITAM and the TCR zeta chain that contains t hree ITAM. The present study explores the protein interactions of the doubly phosphorylated CD3 gamma, delta, epsilon ITAM to determine whet her they have common or unique biochemical properties. The data show t hat the doubly phosphorylated ITAM all bind the PTK ZAP-70, but the IT AM also variably bind the PTK p59fyn and the adapters She. Grb-2 and t he p85 regulatory subunit of phosphoinositol 3' kinase. The CD3 and ze ta ITAM display a hierarchy of ZAP-70 binding: zeta 1 = gamma = delta > zeta 3 > zeta 2 = epsilon. Shc, Grb-2 and p85 could bind the zeta IT AM and the CD3 gamma and delta ITAM, but not the CD3 epsilon ITAM. The re were also subtle differences in the hierarchy of reactivity of thes e adapters for the CD3 gamma,delta and zeta ITAM that show that the ze ta, CD3 gamma, delta and epsilon ITAM have different binding propertie s. The present study thus shows that the different ITAM of the TCR/CD3 complex can interact with different cytosolic effectors, indicating t hat differential ITAM phosphorylation during T cell activation could b e a mechanism to generate signaling diversity by the TCR complex.