Comparative study on the effect of phosphorylated TCR zeta chain ITAM sequences on early activation events in Jurkat T cells.

One of the main dilemma in T cell receptor (TCR) signal transduction is whether the presence of multiple Immunoreceptor Tyrosine-based Activation Motifs (ITAMs) within the TCR signaling module serves for signal amplification or signal distribution. To contribute to answer this question, we analyzed the effect of synthetic oligopeptides representing the three bi-phosphorylated zeta chain-ITAMs on the early signaling events in permeabilized leukemia T cells. Our main observations were as follows: 1/Stimulation of the cells with the bi-phosphorylated membrane proximal and central ITAMs (zeta (1)y(p)y(p) and zeta (2)y(p)y(p), respectively) resulted in a strong phosphorylation of proteins with a similar pattern. In contrast, the membrane distal ITAM, zeta (3)y(p)y(p) had a reduced ability to promote tyrosine phosphorylation and failed to induce the phosphorylation of a number of proteins. 2/ The phospho-peptide induced tyrosine phosphorylation events were at least partially mediated by p56(lck) and Syk/ZAP70 protein tyrosine kinases as it was shown in p56(lck) and Syk/ZAP70 deficient Jurkat variants. 3/The patterns of the association of the adaptor protein, Grb2 with tyrosine phosphorylated proteins following cell stimulation with the bi-phosphorylated membrane proximal or the central ITAMs were similar, while the membrane distal ITAM was unable to induce any of these associations. Our data provide additional evidence that the three zetaITAMs differ in their capacity to induce tyrosine phosphorylation of intracellular proteins in permeabilized T cells, depending to their primary sequence. The first and second ITAM sequences of the zeta chain may have similar but not totally overlapping functions. This conclusion results from their similar but not identical abilities to induce tyrosine phosphorylation and association of Grb-2 with intracellular phosphoproteins. In contrast, the third ITAM (zeta3) may have distinct functions since this peptide fails to induce tyrosine phosphorylation of a number of proteins compared to the other two ITAMs, and it is unable to induce either new association or the increase in the amount of Grb-2 associated phosphoproteins.