REGULATION OF TCR SIGNAL-TRANSDUCTION IN MURINE THYMOCYTES BY MULTIPLE TCR ZETA-CHAIN SIGNALING MOTIFS

The alpha beta TCR is a multimeric protein complex comprising ligand-b inding and signal-transducing subunits. The signal transduction proces ses are mediated by the immunoreceptor tyrosine-based activation motif s (ITAMs), and up to 10 ITAMs are present within a single TCR complex, This multiplicity may allow for signal amplification and/or the forma tion of qualitatively distinct intracellular signals, Notably, the TCR -zeta subunit contains three ITAMs, and exists as a disulfide-linked h omodimer in the TCR complex, In normal murine thymocytes and periphera l T cells, a proportion of TCR-zeta molecules is constitutively tyrosi ne phosphorylated and associated with the ZAP-70 protein tyrosine kina se, We examined the contribution of the different TCR-zeta ITAMs in re gulating the constitutive phosphorylation of the TCR-zeta subunit in t hymocytes by analyzing TCR-zeta-deficient mice that had been reconstit uted with either full-length or single ITAM-containing TCR-zeta subuni ts, We report in this work that in the absence of a full-length TCR-ze ta subunit, there is no apparent constitutive phosphorylation of the r emaining TCR/CD3 ITAMs. Following TCR ligation, all of the CD3 ITAMs b ecome inducibly phosphorylated and associate with the ZAP-70 protein t yrosine kinase, Regardless of the number of TCR-zeta ITAMs present in the TCR complex, we report that a number of molecules involved in down stream signaling events, such as ZAP-70, SLP-76, and pp36, are all ind ucibly tyrosine phosphorylated following TCR ligation, These results s upport the notion that the different TCR ITAMs function in a quantitat ive rather than qualitative manner.