Different cytoplasmic structure of the CD3ζ family dimer modulates the activation signal and function of T cells

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Abstract
The TCR complex transduces the antigen recognition signal through common activation motifs present in both CD3γδε chains and ζ, dimers within the complex. We have investigated functional roles of the cytoplasmic domain in ζ and CD3γδε for T cell activation in early and late responses by comparing the signaling capability of the TCR complexes containing mutant ζ lacking some or all motifs, or η chain, another ζ family molecule. The results with the mutant ζ, lacking all motifs indicated that CD3γδε can transduce signals to cause earty activation events and production of IL-2 upon antigen stimulation in the absence of ζ, motifs. However, any one of the ; motifs was required to respond to Thy-1 stimulation and this requirement cannot be replaced by other CD3 chains. Such ζ, motif-dependent responses were also observed in tyrosine phosphoryiation of a 90 kDa protein upon TCR stimulation. Furthermore, we found that the C-terminal unique region of the η chain exhibits inhibitory function in phosphoryiation and Ca2+ response upon TCR stimulation as well as IL-2 production upon Thy-1 stimulation. Collectively, the present analyses suggest that two types of signals are induced through the TCR-CD3 complex: (I) the common motif-dependent signals which are mediated equally through ζ, dimers and CD3γδε, and (II) ζ, specific motif-dependent signals. Differences in the cytoplasmic domain of ζ, family molecules may modulate the cooperation of these two signals, resulting in alteration of T cell functions.

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