Article: article from journal or magazin.
Basal and antigen-induced exposure of the proline-rich sequence in CD3ε.
Journal of Immunology
The CD3ε cytoplasmic tail contains a conserved proline-rich sequence (PRS) that influences TCR-CD3 expression and signaling. Although the PRS can bind the SH3.1 domain of the cytosolic adapter Nck, whether the PRS is constitutively available for Nck binding or instead represents a cryptic motif that is exposed via conformational change upon TCR-CD3 engagement (CD3Δc) is currently unresolved. Furthermore, the extent to which a cis-acting CD3ε basic amino acid-rich stretch (BRS), with its unique phosphoinositide-binding capability, might impact PRS accessibility is not clear. In this study, we found that freshly harvested primary thymocytes expressed low to moderate basal levels of Nck-accessible PRS ("open-CD3"), although most TCR-CD3 complexes were inaccessible to Nck ("closed-CD3"). Ag presentation in vivo induced open-CD3, accounting for half of the basal level found in thymocytes from MHC(+) mice. Additional stimulation with either anti-CD3 Abs or peptide-MHC ligands further elevated open-CD3 above basal levels, consistent with a model wherein antigenic engagement induces maximum PRS exposure. We also found that the open-CD3 conformation induced by APCs outlasted the time of ligand occupancy, marking receptors that had been engaged. Finally, CD3ε BRS-phosphoinositide interactions played no role in either adoption of the initial closed-CD3 conformation or induction of open-CD3 by Ab stimulation. Thus, a basal level of open-CD3 is succeeded by a higher, induced level upon TCR-CD3 engagement, involving CD3Δc and prolonged accessibility of the CD3ε PRS to Nck.
Amino Acid Motifs/immunology, Animals, Antigen-Presenting Cells/immunology, Antigen-Presenting Cells/metabolism, Antigens, CD3/genetics, Antigens, CD3/immunology, Cell Line, Tumor, Epitopes, T-Lymphocyte/physiology, Hybridomas, Mice, Mice, Inbred C57BL, Mice, Knockout, Mice, Transgenic, Peptide Fragments/genetics, Peptide Fragments/immunology, Proline/immunology, Proline/metabolism, Receptor-CD3 Complex, Antigen, T-Cell/genetics, Receptor-CD3 Complex, Antigen, T-Cell/immunology, T-Lymphocytes/immunology, T-Lymphocytes/metabolism
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