Critical and Multiple Roles for the CD3ε Intracytoplasmic Tail in Double Negative to Double Positive Thymocyte Differentiation

Abstract

The preTCR is associated with signal-transducing CD3γ, δ, ε, and ζ polypeptides. It is generally agreed that CD3 chains play redundant roles in the receptor-mediated signal transduction. In the present study, we show that the intracytoplasmic (IC) domain of CD3ε is essential for early thymocyte maturation. We demonstrate that the IC domain-deleted CD3ε fails to restore the double negative (DN) to double positive (DP) thymocyte development in CD3ε-deficient mice. Additional experiments show that the membrane proximal basic amino acid rich sequence in the IC domain of CD3ε is sufficient for the DN to DP differentiation, whereas the proline rich sequence is required for efficient proliferation. This is probably due to impaired ligand independent recruitment of Nck to the proline rich sequence motif of CD3ε within the context of the preTCR. The data presented in this study elucidates mechanistic basis for the preTCR-induced proliferation of the DN thymocytes and have identified distinct roles for individual motifs of CD3ε in the preTCR-mediated differentiation and proliferation. These data provide the first genetic and phenotypic evidence for requirement of the IC domain of a CD3 chain in thymocyte development.