| Previous studies by our laboratory showed that TCR/CD3 complex could mediate activation as well as activation-induced cell death of T lymphocytes. We previously constructed a chimera molecule (termed CD8s) by fusing the extracellular and transmembrane domains of human CD8α to the intracellular domain of mouse CD3ε and expressed in CD8~- Jurkat T-cells (shorten as JK). Four stable cell lines (shorten as TJK, T1JK, T2JK, and T3JK, respectively) expressing CD8ε, the mutants of Y170F, Y181F, and Y170F/Y181F in the CD3ε-ITAM (immune receptor tyrosine-based activation motifs) were established. Experiments showed that apoptosis could be induced only in the TJK cells with intact CD3s intracellular domain, but not in the T1JK, T2JK and T3JK cells with the mutant CD3s intracellular domain when stimulated with anti-CD8α monoclonal antibody, indicating that the two tyrosines in the CD3ε-ITAM of CD3ε molecule were required for apoptosis signaling of Jurkat T-lymphocytes.In this study we reported that apoptosis only occurred in TJK cells stimulated with precoated anti-CD8 monoclonal antibodies (200μg/ml) for 34 h, but not in JK, TJK and T3JK cells. During this process, caspase-3 was activated and cleaved into two small segments (20KD and 10KD) in TJK cells, indicating that caspase-3 involved in the apoptosis signal pathway. And P53 expression increased obviously in TJK cells, while low expression level of P53 was observed in JK and T3JK cells, indicating for the first time that p53 might play a key role in TCR/CD3-mediated T-lymphocyte apoptosis. We also found that Bid, a member of Bcl-2 family, was cleaved into the truncated form (tBid) with 17KD in TJK cells, suggesting that Bcl-2 family proteins and mitochondria be involved in apoptosis signal transduction in T lymphocytes mediated by TCR/CD3. These results indicated that the two tyrosines in CD3ε-ITAM play an important role in TCR/CD3-mediated signal transduction in T...
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