T cell receptor α-chain tail is required for protein kinase C-mediated down-regulation,but not for signaling

Antigen stimulation through the T cell receptor (TCR) induces phosphorylation of the associated CD3 γδσ- and ζ-chain cytoplasmic tails. These events lead to the induction of the intracellular signaling pathways with concomitant receptor down-regulation. The TCR is down-regulated from the cell surface by the activation of protein kinase C (PKC) and subsequent serine phosphorylation of the CD3 γ-chain. We report here that the TCR α-chain cytoplasmic tail is also necessary for PKC-mediated internalization of the TCR complex. The requirement for the TCR α-chain cytoplasmic tail is specific for internalization of the TCR complex, since down-regulation of CD4 is still intact in hybridoma cells expressing a tailless TCR α-chain. The absence of TCR internalization directly correlates with defective PKC-mediated phosphorylation of the CD3 γ-chain. Despite deficient PKC-mediated TCR down-regulation, the tailless αβ TCR still transduces antigenic signals resulting in the production of interleukin-2. Although the TCR tails are not obviously required for signal transduction, the TCR α-tail may serve as a targeting domain for PKC-mediated down-regulation of the TCR complex.