DIFFERENTIAL CYTOSOLIC TAIL DEPENDENCE AND INTRACELLULAR FATE OF T-CELL RECEPTORS INTERNALIZED UPON ACTIVATION WITH SUPERANTIGEN OR PHORBOLESTER

Activation of T lymphocytes by T-cell receptor (TCR) ligands such as p eptide/MHC complexes, superantigens or anti-TCR mAbs, or by pharmacolo gical activators of protein kinase C such as phorbol esters, results i n the internalization and cell surface downregulation of TCRs. We inve stigated the role of internalization motifs located in the cytosolic r egion of CD3 gamma in the internalization of TCR complexes induced by enterotoxin superantigens, anti-TCR mAbs or phorbol esters. To this en d, a series of CDS gamma mutants were expressed in a CDS gamma-deficie nt variant of the human T-cell line Jurkat. We found that serine(126) and the di-leucine motif (Leu(131)-Leu(132)) are required for phorbol- ester-induced TCR downregulation, but they are not necessary for enter otoxin superantigen or antibody-induced TCR downregulation. Moreover, the tyrosine-based motifs (residues 138 to 141 and 149 to 152) are not required either for phorbol ester or for superantigen or antibody-ind uced TCR downregulation. Confocal microscopy analysis reveals that TCR complexes accumulate in an early endocytic/recycling compartment upon activation of cells with phorbol esters, whereas TCRs internalized up on activation with superantigen or anti-TCR mAbs are routed to lysosom es. Consistent with this intracellular localization, TCRs internalized in response to phorbol ester are not degraded and can be reexpressed on the cell surface, in contrast, TCRs internalized upon superantigen activation are degraded.