ACTIVATORS OF PROTEIN KINASE-C DOWN-REGULATE AND PHOSPHORYLATE THE T3/T-CELL ANTIGEN RECEPTOR COMPLEX OF HUMAN LYMPHOCYTES-T

As judged by indirect immunofluorescence, phorbol 12,13-dibutyrate and 1-oleoyl-2-acetylglycerol induced a rapid, concentration-dependent decrease of about 50% in the surface expression of the T3 antigen on human T lymphoblasts, and of T3 and the T-cell antigen receptor on HPB-ALL cells. Direct binding experiments using 125I-labeled antibody indicated that the reduction in T3 expression corresponded to a decrease in the number of antigen molecules rather than a change in their affinity. Biochemical analyses revealed that phorbol dibutyrate induced a rapid, prominent phosphorylation of the T3 Mr 26,000 .gamma. chain and to a lesser extent of the Mr 21,000 .delta. chain. No phosphorylation of the T3 .epsilon. chain or of the .alpha. and .beta. subunits of the T-cell antigen receptor was detected. The data suggest that protein kinase C induces a phosphorylation of the T3 .gamma. and .delta. chains that may lead to the down-regulation of the T3/T-cell antigen receptor complex.