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Activators of protein kinase C down-regulate and phosphorylate the T3/T-cell antigen receptor complex of human T
Abstract:
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.
Insights
Phorbol esters rapidly decrease T3 antigen and T-cell receptor expression on human T lymphoblasts. This involves phosphorylation of T3 gamma and delta chains, suggesting protein kinase C down-regulates the T3/T-cell receptor complex.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- The T3/T-cell receptor (TCR) complex is crucial for T-cell activation.
- Regulation of T3/TCR surface expression impacts immune responses.
Purpose of the Study:
- To investigate the effect of phorbol esters on T3 antigen and TCR surface expression.
- To elucidate the molecular mechanisms underlying T3/TCR modulation.
Main Methods:
- Indirect immunofluorescence assays to assess surface antigen expression.
- 125I-labeled antibody binding experiments to determine antigen affinity.
- Biochemical analysis, including phosphoprotein analysis, of T3/TCR components.
Main Results:
- Phorbol 12,13-dibutyrate and 1-oleoyl-2-acetylglycerol caused a rapid, dose-dependent 50% reduction in T3 and TCR surface expression on T lymphoblasts and HPB-ALL cells.
- The decrease in expression was due to fewer antigen molecules, not altered affinity.
- Phorbol dibutyrate induced significant phosphorylation of the T3 gamma and delta chains, but not epsilon, or TCR alpha/beta subunits.
Conclusions:
- Protein kinase C activation leads to T3 gamma and delta chain phosphorylation.
- This phosphorylation event is implicated in the down-regulation of the T3/TCR complex surface expression.