Related Experiment Videos
Activation of protein kinase C down-regulates IFN-gamma receptors
Abstract:
Treatment of mouse EL-4 cells with intracellular activators of protein kinase C, namely 4-phorbol 12-myristate 13-acetate (PMA) and diacylglycerol, resulted in 90% reduction in cell surface interferon-gamma (IFN-gamma) receptors as judged by iodinated-IFN-gamma binding. This did not seem to be due to a decreased in the receptor affinity, since that of the remaining surface receptors appeared to be significantly increased as shown in Scatchard plot analysis. Kinetics experiments revealed that a PMA treatment as short as 15 min was sufficient to induce a decrease of 30% of IFN-gamma receptors, whereas the highest levels of down-regulation were observed after 60-90 min. Treatment of EL-4 cells with calcium ionophore, A23187, although ineffective by itself, dramatically increased the ability of suboptimal PMA concentrations to mediate IFN-gamma receptor down-regulation. Finally, specificity studies revealed that PMA is particularly effective in decreasing the binding of IFN-gamma to T-lymphocytes. Altogether these results suggest a possible involvement of protein kinase C in the regulation of IFN-gamma receptor expression.
Insights
Protein kinase C activators like PMA significantly reduce interferon-gamma (IFN-gamma) receptors on T-lymphocytes. This down-regulation, mediated by protein kinase C, affects IFN-gamma receptor expression and binding.
Area of Science:
- Immunology
- Cell Biology
- Molecular Signaling
Background:
- Interferon-gamma (IFN-gamma) is a crucial cytokine in immune responses.
- IFN-gamma receptors on cell surfaces mediate the cytokine's biological effects.
- Understanding the regulation of IFN-gamma receptors is key to modulating immune cell function.
Purpose of the Study:
- To investigate the role of protein kinase C (PKC) in regulating cell surface IFN-gamma receptors.
- To determine the effect of PKC activators on IFN-gamma receptor expression and binding affinity.
Main Methods:
- Treatment of mouse EL-4 T-lymphoma cells with PKC activators (PMA, diacylglycerol) and calcium ionophore (A23187).
- Quantification of cell surface IFN-gamma receptors using iodinated-IFN-gamma binding assays.
- Scatchard plot analysis to assess receptor affinity.
- Kinetic experiments to determine the time course of receptor down-regulation.
Main Results:
- PKC activators (PMA) induced a significant reduction (up to 90%) in cell surface IFN-gamma receptors.
- Receptor affinity was not decreased; Scatchard analysis suggested an increase in affinity for remaining receptors.
- Down-regulation was rapid (30% decrease in 15 min) and maximal by 60-90 min.
- Calcium ionophore potentiated PMA-induced down-regulation.
- PMA specifically reduced IFN-gamma binding to T-lymphocytes.
Conclusions:
- Protein kinase C activation plays a significant role in the down-regulation of IFN-gamma receptors.
- PKC-mediated regulation affects IFN-gamma receptor expression, not affinity.
- These findings suggest a novel mechanism for modulating T-lymphocyte responses to IFN-gamma.