Complex Ca2+ flux inhibition as primary mechanism of staurosporine‐induced impairment of T cell activation

Abstract

The inhibitory effect of the highly effective drug staurosporine on the early activation signal Ca²⁺ flux was investigated via multiparameter flow cytometry in human peripheral blood T lymphocytes. Staurosporine has been reported to be a specific inhibitor of protein kinase C. However, we show that it inhibits the Ca²⁺ influx in anti‐CD3 and phytohemagglutinin‐stimulated human CD4⁺ and CD8⁺ lymphocytes at concentrations between 1.0 and 10.0 ng/ml. Staurosporine decreases the number of Ca²⁺‐positive CD4⁺ and CD8⁺ lymphocytes as well as the Ca²⁺ influx per cell; the drug also delays the time of the maximum response to polyclonal stimulation. In addition, we demonstrate that staurosporine affects the primary Ca²⁺ response via inhibition of the release of the membrane‐bound Ca²⁺ from the endoplasmic reticulum in CD4⁺ and CD8⁺ lymphocytes. Binding studies of the anti‐CD3 antibody to T lymphocytes indicate normal binding capacities in the presence of staurosporine. With respect to the classical scheme of T cell activation via phospholipase C, our data suggest that staurosporine may inhibit T cell activation primarily by its effect on the early Ca²⁺ flux signal.