Cyclosporin A inhibits T cell receptor-induced interleukin-2 synthesis of human T lymphocytes by selectively preventing a transmembrane signal transduction pathway leading to sustained activation of a protein kinase C isoenzyme, protein kinase C-beta.

Stimulation of human peripheral blood lymphocytes via T cell receptor/CD3 complex resulted in a bimodal activation of protein kinase(s) C (PKC). Within 10 min of stimulation PKC-alpha was translocated to, and thus activated in, the plasma membranes of human lymphocytes, followed by a fast dissociation of this isotype from the plasma membrane. This short term activation and translocation PKC-alpha proved to be cyclosporin A (CsA) insensitive. After 90 min of stimulation PKC-beta was translocated to and remained bound to the plasma membranes for up to 4 h. Preincubation of human lymphocytes with 200 ng/ml CsA specifically and completely abolished the sustained activation of PKC-beta. Neither the phorbol ester-induced direct activation of PKC nor the specific activity of the plasma membrane-bound enzyme was influenced by CsA, suggesting that a signal transduction pathway leading to sustained activation of PKC-beta was influenced by the immunosuppressive agent. In fact, CsA inhibited, in a concentration-dependent manner, the activation of lysophosphatid acyltransferase-catalyzed elevated incorporation of cis-polyunsaturated fatty acids into plasma membrane phospholipids. While interleukin-2 (IL-2) synthesis and cellular proliferation were completely inhibited by 200 ng/ml CsA in BMA 030- or BMA 031-stimulated cells, expression of high-affinity IL-2 receptors was not influenced by the immunosuppressive drug. These results suggest that synthesis and expression of high-affinity IL-2 receptors might be regulated by a signal-transducing pathway involving activation and translocation of PKC-alpha. Lysophosphatid acyltransferase-catalyzed incorporation of cis-polyunsaturated fatty acids might represent another mechanism of signal transduction implicated in the activation and translocation of PKC-beta, which is specifically inhibited by CsA. Neutralization of PKC-beta by introducing anti-PKC-beta antibodies prevented IL-2 synthesis and proliferation in stimulated human lymphocytes. The results suggest a possible link between activation of PKC-beta and regulation of IL-2 synthesis in activated human lymphocytes. Thus, inhibition of the activation and translocation of PKC-beta by CsA may result in inhibition of IL-2 gene expression in human lymphocytes.