CYCLOSPORINE-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 (P KC). Within 10 min of stimulation PKC-alpha was translocated to, and t hus 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 cyclosp orin A (CsA) insensitive. After 90 min of stimulation PKC-beta was tra nslocated to and remained bound to the plasma membranes for up to 4 h. Preincubation of human lymphocytes with 200 ng/ml CsA specifically an d completely abolished the sustained activation of PKC-beta. Neither t he phorbol ester-induced direct activation of PKC nor the specific act ivity of the plasma membrane-bound enzyme was influenced by CsA, sugge sting that a signal transduction pathway leading to sustained activati on 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 ci s-polyunsaturated fatty acids into plasma membrane phospholipids. Whil e interleukin-2 (IL-2) synthesis and cellular proliferation were compl etely inhibited by 200 ng/ml CsA in BMA 030- or BMA 031-stimulated cel ls, expression of high-affinity IL-2 receptors was not influenced by t he immunosuppressive drug. These results suggest that synthesis and ex pression of high-affinity IL-2 receptors might be regulated by a signa l-transducing pathway involving activation and translocation of PKC-al pha. Lysophosphatid acyltransferase-catalyzed incorporation of cis-pol yunsaturated fatty acids might represent another mechanism of signal t ransduction implicated in the activation and translocation of PKC-beta , which is specifically inhibited by CsA. Neutralization of PKC-beta b y introducing anti-PKC-beta antibodies prevented IL-2 synthesis and pr oliferation in stimulated human lymphocytes. The results suggest a pos sible link between activation of PKC-beta and regulation of IL-2 synth esis in activated human lymphocytes. Thus, inhibition of the activatio n and translocation of PKC-beta by CsA may result in inhibition of IL- 2 gene expression in human lymphocytes.