INVOLVEMENT OF PROTEIN-KINASE C-DELTA IN CD28-TRIGGERED CYTOTOXICITY MEDIATED BY A HUMAN LEUKEMIC-CELL LINE YT

Ligation of CD28 molecules expressed on the surface of human leukaemic natural killer-like YT cells triggers intracellular signals leading t o cytolysis of target cells expressing CD80 or CD86 molecules. Known i ntracellular events include tyrosine phosphorylation, activation of ph osphatidylinositol 3-kinase, and protein kinase C (PKC). In this study , we report that PKC-delta isoenzyme activity is required for CD28-tri ggered cytotoxicity mediated by YT cells and we also demonstrate that one of the primary targets of bryostatin 1, a modulator of PKC activit y, is PKC-delta. Treatment of YT cells with bryostatin 1 caused degrad ation of PKC-delta, but not other PKC isoenzymes, and completely block ed the cytolytic activity of YT cells. In addition, PKC-delta-specific antibody introduced into YT cells by electroporation inhibited partia lly the YT cell-mediated cytotoxicity of B-lymphoblastoid cell line JY . This effect was specific, since addition of anti-PKC-delta antibody- blocking peptide in combination with anti-PKC-delta antibody to YT cel ls for electroporation, neutralized the effect of this antibody. These results demonstrate that YT cell cytolytic activity is dependent on P KC-delta, which is selectively down-regulated by bryostatin 1.