FC RECEPTOR STIMULATION OF PHOSPHATIDYLINOSITOL 3-KINASE IN NATURAL-KILLER-CELLS IS ASSOCIATED WITH PROTEIN-KINASE C-INDEPENDENT GRANULE RELEASE AND CELL-MEDIATED CYTOTOXICITY

Although diverse signaling events are initiated by stimulation of mult ichain immune recognition receptors on lymphocytes, it remains unclear as to which specific signal transduction pathways are functionally li nked to granule exocytosis and cellular cytotoxicity. In the case of n atural killer (NK) cells, it has been presumed that the rapid activati on of protein kinase C (PKC) enables them to mediate antibody-dependen t cellular cytotoxicity (ADCC) and ''natural'' cytotoxicity toward tum or cells. However, using cloned human NK cells, we determined here tha t Fc receptor stimulation triggers granule release and ADCC through a PKC-independent pathway. Specifically, pretreatment of NK cells with t he selective PKC inhibitor, GF109203X (using concentrations that fully blocked phorbol myristate acetate/ionomycin-induced secretion) had no effect on FcR-initiated granule release or ADCC. In contrast, FcR lig ation led to the rapid activation of phosphatidylinositol 3-kinase (PI 3-kinase), and inhibition of this enzyme with the selective inhibitor , wortmannin, blocked FcR-induced granule release and ADCC. Additional experiments showed that, whereas FcR-initiated killing was wortmannin sensitive and GF109203X insensitive, natural cytotoxic activity towar d the tumor cell line K562 was wortmannin insensitive and GF109203X se nsitive. Taken together, these results suggest that: (a) PI 3-kinase a ctivation induced by FcR ligation is functionally coupled to granule e xocytosis and ADCC; and (b) the signaling pathways involved in ADCC vs natural cytotoxicity are distinct.