PROTEIN-TYROSINE KINASE INHIBITION BLOCKS GRANULE EXOCYTOSIS AND CYTOLYTIC FUNCTION OF LYMPHOKINE-ACTIVATED KILLER-CELLS

Short-term pretreatment of human lymphokine-activated killer cells (LA K) with the protein tyrosine kinase-specific inhibitor Herbimycin A (H erb A) blocked cytotoxic function against the NK-resistant (LAK-sensit ive) tumor targets, SK-Mel-1 (human melanoma) and Daudi (human lymphom a). Greater than 50% inhibition of LAK activity was observed after a 2 .5-h pretreatment with 0.125 mu g/ml (ca. 0.2 mu M) Herb A. Inhibition of LAK occurred over a time interval in which LAK were not dependent upon IL-2 for maintenance of killing function, supporting the conclusi on that the drug interfered with mobilization of cytotoxic function, C onjugate formation between LAK and tumor targets was unaffected by Her b A, indicating that inhibition was occurring at a post-binding step. Granule exocytosis as measured by BLT-esterase release was detected fr om LAK after coincubation with tumor targets, and was inhibited by Her b A pretreatment. The majority of LAK killing was dependent upon extra cellular calcium, supporting the hypothesis that granule exocytosis ra ther than Fas ligand was the principal pathway leading to target cell death. The data suggest that protein tyrosine kinases play a pivotal r ole in LAK cytolytic function by regulating granule exocytosis