INHIBITION OF HUMAN NEUTROPHIL RESPONSES BY ALPHA-CYANO-3,4-DIHYDROXYTHIOCINNAMAMIDE - A PROTEIN-TYROSINE KINASE INHIBITOR

1 Activation of neutrophils results in increased tyrosine phosphorylation of several proteins that may have important roles in receptor/effector coupling. In this study, the effect of a protein tyrosine kinase inhibitor on receptor-mediated neutrophil activation by platelet-activating factor (PAF), leukotriene, B4 (LTB4) and N-formylmethionylleucylphenylalanine (FMLP) is investigated. 2 alpha-Cyano-3,4-dihydroxythiocinnamamide dose-dependently inhibited intracellular calcium release and superoxide generation from human neutrophils activated by 1-mu-M LTB4, PAF, and FMLP. 3 In the presence of cytochalasin B, FMLP stimulated elastase release from neutrophils was also inhibited to unstimulated levels by 5 min pretreatment with alpha-cyano,3,4-dihydroxythiocinnamamide. 4 The inhibitory action of alpha-cyano-3,4-dihydroxythiocinnamamide was found to be at or upstream of phospholipase C activation, blocking both phosphatidylinositol hydrolysis and protein kinase C activation. alpha-Cyano-3,4-dihydroxythiocinnamamide did not affect agonist receptor binding sites or receptor affinity in neutrophils. 5 Immunoblot analysis demonstrated the tyrosine phosphorylation of proteins of 41, 56, 66, and 104 kDa in neutrophils treated with agonists. Treatment of neutrophils with alpha-cyano-3,4-dihydroxythiocinnamamide prior to stimulation with chemoattractants reduced tyrosine phosphorylation of the above phosphoproteins. 6 These results indicate that alpha-cyano-3,4-dihydroxythiocinnamamide might be a useful agent in characterizing the essential proteins and biochemical pathways that regulate neutrophil activation.