EFFECT OF PRENYLCYSTEINE ANALOGS ON CHEMOATTRACTANT RECEPTOR-MEDIATEDG-PROTEIN ACTIVATION

The hypothesis that carboxylmethylation of gamma subunits plays a role in G protein activation was tested by examining the ability of N-acet yl-S-farnesyl-L-cysteine (AFC) and its methyl ester (AFC-ME) to inhibi t G protein-mediated signalling in intact HL-60 granulocytes and isola ted HL-60 plasma membranes. Incubation of HL-60 granule cytes with AFC or AFC-ME inhibited superoxide release stimulated by fMet-Leu-Phe, bu t not by opsonized bacteria. AFC-ME, but not AFC, inhibited NaF- and P MA-stimulated superoxide release. Addition of AFC to HL-60 membranes i nhibited fMet-Leu-Phe-, leukotriene B-4- (LTB(4)) and C5a-stimulated G TP gamma S binding and GTP hydrolysis more potently than it inhibited basal guanine nucleotide exchange. AFC-ME inhibited basal- and ligand- stimulated G protein activation with equal potency, but legs potently than AFC. AFC also inhibited mastoparan-stimulated GTP gamma S binding . Binding of fMet-Leu-Phe and LTB(4) to HL-60 membranes was completely inhibited by AFC, while AFC-ME inhibited ligand binding by less than 50%. Neither AFC nor AFC-ME inhibited pertussis toxin or cholera toxin -catalysed ADP-ribosylation of alpha(i). It was concluded that AFC int errupts signal propagation in G protein-dependent pathways by multiple mechanisms, including inhibition of ligand-receptor interactions, of receptor-G protein coupling and of guanine nucleotide binding to G pro teins. Carboxylmethylation alters the specificity of AFC interruption of signal propagation in intact cells and isolated membranes.