Effect of prenylcysteine analogues on chemoattractant receptor-mediated G protein activation.

The hypothesis that carboxylmethylation of gamma subunits plays a role in G protein activation was tested by examining the ability of N-acetyl-S-farnesyl-L-cysteine (AFC) and its methyl ester (AFC-ME) to inhibit G protein-mediated signalling in intact HL-60 granulocytes and isolated HL-60 plasma membranes. Incubation of HL-60 granulocytes with AFC or AFC-ME inhibited superoxide release stimulated by fMet-Leu-Phe, but not by opsonized bacteria. AFC-ME, but not AFC, inhibited NaF- and PMA-stimulated superoxide release. Addition of AFC to HL-60 membranes inhibited fMet-Leu-Phe-, leukotriene B4- (LTB4) and C5a-stimulated GTP 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 less potently than AFC. AFC also inhibited mastoparan-stimulated GTP gamma S binding. Binding of fMet-Leu-Phe and LTB4 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 interrupts 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 proteins. Carboxylmethylation alters the specificity of AFC interruption of signal propagation in intact cells and isolated membranes.