TNF-ALPHA STIMULATES INCREASED PLASMA-MEMBRANE GUANINE-NUCLEOTIDE-BINDING PROTEIN-ACTIVITY IN POLYMORPHONUCLEAR LEUKOCYTES

TNF-alpha enhances the response of polymorphonuclear leukocytes (PMN) to chemoattractants: however, the mechanism by which this occurs is un clear, We addressed the hypothesis that TNF-alpha enhances the PMN res ponse to chemoattractants by increasing chemoattractant receptor trans membrane signaling, using fMLP as the model chemoattractant. fMLP-stim ulated guanine nucleotide binding (G) protein activation was significa ntly increased in plasma membranes isolated from PMNs exposed to TNF-a lpha 100 U/ml for 10 minutes (TNF-M), compared to membranes from contr ol cells (CM). Formyl peptide receptor number and affinity were not si gnificantly different in CM and TNF-M. G(i) and G(s) content were incr eased in TNF-M as measured by pertussis toxin and cholera toxin (CT) c atalyzed ADP-ribosylation, respectively. The increased G(i) was couple d to the formyl peptide receptor as shown by receptor-specific CT labe ling of G(i). Immunoblot analysis showed that both G(alpha i2) and G(a lpha 3) were increased in TNF-M. The functional activity of the increa sed G protein content was demonstrated by increased NaF-stimulated pho spholipase D activity in TNF-alpha-treated PMNs, We conclude that TNF- alpha rapidly stimulates increased PMN plasma membrane expression of G proteins that couple formyl Peptide receptors to effector enzymes. Re gulation of G protein expression may be a significant mechanism by whi ch TNF regulates PMN function.