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 unclear, We addressed the hypothesis that TNF-alpha enhances the PMN response to chemoattractants by increasing chemoattractant receptor transmembrane signaling, using fMLP as the model chemoattractant. fMLP-stimulated guanine nucleotide binding (G) protein activation was significantly increased in plasma membranes isolated from PMNs exposed to TNF-alpha 100 U/ml for 10 minutes (TNF-M), compared to membranes from control cells (CM). Formyl peptide receptor number and affinity were not significantly different in CM and TNF-M. G(i) and G(s) content were increased in TNF-M as measured by pertussis toxin and cholera toxin (CT) catalyzed ADP-ribosylation, respectively. The increased G(i) was coupled to the formyl peptide receptor as shown by receptor-specific CT labeling of G(i). Immunoblot analysis showed that both G(alpha i2) and G(alpha 3) were increased in TNF-M. The functional activity of the increased G protein content was demonstrated by increased NaF-stimulated phospholipase 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. Regulation of G protein expression may be a significant mechanism by which TNF regulates PMN function.