TNF-α stimulates increased plasma membrane guanine nucleotide binding protein activity in polymorphonuclear leukocytes

Abstract

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. Gi and Gs content were increased in TNF-M as measured by pertussis toxin and cholera toxin (CT) catalyzed ADP-ribosylation, respectively. The increased Gi was coupled to the formyl peptide receptor as shown by receptor-specific CT labeling of Gi. 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.