GTP gamma S-stimulated phospholipase D activation in human neutrophils occurs by protein kinase C-dependent and -independent pathways but not via tyrosine kinases

Addition of GTP gamma S to saponin-permeabilised human neutrophils activated both the NADPH oxidase and phospholipase D (PLD). This PLD activation was hardly affected by staurosporine or Ro31-8220 (at concentrations which inhibited PMA stimulated PLD activity), indicating that it was largely independent of protein kinase C (PKC). This GTP gamma S stimulated PLD activity was enhanced by 1 mM ATP, but this ATP-enhanced activity was blocked by inhibitors of PKC. Addition of GTP gamma S resulted in very low levels of phosphorylation on tyrosine residues, but higher levels of phosphorylation on serine/threonine residues. Addition of pervanadate hydroperoxides stimulated phosphorylation on tyrosine residues and activated PLD which was blocked by addition of inhibitors of tyrosine kinases. Thus, GTP gamma S can stimulate PKC-dependent and -independent pathways of PLD activation. Whilst phosphorylation on tyrosine residues can result in activation of PLD, this is regulated independently of activation via G-proteins. (C) 1996 Academic Press, Inc.