DIVERGING SIGNAL-TRANSDUCTION PATHWAYS ACTIVATED BY INTERLEUKIN-8 ANDRELATED CHEMOKINES IN HUMAN NEUTROPHILS - INTERLEUKIN-8, BUT NOT NAP-2 OR GRO-ALPHA, STIMULATES PHOSPHOLIPASE-D ACTIVITY

Interleukin-8 (IL-8) and the structurally related cytokines neutrophil -activating peptide-2 (NAP-2) and GRO alpha are powerful chemotactic a gents for human neutrophils. Although these three chemokines act by bi nding to overlapping but not identical receptor subsets, the data avai lable to date have stressed the similarities in their mechanisms of ac tion. The present studies were undertaken to further our understanding of the signal transduction mechanisms associated with these neutrophi l agonists. IL-8, NAP-2, and GRO alpha stimulated similar increases in the level of cytoplasmic free calcium. They were also shown to stimul ate qualitatively similar increases in the levels of protein tyrosine phosphorylation. In contrast, only IL-8 enhanced the formation of phos phatidylethanol (PEt), the product catalyzed by phospholipase D (PLD) in the presence of ethanol. The formation of PEt stimulated by IL-8 wa s inhibited by pertussis toxin and the tyrosine kinase inhibitors erbs tatin and herbimycin A. The ability of IL-8 to stimulate the activity of PLD was additively enhanced, or primed, by cytochalasin B and by tu mor necrosis factor alpha. Although all three chemokines increased the level of free cytoplasmic calcium to the same extent, IL-8 was signif icantly more potent than either NAP-2 or GRO alpha with respect to its ability to enhance CD11b expression and to stimulate chemotactic and oxidative responses. The difference between IL-8, NAP-2, and GRO alpha in their ability to stimulate PLD is likely to be related to their re spective binding affinities for the two IL-8 receptors (IL-8R-A and IL -8R-B). These results suggest that the signalling pathways activated b y IL-8R-A and IL-8R-B diverge at a step preceeding the activation of P LD. (C) 1995 by The American Society of Hematology.