Abstract
Interleukin 8 (IL-8) is a member of the rapidly growing superfamily of those cytokines which are thought to be involved in the regulation of inflammatory processes and cell proliferation. In neutrophils, IL-8 triggers a variety of cellular responses by interacting with specific cell-surface receptors. To examine whether IL-8 receptors are coupled to activation of guanine-nucleotide-binding proteins (G-proteins), we have investigated the influence of IL-8 on GTP hydrolysis by and guanosine 5'-[gamma-[35S]thio]triphosphate (GTP[35S]) binding to purified human neutrophil plasma membranes. IL-8 stimulated high-affinity GTPase about 2-fold at 100 nM, and half-maximal stimulation was observed at 1 nM. The peptide-stimulated GTPase was confined to plasma membranes upon subcellular fractionation, and was due to an increase in Vmax. rather than a decrease in Km. High-affinity binding of GTP[35S] to neutrophil plasma membranes was stimulated half-maximally and maximally (up to 5-fold) by IL-8 at about 10 nM and 100 nM respectively. GTP[35S] binding to the membranes was also stimulated by two IL-8-related cytokines, neutrophil-activating peptide 2 (NAP-2) and melanoma growth-stimulatory activity (gro/MGSA). Taken together, these results demonstrate that receptors for IL-8 and related cytokines are coupled to and activate G-proteins in neutrophil plasma membranes, indicating that G-protein activation is an important intermediate step in the induction of neutrophil functions by IL-8 and its congeners.