No abstract

A novel. Bis-indolylmaleimide. Ro 31-8425, bearing a conformationally restricted side chain, inhibits protein kinasc C isolated from rat brain and human neutrophils with a high degree of selectivity over CAMP-dependent kinase and Ca'-/calmodulin-dependent kinase. It also inhibits phorbol ester-induced intracellular events known to be mediated by protein kinase C (p47 phosphorylaticn in intact platelets. CD3 and CD4 down-regulation in T-cells). Ro 31-8425 inhibited supcroxide generation in human neutrophils activated by both receptor stimuli (formyl-methionyl-leucylphcnylalanine. opsonized zymosan. IgG and heat aggrcgatcd IgG) and post-receptor stimuli (I .2-dioctanoylglycerol and fluoride). The compound also blocked antigen driven, but not IL-2 induced, T-cell proliferation. These results support a central role for protein kinase C in the activation of the respiratory burst and antigen-driven T-cell proliferation.

No abstract

A ‘cocktail’ consisting of an inhibitor of diacylglycerol kinase (R59022, 10 μM), an inhibitor of diacylglycerol lipase (RHC80267, 10 μM), and an inhibitor of phospholipase A2 (either 100 μM indomethacin, or 100 μM sodium meclofenamate) markedly enhanced superoxide production by human neutrophils stimulated with post‐receptor stimuli, fluoride and γ‐hexachlorocyclohexane. On the other hand, the response to the C3b/Fc receptor stimulus, opsonized zymosan, was marginally decreased whilst that to the Fc receptor stimulus, aggregated IgG, was virtually unaffected. Since the inhibitors used are deemed to inhibit the main routes of arachidonate production, these results call into question the role of arachidonate in the transduction of O− 2 generation by post‐receptor stimuli, but support a role for arachidonate in receptor‐mediated transduction.

Two compounds, reported to be potent inhibitors of protein kinase C (PKC), K252a and staurosporine, have been examined in order to gain further information as to the possible role played by PKC in the signal transduction sequence of the neutrophil respiratory burst as determined by superoxide (O−2) production. A number of stimuli were used in the study, some acting at receptors i.e. fMet‐Leu‐Phe (fMLP), opsonized zymosan and heat‐aggregated IgG (HAGG), one acting on a G‐protein, fluoride, and two direct PKC activators, dioctanoylglycerol (diC8) and phorbol myristate acetate (PMA). K252a and staurosporine inhibited the respiratory burst with all the stimuli but the order of agonist sensitivity was very different with the two inhibitors. For K252a‐induced inhibition of O−2 release, the order of potency was fluoride > fMLP, HAGG > opsonized zymosan > PMA, DiC8. For staurosporine‐induced inhibition of O−2 release, the order of potency changed to fluoride > DiC8, PMA > HAGG, fMLP > opsonized zymosan. The significance of this unexpected difference in relative rank order of potency is discussed with reference to the reported mechanism of action of the two inhibitors and the events involved in the oxidative burst. Staurosporine at low concentrations increased the fMLP‐stimulated O−2 response by 100%, the maximum effect occurring at 35 nm. To the extent that the compounds used are specific inhibitors of PKC, these findings support a role for the enzyme PKC in stimulus‐activation coupling in O−2 generation with all the stimuli used in this study.