Crystal-induced neutrophil activation. VII. Involvement of Syk in the responses to monosodium urate crystals

The inflammatory response in acute gouty arthritis is in large part a resul t of the interaction between neutrophils and monosodium. urate (MSU) crysta ls. The tyrosine kinase Syk, which has been largely associated with the pha gocytic response by Fe receptors and with spreading mediated by integrins, has been identified as one of the major proteins tyrosine-phosphorylated in human neutrophils upon stimulation by MSU crystals and is known to be medi ated in part by the Fe receptor, CD16. This has led to the present examinat ion of the implication of Syk in the activation pathways used by MSU crysta ls. The tyrosine-phosphorylation patterns induced by MSU crystals and by th e ligation of CD16 were inhibited by piceatannol, which, conversely, only s lightly delayed but did not diminish the peak of tyrosine phosphorylation i nduced by cross-linking CD32 or by the addition of fMet-Leu-Phe. Moreover, piceatannol inhibited the activity of Syk as monitored by in vitro kinase a ssays, by its in situ tyrosine phosphorylation, and by its activity toward exogenous substrates after stimulation by MSU crystals. We also measured th e impact of piceatannol on the mobilization of calcium, the production of s uperoxide anions, and the activity of PLD stimulated by MSU crystals. We no ted a distinct inhibition of all these responses by piceatannol. Finally, t he morphological changes observed in neutrophils as characteristic of MSU c rystal internalization were diminished significantly by piceatannol. The re sults obtained show that Syk plays a critical and central role in the signa l-transduction pathways called upon by MSU crystals subsequent to their int eraction with human neutrophils.