Piceatannol is an effective inhibitor of IgE-mediated secretion from human basophils but is neither selective for this receptor nor acts on syk kinase at concentrations where mediator release inhibition occurs

Background: Syk kinase is probably an early necessary tyrosine kinase involved in IgE-mediated secretion from human basophils. Causal testing of the role ofsyk kinase in the secretion requires a selective pharmacological agent. Piceatannol has previously been used to demonstrate the causal role of syk in secretion but its selectively has recently come into question. Objective: To determine whether piceatannol inhibits IgE-mediated signalling events in a manner consistent with its putative inhibitory effects on syk kinase and at concentrations relevant to its inhibition of mediator release. Methods: Human basophils were examined for the effects of piceatannol on mediator release or various signalling steps. Results: We show that while piceatannol has an IC50 for inhibition of IgE-mediated histamine release of 3-5 μM, these same concentrations inhibit secretion of phorbol 12-myristate 13-acetate (PMA)-induced histamine release (as previously shown) and leukotriene C (LTC)4 release induced by fMLP. Concentrations of piceatannol up to 100 μM also did not inhibit IgE-mediated phosphorylation of shc, a immediate downstream target of syk kinase. Similar concentrations also did not inhibit IgE-mediated cytosolic calcium elevations, another downstream signal thought to be dependent on syk kinase. In contrast, piceatannol did modify the cytosolic calcium response that follows stimulation with formyl methionyl-leucyl-phenylalanine (fMLP). Conclusion: Taken together with published studies using other cell types, we conclude that piceatannol does not inhibit secretion from human basophils by inhibiting the activity of syk kinase.