Variations of the effect of insulin on neutrophil respiratory burst. The role of tyrosine kinases and phosphatases

The priming effect of insulin on the fMLP-induced respiratory burst of mous e neutrophils as well as the involvement of tyrosine. protein kinases and p hosphatases in this process have been studied. Peritoneal evoked neutrophil s of NMRI strain mice were incubated with 0.01-100 nM insulin for 1-60 min at 22, 30, or 37 degreesC and activated by 0.1-50 muM N-formyl-methionyl-le ucyl-phenylalanine (fMLP). The production of reactive oxygen species (ROS) by neutrophils was monitored by luminol-dependent chemiluminescence. We fou nd that I-125-labeled insulin binding by mouse neutrophils occurred with sa turation and high affinity Insulin itself did not change the basal level of the ROS production but could modulate fMLP-induced respiratory burst. The effect of insulin depended on temperature and duration of pretreatment of t he neutrophils with insulin and the concentration combination of the insuli n and fMLP. The tyrosine kinase inhibitor tyrphostin 51 decreased the fMLP- induced respiratory burst significantly. Insulin: did not change the fMLP r esponse of neutrophils pretreated with tyrphostin. However, the effect of t yrphostin on the response to 50 muM fMLP was considerably decreased in neut rophils treated with insulin. There was no such effect during activation by 5 muM fMLP, for which the priming effect of insulin was not observed. Insu lin did not increase the fMLP-induced respiratory burst in neutrophils trea ted with the protein phosphatase inhibitors orthovanadate and pyrophosphate . If the inhibitors were added after insulin, the combined effect was nearl y additive. It is possible that priming by insulin of the fMLP-induced resp iratory burst is triggered by tyrosine phosphorylation, realized with its p articipation, and involves the signaling pathways, initiated by tyrosine ph osphorylation but subsequently is not dependent on the latter. The role of protein phosphatases in priming by insulin is of little importance. The dat a indirectly confirm the idea that priming of the neutrophil respiratory bu rst is a result of crosstalk of signaling pathways of the insulin and fMLP receptors with the participation of tyrosine phosphorylation.