Signal Transduction in Neutrophil Activation - Search for the real 2nd messenger

点击翻译按钮获取中文摘要

We have searched for the signaling molecules which activate or inactivate the superoxide generating enzyme (NADPH oxidase) in neutrophils, and found that hosphatidic acid (PA) may activate the enzyme and spermine inactivate it.PA is derived from phosphatidylcholine by action of phosphlipase D which is known to activate upon cell activation. When added to permeabilised neutrophils, PA elicited the activity immediately. The activation was found independent of Ca^<2+>, diacylglycerol, or protein kinase c. The activation was caused by PA micromolar concentrations. And the rate of O_2^- generation was similar to that by physiological stimuli. These results show that PA may searve as a second messenger to activate NADPH oxidase in the cell.Spermine, a celular plyamine, down-regulates superoxide generation [Ogata, Tamura, Takeshita (1992) Biochem.Biophys.Res.Commun.] . In the present study, to elucidate the mechanism for the inhibition, the effect of spermine on cell-free activation of NADPH oxidase was examined. Spermine suppressed the SDS-induced activation of the oxidase (IC_<50>=18muM). The inhibition was specific for spermine over its precursor amines. Spermine did not alter the K_m for NADPH or the optimal concentration of SDS for the activation. The amine was found to inhibit semi-recombinant cell-free system and may interfere with the assembly of the enzyme components to form active complex especially by binding to p67phox, a cytosolic subunit.These results show that superoxide generation is suppressed by spermine in resting neutrophils and clicited by phosphatidic acid which increases upon the cell stimulation.