标题：Cytoplasmic phospholipase A2 translocates to membrane fraction in human neutrophils activated by stimuli that phosphorylate mitogen-activated protein kinase.
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1994
卷号：91
期号：8
页码：3142-3146
DOI：10.1073/pnas.91.8.3142
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The addition of the chemotactic peptide formylmethionylleucylphenylalanine (fMet-Leu-Phe) to human neutrophils pretreated with the cytokine granulocyte/macrophage colony-stimulating factor (GM-CSF) results in a 10-fold enhanced activity of phospholipase A2, measured as the release of arachidonic acid. It is found that GM-CSF increases the tyrosine phosphorylation, enhances the activity of a mitogen-activated protein kinase, and greatly potentiates the fMet-Leu-Phe-induced tyrosine phosphorylation and enhanced activity of this kinase. Stimuli that increase the tyrosine phosphorylation, enhance the activity of the mitogen-activated protein kinase, and cause a rise in the intracellular concentration of free calcium increase the amount of phospholipase A2 associated with the plasma membrane. This increase corresponds to a decrease in the amount found in the cytosol. Whereas GM-CSF alone produces only a small increase in the amount of phospholipase A2 associated with the membrane, it potentiates greatly the fMet-Leu-Phe-induced increase. The total amount (whole cell) of phospholipase A2, as measured by immunoblotting using anti-phospholipase A2 antibody, does not change upon stimulation of human neutrophils with GM-CSF, fMet-Leu-Phe, or both. In addition, the band that corresponds to phospholipase A2 is shifted upward in membrane isolated from neutrophils stimulated with fMet-Leu-Phe, suggesting that the enzyme has been altered, possibly phosphorylated, though not on tyrosine residues. A working hypothesis is presented. Briefly, stimulation of human neutrophils with GM-CSF, in the absence of an additional stimulus, increases the tyrosine phosphorylation and activation of a mitogen-activated protein kinase, which in turn phosphorylates and activates cytoplasmic phospholipase A2. In the presence of an increased intracellular concentration of free calcium the phospholipase A2 is translocated to the plasma membrane where its substrate is located. GM-CSF also potentiates greatly the fMet-Leu-Phe-induced tyrosine phosphorylation and activation of a mitogen-activated protein kinase and, since fMet-Leu-Phe causes an intracellular calcium rise, the amount of the phospholipase A2 that is associated with the membrane fraction.
