Oncostatin M production and regulation by human polymorphonuclear neutrophils.

Oncostatin M (OSM) is an interleukin-6 (IL-6) family cytokine known in particular to induce the synthesis of acute-phase proteins by hepatocytes. Because human polymorphonuclear neutrophils (PMN) can secrete numerous cytokines, the potential production of OSM by PMN was investigated. Highly purified PMN were found to contain an intracellular stock of preformed OSM that was rapidly mobilized by degranulating agents such as phorbol myristate acetate and granulocyte-macrophage colony-stimulating factor (GM-CSF). Moreover, PMN produced OSM after a few hours of stimulation by various agonists. The most potent effect was observed with the combination of lipopolysaccharide and GM-CSF, which had a concentration- and time-dependent effect at both the protein and mRNA levels. Actinomycin D strongly reduced OSM mRNA induction, suggesting the involvement of gene transcription. Cycloheximide inhibited OSM protein synthesis but did not affect the release of preformed stores. In addition, OSM production was downregulated by dexamethasone, whereas IL-10 had no effect. The OSM produced by PMN was biologically active, as demonstrated by its ability to induce alpha1-acid glycoprotein synthesis by HepG2 cells. OSM secretion thus occurs through a two-step mechanism in PMN, consisting of early release of a preformed stock, followed by de novo protein synthesis. This would allow rapid and sustained OSM release to occur at inflammatory sites, and may contribute to the modulation of local inflammation.