Mannan and peptidoglycan induce COX-2 protein in human PMN via the mammalian target of rapamycin.

The induction of cyclooxygenase-2 (COX-2) protein expression was assessed in human polymorphonuclear leukocytes (PMN) stimulated via receptors of the innate immune system. Peptidoglycan (PGN) and mannan, and at a lower extent the bacterial lipoprotein mimic palmitoyl-3-cysteine-serine-lysine-4, induced COX-2 protein expression. In contrast, lipoteichoic acid and muramyldipeptide were irrelevant stimuli. The mRNA encoding COX-2 was present in resting PMN at an extent quite similar to that detected in stimulated PMN, whereas the expression of COX-2 protein was undetectable. Treatment with the phosphatidylinositol 3-kinase inhibitor (PI3K) wortmaninn, the mammalian target of rapamycin (mTOR) inhibitor rapamycin, and the translation inhibitor cycloheximide blocked the induction of COX-2 protein in response to mannan and PGN, whereas the transcriptional inhibitor actinomycin D did not show a significant effect. These results disclose a capability of pathogen-associated molecular patterns to induce the oxidative metabolism of arachidonic acid more robust than that of PMN archetypal chemoattractants, since mannan and PGN make it coincidental the release of arachidonic acid with a rapid induction of COX-2 protein regulated by a signaling cascade involving PI3K, mTOR, and the translation machinery. This mechanism of COX-2 protein induction expression in PMN is substantially different from that operative in mononuclear phagocytes, which is highly dependent on transcriptional regulation.