Lipoteichoic acid-induced nitric oxide synthase expression in RAW 264.7 macrophages is mediated by cyclooxygenase-2, prostaglandin E₂, protein kinase A, p38 MAPK, and nuclear factor-κB pathways

We recently reported that lipoteichoic acid (LTA), a cell wall component of the gram-positive bacterium Staphylococcus aureus, stimulated inducible nitric oxide synthase (iNOS) expression, nitric oxide (NO) release, and cyclooxygenase-2 (COX-2) expression in RAW 264.7 macrophages. This study was carried out to further investigate the roles of COX-2 and prostaglandin E₂ (PGE₂) in LTA-induced iNOS expression and NO release in RAW 264.7 macrophages. Treatment of RAW 264.7 macrophages with LTA caused a time-dependent increase in PGE₂ release. LTA-induced iNOS expression and NO release were inhibited by a non-selective COX inhibitor (indomethacin), a selective COX-2 inhibitor (NS-398), an adenylyl cyclase (AC) inhibitor (dideoxyadenosine, DDA), and a protein kinase A (PKA) inhibitor (KT-5720). Furthermore, both PGE₂ and the direct PKA activator, dibutyryl-cAMP, also induced iNOS expression in a concentration-dependent manner. Stimulation of RAW 264.7 macrophages with LTA, PGE₂, and dibutyryl-cAMP all caused p38 MAPK activation in a time-dependent manner. LTA-mediated p38 MAPK activation was inhibited by indomethacin, NS-398, and SB 203580, but not by PD 98059. The PGE₂-mediated p38 MAPK activation was inhibited by DDA, KT-5720, and SB 203580, but not by PD 98059. LTA caused time-dependent activation of the nuclear factor-κB (NF-κB)-specific DNA-protein complex formation. The LTA-induced increase in κB-luciferase activity was inhibited by indomethacin, NS-398, KT-5720, and a dominant negative mutant of p38 αMAPK (p38 αMAPK DN). These results suggest that LTA-induced iNOS expression and NO release involve COX-2-generated PGE₂ production, and AC, PKA, p38 MAPK, and NF-κB activation in RAW 264.7 macrophages.