Cigarette smoke extract induces cytosolic phospholipase A₂ expression via NADPH oxidase, MAPKs, AP-1, and NF-κB in human tracheal smooth muscle cells

Up-regulation of cytosolic phospholipase A₂ (cPLA₂) by cigarette smoke extract (CSE) may play a critical role in airway inflammatory diseases. However, the mechanisms underlying CSE-induced cPLA₂ expression in human tracheal smooth muscle cells (HTSMCs) remain unknown. CSE induced cPLA₂ protein and mRNA expression, and ROS generation was attenuated by pretreatment with a reactive oxygen species (ROS) scavenger (N-acetylcysteine), or inhibitors of NADPH oxidase (diphenyleneiodonium chloride, apocynin) and transfection with p47^phox siRNA, suggesting that CSE-induced cPLA₂ expression was mediated through NADPH oxidase activation and ROS production in HTSMCs. Furthermore, CSE-induced cPLA₂ expression was attenuated by pretreatment with the inhibitors of MEK1/2 (U0126), p38 MAPK (SB202190), and JNK (SP600125), which were further confirmed by transfection with siRNAs of JNK1, p42, and p38 to down-regulate the expression of respective proteins and reduce cPLA₂ expression. Induction of cPLA₂ by CSE was attenuated by selective inhibitors of NF-κB (helenalin) and AP-1 (curcumin). Moreover, promoter assays revealed that increases of cPLA₂, NF-κB, and AP-1 luciferase activities stimulated by CSE were attenuated by these inhibitors. These results suggest that in HTSMCs, CSE induced NADPH oxidase activation leading to phosphorylation of p42/p44 MAPK, p38 MAPK, and JNK. These reactions induced nuclear transcription NF-κB and AP-1 activities which were essential for CSE-induced cPLA₂ gene expression.