Activation and induction of cytosolic phospholipase A₂ by IL-1β in human tracheal smooth muscle cells: Role of MAPKs/p300 and NF-κB

Cytosolic phospholipase A₂ (cPLA₂) plays a pivotal role in mediating agonist-induced arachidonic acid (AA) release for prostaglandin (PG) synthesis during inflammation triggered by IL-1β. However, the mechanisms underlying IL-1β-induced cPLA₂ expression and PGE₂ synthesis in human tracheal smooth muscle cells (HTSMCs) remain unknown. IL-1β-induced cPLA₂ protein and mRNA expression, PGE₂ production, or phosphorylation of p42/p44 MAPK, p38 MAPK, and JNK1/2, which was attenuated by pretreatment with the inhibitors of MEK1/2 (U0126), p38 MAPK (SB202190), and JNK1/2 (SP600125) or transfection with siRNAs of MEK1, p42, p38, and JNK2. IL-1β-induced cPLA₂ expression was also inhibited by pretreatment with a NF-κB inhibitor, helenalin or transfection with siRNA of NIK, IKKα, or IKKβ. IL-β-induced NF-κB translocation was blocked by pretreatment with helenalin, but not U0126, SB202190, and SP600125. In addition, transfection with p300 siRNA blocked cPLA₂ expression induced by IL-1β. Moreover, p300 was associated with the cPLA₂ promoter, which was dynamically linked to histone H4 acetylation stimulated by IL-1β. These results suggest that in HTSMCs, activation of MAPKs, NF-κB, and p300 are essential for IL-1β-induced cPLA₂ expression and PGE₂ secretion.