Cytosolic phospholipase A₂ induction and prostaglandin E ₂ release by interleukin-1β via the myeloid differentiation factor 88-dependent pathway and cooperation of p300, Akt, and NF-κB activity in human rheumatoid arthritis synovial fibroblasts

Objective Cytosolic phospholipase A₂ (cPLA₂) is a rate-limiting enzyme that plays a critical role in the biosynthesis of eicosanoids. The aim of this study was to investigate the mechanisms underlying interleukin-1β (IL-1β)-induced cPLA₂ expression in human rheumatoid arthritis synovial fibroblasts (RASFs). Methods Synovial tissue was obtained from patients with RA who were undergoing joint replacement surgery. In a mouse model of IL-1β-mediated inflammatory arthritis, neutrophil infiltration, bone erosion, and cPLA₂ expression in ankle synovium were analyzed by immunohistochemistry. IL-1β-induced cPLA₂ expression was determined by Western blotting, real-time polymerase chain reaction, and gene promoter assay using pharmacologic inhibitors and transfection with short hairpin RNAs or small interfering RNAs. The recruitment of NF-κB and p300 to the cPLA₂ promoter was determined by chromatin immunoprecipitation assay. Prostaglandin E₂ (PGE ₂) biosynthesis was evaluated by enzyme-linked immunosorbent assay. Results IL-1β-induced cPLA₂ expression and PGE₂ release were mediated through a myeloid differentiation factor 88 (MyD88)/c-Src-dependent matrix metalloproteinase (MMP)/heparin-binding epidermal growth factor (HB-EGF) cascade linking to transactivation of the EGF receptor (EGFR)/phosphatidylinositol 3-kinase (PI 3-kinase)/Akt, p300, and NF-κB p65 pathways. IL-1β also stimulated Akt phosphorylation and nuclear translocation. Activation of Akt eventually led to the acetylation of histone residues by phosphorylation and recruitment of p300 and enhanced its histone acetyltransferase activity on the NF-κB elements of the cPLA₂ promoter. IL-1β-induced NF-κB transcriptional activity was mediated through a PI 3-kinase/Akt-dependent cascade. Up-regulation of cPLA₂ by IL-1β increased PGE₂ biosynthesis in RASFs. Conclusion IL-1β-induced cPLA₂ expression is mediated through activation of the MyD88/c-Src, MMP/HB-EGF, EGFR/PI 3-kinase/Akt, p300, and NF-κB pathways. These results provide insights into the mechanisms underlying IL-1β-enhanced joint inflammatory responses in RA and may inspire new targeted therapeutic approaches.