ARTHRITIS & RHEUMATISM Vol. 63, No. 10, October 2011, pp 2905–2917 DOI 10.1002/art.30504 © 2011, American College of Rheumatology Cytosolic Phospholipase A 2 Induction and Prostaglandin E 2 Release by Interleukin-1 via the Myeloid Differentiation Factor 88–Dependent Pathway and Cooperation of p300, Akt, and NF-B Activity in Human Rheumatoid Arthritis Synovial Fibroblasts Pei-Ling Chi, 1 Shue-Fen Luo, 2 Hsi-Lung Hsieh, 3 I-Ta Lee, 1 Li-Der Hsiao, 2 Yuh-Lien Chen, 4 and Chuen-Mao Yang 1 Objective. Cytosolic phospholipase A 2 (cPLA 2 ) 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-1 (IL-1)–induced cPLA 2 expression in human rheuma- toid arthritis synovial fibroblasts (RASFs). Methods. Synovial tissue was obtained from pa- tients with RA who were undergoing joint replacement surgery. In a mouse model of IL-1–mediated inflam- matory arthritis, neutrophil infiltration, bone erosion, and cPLA 2 expression in ankle synovium were analyzed by immunohistochemistry. IL-1–induced cPLA 2 ex- pression 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-B and p300 to the cPLA 2 promoter was determined by chromatin immunoprecipitation as- say. Prostaglandin E 2 (PGE 2 ) biosynthesis was evalu- ated by enzyme-linked immunosorbent assay. Results. IL-1–induced cPLA 2 expression and PGE 2 release were mediated through a myeloid differ- entiation factor 88 (MyD88)/c-Src–dependent matrix metalloproteinase (MMP)/heparin-binding epidermal growth factor (HB-EGF) cascade linking to transactiva- tion of the EGF receptor (EGFR)/phosphatidylinositol 3-kinase (PI 3-kinase)/Akt, p300, and NF-B p65 path- ways. IL-1 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-B elements of the cPLA 2 promoter. IL-1–induced NF-B transcriptional activity was mediated through a PI 3-kinase/Akt– dependent cascade. Up-regulation of cPLA 2 by IL-1 increased PGE 2 biosynthesis in RASFs. Conclusion. IL-1–induced cPLA 2 expression is mediated through activation of the MyD88/c-Src, MMP/ HB-EGF, EGFR/PI 3-kinase/Akt, p300, and NF-B pathways. These results provide insights into the mech- anisms underlying IL-1–enhanced joint inflammatory responses in RA and may inspire new targeted thera- peutic approaches. Rheumatoid arthritis (RA) is a chronic auto- immune inflammatory disease characterized by thicken- ing of the synovial lining layers and predominantly inflammatory responses in joint tissues. In the affected joints of patients with RA, inflammatory cells, including immune cells, infiltrate and produce many proinflamma- tory cytokines, such as interleukin-1 (IL-1) and tumor necrosis factor  (TNF), in the synovial fluid (1,2). Dr. Luo’s work was supported by grant CMRPG350643 from the Chang Gung Medical Research Foundation and grant NSC96- 2314-B-182-012-MY3 from the National Science Council, Taiwan. Dr. Yang’s work was supported by grant CMRPD180062 from the Chang Gung Medical Research Foundation and grant NSC98-2320-B-182- 004-MY3 from the National Science Council, Taiwan. 1 Pei-Ling Chi, MS, I-Ta Lee, PhD, Chuen-Mao Yang, PhD: Chang Gung University, Kwei-San, Tao-Yuan, Taiwan; 2 Shue-Fen Luo, MD, Li-Der Hsiao, MS: Chang Gung Memorial Hospital at Linkou and Chang Gung University, Kwei-San, Tao-Yuan, Taiwan; 3 Hsi-Lung Hsieh, PhD: Chang Gung Institute of Technology, Kwei- San, Tao-Yuan, Taiwan; 4 Yuh-Lien Chen, PhD: College of Medicine, National Taiwan University, Taipei, Taiwan. Address correspondence to Chuen-Mao Yang, PhD, Depart- ment of Pharmacology, Chang Gung University, 259 Wen-Hwa 1st Road, Kwei-San, Tao-Yuan, Taiwan. E-mail: chuenmao@mail.cgu. edu.tw. Submitted for publication September 7, 2010; accepted in revised form June 9, 2011. 2905