Lipopolysaccharide (LPS)/
Toll-like receptor 4 (TLR4)-mediated signaling pathways have caught the attention of strategies designed for
rheumatoid arthritis (RA). In this study, we identified that cPLA(2)alpha acted as a modulator of LPS-induced
VCAM-1 expression and THP-1 (human
acute monocytic leukemia cell line) adherence. Treatment of RA synovial fibroblasts (RASFs) with LPS, a TLR4 agonist, promoted the
VCAM-1 expression and THP-1 adherence which were decreased by pretreatment with a selective cytosolic
phospholipase A(2) (cPLA(2)) inhibitor (AACOCF(3)), implying the involvement of cPLA(2)alpha in these responses. This notion was further confirmed by knockdown of cPLA(2)alpha expression by transfection with cPLA(2)alpha
small interfering RNA (
siRNA) leading to a decrease in
VCAM-1 expression and THP-1 adherence induced by LPS. Subsequently, the LPS-stimulated cPLA(2)alpha phosphorylation was attenuated by pretreatment with a MEK1/2 inhibitor (
U0126), suggesting that LPS-stimulated cPLA(2)alpha phosphorylation and activity are mediated through an ERK-dependent mechanism. Moreover, COX-2-derived
PGE(2) production appeared to involve in LPS-induced
VCAM-1 expression which was attenuated by pretreatment with selective
COX-2 inhibitors (
NS-398 and
celecoxib), transfection with COX-2
siRNA, or
PGE(2) receptor antagonists. In addition, pretreatment with ecosapentaenoic
acid (EPA), a substrate competitor of
arachidonic acid (AA), also blocked LPS-induced
VCAM-1 mRNA and
protein expression, and THP-1 adherence. Collectively, these results suggest that LPS-induced
VCAM-1 expression and adhesion of THP-1 cells are mediated through the TLR4/ERK/cPLA(2)alpha phosphorylation and COX-2 expression/
PGE(2) synthesis in RASFs.