Prostaglandin E 2 downregulates TNF‐α‐induced production of matrix metalloproteinase‐1 in HCS‐2/8 chondrocytes by inhibiting Raf‐1/MEK/ERK cascade through EP4 prostanoid receptor activation

Matrix metalloproteinase‐1 (MMP‐1, collagenase‐1) plays a pivotal role in the process of joint destruction in degenerative joint diseases. We have examined the regulation of MMP‐1 production in human chondrocytic HCS‐2/8 cells stimulated by tumor necrosis factor‐α (TNF‐α). In response to TNF‐α, MMP‐1 is induced and actively released from HCS‐2/8 cells. The induction of MMP‐1 expression correlates with activation of ERK1/2, MEK, and Raf‐1, and is potently prevented by U0126, a selective inhibitor of MEK1/2 activation. In contrast, SB203580, a selective p38 mitogen‐activated protein kinases (MAPK) inhibitor, had no effects on TNF‐α‐induced MMP‐1 release. A serine/threonine kinase, Akt was not activated in TNF‐α‐stimulated HCS‐2/8 cells. TNF‐α stimulated the production of PGE 2 in addition to MMP‐1 in HCS‐2/8 cells. Exogenously added PGE 2 potently inhibited TNF‐α‐induced both MMP‐1 production and activation of ERK1/2. The effects of PGE 2 were mimicked by ONO‐AE1‐329, a selective EP4 receptor agonist but not by butaprost, a selective EP2 agonist. In contrast, blockade of endogenously produced PGE 2 signaling by ONO‐AE3‐208, a selective EP4 receptor antagonist, enhanced TNF‐α‐induced MMP‐1 production. Furthermore, the suppression of MMP‐1 production by exogenously added PGE 2 was reversed by ONO‐AE3‐208. Activation of EP4 receptor resulted in cAMP‐mediated phosphorylation of Raf‐1 on Ser259, a negative regulatory site, and blocked activation of Raf‐1/MEK/ERK cascade. Taken together, these findings indicate that Raf‐1/MEK/ERK signaling pathway plays a crucial role in the production of MMP‐1 in HCS‐2/8 cells in response to TNF‐α, and that the produced PGE 2 downregulates the expression of MMP‐1 by blockage of TNF‐α‐induced Raf‐1 activation through EP4‐PGE 2 receptor activation. J. Cell. Biochem. 100: 783–793, 2007. © 2006 Wiley‐Liss, Inc.