Concomitant Recruitment of ERK1/2 and p38 MAPK Signalling Pathway Is Required for Activation of Cytoplasmic Phospholipase A2via ATP in Articular Chondrocytes

Abstract

Extracellular ATP is a pro-inflammatory mediator involved in the release of prostaglandin from articular chondrocytes, but little is known about its effects on intracellular signaling. ATP triggered the rapid release of prostaglandin E 2 (PGE 2 ) by acting on P2Y 2 receptors in rabbit articular chondrocytes. We have explored the signaling events involved in this synthesis. ATP significantly increased arachidonic acid production, which involved the activation of the 85-kDa cytosolic phospholipase A 2 (cPLA 2 ) but not a secreted form of PLA 2 , as demonstrated by various PLA 2 inhibitors and translocation experiments. We also showed that ATP induced the phosphorylation of p38 and ERK1/2 mitogen-activatedprotein kinases (MAPKs). Both PD98059, an inhibitor of the ERK pathway, and SB203580, an inhibitor of p38 MAPK, completely inhibited the ATP-induced release of PGE 2 . Finally, dominant-negative plasmids encoding p38 and ERK transfected alone into the cells impaired the ATP-induced release of PGE 2 to about the same extent as both plasmids transfected together. These results suggest that PGE 2 production induced by ATP requires the activation of both ERK1/2 and p38 MAPKs. Thus, ATP acts via P2Y 2 -purine receptors to recruit cPLA 2 by activating both ERK1/2 and p38 MAPKs and stimulates the release of PGE 2 from articular chondrocytes.

The role of purinergic signalling in the musculoskeletal system

“…receptor stimulation increased IL-1-mediated PGE2 release from articular chondrocytes (Koolpe et al, 1999) and induced a rapid rise in PGE2 synthesis via the ERK1/2 and p38 MAPK signalling pathways (Berenbaum et al, 2003). In contrast, early work suggested that ATP caused articular cartilage mineralisation by promoting matrix vesicle-mediated calcium deposition (Ryan et al, 1992;Hsu, 1992).…”

Up‐regulation of microsomal prostaglandin E synthase 1 in osteoarthritic human cartilage: Critical roles of the ERK‐1/2 and p38 signaling pathways

“…Cell lysates were separated by 10% or 15% SDS-polyacrylamide gel electrophoresis and transferred to PVDF membranes (31). The blots were soaked in Tween 20 in Tris buffered saline (TBST; 20 mM Tris HCl, pH 7.5, 100 mM NaCl, 0.1% Tween 20, and 5% BSA) for 2 hours at room temperature.…”

“…PGE 2 assay. The PGE 2 concentrations in aliquots of supernatants from cultures of stimulated chondrocytes were measured using a PGE 2 enzyme immunoassay kit (Cayman Chemical, Ann Arbor, MI), as previously described (31). PGE 2 concentrations were assayed in duplicate and were read against a standard curve.…”

Protective effect of p38 MAPK inhibitor on wear debris-induced inflammatory osteolysis through downregulating RANK/RANKL in a mouse model

“…Activation of p38 induces the synthesis of key inflammatory mediators such as TNF-α, IL-1, IL-6, IL-8, and cyclooxygenase-2, either via direct activation of gene transcription or via mRNA stabilization (Winzen et al, 1999;Paccani et al, 2002). In addition, p38 mediates the synthesis of other compounds involved in inflammation, including chemokines and adhesion molecules, the metalloproteinases responsible for cartilage breakdown, and prostaglandins (Berenbaum et al, 2003). In the context of bone erosion, p38 mediates TNF-α-induced IL-1 upregulation in stromal cells and the subsequent IL-1-induced RANKL production.…”