Basic calcium phosphate crystal induction of collagenase 1 and stromelysinexpression is dependent on a p42/44 mitogen-activated protein kinase signal transduction pathway

Synovial fluid basic calcium phosphate (BCP) crystals are markers of severe joint degeneration in osteoarthritis. These crystals are mitogenic and ind uce protooncogene expression and matrix metalloproteinase (MMP) synthesis a nd secretion in human fibroblasts, effects that are specifically blocked by phosphocitrate (PC). We have recently determined that crystals transduce s ignals to the nucleus via the activation of the p42 and p44 mitogen-activat ed protein (MAP) kinases (Nair et at., 1997, J Biol Chem 272:18920-18925). Treatment of human fibroblasts (HF) with BCP induces phosphorylation of p42 /44 MAPK, which is inhibited by PC in a dose-dependent manner. Blocking of p42/44 MAPK signal transduction with an inhibitor (PD98059) of MEK1, an ups tream activator of MAPKs, reduces crystal-induced p42/44 MAPK activation an d significantly inhibits crystal-induced cell proliferation. Based on these findings, we sought to determine the role of the p42/44 MAPK signal transd uction pathway in crystal-induced expression of matrix MMPs. We demonstrate suppression of crystal-induced MMPs via the utilization of two different M EK inhibitors: PD98059 and the recently described U0126, a novel inhibitor of MEK1 and MEK 2. Treatment of HF with PD98059 blocks the induction of cry stal-stimulated collagenase 1 (MMP-1) and stromelysin (MMP-3) expression. P D98059 and PC reduced the level of crystal-induced MMP-1 and MMP-3 mRNA exp ression to that observed in nonstimulated cells. Likewise, PD98059 treatmen t of HF blocked the epidermal growth factor (EGF)- and crystal-induced incr eases in MMP-1 and MMP-3 protein expression and secretion as demonstrated b y Western blotting and zymography. Treatment of HF with U0126 inhibits EGF- induced phosphorylation of p42/44 MAPK as well as crystal- and EGF-induced upregulation of MMP-1 mRNA. Additionally, we demonstrate that treatment of HF with BCP, EGF, or PD98059 does not significantly alter levels of gelatin ase A (MMP-2) mRNA and protein expression. (C) 1999 Wiley-Liss, Inc.