c-Src-dependent transactivation of PDGFR contributes to TNF-α-induced MMP-9 expression and functional impairment in osteoblasts

Matrix metalloproteinases (MMPs), MMP-9 especially, have been shown to be induced by cytokines, including tumor necrosis factor-alpha (TNF-alpha) and may contribute to bone inflammatory diseases and postnatal bone modeling and remodeling. However, the mechanisms underlying MMP-9 expression induced by TNF-alpha in osteoblasts remain unclear. Here, we showed that in MC3T3-E1 cells, TNF-alpha induced MMP-9 gene expression determined by real-time PCR, zymography, and promoter assay. TNF-alpha-mediated responses were attenuated by pretreatment with the inhibitor of protein tyrosine kinase (PM; genistein), c-Src (PP1), PDGFR (AG1296), PI3K (LY294002), Akt (SH-5), MEK1/2 (U0126), p38 MAPK (SB202190), JNK1/2 (SP600125), or AP-1 (Tanshinone IIA) and transfecdon with siRNA of c-Src, PDGFR, p85, Akt, c-Jun, or ATF2. Moreover, TNF-alpha also time-dependently stimulated phosphorylation of c-Src and PDGFR and c-Src/PDGFR complex formation, which were reduced by pretreatment with PP1 or AG1296.TNF-alpha-stimulated Akt phosphorylation was inhibited by genistein,PP1,AG1296,LY294002, or SH5. We further demonstrated that TNF-alpha stimulated ERK1/2, p38 MAPK, and JNK1/2 phosphorylation via a c-Src-dependent PDGFR/PI3K/Akt pathway. TNF-alpha stimulated AP-1 activation, including c-Jun and ATF2 phosphorylation and AP-1 transcription activity via MAPK-dependent pathways. In addition, TNF-alpha-induced MMP-9 promoter activity was mediated through an AP-1 binding domain of the MMP-9 promoter region. Finally, we found that up-regulation of MMP-9 contributes to MMP-mediated type I collagen degradation and osteoblasts detachment. These results suggested that TNF-alpha-induced MMP-9 expression is mediated through a c-Src-dependent PDGFR transactivation and PI3K/Akt cascade linking to MAPK-mediated activation of AP-1 (c-Jun/ATF2) and leading to functional impairment in osteoblasts. (C) 2013 Elsevier Inc. All rights reserved.