EGCG blocks TGFβ1-induced CCN2 by suppressing JNK and p38 in buccal fibroblasts

Transforming growth factor beta (TGF beta) has been suggested as the main trigger for the increased collagen production and decreased matrix degradation pathways in oral submucous fibrosis (OSF). Connective tissue growth factor (CTGF/CCN2) and cyclooxygenase-2 (COX-2) were found to overexpress in OSF. The aim of this study was to investigate the molecular mechanism underlying the TGF beta-induced CCN2 expressions in human buccal mucosal fibroblasts (BMFs) to identify the potential targets for drug intervention or chemoprevention of OSF. TGF beta-induced CCN2 expression and its signaling pathways were assessed by Western blot analyses in BMFs. TGF beta 1 stimulated CCN2 synthesis in BMFs. Pretreatment with c-Jun NH2-terminal kinase (JNK) inhibitor SP600125, p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580, and activin receptor-like kinase 5 (ALK5) inhibitor SB431542 significantly reduced TGF beta 1-induced CCN2 synthesis. Epigallocatechin-3-gallate (EGCG) completely blocked TGF beta 1-induced CCN2 synthesis by inhibiting the phosphorylation of JNK and p38 MAPK. Prostaglandin E-2 (PGE(2)) inhibited the TGF beta 1-induced CCN2 synthesis in human fetal lung fibroblasts IMR90 but not in BMFs. The TGF beta 1-induced CCN2 synthesis in BMFs could be mediated by the ALK5, JNK, and p38 MAPK pathways. EGCG blocks TGF beta 1-induced CCN2 by suppressing JNK and p38 in BMFs. The exceptional signal transduction pathways of TGF beta 1-induced CCN2 production in BMFs contribute to the resistance of PGE(2) downregulation of CCN2 expression; therefore, the CTGF/CCN2 levels are maintained in the OSF tissues in the presence of COX-2. EGCG may serve as a useful agent in controlling OSF.