Transforming growth factor β (TGFβ) is a key regulator associated with the pathogenesis of gingival overgrowth (GO). Connective tissue growth factor (CTGF/CCN2) is overexpressed in GO tissues. CCN2 promotes and sustains fibrosis initiated by TGFβ. Previous studies have shown that JNK and Smad3 activation is required for TGFβ-induced CCN2 expressions in human gingival fibroblasts (HGFs). In this study, we have found that Src is a major signaling mediator for TGFβ-induced CCN2 expressions in HGFs. Pre-treatment with 2 Src kinase inhibitors (PP2, Src inhibitor-1) significantly reduced TGFβ1-induced CCN2 synthesis and JNK and Smad3 activation in HGFs. These results suggest that Src is an upstream signaling transducer of JNK and Smad3 with respect to TGFβ1-stimulated CCN2 expression in HGFs. We further found that curcumin significantly abrogated the TGFβ1-induced CCN2 in HGFs by inhibiting the phosphorylations of Src, JNK, and Smad3. Furthermore, curcumin inhibited TGFβ1-induced HGF migration and α-SMA expression. Curcumin potentially qualifies as a useful agent for the control of GO.
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