Smad3 and Extracellular Signal-Regulated Kinase 1/2 Coordinately Mediate Transforming Growth Factor-β-Induced Expression of Connective Tissue Growth Factor in Human Fibroblasts

Connective tissue growth factor (CTGF) is secreted by fibroblasts stimulated with transforming growth factor-β (TGF-β). CTGF is a potent enhancer of fibroblast proliferation, chemotaxis, and extracellular matrix deposition, and it is thought to mediate some of the fibrogenic effects of TGF-β. Here, we have elucidated signaling pathways involved in regulating the TGF-β-induced production of CTGF in primary fibroblasts. TGF-β induced the expression of CTGF messenger RNA and protein in human gingival fibroblasts after 2 h of treatment. Adenoviral overexpression of Smad3 enhanced the TGF-β-elicited expression of CTGF, whereas Smad7 and dominant-negative Smad3 suppressed the effects of TGF-β on CTGF and Cyr61 expression. Pre-treatment of cells with PD98059, an inhibitor for extracellular signal-regulated kinase (ERK)1/2-activator mitogen-activated protein kinase (MAPK)/ERK kinase (MEK)1, potently inhibited the TGF-β-induced expression of CTGF. Furthermore, co-expression of Smad3 with constitutively active MEK1 resulted in potent induction of CTGF production without exogenous TGF-β stimulation. Together, these results demonstrate that Smad3 and ERK1/2 coordinately mediate TGF-β-induced release of CTGF by fibroblasts. It is conceivable that the crosstalk between Smad3 and ERK1/2 signaling cascades plays an important role in regulating CTGF expression, e.g., in wound repair and tissue fibrosis and could be exploited in therapeutic targeting of fibrotic conditions.