Increased Phosphorylation and Activation of Mitogen-Activated Protein Kinase p38 in Scleroderma Fibroblasts

Transforming growth factor-β (TGF-β) stimulates the transcription of the α2(I) collagen gene. The dermal fibroblast activation in systemic sclerosis (SSc) may be a result of stimulation by autocrine TGF-β. In this study, we investigated whether p38 mitogen-activated protein kinase (MAPK) is involved in TGF-β-induced transcriptional activation of the human α2(I) collagen gene in normal dermal fibroblasts and in upregulated extracellular matrix (ECM) expression in SSc fibroblasts. Type I collagen expression induced by TGF-β was suppressed by the specific p38 MAPK inhibitors SB203580 or SB202190 in normal fibroblasts. TGF-β induced phosphorylation and activation of p38 MAPK in normal dermal fibroblasts. Transient transfection of dominant-negative mutant p38 MAPK into normal fibroblasts abolished TGF-β-induced promoter activity of the human α2(I) collagen gene in normal fibroblasts. Moreover, constitutive phosphorylation and activation of p38 MAPK was demonstrated in SSc fibroblasts, and the inhibition of p38 MAPK using specific p38 MAPK inhibitors or dominant-negative mutant p38 MAPK abolished the upregulated expression of type I collagen or fibronectin in SSc fibroblasts. These results strongly suggest the contribution of p38 MAPK signaling to the TGF-β-mediated regulation of the human α2(I) collagen gene in normal dermal fibroblasts and constitutive upregulated expression of type I collagen and fibronectin in SSc fibroblasts.