Transforming Growth Factor β1-mediated Activation of the Smooth Muscle α-Actin Gene in Human Pulmonary Myofibroblasts Is Inhibited by Tumor Necrosis Factor-α via Mitogen-activated Protein Kinase Kinase 1-dependent Induction of the Egr-1 Transcriptional Repressor

Transforming growth factor (TGF) beta 1 is a mediator of myofibroblast differentiation in healing wounds in which it activates transcription of the smooth muscle alpha-actin (SM alpha A) gene via dynamic interplay of nuclear activators and repressors. Targeting components of TGF beta 1 signaling may be an effective strategy for controlling myofibroblasts in chronic fibrotic diseases. We examined the ability of proinflammatory tumor necrosis factor (TNF)-alpha to antagonize TGF beta 1-mediated human pulmonary myofibroblast differentiation. TNF-alpha abrogated TGF beta 1-induced SM alpha A gene expression at the level of transcription without disrupting phosphorylation of regulatory Smads. Intact mitogen-activated protein kinase kinase (Mek)-extracellular signal-regulated kinase (Erk) kinase signaling was required for myofibroblast repression by TNF-alpha via induction of the early growth response factor-1 (Egr-1) DNA-binding protein. Egr-1 bound to the GC-rich SPUR activation element in the SM alpha A promoter and potently suppressed Smad3-and TGF beta 1-mediated transcription. Reduction in Smad binding to the SM alpha A promoter in TNF-alpha-treated myofibroblasts was accompanied by an increase in Egr-1 and YB-1 repressor binding, suggesting that the molecular mechanism underlying repression may involve competitive interplay between Egr-1, YB-1, and Smads. The ability of TNF-alpha to attenuate myofibroblast differentiation via modulation of a Mek1/Erk/Egr-1 regulatory axis may be useful in designing new therapeutic targets to offset destructive tissue remodeling in chronic fibrotic disease.