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

Abstract

Transforming growth factor (TGF) ␤1 is a mediator of myofibroblast differentiation in healing wounds in which it activates transcription of the smooth muscle ␣-actin (SM␣A) gene via dynamic interplay of nuclear activators and repressors. Targeting components of TGF␤1 signaling may be an effective strategy for controlling myofibroblasts in chronic fibrotic diseases. We examined the ability of proinflammatory tumor necrosis factor (TNF)-␣ to antagonize TGF␤1-mediated human pulmonary myofibroblast differentiation. TNF-␣ abrogated TGF␤1-induced SM␣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-␣ 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␣A promoter and potently suppressed Smad3-and TGF␤1-mediated transcription. Reduction in Smad binding to the SM␣A promoter in TNF-␣-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-␣ 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. INTRODUCTIONMyofibroblasts are specialized stromal cells that synthesize interstitial collagens and contain a smooth muscle ␣-actin (SM␣A)-enriched contractile apparatus designed to generate tensile force needed for wound closure and tissue healing (Skalli and Gabbiani, 1988;Ronnov-Jessen and Petersen, 1996;Zalewski and Shi, 1997;Gabbiani, 2003;Desmouliere et al., 2005;Tomasek et al., 2006). Transforming growth factor (TGF) ␤1) is the principle mediator of myofibroblast differentiation in healing wounds where it accumulates in granulation tissue in activated form during leukocyte infiltration and potently stimulates transcription of the type I␣2 collagen subunit (COL1␣2) and SM␣A genes (Becker et al., 2000;Massague and Wotton, 2000;Cogan et al., 2002;Higashi et al., 2003;Grotendorst et al., 2004;Leask and Abraham, 2004;Subramanian et al., 2004;Zhang et al., 2005). Smad proteins 2 and 3 are activated by TGF␤1 receptor engagement and enter the nucleus in which they directly bind SM␣A and COL1␣2 promoter DNA. Smad3 also reportedly forms additional off-promoter complexes with DNA-binding repressor proteins to govern transcriptional output of the COL1␣2 gene in TGF␤1-activated myofibroblasts (Higashi et al., 2003). Poor termination of TGF␤1-mediated myofibroblast differentiation could contribute to chronic fibroproliferative disease and excessive scar formation in the injured lung, heart, liver, kidney, and skin potentially causing pathobiologic phenomena referred to as "endless healing" (Tomasek et a...

Enhancer RNA profiling predicts transcription factor activity

“…3E), including interferon (IRF7) and STAT2. Furthermore, YBOX1 decreases in colocalization (reduced MD-score), consistent with its known role as a transcriptional repressor that increases in expression after KLA exposure (Liu et al 2009). Collectively, these results indicate that profiles of eRNA transcription-when combined with motif models-identify shifts in TF activity in response to perturbation.…”

Activation of MRTF-A–dependent gene expression with a small molecule promotes myofibroblast differentiation and wound healing

“…Isoxazole may also act independently of MRTF-A in the setting of a healing wound such that stimulation of Erk1/2 signaling by isoxazole contributes to wound closure by promoting the growth response. Alternatively, suppression of the inflammatory response, as demonstrated by reduced TNF-α expression, might contribute to the accumulation of granulation tissue in the isoxazole-treated wound (42,43). To fully elucidate the role of MRTFs in wound healing, deletion of MRTF-A and -B with both fibroblast-and keratinocyte-specific Cre drivers will likely be necessary.…”

Combined effects of interleukin-1α and transforming growth factor-β1 on modulation of human cardiac fibroblast function

“…Moreover, blocking the IL-1 receptor potentiated αSMA expression in the dermal fibroblasts, indicating an inhibitory effect of IL-1 on TGFβ1-induced myofibroblast differentiation (Shephard et al, 2004). In human pulmonary fibroblasts, TGFβ1-induced αSMA expression was inhibited by TNFα, indicating that other pro-inflammatory cytokines show similar inhibitory effects on myofibroblast differentiation (Liu et al, 2009). …”