Redox modification of nuclear actin by MICAL-2 regulates SRF signaling
ABSTRACT The serum response factor (SRF) binds to coactivators, such as myocardin-related transcription factor-A (MRTF-A), and mediates gene transcription elicited by diverse signaling pathways. SRF/MRTF-A-dependent gene transcription is activated when nuclear MRTF-A levels increase, enabling the formation of transcriptionally active SRF/MRTF-A complexes. The level of nuclear MRTF-A is regulated by nuclear G-actin, which binds to MRTF-A and promotes its nuclear export. However, pathways that regulate nuclear actin levels are poorly understood. Here, we show that MICAL-2, an atypical actin-regulatory protein, mediates SRF/MRTF-A-dependent gene transcription elicited by nerve growth factor and serum. MICAL-2 induces redox-dependent depolymerization of nuclear actin, which decreases nuclear G-actin and increases MRTF-A in the nucleus. Furthermore, we show that MICAL-2 is a target of CCG-1423, a small molecule inhibitor of SRF/MRTF-A-dependent transcription that exhibits efficacy in various preclinical disease models. These data identify redox modification of nuclear actin as a regulatory switch that mediates SRF/MRTF-A-dependent gene transcription.
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- "The serum response results in the interaction of SRF protein with the b-actin promoter, through the disassembly of the MAL-actin interaction, resulting also in the assembly of cytoplasmic b-actin filaments (F-actin) from the now-available Gactin monomers. Interestingly, in recent years, the role of actin has been demonstrated in the regulation of gene expression via the nuclear pool of the actin protein (Hendzel et al., 1999; Huet et al., 2012; Jockusch et al., 2006; Lundquist et al., 2014; McDonald et al., 2006; Khanna et al., 2014; Treisman, 2013). Specifically in SRF signaling, G-actin in a mutant nonpolymerizing form, or as NLS-actin, negatively regulates SRF (Posern et al., 2002). "
ABSTRACT: The transcriptional response of β-actin to extra-cellular stimuli is a paradigm for transcription factor complex assembly and regulation. Serum induction leads to a precisely timed pulse of β-actin transcription in the cell population. Actin protein is proposed to be involved in this response, but it is not known whether cellular actin levels affect nuclear β-actin transcription. We perturbed the levels of key signaling factors and examined the effect on the induced transcriptional pulse by following endogenous β-actin alleles in single living cells. Lowering serum response factor (SRF) protein levels leads to loss of pulse integrity, whereas reducing actin protein levels reveals positive feedback regulation, resulting in elevated gene activation and a prolonged transcriptional response. Thus, transcriptional pulse fidelity requires regulated amounts of signaling proteins, and perturbations in factor levels eliminate the physiological response, resulting in either tuning down or exaggeration of the transcriptional pulse. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.Cell Reports 04/2015; 11(3). DOI:10.1016/j.celrep.2015.03.039 · 8.36 Impact Factor
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ABSTRACT: Systemic sclerosis (SSc) or scleroderma, like many fibrotic disorders, lacks effective therapies. Current trials focus on anti-inflammatory drugs or targeted approaches aimed at one of the many receptor mechanisms initiating fibrosis. In light of evidence that a myocardin-related transcription factor (MRTF) and serum response factor (SRF)-regulated gene transcriptional program induced by Rho GTPases is essential for myofibroblast activation, we explore the hypothesis that inhibitors of this pathway may represent novel antifibrotics. MRTF-SRF-regulated genes show spontaneously increased expression in primary dermal fibroblasts from patients with diffuse cutaneous SSc. A novel small-molecule inhibitor of MRTF/SRF-regulated transcription (CCG-203971) inhibits expression of connective tissue growth factor (CTGF), alpha-smooth muscle actin (α-SMA), and collagen 1 (COL1A2) in both SSc fibroblasts and in LPA- and transforming growth factor β (TGFβ)-stimulated fibroblasts. In vivo treatment with CCG-203971 also prevented bleomycin-induced skin thickening and collagen deposition. Thus targeting the MRTF/SRF gene transcription pathway could provide an efficacious new approach to therapy for SSc and other fibrotic disorders.Journal of Pharmacology and Experimental Therapeutics 04/2014; 349(3). DOI:10.1124/jpet.114.213520 · 3.86 Impact Factor
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ABSTRACT: Tissue fibrosis occurs with excessive extracellular matrix (ECM) deposition from myofibroblasts resulting in tissue scarring and inflammation. It is driven by multiple mediators, such as the G-protein coupled receptor ligands lysophosphatidic acid (LPA) and endothelin (ET-1) as well as signaling by transforming growth factor β (TGFβ), connective tissue growth factor (CTGF), and integrins. Fibrosis contributes to 45% of deaths in the developed world. As current therapeutic options for tissue fibrosis are limited and organ transplantation is the only effective treatment for end-stage disease, there is an imminent need for efficacious antifibrotic therapies. This review discusses the various molecular pathways involved in fibrosis. It highlights the Rho GTPase signaling pathway and its downstream gene transcription output through myocardin-related transcription factor (MRTF) and serum response factor (SRF) as a convergence point for targeting this complex set of diseases.AJP Cell Physiology 04/2014; 307(1). DOI:10.1152/ajpcell.00060.2014 · 3.67 Impact Factor