Failed Degradation of JunB Contributes to Overproduction of Type I Collagen and Development of Dermal Fibrosis in Patients With Systemic Sclerosis

Abstract

ObjectiveThe excessive deposition of extracellular matrix, including type I collagen, is a key aspect in the pathogenesis of connective tissue diseases such as systemic sclerosis (SSc; scleroderma). To further our understanding of the mechanisms governing the dysregulation of type I collagen production in SSc, we investigated the role of the activator protein 1 (AP-1) family of transcription factors in regulating COL1A2 transcription.MethodsThe expression and nuclear localization of AP-1 family members (c-Jun, JunB, JunD, Fra-1, Fra-2, and c-Fos) were examined by immunohistochemistry and Western blotting in dermal biopsy specimens and explanted skin fibroblasts from patients with diffuse cutaneous SSc and healthy controls. Gene activation was determined by assessing the interaction of transcription factors with the COL1A2 enhancer using transient transfection of reporter gene constructs, electrophoretic mobility shift assays, chromatin immunoprecipitation analysis, and RNA interference involving knockdown of individual AP-1 family members. Inhibition of fibroblast mammalian target of rapamycin (mTOR), Akt, and glycogen synthase kinase 3β (GSK-3β) signaling pathways was achieved using small-molecule pharmacologic inhibitors.ResultsBinding of JunB to the COL1A2 enhancer was observed, with its coalescence directed by activation of gene transcription through the proximal promoter. Knockdown of JunB reduced enhancer activation and COL1A2 expression in response to transforming growth factor β. In SSc dermal fibroblasts, increased mTOR/Akt signaling was associated with inactivation of GSK-3β, leading to blockade of JunB degradation and, thus, constitutively high expression of JunB.ConclusionIn patients with SSc, the accumulation of JunB resulting from altered mTOR/Akt signaling and a failure of proteolytic degradation underpins the aberrant overexpression of type I collagen. These findings identify JunB as a potential target for antifibrotic therapy in SSc.

Conserved Ankyrin Repeat Proteins and Their NIMA Kinase Partners Regulate Extracellular Matrix Remodeling and Intracellular Trafficking inCaenorhabditis elegans

“…In mammals, ECM remodeling is essential for development, homoeostasis, and physiological wound healing (Cox and Erler 2011 Deregulation of ECM remodeling has also been linked to a number of disease states, most notably cancer cell growth and metastasis (Cox and Erler 2011;Yu et al 2011). Furthermore, the inappropriate deposition of collagens can lead to severe fibrotic diseases such as pulmonary fibrosis (Raghu et al 1989;Specks et al 1995;Todd et al 2012), liver cirrhosis (Murata et al 1984;Nielsen et al 2014), cardiovascular diseases (Zannad and Radauceanu 2005), and systemic sclerosis (Ponticos et al 2015). C. elegans molting thus represents a powerful genetic system for studying conserved molecular mechanisms controlling ECM remodeling.…”

“…Furthermore, the inappropriate deposition of collagens can lead to severe fibrotic diseases such as pulmonary fibrosis (Raghu et al 1989;Specks et al 1995;Todd et al 2012), liver cirrhosis (Murata et al 1984;Nielsen et al 2014), cardiovascular diseases (Zannad and Radauceanu 2005), and systemic sclerosis (Ponticos et al 2015). C. elegans molting thus represents a powerful genetic system for studying conserved molecular mechanisms controlling ECM remodeling.…”

Pentraxin-2 suppresses c-Jun/AP-1 signaling to inhibit progressive fibrotic disease

“…In monocytes, luciferase reporter assays showed strong suppression of AP-1 signaling by PTX-2. It is noteworthy that c-Jun has been strongly implicated in the progression of many diseases, particularly through forming complexes with Fos and Fosl2 (32,52,53), but direct targeting of Jun or its upstream MAPKs has proved pharmacologically challenging (53,54).…”

“…AP-1 binding sites are abundant in the rhPTX-2-dependent differentially expressed gene sets, supporting this possibility. Second, the 3 Jun, 4 Fos, and 19 other AP-1 extended family members vary in their transcriptional activities, binding partners, and abundance, and different combinations of AP-1 homo-and heterodimer complexes can compete with or inhibit one another (32,33,52). Therefore, altering c-Jun likely perturbs the aggregate role of all AP-1-dependent genes, including reversing AP-1-mediated transcriptional repression (31,52,53).…”

“…Second, the 3 Jun, 4 Fos, and 19 other AP-1 extended family members vary in their transcriptional activities, binding partners, and abundance, and different combinations of AP-1 homo-and heterodimer complexes can compete with or inhibit one another (32,33,52). Therefore, altering c-Jun likely perturbs the aggregate role of all AP-1-dependent genes, including reversing AP-1-mediated transcriptional repression (31,52,53). Third, because c-Jun can bind transcription factor partners outside the AP-1 family, c-Jun can control expression of a wide range of genes whose promoters lack a c-Jun binding site or recruit key transcription factors to promoters without their binding sites (29)(30)(31).…”