ABSTRACT
Mechanisms regulating transcription factor interaction with chromatin in intact mammalian tissues are poorly understood. Exploiting an adrenalectomized mouse model with depleted endogenous glucocorticoids, we monitor changes of the chromatin landscape in intact liver tissue following glucocorticoid injection. Upon activation of the glucocorticoid receptor (GR), proximal regions of activated and repressed genes are remodelled, and these remodelling events correlate with RNA polymerase II occupancy of regulated genes. GR is exclusively associated with accessible chromatin and 62% percent of GR-binding sites are occupied by C/EBPß. At the majority of these sites, chromatin is preaccessible suggesting a priming function of C/EBPß for GR recruitment. Disruption of C/EBPß binding to chromatin results in attenuation of pre-programmed chromatin accessibility, GR recruitment and GR-induced chromatin remodelling specifically at sites co-occupied by GR and C/EBPß. Collectively, we demonstrate a highly cooperative mechanism by which C/EBPß regulates selective GR binding to the genome in liver tissue. We suggest that selective targeting of GR in other tissues is likely mediated by the combined action of cell-specific priming proteins and chromatin remodellers.
Subject(s)
CCAAT-Enhancer-Binding Protein-beta/metabolism , Chromatin Assembly and Disassembly , Chromatin/metabolism , Receptors, Glucocorticoid/metabolism , Animals , Binding Sites , CCAAT-Enhancer-Binding Protein-beta/genetics , Cell Line , Dexamethasone/metabolism , Dexamethasone/pharmacology , Gene Expression Regulation , Glucocorticoids/metabolism , Glucocorticoids/pharmacology , Humans , Liver/metabolism , Male , Mice , Mice, Inbred C57BL , Models, Molecular , Nucleosomes , Nucleotide Motifs , Organ Specificity , Protein Binding , Receptors, Glucocorticoid/genetics , Regulatory Elements, Transcriptional , Response Elements/geneticsABSTRACT
With increasing worldwide rates of morbidity and mortality of pulmonary fibrosis, the development of effective therapeutics for this disease is of great interest. Secretoglobin (SCGB) 3A2, a novel cytokine-like molecule predominantly expressed in pulmonary airways epithelium, exhibits anti-inflammatory and growth factor activities. In the current study SCGB3A2 was found to inhibit TGFß-induced differentiation of fibroblasts to myofibroblasts, a hallmark of the fibrogenic process, using pulmonary fibroblasts isolated from adult mice. This induction was through increased phosphorylation of STAT1 and expression of SMAD7 and decreased phosphorylation of SMAD2 and SMAD3. To demonstrate the effect of SCGB3A2 on the TGFß signaling in vivo, a bleomycin-induced pulmonary fibrosis mouse model was used. Mice were administered bleomycin intratracheally followed by intravenous injection of recombinant SCGB3A2. Histological examination in conjunction with inflammatory cell counts in bronchoalveolar lavage fluids demonstrated that SCGB3A2 suppressed bleomycin-induced pulmonary fibrosis. Microarray analysis was carried out using RNAs from lungs of bleomycin-treated mice with or without SCGB3A2 and normal mice treated with SCGB3A2. The results demonstrated that SCGB3A2 affects TGFß signaling and reduces the expression of genes involved in fibrosis. This study suggests the potential utility of SCGB3A2 for targeting TGFß signaling in the treatment of pulmonary fibrosis.
