title: Inhibition of collagen gene expression by interferon-gamma: novel role of the CCAAT/enhancer binding protein beta (C/EBPbeta).
abstract: By inhibiting collagen synthesis, interferon-gamma (IFN-gamma) plays a key role in maintaining connective tissue homeostasis, but the mechanisms are not well-understood. In addition to intracellular signaling through the canonical JAK-STAT transduction pathway, IFN-gamma was recently shown to regulate gene expression via the CCAAT/enhancer-binding protein beta (C/EBPbeta) as well. Because C/EBPbeta is a crucial mediator of immune and inflammatory responses, and has been implicated in regulation of collagen synthesis by tumor necrosis factor-alpha, we examined its role in the inhibitory effects of IFN-gamma. The results demonstrated that IFN-gamma caused increased C/EBPbeta expression in dermal fibroblasts and enhanced its binding to cognate DNA sequences in the alpha2(I) procollagen gene (COL1A2) promoter in vitro and in vivo. Disruption of C/EBP binding by deletion or site-directed mutagenesis abrogated the inhibition of collagen promoter activity in transient transfection assays, as did cotransfection with dominant negative C/EBPbeta, indicating a functional role of cellular C/EBPbeta in mediating the IFN-gamma response. Rapid phosphorylation of the ERK1/2 MAP kinases induced by IFN-gamma was accompanied by phosphorylation and nuclear translocation of cellular C/EBPbeta, and pretreatment of fibroblasts with ERK1/2 kinase inhibitor blocked C/EBPbeta phosphorylation, as well as inhibition of COL1A2 promoter activity, elicited by IFN-gamma. These results provide compelling evidence for a novel C/EBPbeta-dependent IFN-gamma signaling pathway responsible for inhibition of collagen gene transcription. Taken together with recent reports, the findings indicate that intracellular pathways mediating negative regulation of collagen synthesis in response to distinct inflammatory signals that converge on C/EBPbeta.
authors.affiliation: Division of Rheumatology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA.
authors.forename: Asish K
authors.initials: AK
authors.lastname: Ghosh
authors.forename: Swati
authors.initials: S
authors.lastname: Bhattacharyya
authors.forename: Yasuji
authors.initials: Y
authors.lastname: Mori
authors.forename: John
authors.initials: J
authors.lastname: Varga
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism / Q000502:physiology*; D002478:Cells, Cultured; D003094:Collagen / Q000235:genetics*; D024042:Collagen Type I; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology*; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D009154:Mutation; D009838:Oligodeoxyribonucleotides / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D020218:Response Elements / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014162:Transfection
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; D024042:Collagen Type I; D004791:Enzyme Inhibitors; D005419:Flavonoids; D009838:Oligodeoxyribonucleotides; D007371:Interferon-gamma; D003094:Collagen; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one