title: Myocardin-related transcription factor-A complexes activate type I collagen expression in lung fibroblasts.
abstract: Pulmonary fibrosis is characterized by the excessive deposition of a collagen-rich extracellular matrix. The accumulation of collagen within the lung interstitium leads to impaired respiratory function. Furthermore, smooth muscle actin-positive myofibroblasts within the fibrotic lung contribute to disease progression. Because collagen and smooth muscle cell α-actin are coordinately expressed in the setting of fibrosis, the hypothesis was tested that specific transcriptional regulators of the myocardin family might also regulate collagen gene expression in myofibroblasts. Myocardin-related transcription factors (MRTFs), through their interaction with the serum-response factor (SRF) on CArG box regulatory elements (CC(A/T)6GG), are important regulators of myofibroblast differentiation. MRTF-A transactivated type I collagen gene reporters as much as 100-fold in lung myofibroblasts. Loss of functional MRTF-A using either a dominant negative MRTF-A isoform, shRNA targeting MRTF-A, or genetic deletion of MRTF-A in lung fibroblasts significantly disrupted type I collagen synthesis relative to controls. Analysis of the COL1A2 proximal promoter revealed a noncanonical CArG box (CCAAACTTGG), flanked by several Sp1 sites important for MRTF-A activation. Chromatin immunoprecipitation experiments confirmed the co-localization of MRTF-A, SRF, and Sp1 bound to the same region of the COL1A2 promoter. Mutagenesis of either the noncanonical CArG box or the Sp1 sites significantly disrupted MRTF-A activation of COL1A2. Together, our findings show that MRTF-A is an important regulator of collagen synthesis in lung fibroblasts and exhibits a dependence on both SRF and Sp1 function to enhance collagen expression.
authors: Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118.
authors: Larry L
authors: LL
authors: Luchsinger
authors: Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118.
authors: Cassandra A
authors: CA
authors: Patenaude
authors: Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118. Electronic address: bdsmith@bu.edu.
authors: Barbara D
authors: BD
authors: Smith
authors: Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118. Electronic address: mlayne@bu.edu.
authors: Matthew D
authors: MD
authors: Layne
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D024042:Collagen Type I / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D008168:Lung / Q000378:metabolism*; D051379:Mice; D015514:Oncogene Proteins, Fusion / Q000378:metabolism*; D051381:Rats; D026362:Serum Response Factor / Q000378:metabolism*; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D024042:Collagen Type I; D004268:DNA-Binding Proteins; C431575:MRTFA protein, human; C511173:Mrtfa protein, mouse; D015514:Oncogene Proteins, Fusion; D026362:Serum Response Factor; D016329:Sp1 Transcription Factor; D015534:Trans-Activators; D014157:Transcription Factors; C557977:myocardin-related transcription factor-A, rat