Regulatory elements controlling elastin transcription

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Elastin is the primary elastic protein in humans, and provides stretch and recoil to lung tissue, blood vessels, and skin. Elastin is primarily synthesized during fetal development and the neonatal period, and is expressed by specific subsets of cells in these tissues. Normally, elastic fibers are among the most durable structures in the body, but destruction of elastic fibers is central to several chronic lung diseases. Elastic fibers in the lungs of very premature infants are not sufficiently developed to withstand the strain of mechanical ventilation, and can be damaged or deposited in clumps, contributing to abnormal lung development. In adults, when lung elastic fibers are damaged or destroyed in diseases such as emphysema, there is little effective repair. Consequently, loss of elastic fibers in emphysema is central to loss of lung function. Despite a pivotal role in the lung, the mechanisms that control elastin synthesis in a tissue-specific and a developmentally regulated way are still largely unknown. Previous studies found the elastin "promoter" to be weak in transient transfections, and the basis for cell type-specific expression was unknown. In a search for an enhancer-like element that would confer strong activation of the elastin promoter, new studies identified a regulatory region of the elastin gene named T-Exl, found between the start of transcription, and extending into the first exon of the coding region. Inclusion of T-Exl in expression constructs confers cell type-specific expression of elastin in transient transfections, and increases promoter activity in lung myofibroblasts 6-fold. Nuclear extracts from elastin expressing lung myofibroblasts specifically bind this regulatory region in gel shift assays. Further studies have identified the nuclear proteins as members of the SP-1 family of transcription factors. The studies outlined in this proposal will focus on 1) Identifying and delineating the important regulatory sites controlling cell type-specific gene expression using transient transfections with a series of deletion and mutagenized constructs, 2) Characterizing, identifying, and testing the role(s) of transcription factors binding this regulatory region, and 3) Determining the mechanisms that suppress elastin synthesis during chronic inflammation. These approaches will reveal key mechanisms controlling elastin synthesis and identify targets for strategies to modulate elastin synthesis in the lungs of premature infants and in pulmonary emphysema.