Transforming growth factor β inhibitory element in the rabbit matrix metalloproteinase-1 (collagenase-1) gene functions as a repressor of constitutive transcription

摘要

Transforming growth factor β (TGF-β) is a potent modulator of the extracellular matrix, enhancing collagen synthesis and regulating expression of several genes that encode the matrix metalloproteinases (MMPs), enzymes that degrade the extracellular matrix. In this study, we explored the mechanisms whereby TGF-β inhibits expression of the MMP-1 (collagenase 1) gene. We used transient transfection and gel mobility shift assays to characterize a TGFβ inhibitory element (TIE) at -249 bp in the rabbit MMP-1 promoter, which is also conserved at -246 bp in the human gene. This sequence shares homology to a previously identified TIE in the rat stromelysin-1 (MMP-3) promoter, where it is located at -709 bp. Mutational analyses and transient transfections indicate that MMP-1 TIE functions both as a constitutive repressor of MMP-1 gene expression and, in the presence of TGF-β, as an antagonist of transcriptional induction by phorbol esters. c-Fos binds to the TIE in the rabbit MMP-1 promoter, along with other nuclear proteins, even in the absence of treatment with TGF-β. However, the pattern of proteins binding to the TIE is altered in the presence of nuclear extracts from TGF-β-treated cells, suggesting that TGF-β leads to an alteration in protein/DNA interaction, with subsequent modulation of MMP-1 gene expression. We conclude that in the rabbit MMP-1 promoter, the TIE has dual functions as a repressor of basal transcription and as a mediator of the biologic effects of TGF-β. Furthermore, these dual functions provide additional and subtle mechanisms for regulating MMP-1 gene expression under a variety of biological and pathological conditions.