Tumor necrosis factor-alpha down-regulates human elastin gene expression. Evidence for the role of AP-1 in the suppression of promoter activity.

Cytokine modulation of elastin gene expression was examined by assay of elastin mRNA abundance and by transient transfections of cultured human skin fibroblasts and rat aortic smooth muscle cells with elastin promoter/reporter gene (chloramphenicol acetyltransferase, CAT) constructs. Incubation of cells with human recombinant tumor necrosis factor-alpha (TNF-alpha) markedly suppressed the elastin mRNA levels in a time- and dose-dependent manner by up to 91%. TNF-alpha also suppressed the expression of the elastin promoter/CAT construct by up to 70% in transiently transfected cells, indicating regulation at the transcriptional level. This suppression was temporally preceded by rapid and transient up-regulation of c-jun and c-fos genes. The down-regulatory effect of TNF-alpha on elastin promoter activity was abolished by co-transfections with a synthetic double-stranded AP-1 oligomer. Furthermore, co-transfection of the elastin promoter construct with c-jun and c-fos expression plasmids resulted in a marked decrease in the promoter activity. Elucidation of the cis-regulatory elements in the elastin promoter by 5' deletion construct analysis implicated a region -290 to -198 containing one AP-1 binding site. The functional role of this AP-1 site was further tested by gel retardation assays which indicated formation of a DNA-protein complex specific for TNF-alpha treated cells. This complex could be partially dissociated by a competing oligomer containing the consensus AP-1 binding site. These observations suggest that the inhibitory effects of TNF-alpha on elastin gene expression involve the transcription factor AP-1. Interferon-gamma also suppressed the elastin gene expression at the mRNA level by approximately 52%, but it had no effect on the elastin promoter activity, suggesting post-transcriptional mechanisms. These results indicate that mediators released from inflammatory cells can modulate elastin gene expression, and such modulation may play a role in diseases characterized by altered accumulation of elastic fibers in tissues.