Tumor necrosis factor-alpha and interferon-gamma suppress the activation of human type I collagen gene expression by transforming growth factor-beta 1. Evidence for two distinct mechanisms of inhibition at the transcriptional and posttranscriptional levels.

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Abstract
Regulation of human type I procollagen gene expression was studied in cultured fibroblasts both at the transcriptional and posttranscriptional level. Transcriptional regulation was examined in cultures transfected with a human pro alpha 2(I) collagen promoter/reporter gene (chloramphenicol acetyltransferase) construct, while posttranscriptional regulation was assessed by parallel determinations of type I procollagen mRNA steady-state levels. Transforming growth factor-beta 1 (TGF-beta 1) elicited a marked, approximately 5-23-fold, enhancement of pro alpha 2(I) collagen promoter activity, which was accompanied by an elevation of type I procollagen mRNA levels. This enhancement of gene expression was suppressed by tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), as determined at mRNA steady-state level, but two distinct mechanisms were involved. TNF-alpha suppressed the pro alpha 2(I) collagen promoter activity, whereas IFN-gamma had only a minimal effect at transcriptional level. The effects of TNF-alpha and IFN-gamma were synergistic, suggesting that combination of these two factors may potentially provide pharmacologic means to counteract tissue deposition of collagen in diseases involving TGF-beta.