Transcriptional mechanisms of type I collagen gene expression are differentially regulated by interleukin-1 beta, tumor necrosis factor alpha, and transforming growth factor beta in Ito cells.

Abstract

Regulation of the procollagen type I (Pro alpha 1) gene in cultured Ito cells by diverse cytokines was studied. Specifically, we have examined the effect of interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha (TNF alpha), and transforming growth factor beta (TGF beta) on collagen biosynthesis, levels of Pro alpha 1 (I) mRNA, and rate of transcription of Pro alpha 1 (I) gene. TGF beta stimulated procollagen synthesis at least 2-fold at every concentration tested (5-20 ng/ml), whereas TNF alpha inhibited it at the same concentrations. In contrast to what occurs in dermal fibroblasts, IL-1 beta (5-20 units/ml) preferentially inhibited procollagen production as measured by [3H]proline incorporation. A similar pattern was obtained when total protein synthesis was analyzed by [25S]methionine radiolabeling. Interestingly, while TGF beta-treated cells exhibited greater than 3-fold increase in steady-state levels of Pro alpha 1 (I) mRNA, the treatment with IL-1 had no effect on procollagen mRNA levels. TNF alpha treatment resulted in a 2-fold decrease in the amount of collagen mRNA. The treatment with combinations of cytokines indicated that collagen gene expression in Ito cells is differentially regulated by these cytokines. Furthermore, nuclear run-off transcription experiments were performed. The results obtained suggest that TGF beta regulates increasing collagen type I gene expression at transcriptional levels, and TNF alpha inhibits the transcriptional rate of Pro alpha 1 (I) gene. It is noteworthy that IL-1 beta acts on collagen type I gene regulation by a separate mechanism at a posttranscriptional level.