2,3,7,8-Tetrachlorodibenzo-p-dioxin-dependent regulation of transforming growth factors-alpha and -beta 2 expression in a human keratinocyte cell line involves both transcriptional and post-transcriptional control.

Abstract

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), a potent modulator of epithelial cell growth and differentiation, has been shown to induce transforming growth factor (TGF)-alpha in cultures of human keratinocytes and in the human keratinocyte cell line, SCC-12F. In this report, we investigated the mechanisms by which TCDD alters TGF-alpha expression. In addition, we studied the actions of TCDD on TGF-beta 1 and TGF-beta 2 expression. Treatment of SCC-12F cells with TCDD resulted in an increase in TGF-alpha and a reduction in TGF-beta 2 mRNA levels while mRNA levels for TGF-beta 1 were unchanged. Changes in TGF-alpha and TGF-beta 2 expression were maximal by 24 h. No change in the rate of transcription of TGF-alpha was detected following treatment with TCDD as determined by nuclear run-off analysis. TCDD treatment resulted in a stabilization of TGF-alpha mRNA as judged by an approximately 2-fold higher level of TGF-alpha mRNA in treated versus control cells in the presence of actinomycin D. In contrast to TGF-alpha, the rate of transcription of TGF-beta 2 was significantly reduced following TCDD treatment. These findings demonstrate that the induction of TGF-alpha expression in SCC-12F cells by TCDD occurs post-transcriptionally, primarily by mRNA stabilization, while TGF-beta 2 expression is reduced due to a decrease in the rate of TGF-beta 2 gene transcription.