The Actions of 2,3,7,8-Tetrachlorodibenzo-p-dioxin on Transforming Growth Factor-β2Promoter Activity Are Localized to the TATA Box Binding Region and Controlled through a Tyrosine Kinase-Dependent Pathway

• Published in: Toxicology and applied pharmacology 1996-03, Vol.137 (1), p.90-99
• Main Authors: Lee, Douglas C., Barlow, Keith D., Gaido, Kevin W.
• Format: Article
• Language: English
• ISSN: 0041-008X; 1096-0333
• DOI: 10.1006/taap.1996.0060

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), a widespread environmental contaminant and suspected human carcinogen, is believed to act by altering expression of a number of genes involved in cell growth control. In a previous study, we demonstrated the transcriptional down regulation of transforming growth factor-β2(TGF-β2) by TCDD. To identify the region of the TGF-β2promoter necessary for the observed down-regulation by TCDD, we studied the effect of TCDD on a series of TGF-β2gene promoter deletions ranging from 1391 to 64 base pairs upstream of the transcription start site. We demonstrate that the effect of TCDD on TGF-β2promoter activity is localized to the TATA box sequence. The effect of TCDD on TGF-β2transcription is dose-dependent, exhibiting saturation kinetics maximal by 10 nM. Time course experiments show that the maximum decrease (30–50%) in promoter activity by a 10 nMdose of TCDD is complete by 24 hr. DNAase I footprinting and gel shift experiments indicate a single shifted protein complex in this region that we conclude is the transcription initiation complex. TCDD does not appear to significantly alter this complex suggesting that gross alterations in the proteins associated with this sequence do not occur. Treatment of the cells with various protein kinase inhibitors had no significant effect on the TCDD-induced decrease in promoter activity with the exception of genistein, a tyrosine kinase inhibitor. Genistein reverses the effect of TCDD on TGF-β2promoter activity back to control levels. Thus, TCDD can modulate gene transcription by acting at the transcription initiation complex via a tyrosine kinase-dependent pathway.