The actions of 2,3,7,8-tetrachlorodibenzo-p-dioxin on transforming growth factor-beta2 promoter activity are localized to the TATA box binding region and controlled through a tyrosine kinase-dependent pathway.
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-beta2 (TGF-beta2) by TCDD. To identify the region of the TGF-beta2 promoter necessary for the observed down-regulation by TCDD, we studied the effect of TCDD on a series of TGF-beta2 gene promoter deletions ranging from 1391 to 64 base pairs upstream of the transcription start site. We demonstrate that the effect of TCDD on TGF-beta2 promoter activity is localized to the TATA box sequence. The effect of TCDD on TGF-beta2 transcription 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 nM dose 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-beta2 promoter activity back to control levels. Thus, TCDD can modulate gene transcription by acting at the transcription initiation complex via a tyrosine kinase-dependent pathway.