Transcription of the transforming growth factor-β2 gene is dependent on an E-box located between an essential cAMP response element/activating transcription factor motif and the TATA box of the gene

Transforming growth factor-β2 (TGF-β2) is an important regulator of cell proliferation and differentiation; however, its transcriptional regulation is not well understood. Here we report characterization of an essential E-box motif, positioned at -50/-45 between a previously described functional cAMP response element/activating transcription factor site and the TATA box of the human TGF-β2 promoter. By site-directed mutagenesis, we demonstrate that this E-box motif is necessary for the promoter activity, not only in differentiated cells derived from embryonal carcinoma cells, but also in choriocarcinoma cells and in MCF-7 breast carcinoma cells. We also demonstrate that the transcription factors USF1 and USF2 bind to this E-box motif in vitro when nuclear extracts from each of these cell lines are examined by gel retardation assays. Moreover, using a dominant-negative USF2 protein, we show that USF proteins are critical for TGF-β2 promoter activity in vivo. The importance of the E-box motif described in this study is supported by the presence of an E-box motif in the same position in the chicken TGF-β2 gene promoter.