IDENTIFICATION AND CHARACTERIZATION OF THE CHICKEN TRANSFORMING GROWTH FACTOR-BETA-3 PROMOTER

The promoter regions of the three mammalian transforming growth factor-beta genes (TGF-beta-s 1, 2, and 3) have been recently cloned and characterized. The sequences show little similarity, suggesting different mechanisms of transcriptional control of these genes. To study differences in transcriptional regulation of mammalian and avian TGF-beta, we have cloned and sequenced the 5'-flanking region of chicken TGF-beta-3. Characterization of this region showed a TATA box and cAMP-responsive element (CRE) and AP-2 binding site consensus sequences starting at 12 and 28 base pairs, respectively, upstream from the TATA box. Moreover, four additional AP-2-like sites, 10 binding sites for the transcription factor Sp1, as well as two AP-1-like sites were also identified. Except for 32 base pairs of identity centered around the TATA box and CRE site and four other relatively small regions of identity, the chicken TGF-beta-3 promoter was found to be structurally very different from the human TGF-beta-3 promoter. Promoter fragments were cloned into a chloramphenicol acetyltransferase reporter plasmid to study functional activity. Basal transcriptional activity of the promoter was regulated in quail fibrosarcoma QM7 cells and in human adenocarcinoma A375 cells by multiple upstream elements including the TATA, CRE, and AP-2 sites. As in the human TGF-beta-3 promoter, the CRE site showed activation by forskolin, an effect which could be shown by expression of TGF-beta-3 mRNA in cultured chicken and quail cells as well. Our results indicate a complex pattern of transcriptional regulation of the chicken TGF-beta-3 gene and suggest that differences in the regulation of expression of the genes for mammalian and avian TGF-beta-3 may result in part from the unique structure of their 5'-flanking regions.