Molecular Cloning and Structure of the Human Transforming Growth Factor-β2 Gene Promoter

Abstract

Genomic DNA extending over 10 kb 5′ of the transforming growth factor-β2 (TGF-β2) coding region was isolated from a human lung fibroblast lambda phage library. A 5.6 kb Hind III fragment containing the 5′-untranslated region and flanking sequences was sub-cloned and sequenced. SI nuclease protection analysis identified a transcriptional initiation site 1357 nucleotides 5′ of the methionine initiation codon (ATG). A “TATA box” consensus sequence was identified 30 bp from this transcriptional start site; however, consensus “CAT box” sequences were not observed. Approximately 50 nucleotides of homopurine-pyrimidine [d(GA.CT)₅₀] sequence were identified in the 5′-untranslated region, as well as two short open reading frames of 5 and 45 amino acids. Several AP-1, AP-2, CRE and SPl-like DNA consensus sequence elements were also identified surrounding the transcription initiation site. 5′-deletion mutants of the promoter region were fused to the chloramphenicol acetyl transferase (CAT) gene and promoter activity of the isolated genomic DNA was demonstrated in several cell lines. DNA constructs containing nucleotides between -508 to +63 demonstrated high levels of promoter activity. However, sequences between –778 and –508 nucleotides modulated this promoter activity in a manner which was dependent upon the cell line utilized, suggesting that regulation of TGF-β2 gene transcription may be dependent upon the cellular background. The TGF-β2 promoter is markedly different from the promoters that have been recently characterized for TGF-β1 and TGF-β3.