Type beta 1 transforming growth factor gene expression. A corrected mRNA structure reveals a downstream phorbol ester responsive element in human cells.

A combined approach of cDNA cloning and direct oligonucleotide mapping of TGF-beta 1 mRNA from several human cell lines has revealed that the major human TGF-beta 1 transcript is 381 bases shorter than originally reported, and that the reduced mRNA size is due to polyadenylation from an ATTAAA signal at position 2136 rather than use of the expected AATAAA signal at position 2517. Moreover, there is no evidence for a significant amount of structural heterogeneity, as a result of alternative polyadenylation, in the human TGF-beta 1 transcripts. Considering that the 381-base domain is not part of the major human TGF-beta 1 mRNA, we analyzed this sequence for potential transcriptional regulatory elements. We have identified a 16-base pair domain which contains three putative phorbol ester responsive elements (TREs) based on homology to the TRE consensus sequence. We also show that this 16-base pair fragment confers phorbol ester responsiveness to the chloramphenicol acetyltransferase gene after transient transfection of the heterologous construct in NIH-3T3 cells. The identification of a TRE immediately downstream of the last TGF-beta 1 exon suggests that a 3' enhancer may play an important role in human TGF-beta 1 gene transcription, and suggests a basis for growth factor-mediated regulation of TGF-beta 1 expression by activation of protein kinase C.