BINDING OF AP-1 CREB PROTEINS AND OF MDBP TO CONTIGUOUS SITES DOWNSTREAM OF THE HUMAN TGF-BETA-1 GENE/

Transcription of the human gene encoding transforming growth factor be ta 1 (TGF-beta 1), which is a key regulator of cell growth and differe ntiation, is inducible by phorbol esters. DNA sequences resembling pho rbol ester response elements (TREs) are present upstream and downstrea m of this gene. TRES are recognized by proteins from the AP-1 family o f transcription factors. We examined a 16 basepair (bp) sequence downs tream of the TGF-beta 1 gene that contains three putative TREs. This s equence had been shown to stimulate reporter gene expression from a do wnstream location in response to phorbol ester treatment. Electrophore tic mobility shift assays suggest that minor proteins from the related AP-1 and CREB families of transcription factors bind to the overlappi ng TREs within the 16 bp element. A site beginning at the end of this 16 bp element matches the consensus sequence of a DNA-binding protein called MDBP and was shown to bind to this protein. When the intact MDB P site was present in a reporter gene construct in addition to the TRE s, the phorbol ester-induced stimulation of reporter gene expression w as no longer observed. This suggests that MDBP can counteract the stim ulation of transcription by AP-1/CREB-like proteins binding to this do wnstream enhancer element.