Mechanisms of bone morphogenetic protein 2 (BMP2) stimulated inhibitor of DNA binding 3 (Id3) transcription

Bone morphogenetic protein 2 (BMP2) stimulates expression of the inhibitors of DNA binding (Id) 1, 2, and 3 in a variety of cell types. Here, we examined mechanisms mediating BMP2-stimulated Id3 transcription in murine gonadotropes. Using a combination of quantitative RT-PCR, promoter-reporter analyses, over-expression, and RNA interference approaches, we demonstrate that BMP2 signals via the BMPR2 and BMPR1A (ALK3) receptors and intracellular signaling proteins SMADs 1 and 5 to stimulate Id3 transcription. We further define a novel 6-bp cis-element mediating BMP2- and SMAD-dependent transcription, though this site does not appear to bind SMADs directly. A specific DNA binding protein complex binds to this element, but its constituent protein(s) remain undetermined. Recently, a more distal enhancer was shown to mediate BMP4-induction of the human ID3 gene in ovarian cancer cells. This enhancer is conserved in the murine gene and we demonstrate its role in BMP2-induced Id3 promoter activity in gonadotropes. Conversely, the proximal cis-element defined here is also conserved in human ID3 and we demonstrate its functional role in BMP2-induction of ID3 transcription. Finally, we show that the two regulatory elements also mediate BMP2-induction of Id3 promoter activity in murine fibroblasts. Collectively, we have defined a general mechanism whereby BMP2 regulates Id3/ID3 transcription in different cell types and in different species.