Smad6 is a Smad1/5-induced smad inhibitor - Characterization of bone morphogenetic protein-responsive element in the mouse Smad6 PROMOTER

Smad6 is an inhibitory Smad that is induced by bone morphogenetic proteins (BMPs) and interferes with BMP signaling. We have isolated the mouse Smad6 promoter and identified the regions responsible for transcriptional activat ion by BMPs. The proximal BMP-responsive element (PBE) in the Smad6 promote r is important for the transcriptional activation by BMPs and contains a 28 base pair GC-rich sequence including four overlapping copies of the GCCGnC GC-like motif, which is a binding site for Drosophila Mad and Medea. We gen erated a luciferase reporter construct (3GC2-Lux) containing three repeats of the GC-rich sequence derived from the PBE. BMPs and BMP receptors induce d transcriptional activation of 3GC2-Lux in various cell types, and this ac tivation was enhanced by cotransfection of BMP-responsive Smads, i.e. Smad1 or Smad5, Moreover, direct DNA binding of BMP-responsive Smads and common- partner Smad4 to the GC-rich sequence of PBE was observed. These results in dicate that the expression of Smad6 is regulated by the effects of BMP-acti vated Smad1/5 on the Smad6 promoter.