Fig. 2. Opposing roles of TGF-β1 and BMP-7 signaling pathways.

Similar to other members of the TGF-β superfamily, BMP-7 signals via heteromeric interactions of BMP receptors type I (BMPRI) and type II (BMPRII) to activate its R-Smads, Smad1/5/8. Phosphorylated R-Smads form complexes with common signalling component Smad4, which then translocate into the nucleus to regulate transcription of their target genes. Smad6 is an inhibitory Smad that is induced by BMPs and inhibits both TGF-β and BMP signaling. BMP, bone morphogenic protein; BMPR, BMP receptor; TGF-β1, transforming growth factor-β1; TβR, TGF-β receptor.