Figure 2.

Transforming growth factor beta (TGFβ) and bone morphogenetic protein (BMP) receptor signal transduction. TGFβ and BMP bind to their respective type I and II receptors to activate the downstream canonical Smad-signaling to initiate gene transcription by binding various co-activators and co-repressors. While TGFβ activates Smad2/3 and BMP activates Smad1/5/8, both require the common Smad, Smad4, to form a complex for nuclear translocation. Inhibitory Smads (Smad6/7) and Smurf1/2 act as intracellular negative regulators of the TGFβ- and/or BMP-pathway. Several extracellular BMP antagonists/agonists and the pseudo-receptor, BAMBI, regulate BMP-signaling.