Module 2: Figure Smad signalling
The Smad signalling pathway links cell-surface transforming growth factor β (TGF-β) receptors to gene transcription.
There are two main types of Smad signalling. In the one shown on the left, receptors activated by ligands such as transforming growth factor β (TGF-β), activin and Nodal phosphorylate either Smad2 or Smad3. The phosphorylated Smads then heterodimerize with the co-mediator Smad (Co-Smad) Smad4 to form a dimer that then translocates into the nucleus. Once in the nucleus, the Smad dimer then binds to a specific Smad-binding element (SBE), which has a GTCT motif that is recognized by the MAD homology domain 1 (MH1).