Intracellular signal transduction of TGF-β signalling. TGF-β ligand binds to TβRI and TβRII to constitute active heterodimers that possess serin-threonin kinase activity. Activated TβRI phosphorylates Smad2 and Smad3, which in turn form a complex with Smad4. Smad2 or Smad3/Smad4 complex translocates into the nucleus where interacts with other DNA-binding transcription factors, coactivators and corepressors, regulating the transcription of target genes.
