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| Figure 1: Schematic representation of Smad protein domains and sites of phosphorylation by multiple kinases. Membrane-bound TGF-β type I receptor (TβRI) phosphorylates 2 serine residues in the C-tail. Thr-220 in Smad2L and Thr-179 in Smad3L are preferred phosphorylation sites for nuclear CDK4 in response to TGF-β, while 3 clustered Ser residues are shown as phosphorylation sites for cytoplasmic JNK activated by RTK growth factors and proinflammatory cytokines. |
