Rabbit polyclonal antibody to Smad3 (Ser213)

Members of the SMAD family of signal transduction molecules are components of a critical intracellular pathway that transmit TGF~β signals from the cell surface into the nucleus. Three distinct classes of SMADs have been defined: the receptor~regulated SMADs (R~SMADs), which include SMAD1, 2, 3, 5, and 9; the common~mediator SMAD (co~SMAD), SMAD4; and the antagonistic or inhibitory SMADs (I~SMADs), SMAD6 and 7. Activated type I receptors associate with specific R~SMADs and phosphorylate them on a conserved carboxy~terminal SSXS motif. The phosphorylated R~SMADs dissociate from the receptor and form a heteromeric complex with SMAD4, initiating translocation of the heteromeric SMAD complex to the nucleus. Once in the nucleus, SMADs recruit a variety of DNA binding proteins that function to regulate transcriptional activity. Following stimulation by TGF~β, Smad2 and Smad3 become phosphorylated at their carboxyl termini (Ser465 and 467 on Smad2; Ser423 and 425 on Smad3) by TGF~β Receptor I. Phosphorylated Smad 2/3 can complex with Smad4, translocate to the nucleus and regulate gene expression.