Identification of a Smad Phosphatase

Activation of Smad signaling pathways downstream of TGF-β superfamily ligands via receptor-mediated Smad phosphorylation is well understood, but little is known about the phosphatases that turn off Smad activity. Now in Cell, Feng and colleagues (Lin, X., et al. (2006) Cell 125, 915–928) report their discovery that PPM1A acts as a Smad phosphatase to terminate TGF-β signaling.