Phosphoserine-dependent regulation of protein-protein interactions in the Smad pathway.

Transforming growth factor beta (TGF-beta) is a secreted growth factor that regulates the transcriptional program of cells via heteromeric complexes of transmembrane type II and type I Ser/Thr kinase receptors and the Smad intracellular signal transduction pathway [1]. The activity of this pathway is tightly controlled by serine phosphorylation, which plays a key role in regulating protein-protein interactions that are critical in the elaboration of transcriptional responses.