Research on the TGF-β family of ligands and receptors has exploded recently with the identification of downstream signaling proteins and further characterization of signaling regulators. Massagué and Chen discuss in great detail the mechanisms that control TGF-β signaling from the extracellular milieu (agonists to antagonists to antagonists of antagonists), to transmembrane receptor decoys, to regulation of protein association with the cytoplasmic domains of the receptor complexes. The authors cover the role of Ras and MAP kinases in the negative and positive regulation of Smads, and the internetworking of Smads with other pathways. For an outstanding review on the specifics of Smad crosstalk and interactions, see the review by Wrana in the STKE Reviews section.
Massagué, J., and Chen, Y.-G. (2000) Controlling TGF-signaling. Genes Dev. 14: 627-644. [Full Text]