TGF-β receptor-binding proteins: Complex interactions

Members of the Smad protein family are fundamental downstream mediators of TGF-β signals. However, the basic, linear Smad signaling pathway is unlikely to be the sole contributor to the plethora of cell type-specific TGF-β responses. Investigators have identified a number of molecules that interact with the TGF-β receptors (TβRs) and may explain, at least in part, the tight regulation of TGF-β effects. Understanding these TβR-interacting molecules is thus a matter of great potential significance for elucidating TGF-β-family signal transduction. The present article reviews our current understanding of the roles and mechanisms of action of this relatively understudied group of molecules.