SARA, a FYVE domain protein that recruits Smad2 to the TGF beta receptor

Smads transmit signals from transmembrane ser/thr kinase receptors to the n ucleus. We now identify SARA (for Smad anchor for receptor activation), a F YVE domain protein that interacts directly with Smad2 and Smad3. SARA funct ions to recruit Smad2 to the TGF beta receptor by controlling the subcellul ar localization of Smad2 and by interacting with the TGF beta receptor comp lex. Phosphorylation of Smad2 induces dissociation from SARA with concomita nt formation of Smad2/Smad4 complexes and nuclear translocation. Furthermor e, mutations in SARA that cause mislocalization of Smad2 inhibit TGF beta-d ependent transcriptional responses, indicating that the regulation of Smad localization is important for TGF beta signaling. These results thus define SARA as a component of the TGF beta pathway that brings the Smad substrate to the receptor.