Internalization-dependent and -independent requirements for transforming growth factor beta receptor signaling via the Smad pathway.
Members of the transforming growth factor beta (TGF-beta) family of proteins signal through cell surface transmembrane serine/threonine protein kinases known as type I and type II receptors. The TGF-beta signal is extended through phosphorylation of receptor-associated Smad proteins by the type I receptor. Although numerous investigations have established the sequence of events in TGF-beta receptor (TGF-beta R) activation, none have examined the role of the endocytic pathway in initiation and/or maintenance of the signaling response. In this study we investigated whether TGF-beta R internalization modulates type I receptor activation, the formation of a functional receptor/Smad/SARA complex, Smad2/3 phosphorylation or nuclear translocation, and TGF-beta-dependent reporter gene activity. Our data provide evidence that, whereas type I receptor phosphorylation and association of SARA and Smad2 with the TGF-beta R complex take place independently of clathrin lattice formation, Smad2 or Smad3 activation and downstream signaling only occur after endocytic vesicle formation. Thus, TGF-beta R endocytosis is not simply a way to dampen the signaling response but instead is required to propagate signaling via the Smad pathway.
Penheiter
Sumedha G
SG
Thoracic Diseases Research Unit and Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota 55905, USA.
Mitchell
Hugh
H
Garamszegi
Nandor
N
Edens
Maryanne
M
Doré
Jules J E
JJ
Leof
Edward B
EB
D030201:Activin Receptors, Type I / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002478:Cells, Cultured; D022163:Clathrin-Coated Vesicles / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D034281:Dynamins; D004705:Endocytosis; D020558:GTP Phosphohydrolases / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic
D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D018125:Receptors, Transforming Growth Factor beta; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I; D020558:GTP Phosphohydrolases; D034281:Dynamins