Signaling activity of homologous and heterologous transforming growth factor-beta receptor kinase complexes.
Transforming growth factor-beta (TGF-beta) signaling in Mv1Lu lung epithelial cells requires coexpression of TGF-beta receptors I (T beta R-I) and II (T beta R-II), two distantly related transmembrane serine/threonine kinases that form a heteromeric complex upon ligand binding. Here, we examine the formation of TGF-beta receptor homo-oligomers and their possible contribution to signaling. T beta R-I can contact ligand bound to T beta R-II, but not ligand free in the medium, and thus cannot form ligand-induced homo-oligomers. T beta R-II, which binds ligand on its own, formed oligomeric complexes when overexpressed in transfected COS cells. However, these complexes were largely ligand-independent and involved immature receptor protein. Since ligand-induced homo-oligomers could not be obtained with the wild-type TGF-beta receptors, we studied receptor cytoplasmic domain homo-oligomerization by using receptor chimeras. The extracellular domain of T beta R-II was fused to the transmembrane and cytoplasmic domains of T beta R-I, yielding T beta R-II/I, and the extracellular domain of T beta R-I was fused to the transmembrane and cytoplasmic domains of T beta R-II, yielding T beta R-I/II. When contransfected with wild-type receptors and exposed to ligand, T beta R-II/I formed a complex with T beta R-I, and T beta R-I/II formed a complex with T beta R-II, thus yielding complexes with homologous cytoplasmic domains. T beta R-II/I transfected alone or with T beta R-I did not restore TGF-beta responsiveness in T beta R-II-defective cell mutants. Furthermore, T beta R-II/I acted in a dominant negative fashion, inhibiting restoration of TGF-beta responsiveness by a cotransfected T beta R-II in T beta R-II-defective cells and by a cotransfected T beta R-I in T beta R-I-defective cells. Similarly, T beta R-I/II transfected alone or with T beta R-II did not restore TGF-beta responsiveness and acted in a dominant negative fashion against T beta R-I. Together with previous genetic and biochemical evidence, these results suggest that TGF-beta mediates transcriptional and antiproliferative responses through the heteromeric T beta R-I.T beta R-II complex and not through homo-oligomeric T beta R-I or T beta R-II complexes.
Vivien
D
D
Cell Biology and Genetics Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Attisano
L
L
Wrana
J L
JL
Massagué
J
J
D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007668:Kidney; D007700:Kinetics; D008156:Luciferases / Q000378:metabolism; D008907:Mink; D016133:Polymerase Chain Reaction; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D018125:Receptors, Transforming Growth Factor beta / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D018125:Receptors, Transforming Growth Factor beta; D011993:Recombinant Fusion Proteins; D016212:Transforming Growth Factor beta; D008156:Luciferases; D020794:Receptor Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases