Biochemical evidence for the autophosphorylation and transphosphorylation of transforming growth factor beta receptor kinases.
Transforming growth factor beta (TGF-beta) signals through a receptor complex containing the type I (TGF-beta RI) and type II (TGF-beta RII) receptors. We describe here biochemical studies on early events in the TGF-beta signaling pathways. TGF-beta RII is highly phosphorylated when expressed alone in COS-1 cells; its autophosphorylation occurs via an intramolecular (cis) mechanism that is independent of ligand binding. TGF-beta RI is also highly phosphorylated when expressed alone in COS-1 cells. Both wild-type TGF-beta RI and a kinase-deficient mutant thereof are transphosphorylated by the coexpressed TGF-beta RII kinase in a ligand-independent fashion in these cells. We propose that the association of TGF-beta RI and TGF-beta RII, induced by ligand binding or over-expression, leads to transphosphorylation of the TGF-beta RI by the TGF-beta RII kinase. This represents a mechanism of activation of receptors distinct from that of tyrosine kinase receptors and may apply to other serine/threonine kinase receptors.
Chen
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Whitehead Institute for Biomedical Research, Cambridge, MA 02142.
Weinberg
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RA
D002478:Cells, Cultured; D006801:Humans; D066298:In Vitro Techniques; D008024:Ligands; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D018125:Receptors, Transforming Growth Factor beta / Q000145:classification / Q000378:metabolism*; D011994:Recombinant Proteins; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000378:metabolism
D008024:Ligands; D018125:Receptors, Transforming Growth Factor beta; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases