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Complementation between kinase-defective and activation-defective TGF-beta receptors reveals a novel form of receptor
1Howard Hughes Medical Institute, Memorial Sloan-Kettering Cancer Center, New York, 10021, USA.
Abstract:
Transforming growth factor-beta (TGF-beta) signals through two transmembrane serine/threonine kinases, T beta R-I and T beta R-II. TGF-beta binds to T beta R-II, allowing this receptor to associate with and phosphorylate T beta R-I which then propagates the signal. T beta R-I is phosphorylated within its GS domain, a region immediately preceding the kinase domain. To further understand the function of T beta R-I in this complex, we analyzed T beta R-I-inactivating mutations identified in cell lines that are defective in TGF-beta signaling yet retain ligand binding ability. The three mutations identified here all fall in the kinase domain of T beta R-I. One mutation disrupts the kinase activity of T beta R-I, whereas the other two mutations prevent ligand-induced T beta R-I phosphorylation, and thus activation, by T beta R-II. Unexpectedly, a kinase-defective T beta R-I mutant can functionally complement an activation- defective T beta R-I mutant, by rescuing its T beta R-II- dependent phosphorylation. Together with evidence that the ligand-induced receptor complex contains two or more T beta R-I molecules, these results support a model in which the kinase domain of one T beta R-I molecule interacts with the GS domain of another, enabling its phosphorylation and activation by T beta R-II. This cooperative interaction between T beta R-I molecules appears essential for TGF-beta signal transduction.
Insights
Transforming growth factor-beta (TGF-beta) signaling requires cooperative interaction between T beta R-I kinase domains. This interaction is essential for TGF-beta receptor activation and signal transduction.
Area of Science:
- Cellular signaling pathways
- Molecular biology
- Biochemistry
Background:
- Transforming growth factor-beta (TGF-beta) is a crucial signaling molecule.
- TGF-beta exerts its effects through transmembrane serine/threonine kinases, T beta R-I and T beta R-II.
- Ligand binding to T beta R-II initiates receptor complex formation and T beta R-I phosphorylation.
Purpose of the Study:
- To investigate the function of T beta R-I in TGF-beta signaling.
- To analyze T beta R-I mutations affecting TGF-beta signal transduction.
- To elucidate the mechanism of T beta R-I activation.
Main Methods:
- Analysis of T beta R-I-inactivating mutations in cell lines with defective TGF-beta signaling.
- Characterization of mutations within the kinase domain of T beta R-I.
- Functional complementation assays using kinase-defective and activation-defective T beta R-I mutants.
Main Results:
- Three T beta R-I mutations were identified in the kinase domain.
- One mutation abolished kinase activity; two prevented T beta R-II-mediated phosphorylation.
- A kinase-defective T beta R-I mutant rescued the activation defect of an activation-defective mutant.
- Evidence suggests the involvement of at least two T beta R-I molecules in the activated complex.
Conclusions:
- T beta R-I activation involves a cooperative interaction between the kinase domains of T beta R-I molecules.
- The kinase domain of one T beta R-I interacts with the GS domain of another, facilitating activation by T beta R-II.
- This intermolecular interaction is critical for TGF-beta signal transduction.