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Transforming growth factor-beta type-II receptor signalling: intrinsic/associated casein kinase activity, receptor
F L Hall1, P D Benya, S R Padilla
1Department of Surgery, Childrens Hospital Los Angeles Research Institute, CA 90027, USA.
Abstract:
The transforming growth factor beta (TGF-beta) family of growth factors control proliferation, extracellular matrix synthesis and/ or differentiation in a wide variety of cells. However, the molecular mechanisms governing ligand binding, receptor oligomerization and signal transduction remain incompletely understood. In this study, we utilized a set of antibodies selective for the extracellular and intracellular domains of the TGF-beta type-II receptor as probes to investigate the intrinsic kinase activity of this receptor and its physical association in multimeric complexes with type-I and type-III receptors. The type-II receptor immuno-precipitated from human osteosarcoma cells exhibited autophosphorylation and casein kinase activity that was markedly stimulated by polylysine yet was insensitive to heparin. Affinity cross-linking of 125I-TGF-beta 1 ligand to cellular receptors followed by specific immunoprecipitation demonstrated that type-II receptors form stable complexes with both type-I and type-III receptors expressed on the surfaces of both human osteosarcoma cells and rabbit chondrocytes. Pretreatment of the cultured cells with an antibody directed against a distinct extracellular segment of the type-II receptor (anti-TGF-beta-IIR-NT) effectively blocked the 125I-TGF-beta labelling of type-I receptors without preventing the affinity labelling of type-II or type-III receptors, indicating a selective disruption of the type-I/type-II hetero-oligomers. The anti-TGF-beta-IIR-NT antibodies also blocked the TGF-beta-dependent induction of the plasminogen activator inhibitor (PAI-1) promoter observed in mink lung epithelial cells. However, the same anti-TGF-beta-IIR-NT antibodies did not prevent the characteristic inhibition of cellular proliferation by TGF-beta 1, as determined by [3H]thymidine incorporation into DNA. The selective perturbation of PAI-1 promoter induction versus cell-cycle-negative regulation suggests that strategic disruption of TGF-beta type-I and -II receptor interactions can effectively alter specific cellular responses to TGF-beta signalling.
Insights
Antibodies targeting the TGF-beta type-II receptor selectively disrupt specific signaling pathways, altering cellular responses without affecting all TGF-beta functions. This reveals distinct roles for receptor interactions in TGF-beta signal transduction.
Area of Science:
- Cellular Biology
- Molecular Biology
- Biochemistry
Background:
- The transforming growth factor beta (TGF-beta) family regulates crucial cellular processes like proliferation and differentiation.
- Molecular mechanisms of TGF-beta ligand binding, receptor assembly, and signal transduction are not fully understood.
Purpose of the Study:
- To investigate the kinase activity of the TGF-beta type-II receptor.
- To examine the physical association of TGF-beta receptors (types I, II, and III) in multimeric complexes.
- To explore how specific antibody interventions affect TGF-beta signaling pathways.
Main Methods:
- Utilized antibodies targeting extracellular and intracellular domains of the TGF-beta type-II receptor.
- Assessed receptor kinase activity via autophosphorylation and casein kinase assays.
- Employed affinity cross-linking and immunoprecipitation to study receptor complex formation.
- Investigated the impact of specific antibodies on TGF-beta-induced gene expression and cellular proliferation.
Main Results:
- TGF-beta type-II receptor exhibits intrinsic kinase activity, stimulated by polylysine.
- Type-II receptors form stable complexes with type-I and type-III receptors.
- An antibody against the TGF-beta type-II receptor extracellular domain selectively disrupted type-I/type-II hetero-oligomers.
- This antibody blocked PAI-1 promoter induction but not TGF-beta-mediated inhibition of cell proliferation.
Conclusions:
- Specific disruption of TGF-beta type-I and type-II receptor interactions can selectively modulate cellular responses to TGF-beta.
- This suggests distinct molecular mechanisms underlie different TGF-beta signaling outcomes.
- Targeting specific receptor interactions offers a strategy to fine-tune TGF-beta pathway effects.