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The 260-kDa transforming growth factor (TGF)-beta binding protein in rat glomeruli is a complex comprised of 170- and
K MacKay1, D Danielpour, D Miller
1Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Abstract:
In a previous study (MacKay, K., Robbins, A. R., Bruce, M. D., and Danielpour, D. (1990) J. Biol. Chem. 265, 9351-9356) we showed that rat glomeruli contain transforming growth factor (TGF)-beta 1 binding proteins with apparent molecular masses of 260, 170, and 85 kDa (Gl-260, Gl-170, Gl-85) as determined by electrophoresis under nonreducing conditions. We demonstrate here that Gl-260 is a complex of 170- and 85-kDa TGF-beta binding proteins. Under denaturing conditions the integrity of Gl-260 is maintained through the cross-linking of one monomer of the disulfide-linked TGF-beta 1 homodimer to Gl-85 and of the other monomer to the 100-kDa subunit of Gl-170. In addition, some Gl-260 complexes are maintained by direct cross-linking of Gl-85 to the 100-kDa subunit of Gl-170. One-dimensional peptide maps of Gl-85 and the 100-kDa subunit of Gl-170 indicate that they have distinctly different ligand binding domains. In contrast, peptide maps of Gl-85 and the type II receptor of normal rat kidney fibroblasts are similar. The biological responses of isolated glomeruli to TGF-beta appear to parallel those of cultured glomerular cells which are without detectable Gl-170 and Gl-260 binding proteins.
Insights
Rat glomeruli possess transforming growth factor-beta 1 (TGF-β1) binding proteins. Glomerular TGF-β1 binding protein Gl-260 is a complex of Gl-170 and Gl-85 proteins, with distinct ligand binding domains.
Area of Science:
- Biochemistry
- Cell Biology
- Nephrology
Background:
- Rat glomeruli contain TGF-β1 binding proteins (Gl-260, Gl-170, Gl-85) identified previously.
- These proteins play a role in TGF-β1 signaling within the glomerulus.
Purpose of the Study:
- To elucidate the molecular composition and interactions of TGF-β1 binding proteins in rat glomeruli.
- To investigate the relationship between glomerular TGF-β1 binding proteins and cellular responses.
Main Methods:
- Electrophoresis under non-reducing and denaturing conditions.
- Chemical cross-linking to study protein complexes.
- One-dimensional peptide mapping to compare protein domains.
- Comparison with type II receptor of rat kidney fibroblasts.
Main Results:
- Gl-260 is a complex of Gl-170 and Gl-85 TGF-β1 binding proteins.
- Gl-260 integrity is maintained by cross-linking of TGF-β1 homodimer to Gl-85 and Gl-170 subunits, or direct cross-linking between Gl-85 and Gl-170.
- Gl-85 and the 100-kDa subunit of Gl-170 possess distinct ligand binding domains.
- Gl-85 shares similarities with the type II receptor of rat kidney fibroblasts.
- Isolated glomeruli responses to TGF-β1 mirror cultured glomerular cells lacking Gl-170 and Gl-260.
Conclusions:
- Gl-260 represents a complex of Gl-170 and Gl-85, crucial for TGF-β1 binding in glomeruli.
- Distinct ligand binding domains in Gl-85 and Gl-170 suggest specialized roles.
- The absence of Gl-170 and Gl-260 in cultured cells correlates with their biological responses, highlighting their importance in glomerular TGF-β1 signaling.