Browsing by Author "Schönherr, E"

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    Antisense inhibition of decorin expression in myoblasts decreases cell responsiveness to transforming growth factor β and accelerates skeletal muscle differentiation
    (2001) Riquelme, C; Larraín, J; Schönherr, E; Henriquez, JP; Kresse, H; Brandan, E
    Decorin is a member of the family of the small leucine-rich proteoglycans. In addition to its function as an extracellular matrix organizer, it has the ability to activate the epidermal growth factor receptor, and it forms complexes with various isoforms of transforming growth factor beta (TGF-beta), Decorin is expressed during skeletal muscle differentiation and is up-regulated in dystrophic muscle. In this study we investigated the role of decorin in TGF-beta -dependent inhibition of myogenesis, To probe the function of decorin during myogenesis, C2C12 myoblasts were stably transfected with a plasmid expressing antisense decorin mRNA. The re; suiting inhibition of decorin expression led to the expression of myogenin, a master transcription factor for muscle differentiation, under growth conditions and accelerated skeletal muscle differentiation as determined by the expression of creatine kinase, In contrast myogenin expression was inhibited by adenovirally induced decorin expression or by adding exogenous decorin, Reduced synthesis of decorin resulted in a 7-fold decreased sensitivity to TGF-beta -mediated inhibition of myogenin expression. In contrast, adenovirally induced decorin expression in wild type cells resulted in a 5-fold increased sensitivity to TGF-beta -mediated inhibition of myogenin expression. Transfection studies with the TGF-beta -dependent promoter of the plasminogen activator inhibitor-1 coupled with luciferase revealed that the transducing receptors for TGF-beta1 and TGF-beta2 were involved in the different responses of wild type and anti-sense decorin myoblasts, These results demonstrate that a reduction of decorin expression or of decorin availability results in a decreased responsiveness to TGF-beta. These findings strongly suggest a new role for decorin during skeletal muscle terminal differentiation by activating TGF-beta -dependent signaling pathways.
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    Decorin core protein fragment Leu155-Val260 interacts with TGF-β but does not compete for decorin binding to type I collagen
    (1998) Schönherr, E; Broszat, M; Brandan, E; Bruckner, P; Kresse, H
    It has been shown that small proteoglycans containing leucine-rich repeats in their core proteins can form complexes with TGF-beta. Decorin, a ubiquitously found molecule of the extracellular matrix, is the best-studied example. Therefore, binding domains on its core protein were investigated using recombinant decorin fragments generated as fusion proteins in prokaryotes. The peptide Leu155-Val260 immobilized by the polyhistidine tag on a nickel chelate column bound TGF-beta 1 and -beta 2 almost as effectively as the largest fragment (Asp45-Lys359) studied. Other peptides were less effective. For the two peptides Asp45-Lys359 and Leu155-Val260 dissociation constants in the nanomolar range for high-affinity binding sites were calculated in a solid-phase assay with immobilized TGF-beta 2. Peptide Asp45-Lys359 also contained a lower affinity binding site. Domains with lower affinity were also found in peptides Asp45-Leu155 and Arg63-Gly190. Peptide Leu155-Val260 also formed complexes with TGF-beta in the liquid phase as determined by equilibrium gel filtration. Furthermore, F(ab') fragments of polyclonal antibodies against peptide Leu155-Val260 interfered with TGF-beta binding to peptide Asp45-Lys359 in a dose-dependent manner. Peptide Leu155-Val260, however, is only a weak competitor of the binding of wild-type decorin to reconstituted type I collagen fibrils. Therefore, independent binding sites of decorin for TGF-beta and type I collagen should exist. In support of this hypothesis saturable binding of TGF-beta 1 and TGF-beta 2 to collagen-bound native decorin could be demonstrated. The bound cytokine could be released in a biologically active form by collagenase treatment. Thus, decorin may play a biological role in storing this cytokine temporarily in the extracellular matrix and in thereby modulating an interaction of TGF-beta with its signaling receptors. (C) 1998 Academic Press.