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The small leucine-rich repeat proteoglycan biglycan binds to alpha-dystroglycan and is upregulated in dystrophic muscle.

Bowe MA, Mendis DB, Fallon JR - J. Cell Biol. (2000)

Bottom Line: The dystrophin-associated protein complex (DAPC) is necessary for maintaining the integrity of the muscle cell plasma membrane and may also play a role in coordinating signaling events at the cell surface.Biglycan binding to alpha-dystroglycan was confirmed by coimmunoprecipitation with both native and recombinant alpha-dystroglycan.These findings reveal a novel binding partner for alpha-dystroglycan and demonstrate a novel avenue for interaction of the DAPC and the extracellular matrix.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Brown University, Providence, Rhode Island 02912, USA.

ABSTRACT
The dystrophin-associated protein complex (DAPC) is necessary for maintaining the integrity of the muscle cell plasma membrane and may also play a role in coordinating signaling events at the cell surface. The alpha-/beta-dystroglycan subcomplex of the DAPC forms a critical link between the cytoskeleton and the extracellular matrix. A ligand blot overlay assay was used to search for novel dystroglycan binding partners in postsynaptic membranes from Torpedo electric organ. An approximately 125-kD dystroglycan-binding polypeptide was purified and shown by peptide microsequencing to be the Torpedo ortholog of the small leucine-rich repeat chondroitin sulfate proteoglycan biglycan. Biglycan binding to alpha-dystroglycan was confirmed by coimmunoprecipitation with both native and recombinant alpha-dystroglycan. The biglycan binding site was mapped to the COOH-terminal third of alpha-dystroglycan. Glycosylation of alpha-dystroglycan is not necessary for this interaction, but binding is dependent upon the chondroitin sulfate side chains of biglycan. In muscle, biglycan is detected at both synaptic and nonsynaptic regions. Finally, biglycan expression is elevated in muscle from the dystrophic mdx mouse. These findings reveal a novel binding partner for alpha-dystroglycan and demonstrate a novel avenue for interaction of the DAPC and the extracellular matrix. These results also raise the possibility of a role for biglycan in the pathogenesis, and perhaps the treatment, of muscular dystrophy.

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Upregulation of biglycan expression in dystrophic muscle. Frozen sections of normal (wt) and mdx muscle from 6-wk-old mice were mounted on the same slides and incubated with rabbit antibiglycan (wt and mdx) as described in Materials and Methods. The overall pattern of immunoreactivity was similar in both cases. However, the expression of biglycan was elevated in mdx as compared with normal muscle. Very low levels of staining were observed when either normal (control) or mdx muscle sections (not shown) were incubated with nonimmune rabbit IgG in the first layer. Similar results were obtained in sections prepared from two other animals. Bar, 20 μm.
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Figure 7: Upregulation of biglycan expression in dystrophic muscle. Frozen sections of normal (wt) and mdx muscle from 6-wk-old mice were mounted on the same slides and incubated with rabbit antibiglycan (wt and mdx) as described in Materials and Methods. The overall pattern of immunoreactivity was similar in both cases. However, the expression of biglycan was elevated in mdx as compared with normal muscle. Very low levels of staining were observed when either normal (control) or mdx muscle sections (not shown) were incubated with nonimmune rabbit IgG in the first layer. Similar results were obtained in sections prepared from two other animals. Bar, 20 μm.

Mentions: Previous reports have shown that biglycan mRNA and protein are expressed in muscle (Bianco et al. 1990; Bosse et al. 1993). Since we purified biglycan from synaptic membranes, we asked whether it is also expressed at the neuromuscular junction. Biglycan is localized around the periphery of the muscle fiber and at all synapses. Further, biglycan is enriched at a subset of neuromuscular junctions (Fig. 6). Finally, since biglycan binds to a component of the DAPC, we asked whether or not its expression was altered in a mouse model of muscular dystrophy where dystrophin is absent, mdx. We examined adult mice, which contain almost exclusively regenerated muscle fibers that survive due to utrophin compensation (Grady et al. 1997). Immunostaining revealed that the level of biglycan expressed in mdx muscle is elevated compared with control animals (Fig. 7). These observations raise the possibility that biglycan could be part of the compensatory mechanism that allows survival of dystrophin-negative muscle fibers.


The small leucine-rich repeat proteoglycan biglycan binds to alpha-dystroglycan and is upregulated in dystrophic muscle.

Bowe MA, Mendis DB, Fallon JR - J. Cell Biol. (2000)

Upregulation of biglycan expression in dystrophic muscle. Frozen sections of normal (wt) and mdx muscle from 6-wk-old mice were mounted on the same slides and incubated with rabbit antibiglycan (wt and mdx) as described in Materials and Methods. The overall pattern of immunoreactivity was similar in both cases. However, the expression of biglycan was elevated in mdx as compared with normal muscle. Very low levels of staining were observed when either normal (control) or mdx muscle sections (not shown) were incubated with nonimmune rabbit IgG in the first layer. Similar results were obtained in sections prepared from two other animals. Bar, 20 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2169361&req=5

Figure 7: Upregulation of biglycan expression in dystrophic muscle. Frozen sections of normal (wt) and mdx muscle from 6-wk-old mice were mounted on the same slides and incubated with rabbit antibiglycan (wt and mdx) as described in Materials and Methods. The overall pattern of immunoreactivity was similar in both cases. However, the expression of biglycan was elevated in mdx as compared with normal muscle. Very low levels of staining were observed when either normal (control) or mdx muscle sections (not shown) were incubated with nonimmune rabbit IgG in the first layer. Similar results were obtained in sections prepared from two other animals. Bar, 20 μm.
Mentions: Previous reports have shown that biglycan mRNA and protein are expressed in muscle (Bianco et al. 1990; Bosse et al. 1993). Since we purified biglycan from synaptic membranes, we asked whether it is also expressed at the neuromuscular junction. Biglycan is localized around the periphery of the muscle fiber and at all synapses. Further, biglycan is enriched at a subset of neuromuscular junctions (Fig. 6). Finally, since biglycan binds to a component of the DAPC, we asked whether or not its expression was altered in a mouse model of muscular dystrophy where dystrophin is absent, mdx. We examined adult mice, which contain almost exclusively regenerated muscle fibers that survive due to utrophin compensation (Grady et al. 1997). Immunostaining revealed that the level of biglycan expressed in mdx muscle is elevated compared with control animals (Fig. 7). These observations raise the possibility that biglycan could be part of the compensatory mechanism that allows survival of dystrophin-negative muscle fibers.

Bottom Line: The dystrophin-associated protein complex (DAPC) is necessary for maintaining the integrity of the muscle cell plasma membrane and may also play a role in coordinating signaling events at the cell surface.Biglycan binding to alpha-dystroglycan was confirmed by coimmunoprecipitation with both native and recombinant alpha-dystroglycan.These findings reveal a novel binding partner for alpha-dystroglycan and demonstrate a novel avenue for interaction of the DAPC and the extracellular matrix.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Brown University, Providence, Rhode Island 02912, USA.

ABSTRACT
The dystrophin-associated protein complex (DAPC) is necessary for maintaining the integrity of the muscle cell plasma membrane and may also play a role in coordinating signaling events at the cell surface. The alpha-/beta-dystroglycan subcomplex of the DAPC forms a critical link between the cytoskeleton and the extracellular matrix. A ligand blot overlay assay was used to search for novel dystroglycan binding partners in postsynaptic membranes from Torpedo electric organ. An approximately 125-kD dystroglycan-binding polypeptide was purified and shown by peptide microsequencing to be the Torpedo ortholog of the small leucine-rich repeat chondroitin sulfate proteoglycan biglycan. Biglycan binding to alpha-dystroglycan was confirmed by coimmunoprecipitation with both native and recombinant alpha-dystroglycan. The biglycan binding site was mapped to the COOH-terminal third of alpha-dystroglycan. Glycosylation of alpha-dystroglycan is not necessary for this interaction, but binding is dependent upon the chondroitin sulfate side chains of biglycan. In muscle, biglycan is detected at both synaptic and nonsynaptic regions. Finally, biglycan expression is elevated in muscle from the dystrophic mdx mouse. These findings reveal a novel binding partner for alpha-dystroglycan and demonstrate a novel avenue for interaction of the DAPC and the extracellular matrix. These results also raise the possibility of a role for biglycan in the pathogenesis, and perhaps the treatment, of muscular dystrophy.

Show MeSH
Related in: MedlinePlus