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© The Rockefeller University Press,
0021-9525/2000//801 $5.00
The Journal of Cell Biology, Volume 148, Number 4,
, 2000 801-810
Original Article |
The Small Leucine-Rich Repeat Proteoglycan Biglycan Binds to 
-Dystroglycan and Is Upregulated in Dystrophic Muscle
justin_fallon{at}brown.edu
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
-/β-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 
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 -dystroglycan was confirmed by coimmunoprecipitation with both native and recombinant -dystroglycan. The biglycan binding site was mapped to the COOH-terminal third of -dystroglycan. Glycosylation of -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 -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.
Key Words: muscular dystrophy • dystrophin-associated protein complex • chondroitin sulfate proteoglycan • agrin • neuromuscular junction
© 2000 The Rockefeller University Press
Mark A. Bowe's current address is Genetic Therapy, Inc., Gaithersburg, MD 20878.Duane B. Mendis' current address is MJ Research, Inc., Waltham, MA 02541.
Abbreviations used in this paper: aa, amino acid; AChR, acetylcholine receptor; DAG-125, dystroglycan-associated glycoprotein of 125 kD; DAPC, dystrophin-associated protein complex; ECM, extracellular matrix; GST, glutathione S-transferase; SLRP, small leucine-rich repeat proteoglycan.
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