Core 1 Glycans on α-Dystroglycan Mediate Laminin-induced Acetylcholine Receptor Clustering but Not Laminin Binding

Abstract

Although unique O-linked oligosaccharides on ␣-dystroglycan are important for binding to a variety of extracellular ligands, the function(s) of more generic carbohydrate structures on ␣-dystroglycan remain unclear. Recent studies suggest a role for glycoconjugates bearing the core 1 disaccharide Gal␤(1-3)GalNAc in acetylcholine receptor (AChR) clustering on the surface of muscle cells. Here, we report experiments demonstrating that the core 1-specific lectin jacalin almost completely abrogated laminin-induced AChR clustering in C2C12 myotubes and that ␣-dystroglycan was the predominant jacalin-binding protein detected in C2C12 myotube lysates. Although jacalin likely inhibited laminin-induced AChR clustering by directly binding to ␣-dystroglycan, jacalin had no effect on laminin binding to the myotube surface or to ␣-dystroglycan. Like jacalin, peanut agglutinin lectin also binds the core 1 disaccharide but not when it is terminally sialylated as expressed on ␣-dystroglycan. We show that C2C12 ␣-dystroglycan bound to peanut agglutinin only after digestion with neuraminidase. Simultaneous treatment of myotubes with neuraminidase and endo-O-glycosidase diminished ␣-dystroglycan binding to peanut agglutinin and inhibited neuraminidase-induced AChR clustering. We conclude that sialylated core 1 oligosaccharides of ␣-dystroglycan are important for laminin-induced AChR clustering and that their function in this process is distinct from the established role of ␣-dystroglycan oligosaccharides in laminin binding.

An Extracellular Pathway for Dystroglycan Function in Acetylcholine Receptor Aggregation and Laminin Deposition in Skeletal Myotubes

“…We hypothesized that DG functions via an extracellular as well as an intracellular matrix of proteins (38); consistent with this, a recent report suggests novel extracellular interactions of ␣-DG in AChR aggregation (39). Here we show that ␣-DG is glycosylated and targeted to the cell surface in absence of ␤-DG (Fig.…”

“…Also, we proposed that ␣-and ␤-DG function coordinately to assemble an extracellular and intracellular matrix of proteins (38), which is consistent with a recent report suggesting novel extracellular interactions for DG (39). In this study, we have taken advantage of the well defined role of DG at NMJs to determine whether the extracellular domains of DG function independently in AChR aggregation.…”

Old World and Clade C New World Arenaviruses Mimic the Molecular Mechanism of Receptor Recognition Used by α-Dystroglycan's Host-Derived Ligands

“…These more generic O-glycans are not involved in the binding of ␣-DG to ECM proteins (18) but were recently found to be important for the ability of ␣-DG to mediate the clustering of acetylcholine receptors during muscle differentiation (34). This function of ␣-DG's core 1 Oglycans in a molecular recognition process raises the question of whether arenaviruses have also evolved to recognize these glycan structures.…”

Neuregulin Inhibits Acetylcholine Receptor Aggregation in Myotubes

“…We therefore examined the ability of ErbB receptors to modulate AChR distribution in C2C12 myotubes. The mouse muscle cell line C2 and its subclone C2C12 have been used extensively to characterize AChR clustering on the surface of muscle cells (15)(16)(17)(18). We demonstrate that the EGF domain of neuregulin-␤ 1 is able to inhibit both spontaneous and agrin-induced AChR aggregation.…”