alpha-Dystroglycan functions in acetylcholine receptor aggregation but is not a coreceptor for agrin-MuSK signaling.
alpha-dystroglycan (alpha-DG) is an agrin-binding protein that has been implicated in acetylcholine receptor (AChR) clustering, but it is unclear whether it acts as a coreceptor involved in initial agrin signaling or as a component involved in later events. To investigate its role, we have generated antisense derivatives of the C2 mouse muscle cell line, which have reduced alpha-DG expression. When compared with wild-type cells, the alpha-DG-deficient myotubes have a dramatic reduction in the number of spontaneous and agrin-induced AChR clusters. Several findings suggest that this decrease in AChR clustering is likely not because of a defect in agrin signaling through the MuSK receptor tyrosine kinase. Compared with wild-type cells, the alpha-DG-deficient cell lines showed only a transient reduction in the level of agrin-induced MuSK tyrosine phosphorylation and no reduction in AChR beta-subunit tyrosine phosphorylation. Additionally, agrin-induced phosphorylation of MuSK in wild-type myotubes was not decreased using agrin fragments that lack the domain primarily responsible for binding to alpha-DG. Finally, neural agrin-induced phosphorylation of MuSK was unaffected by treatments such as excess muscle agrin or anti-alpha-DG antibodies, both of which block agrin-alpha-DG binding. Together, these results suggest that alpha-DG is not required for agrin-MuSK signaling but rather that it may play a role elsewhere in the clustering pathway, such as in the downstream consolidation or maintenance of AChR clusters.
Departments of Biology and Neurology and Neurosurgery, McGill University and the Centre for Research in Neuroscience, Montreal, Quebec, H3G 1A4 Canada.
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C
Jacobson
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Montanaro
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M
Lindenbaum
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Carbonetto
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Ferns
D018171:Agrin / Q000502:physiology*; D000818:Animals; D001667:Binding, Competitive; D002460:Cell Line / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000502:physiology*; D049030:Dystroglycans; D006493:Heparin / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000502:physiology*; D051379:Mice; D010766:Phosphorylation; D011940:Receptor Aggregation / Q000502:physiology*; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology*; D011950:Receptors, Cholinergic / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
D018171:Agrin; D003598:Cytoskeletal Proteins; C483081:DAG1 protein, human; D008562:Membrane Glycoproteins; D011950:Receptors, Cholinergic; D049030:Dystroglycans; D006493:Heparin; C095714:MUSK protein, human; D020794:Receptor Protein-Tyrosine Kinases