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.
Jacobson
C
C
Departments of Biology and Neurology and Neurosurgery, McGill University and the Centre for Research in Neuroscience, Montreal, Quebec, H3G 1A4 Canada.
Montanaro
F
F
Lindenbaum
M
M
Carbonetto
S
S
Ferns
M
M
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