Differential Vicia villosa agglutinin reactivity identifies three distinct dystroglycan complexes in skeletal muscle.
We present evidence for the expression of three alpha-dystroglycan glycoforms in skeletal muscle cells, including two minor glycoforms marked by either patent or latent reactivity with the N-acetylgalactosamine-specific lectin Vicia villosa agglutinin. Both minor glycoforms co-isolated with beta-dystroglycan, but not with other dystrophin/utrophin-glycoprotein complex components, suggesting that they may perform distinct or modified cellular functions. We also confirmed that both patent and latent V. villosa agglutinin-reactive alpha-dystroglycan glycoforms are expressed in C2C12 myotubes. However, we found that the combined effect of saturating concentrations of V. villosa agglutinin and laminin-1 were strictly additive with respect to acetylcholine receptor cluster formation in C2C12 myotubes, which suggests that laminin-1 and V. villosa agglutinin do not compete for the same binding site on the cell surface. Finally, although beta-N-acetylhexosaminidase digestion dramatically inhibited agrin-, V. villosa agglutinin-, and laminin-1-induced acetylcholine receptor clustering in C2C12 myotubes, treatment with this enzyme had no effect on the amount of alpha-dystroglycan that was bound to V. villosa agglutinin-agarose. We conclude that alpha-dystroglycan is not the V. villosa agglutinin receptor implicated in acetylcholine receptor cluster formation. However, our data provide new support for the hypothesis that different glycoforms of alpha-dystroglycan may perform distinct functions even within the same cell.
McDearmon
E L
EL
Graduate Program in Molecular and Cellular Pharmacology, University of Wisconsin-Madison Medical School, Madison, Wisconsin 53706, USA.
Combs
A C
AC
Ervasti
J M
JM
D000818:Animals; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000032:analysis* / Q000502:physiology; D049030:Dystroglycans; D007797:Laminin / Q000494:pharmacology; D037102:Lectins / Q000378:metabolism* / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000032:analysis* / Q000502:physiology; D018482:Muscle, Skeletal / Q000737:chemistry*; D009439:Neuraminidase / Q000494:pharmacology; D009469:Neuromuscular Junction / Q000737:chemistry; D037121:Plant Lectins; D011817:Rabbits; D011950:Receptors, Cholinergic / Q000187:drug effects; D001619:beta-N-Acetylhexosaminidases / Q000494:pharmacology
D003598:Cytoskeletal Proteins; D007797:Laminin; D037102:Lectins; D008562:Membrane Glycoproteins; D037121:Plant Lectins; D011950:Receptors, Cholinergic; C042242:Vicia lectins; C121346:laminin 1; D049030:Dystroglycans; D009439:Neuraminidase; D001619:beta-N-Acetylhexosaminidases