Synergistic effects of neuregulin and agrin on muscle acetylcholine receptor expression.
The proper function of neuromuscular junctions requires an extremely high density of acetylcholine receptors (AChRs) that may be achieved from neuron-derived factors including agrin and neuregulin. Here, we show that neuregulin-1 and agrin co-localize at neuromuscular junctions in vivo and form complexes when co-transfected into COS-7 cells. When these COS-7 cells are cultured with myotubes, synergistic effects are observed for AChR clustering, membrane insertion of new AChRs, and induction of AChR mRNA. Even a muscle form of agrin that lacks intrinsic clustering activities by itself, significantly enhances neuregulin-induced clustering and insertion of AChRs. While the heparin-binding (A) domain of agrin is required for agrin localization in the extracellular matrix adjacent to AChR clusters, the heparan sulfate-containing domain of agrin is needed for the synergistic effects and co-localization with neuregulin-1. These results suggest that matrix interactions between exogenously supplied agrin and neuregulin-1 on the muscle surface provide a localized source of signaling factors needed to produce high densities of AChRs at neuromuscular junctions.
Li
Qunfang
Q
Department of Neurology and The Center for Molecular Medicine and Genetics, Wayne State University School of Medicine, Detroit, MI 48201, USA.
Esper
Raymond M
RM
Loeb
Jeffrey A
JA
D018171:Agrin / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D030161:Avian Proteins; D001665:Binding Sites / Q000235:genetics; D019556:COS Cells; D002462:Cell Membrane / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D002642:Chick Embryo; D018920:Coculture Techniques; D005109:Extracellular Matrix / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000235:genetics; D006493:Heparin / Q000378:metabolism; D006497:Heparan Sulfate / Q000378:metabolism; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000196:embryology / Q000294:innervation* / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D020890:Neuregulin-1; D009469:Neuromuscular Junction / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D011940:Receptor Aggregation / Q000187:drug effects / Q000235:genetics; D011978:Receptors, Nicotinic / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
D018171:Agrin; D030161:Avian Proteins; D006493:Heparin; D006497:Heparan Sulfate; D009419:Nerve Tissue Proteins; D020890:Neuregulin-1; D012333:RNA, Messenger; D011978:Receptors, Nicotinic; C490582:NRG1 protein, Gallus gallus