Characterisation of alpha-dystrobrevin in muscle.
Dystrophin-related and associated proteins are important for the formation and maintenance of the mammalian neuromuscular junction. Initial studies in the electric organ of Torpedo californica showed that the dystrophin-related protein dystrobrevin (87K) co-purifies with the acetylcholine receptors and other postsynaptic proteins. Dystrobrevin is also a major phosphotyrosine-containing protein in the postsynaptic membrane. Since inhibitors of tyrosine protein phosphorylation block acetylcholine receptor clustering in cultured muscle cells, we examined the role of alpha-dystrobrevin during synapse formation and in response to agrin. Using specific antibodies, we show that C2 myoblasts and early myotubes only produce alpha-dystrobrevin-1, the mammalian orthologue of Torpedo dystrobrevin, whereas mature skeletal muscle expresses three distinct alpha-dystrobrevin isoforms. In myotubes, alpha-dystrobrevin-1 is found on the cell surface and also in acetylcholine receptor-rich domains. Following agrin stimulation, alpha-dystrobrevin-1 becomes re-localised beneath the cell surface into macroclusters that contain acetylcholine receptors and another dystrophin-related protein, utrophin. This redistribution is not associated with tyrosine phosphorylation of alpha-dystrobrevin-1 by agrin. Furthermore, we show that alpha-dystrobrevin-1 is associated with both utrophin in C2 cells and dystrophin in mature skeletal muscle. Thus alpha-dystrobrevin-1 is a component of two protein complexes in muscle, one with utrophin at the neuromuscular junction and the other with dystrophin at the sarcolemma. These results indicate that alpha-dystrobrevin-1 is not involved in the phosphorylation-dependent, early stages of receptor clustering, but rather in the stabilisation and maturation of clusters, possibly via an interaction with utrophin.
Nawrotzki
R
R
Genetics Unit, Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK.
Loh
N Y
NY
Ruegg
M A
MA
Davies
K E
KE
Blake
D J
DJ
D018171:Agrin / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000378:metabolism; D004195:Disease Models, Animal; D049029:Dystrophin-Associated Proteins; D005333:Fetus; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D018101:Mice, Inbred mdx; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000737:chemistry* / Q000235:genetics; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000166:cytology; D009479:Neuropeptides / Q000737:chemistry* / Q000235:genetics; D019000:Phosphotyrosine / Q000378:metabolism; D020033:Protein Isoforms / Q000737:chemistry; D013569:Synapses / Q000737:chemistry / Q000502:physiology; D049411:Utrophin; D014638:Vanadates / Q000494:pharmacology
D018171:Agrin; D003598:Cytoskeletal Proteins; C490915:DTNA protein, human; C098884:Dtna protein, mouse; D049029:Dystrophin-Associated Proteins; D008565:Membrane Proteins; D009124:Muscle Proteins; D009479:Neuropeptides; D020033:Protein Isoforms; C483600:Utrn protein, mouse; D049411:Utrophin; C098885:dystrobrevin; C076715:pervanadate; D019000:Phosphotyrosine; D014638:Vanadates