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.
Genetics Unit, Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK.
R
R
Nawrotzki
N Y
NY
Loh
M A
MA
Ruegg
K E
KE
Davies
D J
DJ
Blake
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