Regulation Of AChR Clustering By Dishevelled Interacting With MuSK And PAK1

Synapses are characterized by highly concentratedneurotransmitter receptors in the postsynaptic membrane. Theformation of neuromuscular junction (NMJ) and the clustering ofnAChR (nicotinic acetylcholine receptor) at NMJ had been studiedextensively. Although it is already known that MuSK acts as anessential component of agrin receptor complex and is requiredfor nAChR clustering at the NMJ, the underlying molecularmechanisms remain unclear. In present study, we devoted oureffort to identifying possible signaling pathway involving inAChR clustering by studying MuSK interacting proteins in musclecells.We report here that using MuSK intracellular domain as bait, wepulled out Dishevelled (Dvl), a signaling molecule important forcell polarity, as MuSK interacting protein in yeast two hybridassay. MuSK interacts with Dvl in muscle cells directly and 3specifically. The tempo and spatial expression profiles of MuSKand Dvl are similar in muscle. Disruption of the MuSK-Dvlinteraction inhibits Agrin-induced and neuron-induced AChRclustering. Expression of dominant negative Dvl1 in thepostsynaptic muscle cells reduces the amplitude of spontaneoussynaptic currents at the NMJ.Moreover, Dvl1 interacts with a downstream kinase P21-activated-kinase1 (PAK1). MuSK, Dvl and PAK1 form complex among them.Agrin activates PAK1, and the activation of PAK1 by agrinrequires Dvl. Inhibition of PAK1 activity attenuates AChRclustering.These results demonstrate the important roles of Dvl and PAK inAgrin/MuSK induced AChR clustering, and reveal a novel functionof Dvl in synapse development.