title: Endosomal trafficking of the receptor tyrosine kinase MuSK proceeds via clathrin-dependent pathways, Arf6 and actin.
abstract: Muscle-specific kinase (MuSK), a receptor tyrosine kinase, is the key player during the formation of the neuromuscular junction. Signal transduction events downstream of MuSK activation induce both pre- and postsynaptic differentiation, which, most prominently, includes the clustering of acetylcholine receptors at synaptic sites. More recently, regulated MuSK endocytosis and degradation have been implicated as crucial events for MuSK signalling activity, implicating a cross-talk between signalling and endocytosis. In the present study, we use a live imaging approach to study MuSK endocytosis. We find that MuSK is internalized via a clathrin-, dynamin-dependent pathway. MuSK is transported to Rab7-positive endosomes for degradation and recycled via Rab4- and Rab11-positive vesicles. MuSK activation by Dok7 mildly affects the localization of MuSK on the cell surface but has no effect on the rate of MuSK internalization. Interestingly, MuSK colocalizes with actin and Arf6 at the cell surface and during endosomal trafficking. Disruption of the actin cytoskeleton or the proper function of Arf6 concentrates MuSK in cell protrusions. Moreover, inhibition of Arf6 or cytoskeletal rearrangements impairs acetylcholine receptor clustering and phosphorylation. These results suggest that MuSK uses both classical and nonclassical endosomal pathways that involve a variety of different components of the endosomal machinery.
authors.affiliation: Center for Brain Research, Medical University of Vienna, Vienna, Austria.
authors.forename: Susan
authors.initials: S
authors.lastname: Luiskandl
authors.forename: Barbara
authors.initials: B
authors.lastname: Woller
authors.forename: Marlies
authors.initials: M
authors.lastname: Schlauf
authors.forename: Johannes A
authors.initials: JA
authors.lastname: Schmid
authors.forename: Ruth
authors.initials: R
authors.lastname: Herbst
mesh_terms: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D018171:Agrin / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D002966:Clathrin / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D034281:Dynamins / Q000378:metabolism; D004705:Endocytosis; D011992:Endosomes / Q000201:enzymology; D051379:Mice; D009124:Muscle Proteins / Q000378:metabolism; D021381:Protein Transport; D059748:Proteolysis; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D011950:Receptors, Cholinergic / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000378:metabolism; D020695:rab4 GTP-Binding Proteins / Q000378:metabolism; D000090802:rab7 GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins
chemical_list: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors; D000199:Actins; D018171:Agrin; D002966:Clathrin; D034281:Dynamins; D009124:Muscle Proteins; D020794:Receptor Protein-Tyrosine Kinases; D011950:Receptors, Cholinergic; D020691:rab GTP-Binding Proteins; D020695:rab4 GTP-Binding Proteins; D000090802:rab7 GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins; C511694:Dok-7 protein, mouse; C000716465:rab7 GTP-binding proteins, mouse; C511695:MuSK protein, mouse; C000715727:Arf6 protein, mouse
keywords: Arf6; MuSK; clathrin-independent endocytosis; endocytosis; receptor tyrosine kinase