Agrin Regulates Rapsyn Interaction with Surface Acetylcholine Receptors, and This Underlies Cytoskeletal Anchoring and Clustering

Moransard, Martijn; Borges, Lúcia S.; Willmann, Raffaella; Marangi, P. Angelo; Brenner, Hans Rudolf; Ferns, Michael J.; Fuhrer, Christian

doi:10.1074/jbc.m210865200

Cited by 94 publications

(104 citation statements)

References 41 publications

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“…AChRs and associated proteins were revealed by immunoblotting with antibodies against the AChR␣, rapsyn, and ␤-catenin. As shown in Figure 1C, rapsyn was detectable in the AChR complex, and such interaction was increased by agrin, indicating that agrin regulates the rapsynAChR interaction in agreement with a previous report (Moransard et al, 2003). Interestingly, ␤-catenin coprecipitated with biotinylated AChRs, suggesting that it associates with the AChR complex.…”

Section: ␤-Catenin Associates With the Achr Complex Through Rapsynsupporting

confidence: 76%

“…Mice deficient in agrin or MuSK do not form the NMJ (DeChiara et al, 1996;Gautam et al, 1996). A third protein that is essential for NMJ formation is rapsyn, an intracellular molecule (Burden et al, 1983;LaRochelle and Froehner, 1986;Gautam et al, 1995;Moransard et al, 2003). This protein is associated with AChRs and is thought to link AChRs to actin cytoskeleton (Dai et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

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β-Catenin Regulates Acetylcholine Receptor Clustering in Muscle Cells through Interaction with Rapsyn

Zhang¹,

Luo²,

Dong³

et al. 2007

J. Neurosci.

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Agrin is believed to be a factor used by motoneurons to direct acetylcholine receptor (AChR) clustering at the neuromuscular junction. However, exactly how agrin mediates this effect remains unclear. Here we demonstrate that the ␤-catenin interacts with rapsyn, a molecule key for AChR clustering. Agrin stimulation increases the association of ␤-catenin with surface AChRs. Suppression of ␤-catenin expression inhibited agrin-induced AChR clustering, suggesting a necessary role of ␤-catenin in this event. The ␤-catenin action did not appear to require the function of T-cell factors (TCFs), suggesting a mechanism independent of TCF-mediated transcription. In contrast, prevention of ␤-catenin from interacting with ␣-catenin attenuated agrin-induced AChR clustering. These results suggest that ␤-catenin may serve as a link between AChRs and ␣-catenin-associated cytoskeleton, revealing a novel function of ␤-catenin in synaptogenesis.

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Section: ␤-Catenin Associates With the Achr Complex Through Rapsynsupporting

confidence: 76%

Section: Introductionmentioning

confidence: 99%

β-Catenin Regulates Acetylcholine Receptor Clustering in Muscle Cells through Interaction with Rapsyn

Zhang¹,

Luo²,

Dong³

et al. 2007

J. Neurosci.

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“…Moreover, mice with targeted mutations of the β subunit intracellular tyrosines have neuromuscular junctions that are simplified and reduced in size, with decreased density and total numbers of AChRs (Friese et al, 2007). Phosphorylation of the β subunit contributes to AChR localization, therefore, but it is unclear whether it does so by regulating rapsyn interaction (Fuhrer et al, 1999, Moransard et al, 2003.In addition to its structural role, rapsyn also functions in agrin signaling. Notably, agrin-induced phosphorylation of the AChR β and δ subunits is significantly decreased in rapsyn null myotubes (Apel et al, 1997, and rapsyn activates src family kinases in heterologous cells (Qu et al, 1996, Mohamed andSwope, 1999), resulting in tyrosine phosphorylation of multiple cellular proteins.…”

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confidence: 99%

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confidence: 99%

Rapsyn carboxyl terminal domains mediate muscle specific kinase–induced phosphorylation of the muscle acetylcholine receptor

et al. 2008

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At the developing vertebrate neuromuscular junction, postsynaptic localization of the acetylcholine receptor (AChR) is regulated by agrin signaling via the muscle specific kinase (MuSK) and requires an intracellular scaffolding protein called rapsyn. In addition to its structural role, rapsyn is also necessary for agrin-induced tyrosine phosphorylation of the AChR, which regulates some aspects of receptor localization. Here, we have investigated the molecular mechanism by which rapsyn mediates AChR phosphorylation. In a heterologous COS cell system, we show that MuSK and rapsyn induced phosphorylation of β subunit tyrosine 390 (Y390) and δ subunit Y393, as in muscle cells. Mutation of β Y390 or δ Y393 did not inhibit MuSK/rapsyn-induced phosphorylation of the other subunit in COS cells, and mutation of β Y390 did not inhibit agrin-induced phosphorylation of the δ subunit in Sol8 muscle cells; thus, their phosphorylation occurs independently, downstream of MuSK activation. In COS cells, we further show that MuSK-induced phosphorylation of the β subunit was mediated by rapsyn, as MuSK plus rapsyn increased β Y390 phosphorylation more than rapsyn alone and MuSK alone had no effect. Intriguingly, MuSK also induced tyrosine phosphorylation of rapsyn itself. We then used deletion mutants to map the rapsyn domains responsible for activation of cytoplasmic tyrosine kinases that phosphorylate the AChR subunits. We found that rapsyn C-terminal domains (amino acids 212-412) are both necessary and sufficient for activation of tyrosine kinases and induction of cellular tyrosine phosphorylation. Moreover, deletion of the rapsyn RING domain (365-412) abolished MuSK-induced tyrosine phosphorylation of the AChR β subunit. Together, these findings suggest that rapsyn facilitates AChR phosphorylation by activating or localizing tyrosine kinases via its C-terminal domains. Keywords neuromuscular junction; synaptogenesis; agrin; postsynaptic membraneAt the developing neuromuscular junction in vertebrates, several nerve-derived signals combine to localize the acetylcholine receptor at postsynaptic sites (Sanes and Lichtman, 2001, Burden, 2002, Kummer et al., 2006. One essential factor is agrin, which signals via the MuSK receptor tyrosine kinase and induces and/or stabilizes clustering of the AChR in the postsynaptic membrane (reviewed in (Kummer et al., 2006 Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. is prepatterned and AChR clusters occur in the central region of the muscle prior to and even in the absence of neural innervation (Lin et al., 2001, Yang et al., 2001). However, upo...

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“…Moreover, Rac is proposed to play a role in the formation of agrin-induced small AChR aggregates; RhoA is required, subsequently, to condense those small aggregates as large agrin-induced AChR aggregates. The small GTPases are known to induce the re-arrangement of intracellular cytoskeleton (40), which, therefore, could explain the clustering of AChRs in the post-synaptic muscle (12,41). Here, we demonstrate further the potentiation role of P2Y 1 receptor in agrininduced AChR aggregation could also involve the small GTPases.…”

Section: Discussionmentioning

confidence: 65%

ATP Potentiates Agrin-induced AChR Aggregation in Cultured Myotubes

Siow¹,

Choi²,

Ting

et al. 2004

Journal of Biological Chemistry

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At vertebrate neuromuscular junctions, ATP is known to stabilize acetylcholine in the synaptic vesicles and to be co-released with it. We have shown previously that a nucleotide receptor, P2Y 1 receptor, is localized at the nmjs, and we propose that this mediates a trophic role for synaptic ATP there. In cultured myotubes, the activation of P2Y 1 receptors modulated agrin-induced acetylcholine receptor (

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Agrin Regulates Rapsyn Interaction with Surface Acetylcholine Receptors, and This Underlies Cytoskeletal Anchoring and Clustering

Cited by 94 publications

References 41 publications

β-Catenin Regulates Acetylcholine Receptor Clustering in Muscle Cells through Interaction with Rapsyn

β-Catenin Regulates Acetylcholine Receptor Clustering in Muscle Cells through Interaction with Rapsyn

Rapsyn carboxyl terminal domains mediate muscle specific kinase–induced phosphorylation of the muscle acetylcholine receptor

ATP Potentiates Agrin-induced AChR Aggregation in Cultured Myotubes

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