Rapsyn interaction with calpain stabilizes AChR clusters at the neuromuscular junction.
Agrin induces, whereas acetylcholine (ACh) disperses, ACh receptor (AChR) clusters during neuromuscular synaptogenesis. Such counteractive interaction leads to eventual dispersal of nonsynaptic AChR-rich sites and formation of receptor clusters at the postjunctional membrane. However, the underlying mechanisms are not well understood. Here we show that calpain, a calcium-dependent protease, is activated by the cholinergic stimulation and is required for induced dispersion of AChR clusters. Interestingly, the AChR-associated protein rapsyn interacted with calpain in an agrin-dependent manner, and this interaction inhibited the protease activity of calpain. Disrupting the endogenous rapsyn/calpain interaction enhanced CCh-induced dispersion of AChR clusters. Moreover, the loss of AChR clusters in agrin mutant mice was partially rescued by the inhibition of calpain via overexpressing calpastatin, an endogenous calpain inhibitor, or injecting calpeptin, a cell-permeable calpain inhibitor. These results demonstrate that calpain participates in ACh-induced dispersion of AChR clusters, and rapsyn stabilizes AChR clusters by suppressing calpain activity.
Chen
Fei
F
Institute of Neuroscience and Key Laboratory of Neurobiology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
Qian
Lei
L
Yang
Zhi-Hua
ZH
Huang
Ying
Y
Ngo
Shyuan T
ST
Ruan
Nan-Jie
NJ
Wang
Jia
J
Schneider
Claudio
C
Noakes
Peter G
PG
Ding
Yu-Qiang
YQ
Mei
Lin
L
Luo
Zhen-Ge
ZG
D018171:Agrin / Q000378:metabolism*; D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002154:Calpain / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D018679:Cholinergic Agonists / Q000494:pharmacology; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism; D009124:Muscle Proteins / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000187:drug effects / Q000378:metabolism*; D011940:Receptor Aggregation / Q000187:drug effects / Q000502:physiology*; D011950:Receptors, Cholinergic / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013570:Synaptic Membranes / Q000187:drug effects / Q000378:metabolism
D018171:Agrin; D002135:Calcium-Binding Proteins; D018679:Cholinergic Agonists; D009124:Muscle Proteins; D011950:Receptors, Cholinergic; C051609:peripheral membrane protein 43K; C033668:calpastatin; D002217:Carbachol; D002154:Calpain