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Overexpression of rapsyn modifies the intracellular trafficking of acetylcholine receptors

✍ Scribed by Hong Han; Shi-Hong Yang; William D. Phillips

Publisher
John Wiley and Sons
Year
2000
Tongue
English
Weight
367 KB
Volume
60
Category
Article
ISSN
0360-4012

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✦ Synopsis

Rapsyn is a protein that interacts with the cytoplasmic face of the nicotinic acetylcholine receptors (AChR) to cluster them within postsynaptic membrane of muscle.

Here we show that intracellular AChRs are also affected by rapsyn. When rapsyn was co-transfected with AChR into QT-6 fibroblasts, 125 I-␣-bungarotoxin binding indicated a reduction in the fraction of AChRs expressed on the cell surface, compared to cells expressing AChRs alone. Double fluorescent labeling showed that intracellular AChRs accumulated in patches at the cell periphery, beneath rapsyn-associated cell surface AChR clusters. These patches were observed even when cells were grown in medium containing excess unlabelled ␣-bungarotoxin to mask internalized AChRs, suggesting that they arose from hindered trafficking of newly formed AChRs to the cell surface. Similarly, in the muscle cell line, C2, overexpression of rapsyn resulted in the colocalization of aggregates of intracellular ␣-bungarotoxin binding sites with rapsyn beneath cell surface AChR microaggregates. The results indicate that rapsyn can modify the trafficking of AChRs within the cell and suggest a role in selectively targeting newly synthesized intracellular AChRs to the postsynaptic membrane.

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