β-catenin regulates acetylcholine receptor clustering in muscle cells through interaction with rapsyn

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 β-catenin interacts with rapsyn, a molecule key for AChR clustering. Agrin stimulation increases the association of β-catenin with surface AChRs. Suppression of β-catenin expression inhibited agrin-induced AChR clustering, suggesting a necessary role of β-catenin in this event. The β-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 β-catenin from interacting with α-catenin attenuated agrin-induced AChR clustering. These results suggest that β-catenin may serve as a link between AChRs and α-catenin- associated cytoskeleton, revealing a novel function of β-catenin in synaptogenesis.