Figure 6. Rapsyn interacts with CD4-β407–469 in muscle.

(A) CD4^ct-β407–469 was expressed in Sol8 myotubes, either alone or with additional rapsyn. CD4^ct-β407–469 and AChR were then isolated from muscle cell lysates and rapsyn association assayed by immunoblotting with a rapsyn polyclonal antibody. Rapsyn was readily co-immunoprecipitated together with CD4^ct-β407–469 when they were co-expressed, but only trace amounts of endogenous rapsyn associated with CD4^ct-β407–469 expressed alone. Treatment with agrin also increased the interaction of rapsyn and the endogenous AChR, but had no effect on rapsyn/CD4^ct-β407–469 association. Reprobing with CD4 and AChR α-subunit (mAb210) antibodies confirms that CD4^ct-β407–469 does not associate with the AChR. (B) Rapsyn co-immunoprecipitated with CD4^ct-β407–469 but not CD4.