FUNCTIONAL INTERACTION OF SRC FAMILY KINASES WITH THE ACETYLCHOLINE-RECEPTOR IN C2 MYOTUBES

Tyrosine phosphorylation of the beta subunit of the acetylcholine rece ptor (AChR) has been postulated to play a role in AChR clustering duri ng development of the neuromuscular junction. me have investigated the mechanism of this phosphorylation in mammalian C2 myotubes and report that the tyrosine kinase Src binds and phosphorylates glutathione S-t ransferase fusion proteins containing the N-terminal half of the cytop lasmic loop of the beta subunit. No binding occurs to the related kina ses Fyn or Yes or to the corresponding regions from the gamma and delt a subunits. Furthermore, AChRs affinity-isolated from C2 myotubes usin g alpha-bungarotoxin-Sepharose mere specifically associated with Src a nd Fyn and had tyrosine-phosphorylated beta subunits. We suggest that AChRs are initially phosphorylated by Src and subsequently bind Fyn in a phosphotyrosine-dependent manner. These interactions are likely to play an important role in construction of the specialized postsynaptic membrane during synaptogenesis.