TYROSINE KINASE PHOSPHORYLATION OF GABA(A) RECEPTORS

Phosphorylation of purified bovine brain GABA(A) receptors by the tyrosine kinase, pp60(v-src) was examined. pp60(v-src) phosphorylated two bands of 54-62 kDa and 48-51 kDa that migrated to approximately the same position as bands recognized by antisera against the beta 2 and gamma 2 GABA(A) receptor subunits, respectively. Bacterially expressed proteins containing the putative large cytoplasmic loops of the beta 1 and gamma 2L subunits were phosphorylated by pp60(v-src), indicating that the phosphorylation sites are located in these subunit domains. The tyrosine kinase inhibitors, genistein and the tyrphostins B-42 and B-44, inhibited muscimol-stimulated Cl-36(-) uptake in mouse brain membrane vesicles (microsacs). The magnitude of the tyrphostin B44-induced inhibition of muscimol-stimulated Cl-36(-) uptake was significantly reduced in microsacs that were lysed and resealed under conditions that inhibit phosphorylation. GABA-gated Cl- currents were also inhibited by genistein and tyrphostin B-44 in Xenopus oocytes expressing alpha 1 beta 1 and alpha 1 beta 1 gamma 2L subunits. Consequently, protein tyrosine kinase-dependent phosphorylation appears to be another mechanism of regulating the function of GABA(A) receptors.