MODULATION OF GABA(A) RECEPTOR FUNCTION BY TYROSINE PHOSPHORYLATION OF BETA-SUBUNITS

Protein tyrosine phosphorylation is a key event in diverse intracellul ar signaling pathways and has been implicated in modification of neuro nal functioning. We investigated the role of tyrosine phosphorylation in regulating type A GABA (GABA(A)) receptors in cultured CNS neurons. Extracellular application of genistein (50 mu M), a membrane-permeabl e inhibitor of protein tryrosine kinases (PTKs), produced a reversible reduction in the amplitude of GABA(A) receptor-mediated whole-cell cu rrents, and this effect was not reproduced by daidzein (50 mu M), an i nactive analog of genistein, In contrast, intracellular application of the PTK pp60(c-src) (30 U/ml) resulted in a progressive increase in c urrent amplitude, and this potentiation was pre vented by pretreatment of the neurons with, genistein. Immunoprecipitation and immunoblottin g of cultured neuronal homogenates indicated that the beta 2/beta 3 su bunit(s) of the GABA(A) receptor are tyrosine phosphorylated in situ. Moreover, genistein (50 mu M) was found to be capable of decreasing GA BA(A) currents in human embryonic kidney 293 cells transiently express ing functional GABA(A) receptors containing the beta 2 subunit. Thus, the present work provides the first evidence that native GABA(A) recep tors are phosphorylated and modulated in situ by endogenous PTKs in cu ltured CNS neurons and that phosphorylation of the beta subunits may b e sufficient to support such a modulation, Given the prominent role of GABA(A) receptors in mediating many brain functions and dysfunctions, modulation of these receptors by PTKs may be important in a wide rang e of physiological and pathological processes in the CNS.