Interaction of GABA receptor/channel rho(1) and gamma(2) subunit

To determine whether protein-protein and functional interactions can occur between gamma-aminobutyric acid (GABA)(A) receptor/channels gamma(2) subunit and the retina-specific GABA(C) rho(1) subunit.

Protein-protein interaction was characterized by immunocoprecipitation of these subunits in brain and spinal cord with anti-gamma(2) subunit antibody and by Western blot analysis with anti-rho(1) subunit antibody. The rho(1) and gamma(2) subunits were detected in the adult rat brain and spinal cord lysates that had been previously precipitated with the specific antibodies against the rho(1) and gamma(2) subunits, respectively. A two-microelectrode voltage clamp was used to measure GABA-induced currents in oocytes. In addition, a yeast two-hybrid system was used to detect the interactions of these subunits in vivo.

Based on yeast transformed with the N-terminal fragment of the gamma(2) subunit (gamma(2)-N'), the N-terminal fragment of the rho(1) subunit (rho(1)-N'), and the full-length rho(1) subunit, the protein-protein interaction of the GABA(A) gamma(2) subunit and the GABA(C) rho(1) subunit was found in yeast grown in triple-dropout medium (deficient in Leu, Trp, and His) and expressing the LacZ reporter gene. Interaction of the rho(1) and gamma(2) subunits was investigated by functional studies in which gamma(2) (gamma(2)-N' with 837 bp) and rho(1) cRNAs were coinjected in Xenopus oocytes. In studies of the functional interaction, after injection of the gamma(2) subunit mutant cRNA containing a N-terminal fragment, GABA-induced rho(1) originated currents declined to 16% of the control level of homooligomeric rho(1) current. This inhibitory effect of coexpressing gamma(2) subunit mutants with rho(1) subunit on the rho(1)-originated current in oocytes was dose dependent. In addition, coexpression of the GABA rho(1) and gamma(2) subunits in oocytes altered pharmacologic properties of the homooligomeric receptor/channel formed by rho(1) or gamma(2) subunits. Further evidence was provided by results obtained with specific antibodies showing that the rho(1) subunit was coimmunoprecipitated with the gamma(2) subunit from the retina, brain, and spinal cord.

The results indicate that protein-protein and functional interactions can occur between the GABA(A) gamma(2) subunit and the GABA(C) rho(1) subunit. Therefore, the functional role of GABA receptor/channels in the brain, retina, and spinal cord is more diversified because of the possible assembly between the GABA(A) gamma(2) subunit and GABA(C) rho(1) subunit.