RGS4 exerts inhibitory activities on the signaling of dopamine D2 receptor and D3 receptor through the N-terminal region.

Dopamine D(2) receptor and D(3) receptor (D(2)R and D(3)R) are the major targets for current antipsychotic drugs, and their proper regulation has pathological and pharmacological significance. This study was conducted to understand the functional roles and molecular mechanisms of RGS proteins (RGS2, RGS4, and RGS9-2) on the signaling of D(2)R and D(3)R. RGS proteins were co-expressed with D(2)R and D(3)R in HEK-293 cells. The protein interactions between RGS proteins and D(2)R/D(3)R, and effects of RGS proteins on the internalization, signaling, and desensitization of D(2)R/D(3)R were determined. In addition, the RGS4 proteins were subdivided into N-terminal region, RGS domain, and the C-terminal region, and the specific subdomain of RGS4 protein involved in the regulation of the signaling of D(2)R/D(3)R was determined. All of RGS proteins we tested interacted with D(2)R/D(3)R. RGS4 exerted potent inhibitory activities on the signaling of D(2)R/D(3)R. RGS9-2 exerted selective but moderate inhibitory activity on D(3)R and the internalization of D(2)R. RGS2 had no effect. The N-terminal domain of RGS4 was involved in its interaction with D(2)R and D(3)R and was required for the inhibitory activity of the RGS domain. The study for the first time showed that RGS4 is the major RGS protein which interacts through the N-terminal region and exerts potent inhibitory activities on the signaling of D(2)R and D(3)R.