Differential Dependence of the D sub(1) and D sub(5) Dopamine Receptors on the G Protein gamma sub(7) Subunit for Activation of Adenylylcyclase

The D sub(1) dopamine receptor, G protein gamma sub(7) subunit, and adenylylcyclase are selectively expressed in the striatum, suggesting their potential interaction in a common signaling pathway. To evaluate this possibility, a ribozyme strategy was used to suppress the expression of the G protein gamma sub(7) subunit in HEK 293 cells stably expressing the human D sub(1) dopamine receptor. Prior in vitro analysis revealed that the gamma sub(7) ribozyme possessed cleavage activity directed exclusively toward the gamma sub(7) RNA transcript (Wang, Q., Mullah, B., Hansen, C., Asundi, J., and Robishaw, J. D. (1997) J. Biol. Chem. 272, 26040-26048). In vivo analysis of cells transfected with the gamma sub(7) ribozyme showed a specific reduction in the expression of the gamma sub(7) protein. Coincident with the loss of the gamma sub(7) protein, there was a noticeable reduction in the expression of the beta sub(1) protein, confirming their interaction in these cells. Finally, functional analysis of ribozyme-mediated suppression of the beta sub(1) and gamma sub(7) proteins revealed a significant attenuation of SKF81297-stimulated adenylylcyclase activity in D sub(1) dopamine receptor-expressing cells. By contrast, ribozyme-mediated suppression of the beta sub(1) and gamma sub(7) proteins showed no reduction of SKF81297-stimulated adenylylcyclase activity in D sub(5) dopamine receptor-expressing cells. Taken together, these data indicate that the structurally related D sub(1) and D sub(5) dopamine receptor subtypes utilize G proteins composed of distinct beta gamma subunits to stimulate adenylylcyclase in HEK 293 cells. Underscoring the physiological relevance of these findings, single cell reverse transcriptase-polymerase chain reaction analysis revealed that the D sub(1) dopamine receptor and the G protein gamma sub(7) subunit are coordinately expressed in substance P containing neurons in rat striatum, suggesting that the G protein gamma sub(7) subunit may be a new target for drugs to selectively alter dopaminergic signaling within the brain.