Differential dependence of the D-1 and D-5 dopamine receptors on the G protein gamma(7) subunit for activation of adenylylcyclase

The D-1 dopamine receptor, G protein gamma (7) subunit, and adenylylcyclase are selectively expressed in the striatum, suggesting their potential inte raction in a common signaling pathway. To evaluate this possibility, a ribo zyme strategy was used to suppress the expression of the G protein gamma (7 ) subunit in HEK 293 cells stably expressing the human Dl dopamine receptor . Prior in vitro analysis revealed that the gamma (7) ribozyme possessed cl eavage activity directed exclusively toward the gamma (7) RNA transcript (W ang, Q., Mullah, B., Hansen, C., Asundi J., and Robishaw, J. D. (1997) J. B iol. Chem. 272, 26040 -26048). In vivo analysis of cells transfected with t he gamma (7) ribozyme showed a specific reduction in the expression of the gamma (7) protein. Coincident with the loss of the gamma (7) protein, there was a noticeable reduction in the expression of the beta (1) protein, conf irming their interaction in these cells. Finally, functional analysis of ri bozyme-mediated suppression of the beta (1) and gamma (7) proteins revealed a significant attenuation of SKF81297-stimulated adenylylcyclase activity in D-1 dopamine receptor-expressing cells. By contrast, ribozyme-mediated s uppression of the beta (1) and gamma (7) proteins showed no reduction of SK F81297-stimulated adenylylcyclase activity in D-5 dopamine receptor-express ing cells. Taken together, these data indicate that the structurally relate d Dl and D5 dopamine receptor subtypes utilize G proteins composed of disti nct beta gamma subunits to stimulate adenylylcyclase in HEK 293 cells. Unde rscoring the physiological relevance of these findings, single cell reverse transcriptase-polymerase chain reaction analysis revealed that the D-1 dop amine receptor and the G protein gamma (7) subunit are coordinately express ed in substance P containing neurons in rat striatum, suggesting that the G protein gamma (7) subunit may be a new target for drugs to selectively alt er dopaminergic signaling within the brain.