Adenylyl cyclase type-VIII activity is regulated by G βγ subunits

Abstract

The Ca 2+-activated adenylyl cyclase type VIII (AC-VIII) has been implicated in several forms of neural plasticity, including drug addiction and learning and memory. It has not been clear whether G i/o proteins and G-protein coupled receptors regulate the activity of AC-VIII. Here we show in intact mammalian cell system that AC-VIII is inhibited by μ-opioid receptor activation and that this inhibition is pertussis toxin sensitive. Moreover, we show that G βγ subunits inhibit AC-VIII activity, while constitutively active α i/o subunits do not. Different G β isoforms varied in their efficacies, with G β1γ2 or G β2γ2 being more efficient than G β3γ2 and G β4γ2, while G β5 (transfected with γ 2) had no effect. As for the G γ subunits, G β1 inhibited AC-VIII activity in the presence of all γ subunits tested except for γ 5 that had only a marginal activity. Moreover, cotransfection with proteins known to serve as scavengers of G βγ dimers, or to reduce G βγ plasma membrane anchorage, markedly attenuated the μ-opioid receptor-induced inhibition of AC-VIII. These results demonstrate that G βγ (originating from agonist activation of these receptors) and probably not G αi/o subunits are involved in the agonist inhibition of AC-VIII.