Regulation of Adenylyl Cyclase Isozymes on Acute and Chronic Activation of Inhibitory Receptors

Abstract

Adenylyl cyclase superactivation, a phenomenon by which chronic activation of inhibitory Gi/o-coupled receptors leads to an increase in cAMP accumulation, is believed to play an important role as a compensatory response of the cAMP signaling system in the cell. However, to date, the mechanism by which adenylyl cyclase activity is regulated by chronic exposure to inhibitory agonists and the nature of the adenylyl cyclase isozymes participating in this process remain largely unknown. Here we show, using COS-7 cells transfected with the various AC isozymes, that acute activation of the D2 dopaminergic and m4 muscarinic receptors inhibited the activity of adenylyl cyclase isozymes I, V, VI, and VIII, whereas types II, IV, and VII were stimulated and type III was not affected. Conversely, chronic receptor activation led to superactivation of adenylyl cyclase types I, V, VI, and VIII and to a reduction in the activities of types II, IV, and VII. The activity of AC-III also was reduced. This pattern of inhibition/stimulation of the various adenylyl cyclase isozymes is similar to that we recently observed on acute and chronic activation of the mu-opioid receptor, suggesting that isozyme-specific adenylyl cyclase superactivation may represent a general means of cellular adaptation to the activation of inhibitory receptors and that the presence/absence and intensity of the adenylyl cyclase response in different brain areas (or cell types) could be explained by the expression of different adenylyl cyclase isozyme types in these areas.

Differential Effect of Membrane Cholesterol Removal on μ- and δ-Opioid Receptors

“…In addition, many of the adenylyl cyclase isoforms that can be sensitized (AC 5, 6, and 8 (21)) have also been found in cholesterolenriched domains (AC 5/6 (9, 18, 19) and 8 (20)). Exceptions to this include AC 1, which can be sensitized by a variety of agonists (52-54) but has not been found in rafts (18), and AC 3, which is preferentially found in cholesterol-enriched membranes (18) but is not sensitized by several agonists, including the -opioid agonist morphine (52,53). Additionally, sensitization caused by chronic agonist treatment may require a redistribution of the heterotrimeric G protein to detergent-insoluble domains.…”

Molecular Mechanisms for Heterologous Sensitization of Adenylate Cyclase

“…Although the present article will often focus on heterologous sensitization following persistent stimulation of the D 2 dopamine receptor (Fig. 2), it is likely that the mechanisms associated with one G␣ i/o -coupled receptor are similar to those associated with other G␣ i/o -coupled receptors, including -opioid, CB 1 cannabinoid, ␣ 2 adrenergic, M 2 and M 4 muscarinic, A 3 adenosine, and 5-hydroxytryptamine 1A serotonin receptors (Avidor-Reiss et al, 1995;Hensler et al, 1996;Thomas and Hoffman, 1996;Palmer et al, 1997;Nevo et al, 1998;Rhee et al, 2000).…”

Adenosine A1 receptor agonist N6-cyclohexyl-adenosine induced phosphorylation of delta opioid receptor and desensitization of its signaling

“…The levels of intracellular cAMP were measured as described [25,26] . In brief, cells were cultured in 24-well plates, serum starved, and incubated at 37 °C for 2 h in 0.5 mL/well of fresh growth medium containing 5 μCi/mL [8-3 H]-adenine, 0.5 mmol/L 1-methyl-3-isobutylxanthine (IBMX), and with or without 1 μmol/L CHA of indicated duration.…”