Chronic Opioid Treatment Induces Adenylyl Cyclase V Superactivation

Abstract

It has been known for some time that chronic treatment of neuronal cells and tissues with opioids, contrary to their acute effect, leads to an increase in cAMP accumulation. This phenomenon, defined as adenylyl cyclase superactivation, has been implicated in opiate addiction, yet the mechanism by which it is induced remains unclear. Here, we show that this phenomenon can be reproduced and studied in COS-7 cells cotransfected with adenylyl cyclase type V and mu-opioid receptor cDNAs. These cells display acute opioid inhibition of adenylyl cyclase activity, whereas prolonged exposure to the mu-agonist morphine or [-Ala2, N-methyl-Phe4, Gly-ol5]enkephalin leads to a time-dependent superactivation of adenylyl cyclase. This superactivated state is reversible, because it is gradually lost following agonist withdrawal. Adenylyl cyclase superactivation can be prevented by pertussis toxin pretreatment, indicating the involvement of Gi/o proteins, or by cotransfection with the carboxyl terminus of beta-adrenergic receptor kinase or with alpha-transducin (scavengers of Gbetagamma dimers), indicating a role for the G protein betagamma dimers in adenylyl cyclase superactivation. However, contrary to several other Gbetagamma-dependent signal transduction mechanisms (e.g. the extracellular signal-regulated kinase 2/MAP kinase pathway), adenylyl cyclase superactivation is not affected by the Ras dominant negative mutant N17-Ras.

Molecular Changes in Opioid Addiction: The Role of Adenylyl Cyclase and cAMP/PKA System

“…Under these conditions, Gα s may be stimulated, leading to G βγ -subunit-enhanced AC activity. 34 Furthermore, chronic morphine has been shown to produce a superactive state of AC 34 via G βγ stimulation of plasma-membrane-bound AC 1 and 8. 35 Under continuous agonist exposure, receptors appear to be desensitized or downregulated.…”

Identity of adenylyl cyclase isoform determines the G protein mediating chronic opioid‐induced adenylyl cyclase supersensitivity

“…Transfection with AC isoenzymes increased levels of both basal and forskolin (1 lmol/L) stimulated cAMP production, which was not influenced by coexpression of the l-OR and G z a. Chronic opioid treatment was initiated by the addition of morphine (1 lmol/L) to the incubation medium during the last 18 h. This treatment protocol has been shown to induce strong degrees of tolerance/dependence in opioid receptor transfected COS-7 cells, as judged by the expression of AC supersensitivity following opioid withdrawal (Avidor-Reiss et al 1996). In some experiments, PTX (25 ng/L) was added to the incubation medium 3 h before starting chronic morphine treatment.…”

“…COS-7 cells turned out ideal for such studies, because they contain only a single AC isoform (type IX; Premont 1994) that is not subject to direct regulation by inhibitory G proteins and does not facilitate the development of tolerance/dependence (Avidor-Reiss et al 1996). COS-7 cells also contain PTX-sensitive (G i a2/3) as well as PTXinsensitive G proteins (G z a), permitting separate analysis of l-OR-generated effects via both signal transduction pathways after PTX treatment (Fig.…”

“…Heterotrimeric G proteins are composed of a guanine nucleotide binding regulatory G a subunit and a functional Gbc dimer (Neer 1995). In naive cells, acute OR activation results in attenuation of AC activity which is mediated via inhibitory G a subunits (Avidor-Reiss et al 1996). Although relatively simple from its principle organization, investigation into chronic opioid adaptation of AC regulation turned out highly complicated because of the existence of a considerable molecular diversity at each level of the signal transduction cascade.…”

Complications of Long-Term Opioid Therapy for Management of Chronic Pain: the Paradox of Opioid-Induced Hyperalgesia

“…Following acute exposure to morphine, cultured cells exhibit inhibition of AC activity [10]. Paradoxically, chronic exposure enhances the activity of AC.…”