The molecular mechanism of chronic delta-opioid-mediated adenylyl cyclase superactivation in Chinese hamster ovary cells stably expressing the delta-opiod receptor: A cellular model for tolerance and withdrawal

Persistent Link:
http://hdl.handle.net/10150/289820
Title:
The molecular mechanism of chronic delta-opioid-mediated adenylyl cyclase superactivation in Chinese hamster ovary cells stably expressing the delta-opiod receptor: A cellular model for tolerance and withdrawal
Author:
Rubenzik, Marc
Issue Date:
2002
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
We are studying the pharmacology of the human delta-opioid receptor stably expressed in Chinese hamster ovary cells (hDOR/CHO). The delta-opioid receptor mediates analgesia, without the negative side effects noted by mu- and kappa-opioid agonists. However, tolerance to delta-opioid agonists still occurs. One mechanism of drug tolerance in CHO cells involves a compensatory response by adenylyl cyclase VI. This response, termed adenylyl cyclase (AC) superactivation, arises from the observation that acute hDOR activation leads to inhibition of AC, whereas chronic activation of the receptor (greater than 4 hours) leads to a compensatory increase in AC activity, effectively negating the acute inhibition normally seen in the presence of the delta-opioid agonist. The increased AC activity also causes an overshoot of cAMP formation upon the removal of the agonistic inhibitory influence. The loss of receptor-mediated AC inhibition after chronic agonist treatment is thought to contribute to in vivo drug tolerance, and the resulting cAMP overshoot may contribute to opioid withdrawal. In studying this phenomenon, we have demonstrated a requirement for G-protein betagamma subunits (Gbetagamma) by expressing scavengers of Gbetagamma, such as alpha-transducin and phosducin. Additionally, we have shown AC VI phosphorylation by chronic agonist treatment, which may cause AC superactivation, and that this phosphorylation is sensitive to calmodulin antagonists and inhibitors of the atypical protein kinase C enzymes. We have also recently postulated the involvement of Raf-1 kinase. Inhibitors of Raf-1, as well as pathways that lead to activation of this enzyme, significantly attenuate the cAMP overshoot, suggesting that hDOR-activated Raf-1 can phosphorylate and superactivate AC VI in CHO cells.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Biology, Neuroscience.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Pharmacology and Toxicology
Degree Grantor:
University of Arizona
Advisor:
Yamamura, Henry I.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleThe molecular mechanism of chronic delta-opioid-mediated adenylyl cyclase superactivation in Chinese hamster ovary cells stably expressing the delta-opiod receptor: A cellular model for tolerance and withdrawalen_US
dc.creatorRubenzik, Marcen_US
dc.contributor.authorRubenzik, Marcen_US
dc.date.issued2002en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractWe are studying the pharmacology of the human delta-opioid receptor stably expressed in Chinese hamster ovary cells (hDOR/CHO). The delta-opioid receptor mediates analgesia, without the negative side effects noted by mu- and kappa-opioid agonists. However, tolerance to delta-opioid agonists still occurs. One mechanism of drug tolerance in CHO cells involves a compensatory response by adenylyl cyclase VI. This response, termed adenylyl cyclase (AC) superactivation, arises from the observation that acute hDOR activation leads to inhibition of AC, whereas chronic activation of the receptor (greater than 4 hours) leads to a compensatory increase in AC activity, effectively negating the acute inhibition normally seen in the presence of the delta-opioid agonist. The increased AC activity also causes an overshoot of cAMP formation upon the removal of the agonistic inhibitory influence. The loss of receptor-mediated AC inhibition after chronic agonist treatment is thought to contribute to in vivo drug tolerance, and the resulting cAMP overshoot may contribute to opioid withdrawal. In studying this phenomenon, we have demonstrated a requirement for G-protein betagamma subunits (Gbetagamma) by expressing scavengers of Gbetagamma, such as alpha-transducin and phosducin. Additionally, we have shown AC VI phosphorylation by chronic agonist treatment, which may cause AC superactivation, and that this phosphorylation is sensitive to calmodulin antagonists and inhibitors of the atypical protein kinase C enzymes. We have also recently postulated the involvement of Raf-1 kinase. Inhibitors of Raf-1, as well as pathways that lead to activation of this enzyme, significantly attenuate the cAMP overshoot, suggesting that hDOR-activated Raf-1 can phosphorylate and superactivate AC VI in CHO cells.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectBiology, Neuroscience.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplinePharmacology and Toxicologyen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorYamamura, Henry I.en_US
dc.identifier.proquest3060961en_US
dc.identifier.bibrecord.b4303830xen_US
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