Identity of adenylyl cyclase isoform determines the G protein mediating chronic opioid-induced adenylyl cyclase supersensitivity.
To determine the intracellular signal transduction pathway responsible for the development of tolerance/dependence, the ability of Gzalpha to substitute for pertussis toxin (PTX)-sensitive G proteins in mediating adenylyl cyclase (AC) supersensitivity was examined in the presence of defined AC isoforms. In transiently micro-opioid receptor (OR) transfected COS-7 cells (endogenous inhibitory G proteins: Gialpha2, Gialpha3 and Gzalpha), neither acute (1 micro mol/L) nor chronic morphine treatment (1 micromol/L; 18 h) influenced intracellular cAMP production. Coexpression of the micro -OR together with AC type V and VI fully restored the ability of morphine to acutely inhibit cAMP generation. Chronic morphine treatment further resulted in the development of tolerance/dependence, as assessed by desensitization of the acute inhibitory opioid effect (tolerance) as well as the induction of AC supersensitivity after drug withdrawal (dependence). Specific direction of micro -OR signalling via Gzalpha by both PTX treatment and Gzalpha over-expression had no effect on chronic morphine regulation of AC type V, but completely abolished the development of tolerance/dependence with AC type VI. Similar results were obtained in stably micro -OR-expressing HEK293 cells transiently cotransfected with Gzalpha and either AC type V or VI. Coprecipitation studies further verified that Gzalpha specifically binds to AC type V but not type VI. Taken together, these results demonstrate that in principle each of the OR-activated G proteins per se is able to mediate AC supersensitivity. However, they also indicate that it is the molecular nature of AC isoform that selects and determines the OR-activated G protein mediating tolerance/dependence.
Ammer
Hermann
H
Institute of Pharmacology, Toxicology and Pharmacy, University of Munich, Munich, Germany. ammer@pharmtox.vetmed.uni-muenchen.de
Christ
Thomas E
TE
D000262:Adenylyl Cyclases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D019556:COS Cells; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance / Q000502:physiology; D004789:Enzyme Activation / Q000187:drug effects; D044385:GTP-Binding Protein alpha Subunits; D019204:GTP-Binding Proteins / Q000378:metabolism*; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D009020:Morphine / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology*; D011485:Protein Binding / Q000502:physiology; D017450:Receptors, Opioid, mu / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D019966:Substance-Related Disorders / Q000378:metabolism; D013995:Time; D014162:Transfection
C099387:GNAZ protein, human; D044385:GTP-Binding Protein alpha Subunits; D007527:Isoenzymes; D009294:Narcotics; D017450:Receptors, Opioid, mu; D005576:Colforsin; D009020:Morphine; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D020962:Heterotrimeric GTP-Binding Proteins; D000262:Adenylyl Cyclases; C121100:adenylyl cyclase 6; C419510:adenylyl cyclase type V