The Molecular Mechanisms of Cellular Tolerance to δ-Opioid Agonists
Chronic treatment with δ-opioid agonists, similar to other agonist drugs, causes tolerance. Tolerance is a complex adaptation process that consists of multiple, cellular and neural-system adaptations. Cellular tolerance to δ-opioid agonists involves feedback-regulation of the function, concentration, and localization of the δ-opioid receptors (receptor desensitization) as well as of intracellular effectors (functional desensitization). We are using a recombinant Chinese hamster ovary cell line expressing the human δ-opioid receptors (hDOR/CHO) to investigate the molecular mechanisms of cellular tolerance We found that the structurally distinct δ-opioid agonists mediate receptor down-regulation by different mechanisms. Thus, truncation of the last 35 C-terminal amino acids of the hDOR completely abolished DPDPE, but not SNC 80-mediated receptor down-regulation. In addition, down-regulation of the wild type-, and the truncated hDORs exhibited different inhibitor sensitivity-profile. Chronic δ-opioid agonist treatment also causes functional desensitization of forskolin-stimulated cAMP formation and cAMP overshoot in the hDOR/CHO cells. We have demonstrated that chronic SNC 80 treatment also causes concurrent phosphorylation of the adenylyl cyclase (AC) VI isoenzyme hDOR/CHO cells. Both AC superactivation and AC VI phosphorylation were SNC 80 dose-dependent, naltrindole-sensitive, and exhibited similar time course-, and protein kinase inhibitor-sensitivity profile. We hypothesize that phosphorylation of AC VI plays an important role in δ-opioid agonist-mediated AC superactivation in hDOR/CHO cells.
KeywordsHuman δ-opioid receptor cellular tolerance receptor down-regulation adenylyl cyclase superactivation adenylyl cyclase phosphorylation
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- 3.Bayewitch, M. L., Nevo, I., Avidor-Reiss, T., Levy, R., Simmonds, W. F., Vogel, Z. (2000) Alterations in detergent solubility of heterotrimeric G proteins after chronic activation of Gi/o-coupled receptors: Changes in detergent solubility are in correlation with onset of adenylyl cyclase superac-tivation. Mol. Pharmacol. 57, 820–825.PubMedGoogle Scholar
- 11.Cussack, D., Newman- Tancredi, A., Pasteau, V., Millan, M. J. (1999) Human dopamine D3 receptors mediate MAP kinase activation via PI-3-kinase and an atypical protein kinase C dependent mechanism. Mol. Pharmacol. 56, 1025–1030.Google Scholar
- 14.Hosohata, Y., Varga, E. V., Stropova, D., Li, X., Knapp, R. J., Hruby, V. J., Rice, K. C., Nagase, H., Roeske, W. R., Yamamura, H. I. (2001) Mutation W284L of the human delta opioid receptor reveals agonist specific receptor conformations for G protein activation. Life Sci. 68, 22–33, 2001.Google Scholar
- 22.Malatynska, E., Wang, Y., Knapp, R. J., Waite, S., Calderon, S., Rice, K., Hruby, V. J., Yamamura, H. I., Roeske, W. R. (1996) Human delta opioid receptor: Functional studies on stably transfected Chinese hamster ovary cells after acute and chronic treatment with the selective nonpeptidic agonist SNC-80. J. Pharmacol. Exp. Ther. 278, 1083–1094.Google Scholar
- 23.Mellman, I. (1996) Endocytosis and molecular sorting. Ann. Rev. Cell. Dev. Biol. 12, 575–592.Google Scholar
- 24.Menard, L., Ferguson, S. S. G., Zhang, J., Lin, F.-T., Lefkowitz, R. J., Caron, M. G., Barak, L. S. (1997) Synergistic regulation of ß2-adrenergic receptor sequestration: Intracellular complement of ß-adrenergic receptor kinase and ß-arrestin determine kinetics of internalization. Mol. Pharmacol. 51, 800–808.PubMedGoogle Scholar
- 30.Quock, R. M., Burkey, T. H., Varga, E. V, Hosohata, Y, Hosohata, K., Cowell, S. M., Slate, C. A., Ehlert, F. J., Roeske, W. R., Yamamura, H. I. (1999) The 5-opioid receptor: molecular pharmacology, signal transduction, and the determination of drug efficacy. Pharmacol. Rev. 51, 503–532.PubMedGoogle Scholar
- 43.Varga, E. V., Rubenzik, M. K., Stropova, D., Sugiyama, M., Grife, V., Hruby, V. J., Rice, K. C., Roeske, W. R., Yamamura, H. I. (2003) Converging protein kinase pathways mediate adenylyl cyclase superactivation upon chronic δ-opioid agonist treatment, J. Pharmacol. Exp. Ther. (in press).Google Scholar
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