Abstract
Effective medical treatment of opiate addiction is limited by a high relapse rate in abstinent addicts. Opiate withdrawal causes cAMP superactivation, but the underlying molecular mechanisms are not clear. Recent evidence implicates an activator of G-protein signaling 3 (AGS3) in opiate addiction. We found previously that during a 10-min activation of opioid receptors, AGS3 binds Gαi-GDP to promote free Gβγ stimulation of adenylyl cyclase (AC) 2 and 4, and/or inactivate Gαi inhibitory function, thereby transiently enhancing cAMP-dependent protein kinase A (PKA) activity. In contrast, we report here that in nucleus accumbens/striatal neurons, morphine withdrawal induces cAMP superactivation, which requires up-regulation of AGS3. cAMP increases as a function of withdrawal time, by approximately 20% at 10 min and 75% at 5 h. However, cAMP superactivation does not require Gβγ. Instead, adenosine A2A receptor activation of Gαs/olf seems to initiate cAMP superactivation and promote AGS3 up-regulation. Elevated AGS3 binds to Gαi to prevent its inhibition on AC activation. Moreover, withdrawal-induced increases in cAMP/PKA activate phospholipase C and ϵ protein kinase C to further stimulate AC5 and AC7, causing cAMP superactivation. Our findings identify a critical role for AC 5 and 7 and A2A receptors for up-regulation of AGS3 in morphine withdrawal-induced cAMP superactivation.
Footnotes
- Received May 15, 2009.
- Accepted June 23, 2009.
This work was supported by National Institutes of Health National Institute on Alcohol Abuse and Alcoholism [Grant AA010030-12].
ABBREVIATIONS: AC, adenylyl cyclase; PKA, cAMP-dependent protein kinase A; CRE, cAMP response element; MOR, μ-opioid receptor; DOR, δ-opioid receptor; PTX, pertussis toxin; PLC, phospholipase C; AGS3, activator of G-protein signaling 3; NAc, nucleus accumbens; Rp-cAMPS, adenosine-3′,5′-cyclic monophosphorothioate, Rp-isomer; GF109203X, bisindolylmaleimide I; siRNA, small interfering RNA; PBS, phosphate-buffered saline; CTOP, H-d-Phe-Cys-Tyr-d-Trp-Orn-Thr-Pen-Thr-NH2; PKC, protein kinase C; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; ANOVA, analysis of variance; A2A, adenosine A2A receptor; Et-18-OCH3, 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphorylcholine (edelfosine); KW6002, 7-methyl-3,7-dihydro-1H-purine-2,6-dione (istradefylline).
- The American Society for Pharmacology and Experimental Therapeutics
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