Naloxone's pentapeptide binding site on filamin A blocks Mu opioid receptor-Gs coupling and CREB activation of acute morphine

• Published in: PloS one Vol. 4; no. 1; p. e4282
• Main Authors: Wang, Hoau-Yan, Burns, Lindsay H
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 27.01.2009; Public Library of Science (PLoS)
• Subjects: Addictions; Analgesics, Opioid - metabolism; Anesthesiology and Pain Management/Basic Science of Pain Management; Animals; Attenuation; Binding Sites; Brain - metabolism; Cell Biology/Neuronal Signaling Mechanisms; Cocaine; Contractile Proteins - chemistry; Coupling; Cyclic adenosine monophosphate; Cyclic AMP response element-binding protein; Cyclic AMP Response Element-Binding Protein - metabolism; Drug dosages; Drug tolerance; Filamins; Kinases; Laboratories; Male; Mediation; Microfilament Proteins - chemistry; Morphine; Morphine - pharmacology; Naloxone; Naloxone - chemistry; Naloxone - pharmacology; Naltrexone; Narcotic Antagonists - chemistry; Narcotic Antagonists - pharmacology; Narcotics; Neostriatum; Neurobiology; Neuroscience/Neuronal Signaling Mechanisms; Neurosciences; Opioid receptors (type mu); Pain; Peptides - chemistry; Phosphorylation; Proteins; Rats; Rats, Sprague-Dawley; Receptors, G-Protein-Coupled - metabolism; Receptors, Opioid, mu - metabolism; Rodents; Scaffolding; Signal Transduction; Stimulation; Trends
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0004282

Chronic morphine causes the mu opioid receptor (MOR) to switch its coupling from Gi/o to Gs, resulting in excitatory signaling via both Galphas and its Gbetagamma dimer. Ultra-low-dose naloxone (NLX) prevents this switch and attenuates opioid tolerance and dependence. This protective effect is mediated via a high-affinity interaction of NLX to a pentapeptide region in c-terminal filamin A (FLNA), a scaffolding protein interacting with MOR. In organotypic striatal slice cultures, we now show that acute morphine induces a dose-dependent Go-to-Gs coupling switch at 5 and 15 min that resolves by 1 hr. The acute Gs coupling induced by 100 microM morphine was completely prevented by co-treatment with 100 pM NLX, (+)NLX, or naltrexone (NTX), or their pentapeptide binding site (FLNA(2561-2565)), which we show can act as a decoy for MOR or bind to FLNA itself. All of these co-treatments presumably prevent the MOR-FLNA interaction. Since ultra-low-dose NTX also attenuates the addictive properties of opioids, we assessed striatal cAMP production and CREB phosphorylation at S(133). Correlating with the Gs coupling, acute morphine induced elevated cAMP levels and a several-fold increase in pS(133)CREB that were also completely blocked by NLX, NTX or the FLNA pentapeptide. We propose that acute, robust stimulation of MOR causes an interaction with FLNA that allows an initially transient MOR-Gs coupling, which recovers with receptor recycling but persists when MOR stimulation is repeated or prolonged. The complete prevention of this acute, morphine-induced MOR-Gs coupling by 100 pM NLX/NTX or 10 microM pentapeptide segment of FLNA further elucidates both MOR signaling and the mechanism of action of ultra-low-dose NLX or NTX in attenuating opioid tolerance, dependence and addictive potential.