GX/Z and Gi2 transducer proteins on μ/δ opioid-mediated supraspinal antinociception

doi:10.1016/0024-3205(93)90166-Z

Life Sciences

Volume 53, Issue 23, 1993, Pages PL381-PL386

https://doi.org/10.1016/0024-3205(93)90166-Z Get rights and content

Abstract

Intracerebroventricular (i.c.v.) administration of immune sera raised against G_i2α subunits to mice, significantly reduced the supraspinal antinociceptive effect of opioids when evaluated 24 h later in the tail-flick test. Antisera directed against G_i1α subunits did not modify this opioid activity. In mice injected with sera anti-G_X/Zα, the μ-preferential agonists, DAMGO and morphine, and the endogenous μ/δ opioid peptide β-endorphin-(1–31) displayed a reduced antinociceptive activity, whereas, the potency of the δ-selective agonists DPDPE and [D-Ala²] Deltorphin II, was not altered. This reduction was present for 3 to 7 days and returned to the control values after 10 days. Anti-G_i2α and anti-G_X/Zα, but not anti-G_i1α, reduced the e specific binding of [³H]DAMGO to the opioid receptor in PAG. These results suggest the ability of the μ receptor to interact in vivo with different classes of G transducer proteins (G_X/Z/G_i2) to produce an effect. This work also indicates a functional role of the pertussis toxin insensitive G_X/Z protein, on the μ-mediated (but not δ-mediated) supraspinal antinociception in mice.

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Cited by (49)

Gz- and not Gi-proteins are coupled to pre-junctional μ-opioid receptors in bovine airways
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Citation Excerpt :
Opioid receptors are localized on the vagus nerve endings but not on airway smooth muscle cells (Atweh et al., 1978; Cabot et al., 1994). Studies on opioid pharmacology using different neural tissues or cell lines from different species have convincingly shown that the major pathways for intracellular signal transmission from the receptors to the effectors are through coupling to the inhibitory Gi (Garzón et al., 1997; Sánchez-Blázquez et al., 1993) and/or Gz (Garzón et al., 1997, 2004; Lai et al., 1995; Sánchez-Blázquez et al., 1993) proteins. In murine sympathetic nerves Gz protein may couple neurotransmitter receptors to N-type Ca2+ channels via a pertussis toxin (PTX)-insensitive pathway (Jeong and Ikeda, 1998).
We investigated the signal transmission pathway by which activation of μ-opioid receptors attenuates acetylcholine (ACh) release in bovine trachealis. Electrical stimulation (ES)-induced [³H]-ACh release was determined in bovine tracheal smooth muscle strips pre-incubated with either the Gi-protein inhibitor pertussis toxin (PTX, 500 ng/ml and 1 μg/ml) or the Gz-protein specific inhibitor arachidonic acid (AA, 10⁻⁶ M and 10⁻⁵ M) and then treated with DAMGO (D-Ala²,N-MePhe⁴,Gly-ol⁵-enkephalin) 10⁻⁵ M. Indomethacin 10⁻⁵ M was used to block AA cascade. The inhibitory effect of DAMGO on ES-induced [³H]-ACh release was PTX-insensitive, but, by contrast, ablated by AA in a concentration-dependent manner. AA 10⁻⁵ M alone reduced [³H]-ACh release, an effect that was prevented by iberiotoxin 10⁻⁷ M, suggesting an involvement of Ca²⁺-activated K⁺-channels. Western blot analysis consistently showed immunoreactive bands against a specific antibody anti-Gz-α subunit at ∼40 kDa, consistent with the presence of Gz-protein. The present findings suggest that in isolated bovine trachealis, activation of μ-opioid receptors inhibits ACh-release through a signal transmission pathway involving Gz-protein rather than Gi-protein.
Signaling Through G<inf>z</inf>
2009, Handbook of Cell Signaling, Second Edition
Several studies have been carried out to pinpoint specific brain regions and developmental stages where Gz is transcribed or expressed. The limited tissue distribution of Gαz, its unusual biochemical properties, the identification of Gαz-specific effectors, and the inability of other Gαi subfamily members to substitute for Gαz in vivo support unique physiologic roles for Gz. The rate of GDP dissociation from Gαz is extremely slow as compared to that of most other G-protein α subunits, and almost completely suppressed at Mg²⁺ concentrations greater than 100 μM. Most receptors that couple to Gi proteins can also activate Gz if the G protein or receptors are overexpressed in cells. Although the precise roles of Gz in cellular signaling are still being established, accumulating evidence points to the involvement of this unique Gi subfamily member in several facets of cell biology. First, the temporal and spatial expression patterns of Gαz suggest a possible role in neuron growth and/or differentiation. Gz also appears to regulate platelet function through adrenergic receptor signaling. In addition, Gz participates in the physiologic regulation of insulin secretion from the pancreatic β cells. Finally, Gz may be involved in processes impacting on mood or behavior. These distinct roles further define Gz as unique among the Gi subfamily of heterotrimeric G proteins.
NMDAR-nNOS generated zinc recruits PKCγ to the HINT1-RGS17 complex bound to the C terminus of Mu-opioid receptors
2008, Cellular Signalling
In neurons, the C terminus of the Mu-opioid receptor (MOR) binds to the protein kinase C-interacting protein/histidine triad nucleotide binding protein 1 (PKCI/HINT1) which in turn binds the regulator of G-protein signalling RGSZ1/Z2 (RGSZ) protein. In this study, we found that intracerebroventricular (icv) administration of morphine recruits PKC isoforms, mostly PKCγ, to the MOR via the HINT1/RGSZ complex. There, diacylglycerol (DAG) activates this PKCγ to phosphorylate the MOR and thus, its signal strength was reduced. When PKCI/HINT1 expression is depressed, morphine produces stronger analgesic effects and neither the PKCγ–MOR complex nor serine phosphorylation of this receptor is detected. This MOR–PKC association involves the cysteine rich domains (CRDs) in the regulatory C1 region of PKC, as well as requiring free zinc ions, HINT1 and RGSZ proteins. Increasing the availability of this metal ion recruits inactive PKCγ to the MOR, while phorbol esters prevent this binding and even disrupt it. The nitric oxide donor (S)-Nitroso-N-acetylpenicillamine (SNAP) foments the association of PKCγ with the MORs, effect that was prevented by the heavy metal chelator N,N,N′,N′-tetrakis(2-pyridylmethyl) ethylenediamine (TPEN), suggesting a role for endogenous zinc and neural nitric oxide synthase. The N-methyl-D-aspartate receptor (NMDAR) antagonist, MK801, also prevented PKCγ recruitment to MORs and serine phosphorylation of the receptors following icv morphine. These results indicate that the NMDAR/nNOS cascade, activated via MORs, provide the free zinc ions required for inactive PKCγ to bind to HINT1/RGSZ complex at the C terminus of the receptor.
Reversal of ongoing thermal hyperalgesia in mice by a recombinant herpesvirus that encodes human preproenkephalin
2004, Molecular Therapy
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Cell lines coexpressing Gz and opioid receptors implicate Gz in the regulation of Ca2+channels critical to neurotransmitter release [14]. Similarly, antisense oligonucleotide strategies have demonstrated the involvement of Gz in μ and δ opioid-mediated antinociception in the central nervous system [15–17]. Thus, although PTX treatment induces a robust hyperalgesia, likely by disabling some G proteins linked to inhibitory neurotransmitter receptors, the reversal of this hyperalgesia by an opioid-encoding herpesvirus suggests that G proteins unaffected by PTX are capable of overcoming this disability.
Herpesvirus-mediated transfer of the human preproenkephalin gene to primary afferent nociceptors prevents phasic thermal allodynia/hyperalgesia in mice. It is not known, however, whether similar viral treatments would reverse ongoing or chronic pain and allodynia/hyperalgesia. To this end, mice were given intrathecal injections of pertussis toxin (PTX), which produces a weeks-long thermal hyperalgesia apparently by uncoupling certain G proteins from inhibitory neurotransmitter receptors. This treatment produced profound thermal hyperalgesia in both Aδ and C-fiber thermonociceptive tests lasting at least 6 weeks. However, treatment of skin surfaces with an enkephalin-encoding herpesvirus, but not control virus or vehicle, completely reversed this hyperalgesia. This profound antihyperalgesia was observed for both Aδ- and C-fiber-mediated responses. Interestingly, however, while the antihyperalgesic effect of the enkephalin-encoding virus on C-fiber-mediated responses was reversed by intrathecal application of μ or δ opioid antagonists, only δ antagonists reversed the effect of this virus on Aδ hyperalgesia. Thus, virus-mediated delivery of the proenkephalin cDNA reverses thermal hyperalgesia produced by PTX-induced ribosylation of inhibitory G proteins by an opioid-mediated mechanism. These results suggest that herpesvirus vectors encoding analgesic peptides may be useful in attenuating centrally mediated, ongoing neuropathic pain and/or hyperalgesia.
Opioid receptor-induced GTPγ<sup>35</sup>S binding during mouse development
2003, Developmental Biology
Although a large superfamily of G-protein-coupled receptors serves multiple functions, little is known about their functional activation during ontogeny. To examine the functional activation of the mu-opioid receptor (MOR) and the delta-opioid receptor (DOR) during development, sections of mouse embryos and fetuses from e11.5 until birth were treated with DAMGO and DPDPE, respectively, and the ability of these drugs to induce G-protein coupling was assessed by using GTPγ³⁵S binding autoradiography. MOR activation was first detected in the caudate-putamen (CPU) at e12.5, and by e15.5, activity had not only increased in this region but also expanded to include the midbrain, medial habenula, hypothalamus, pons, and medulla. DOR activity first appeared at e17.5 in the hypothalamus, pons, medial habenula, and medulla and at p1 in the CPU at levels noticeably less than those of the MOR. In general, MOR and DOR activation lagged only slightly behind the appearance of MOR-1 and DOR-1 mRNA but delayed activation was particularly pronounced in the trigeminal ganglia, where MOR-1 gene expression was first detected at e13.5, but MOR activity was not observed even at birth. Thus, the data demonstrate temporal and often region-specific differences in the appearance and magnitude of functional activity in cell groups expressing either the MOR-1 or DOR-1 genes, suggesting that interaction between the opioid receptors, G-proteins, and other signaling cofactors is developmentally regulated.
Morphine and morphine-6β-glucuronide-induced feeding are differentially reduced by G-protein α-subunit antisense probes in rats
2000, Brain Research
Citation Excerpt :
Interactions between specific G-proteins and their receptors have shown that a variety of pharmacological mechanisms may underlie a given behavioral response. The decreases in morphine-induced feeding induced by an AS ODN probe directed against the Giα2 subunit provide similar profiles to that observed in supraspinal morphine analgesia studies using antibodies targeting individual G-proteins [11,48,49] or an AS ODN probe targeted against the Giα2 subunit [37,38,47,55]. Since only the Giα2 AS ODN probe was effective in attenuating morphine-induced feeding as well as morphine-induced analgesia, it appears that the μ-receptor, a primary receptor target of morphine, mediates morphine-induced feeding either through its direct coupled activation with the Giα2 subunit, and/or with another unidentified transmitter system downstream that also requires activation of the Giα2 subunit.
Although morphine and its active metabolite, morphine-6β-glucuronide (M6G), each induce μ-opioid receptor-sensitive feeding, different antisense oligodeoxynucleotide (AS ODN) probes directed against the MOR-1 clone produce distinct effects. Thus, MOR-1 AS ODN probes directed against exons 1 or 4 reduce morphine-, but not M6G-induced feeding, whereas probes directed against exons 2 or 3 reduce M6G-, but not morphine-induced feeding. AS ODN probes directed against different G-protein α-subunits differentially reduced morphine (G_iα2) and M6G (G_iα1)-induced analgesia. The present study evaluated the ability of AS ODN probes directed against G-protein α-subunits to reduce feeding induced by morphine and M6G in rats. The AS ODN probes (25 μg, i.c.v.) were administered once 24 h prior to morphine (5 μg, i.c.v.) or M6G (250 ng) and spontaneous free feeding was assessed 1, 2 and 4 h thereafter. In agreement with analgesic studies, morphine-induced feeding was significantly reduced by the G_iα2 AS ODN probe. Morphine-induced feeding was unaffected by AS ODN probes directed against either G_iα1, G_iα3, G_oα, G_x/zα, G_qα or a nonsense control probe, and was significantly enhanced by pretreatment with the G_sα probe. In contrast, M6G-induced feeding was significantly reduced by AS ODN probes directed against either G_iα1, G_iα3 or G_x/zα, whereas AS ODN probes targeting G_iα2, G_oα, G_sα, G_qα or a nonsense control probe were ineffective. When M6G-induced feeding was assessed at a dose (500 ng) which was sensitive to MOR-1 AS ODN effects, none of the G-protein α-subunit AS ODN probes were effective. These data indicate that morphine and M6G-induced feeding are mediated through different G-protein α-subunits, and provide further evidence for separate and distinct molecular mechanisms mediating these functional responses through different opioid receptors. This strongly suggests that M6G may act through a novel opioid receptor displaying a distinct pharmacological mechanism.

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Pharmacology letterGX/Z and Gi2 transducer proteins on μ/δ opioid-mediated supraspinal antinociception

Abstract

European J. Pharmacol.

European J. Pharmacol.

Life Sci.

Life Sci.

Life Sci.

Life Sci.

Peptides

Trends Pharmacol. Sci.

J. Biol. Chem.

J. Biol. Chem.

European J. Pharmacol.

European J. Pharmacol.

Pharmacology letter
G_X/Z and G_i2 transducer proteins on μ/δ opioid-mediated supraspinal antinociception