Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Nociceptin/OFQ is the endogenous ligand for the G protein-coupled opioid receptor-like (ORL1) receptor. To elucidate the cellular functions of the ORL1 receptor, we examined its ability to interact with Gz and G16, two pertussis toxin (PTX)-insensitive G proteins that are known molecular partners for the opioid receptors. In HEK 293 cells transiently expressing the ORL1 and dopamine D1 receptors, nociceptin/OFQ dose-dependently inhibited dopamine-stimulated cyclic AMP (cAMP) accumulation in a PTX-sensitive manner. However, PTX failed to block the nociceptin/OFQ-induced inhibition of dopamine-stimulated cAMP accumulation in HEK 293 cells co-expressing the alpha-subunit of Gz. This result indicates functional interaction between the ORL1 receptor and Gz. A similar result was obtained with retinoic acid-differentiated SH-SY5Y cells, which endogenously express both the ORL1 receptor and Gz. When the ORL1 receptor was transiently co-expressed in COS-7 cells with the alpha-subunit of G16, nociceptin/OFQ dose-dependently stimulated the formation of inositol phosphates. Nociceptin-induced stimulation of phospholipase C was absolutely dependent on the co-expression of alpha16 and exhibited the appropriate ligand selectivity. In terms of its ability to interact with PTX-insensitive G proteins, the ORL1 receptor behaves very much like the opioid receptors.
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PMID:Pertussis toxin-insensitive signaling of the ORL1 receptor: coupling to Gz and G16 proteins. 979 48

In most tissues and cells the opioid receptor-like (ORL1) receptor regulates effectors primarily through the pertussis toxin (PTX)-sensitive guanine nucleotide-binding regulatory proteins (G proteins) Gi/Go. Many Gi-coupled receptors possess additional capability to interact with one or more PTX-insensitive G proteins. Using the betagamma-induced stimulation of type 2 adenylyl cyclase as a readout, we screened the ability of ORL1 receptor to interact with a panel of PTX-insensitive G proteins. In the presence of PTX, activation of the ORL1 receptor resulted in the stimulation of type 2 adenylyl cyclase only in HEK 293 cells coexpressing the alpha subunit of Gz, G12, G14, or G16, but not in cells coexpressing G11, G13, or Gq. Coupling to both Gz and G16 was expected because close relatives of the ORL1 receptor, the opioid receptors, are known to couple productively to these G proteins. ORL1 receptor coupling to either G12 or G14 has not been demonstrated. As predicted by the type 2 adenylyl cyclase assays, activation of the ORL1 receptor resulted in the formation of inositol phosphates in COS-7 cells transiently cotransfected with Galpha14. The ORL1 receptor-mediated stimulation of phospholipase C was found to be Galpha14 dependent, agonist dose dependent, ligand selective, and PTX insensitive. We conclude that G14 can link the ORL1 receptor to regulation of phopholipase C.
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PMID:GalphaL1 (Galpha14) couples the opioid receptor-like1 receptor to stimulation of phospholipase C. 986 75

Opioid receptors (mu, delta and kappa) are known to regulate diverse physiological functions and yet, at the molecular level, they are coupled to a seemingly identical set of G proteins. A recent study has discerned subtle differences between the opioid receptors in their ability to activate the pertussis toxin-insensitive G16. Differences in microarchitecture might be magnified when these receptors are provided with 'non-native' partners. Here, we examined whether the opioid receptors can interact productively with a set of chimeric Galphaq subunits which are known to link many Gi-coupled receptors to phosphoinositide-specific phospholipase C (PI-PLC). The qi5, qo5 and qz5 chimeras have the last five residues of Galphaq replaced by those of Galphai, Galphao and Galphaz, respectively. Except for mu-receptor and qo5, each pair of opioid receptor and Galphaq chimera allowed opioid agonists to stimulate PI-PLC in transfected COS-7 cells. The Galphaq chimera-mediated responses were ligand selective, agonist dose dependent and saturable. The most robust responses were obtained with kappa-receptor and qi5 or qz5, whereas the coupling of delta- and mu-receptors to Galphaq chimeras produced much weaker responses. Among the Galphaq chimeras, qo5 was less efficiently coupled to the opioid receptors. As revealed by radioligand binding assays and immunoblot analysis, differences in the efficiency of coupling were not due to variations in the expression of receptors and Galphaq chimeras. Differences in the magnitude of PI-PLC responses are thus likely to represent structural incompatibility between opioid receptors and Galphaq chimeras, suggesting that each opioid receptor possesses unique structural surfaces for the binding of G proteins.
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PMID:Stimulation of phospholipase C by the cloned mu, delta and kappa opioid receptors via chimeric G alpha(q) mutants. 1005 38

A naturally occurring point mutation (R231H) within one of the major 3gamma-binding surface (switch II region) on the a subunit of Gs (alpha(s)) has previously been found to disrupt receptor-mediated activation of Gs. The disruption caused by mutating this conserved residue may be a general phenomenon for all a subunits. Homologous mutants of the alpha subunit of Gz [alpha(z); a negative regulator of adenylyl cyclase (AC)] and G16 (alpha16; a stimulator of phospholipase C) were constructed and examined for receptor-mediated regulation of their corresponding effectors. The mutant alphazR209H cannot be fully activated by the delta-opioid receptor, as indicated by the impairment of the inhibition of alpha(s)-stimulated AC and betagamma-mediated stimulation of AC type II (AC2). Similarly, the mutant alpha16R216H lost the ability to mediate receptor-induced activation of phospholipase C and AC2. The receptor coupling efficacy and promiscuity of alpha16R216H were eradicated. The mutation of the conserved arginine has no observable effect on the constitutive activities of the GTPase-deficient derivatives of both alpha(z) and alpha16. The alpha subunit of Gt1 (transducin; alphat1) attenuated betagamma-mediated stimulation of AC2 by sequestrating free betagamma subunits, but the mutant alphat1R204H showed reduced ability to scavenge betagamma-mediated AC2 activation. Presumably, mutation of the conserved arginine disrupted the subunit interactions in addition to the impairment of receptor interaction.
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PMID:Disruption of receptor-mediated activation of G protein by mutating a conserved arginine residue in the switch II region of the alpha subunit. 1053 70

The family of melatonin receptors is composed of the mt1, MT2, and Mel1c subtypes. The Mel1c is further divided into one long and two short isoforms. A recent study has shown that, unlike mt1 and MT2, the long form of Mel1c is incapable of activating the pertussis toxin-insensitive G16. Here we used three well-characterized Galphaq chimeras to explore the coupling specificity of the melatonin receptors. The qi5, qo5, and qz5 chimeras can link numerous Gi-coupled receptors to the stimulation of phosphoinositide-specific phospholipase C. Both mt1 and MT2 receptors interacted productively with the Galphaq chimeras, while the long form of Mel1c was totally ineffective. Among the Galphaq chimeras, qo5 was less efficiently coupled to the melatonin receptors. Such differential coupling is best explained by structural differences between the melatonin receptors as well as among the Galphaq chimeras. Since the long form of Mel1c receptor possesses an exceptionally large C-terminal tail, we tested the ability of four melatonin receptor C-terminal tail chimeras (Chi 1-4) to interact with the Galphaq chimeras. The presence of the large C-terminal tail of Mel1c in Chi 1 and Chi 3 markedly hindered their coupling to the Galphaq chimeras. On the other hand, the attachment of either the mtl or MT2 C-terminal tail to a Mel1c backbone produced chimeras (Chi 2 and Chi 4) that were capable of activating the Galphaq chimeras. These findings suggest the involvement of C-terminal regions of melatonin receptors in the recognition of G proteins.
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PMID:Chimeric Galphaq subunits can distinguish the long form of the Xenopus Mel1c melatonin receptor from the mammalian mt1 and MT2 melatonin receptors. 1131 28

The mammalian G proteins G15 and G16 couple a wide variety of receptors to phospholipase C (PLC) in co-transfected systems, and it has been suggested that they can be used as tools in agonist-screening systems. Using the reversed tetracycline-controlled transactivation system we generated rat pituitary GH3 cell clones that expressed Galphal5 and Galpha16 conditionally to study the coupling of endogenous receptors to both G proteins. In cells expressing moderate levels of Galpha15, activation of various endogenous receptors increased inositol phosphate production, whereas conditional expression of Galpha16 had no significant effect on agonist-dependent PLC activity. Activation of PLC through Galpha15 in response to carbachol did not increase cytosolic [Ca2+] ([Ca2+]i) but stimulated protein kinase C. While carbachol decreased the secretory activity in non-induced GH3 cells, it increased secretion in cells expressing Galpha15. Our data demonstrate that Galpha15 has a higher functional promiscuity than Galpha16 when studied in a system that preserves physiological G protein and receptor levels. In addition, Galpha15-mediated coupling of a receptor to PLC can change the cellular response to receptor agonists, indicating that downstream cellular functions can be used to detect receptor activation in screening systems employing a promiscuous G protein.
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PMID:Conditionally expressed G alpha 15 couples to endogenous receptors in GH3 cells. 1153 53

Opioid peptides exert their regulatory effects on both central and peripheral nervous systems via multiple opioid receptors that are linked to seemingly identical sets of guanine nucleotide-binding regulatory proteins (G proteins). In contrast to the mu-opioid receptor, the delta-opioid receptor can efficiently stimulate phospholipase C via G16. We used a series of mu/delta-opioid receptor chimeras to examine the involvement of intracellular receptor domains in the recognition of G16. After ascertaining that the chimeras can bind opioid ligands with high affinity and elicit inhibition of adenylyl cyclase, COS-7 cells were cotransfected with cDNAs encoding Galpha16 and a mu/delta-opioid receptor chimera and assayed for [D-Ala2,D-Leu5]enkephalin-induced stimulation of phospholipase C. Our results indicate that (i) the carboxy terminal tail of the delta-opioid receptor is necessary but insufficient for conferring coupling to Galpha16, (ii) the third inner loop together with the carboxy terminal tail of the delta-opioid receptor can provide sufficient contact domains for Galpha16, and (iii) the first inner loop of the delta-opioid receptor, in particular Leu80, as well as the fifth transmembrane domain and/or the third extracellular loop may also contribute in defining the fidelity of interaction between the delta-opioid receptor and Galpha16. These results indicate that efficient coupling of the delta-opioid receptor to Galpha16 requires the participation of most of the intracellular regions, including the first intracellular loop.
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PMID:The first and third intracellular loops together with the carboxy terminal tail of the delta-opioid receptor contribute toward functional interaction with Galpha16. 1453 52


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