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Selectivity and evolutionary divergence of metabotropic glutamate receptors for endogenous ligands and G proteins coupled to phospholipase C or TRP channels.

ABSTRACT: To define the upstream and downstream signaling specificities of metabotropic glutamate receptors (mGluR), we have examined the ability of representative mGluR of group I, II, and III to be activated by endogenous amino acids and catalyze activation of G proteins coupled to phospholipase C (PLC), or activation of G(i/o) proteins coupled to the ion channel TRPC4?. Fluorescence-based assays have allowed us to observe interactions not previously reported or clearly identified. We have found that the specificity for endogenous amino acids is remarkably stringent. Even at millimolar levels, structurally similar compounds do not elicit significant activation. As reported previously, the clear exception is L-serine-O-phosphate (L-SOP), which strongly activates group III mGluR, especially mGluR4,-6,-8 but not group I or II mGluR. Whereas L-SOP cannot activate mGluR1 or mGluR2, it acts as a weak antagonist for mGluR1 and a potent antagonist for mGluR2, suggesting that co-recognition of L-glutamate and L-SOP arose early in evolution, and was followed later by divergence of group I and group II mGluR versus group III in l-SOP responses. mGluR7 has low affinity and efficacy for activation by both L-glutamate and L-SOP. Molecular docking studies suggested that residue 74 corresponding to lysine in mGluR4 and asparagine in mGluR7 might play a key role, and, indeed, mutagenesis experiments demonstrated that mutating this residue to lysine in mGluR7 enhances the potency of L-SOP. Experiments with pertussis toxin and dominant-negative G?(i/o) proteins revealed that mGluR1 couples strongly to TRPC4? through G?(i/o), in addition to coupling to PLC through G?(q/11).

SUBMITTER: Kang HJ

PROVIDER: S-EPMC4208005 | biostudies-literature | 2014 Oct

REPOSITORIES: biostudies-literature

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Selectivity and evolutionary divergence of metabotropic glutamate receptors for endogenous ligands and G proteins coupled to phospholipase C or TRP channels.

Kang Hye Jin HJ Menlove Kit K Ma Jianpeng J Wilkins Angela A Lichtarge Olivier O Wensel Theodore G TG

The Journal of biological chemistry 20140905 43

To define the upstream and downstream signaling specificities of metabotropic glutamate receptors (mGluR), we have examined the ability of representative mGluR of group I, II, and III to be activated by endogenous amino acids and catalyze activation of G proteins coupled to phospholipase C (PLC), or activation of G(i/o) proteins coupled to the ion channel TRPC4β. Fluorescence-based assays have allowed us to observe interactions not previously reported or clearly identified. We have found that th ...[more]

PMID: 25193666

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Project description:Transient receptor potential (TRP) channels are a group of membrane proteins involved in the transduction of a plethora of chemical and physical stimuli. These channels modulate ion entry, mediating a variety of neural signaling processes implicated in the sensation of temperature, pressure, and pH, as well as smell, taste, vision, and pain perception. Many diseases involve TRP channel dysfunction, including neuropathic pain, inflammation, and respiratory disorders. In the pursuit of new treatments for these disorders, it was discovered that cannabinoids can modulate a certain subset of TRP channels. The TRP vanilloid (TRPV), TRP ankyrin (TRPA), and TRP melastatin (TRPM) subfamilies were all found to contain channels that can be modulated by several endogenous, phytogenic, and synthetic cannabinoids. To date, six TRP channels from the three subfamilies mentioned above have been reported to mediate cannabinoid activity: TRPV1, TRPV2, TRPV3, TRPV4, TRPA1, and TRPM8. The increasing data regarding cannabinoid interactions with these receptors has prompted some researchers to consider these TRP channels to be "ionotropic cannabinoid receptors." Although CB1 and CB2 are considered to be the canonical cannabinoid receptors, there is significant overlap between cannabinoids and ligands of TRP receptors. The first endogenous agonist of TRPV1 to be discovered was the endocannabinoid, anandamide (AEA). Similarly, N-arachidonyl dopamine (NADA) and AEA were the first endogenous TRPM8 antagonists discovered. Additionally, Δ9-tetrahydrocannabinol (Δ9-THC), the most abundant psychotropic compound in cannabis, acts most potently at TRPV2, moderately modulates TRPV3, TRPV4, TRPA1, and TRPM8, though Δ9-THC is not reported to modulate TRPV1. Moreover, TRP receptors may modulate effects of synthetic cannabinoids used in research. One common research tool is WIN55,212-2, a CB1 agonist that also exerts analgesic effects by desensitizing TRPA1 and TRPV1. In this review article, we aim to provide an overview and classification of the cannabinoid ligands that have been reported to modulate TRP channels and their therapeutic potential.

Project description:1. Phospholipase D (PLD) is the key enzyme in a signal transduction pathway leading to the formation of the second messengers phosphatidic acid and diacylglycerol. In order to define the pharmacological profile of PLD-coupled metabotropic glutamate receptors (mGluRs), PLD activity was measured in slices of adult rat brain in the presence of mGluR agonists or antagonists. Activation of the phospholipase C (PLC) pathway by the same agents was also examined. 2. The mGluR-selective agonist (1S,3R)-l-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD] induced a concentration-dependent (10-300 microM) activation of PLD in the hippocampus, neocortex, and striatum, but not in the cerebellum. The effect was particularly evident in hippocampal slices, which were thus used for all subsequent experiments. 3. The rank order of potencies for agonists stimulating the PLD response was: quisqualate > ibotenate > (2S,3S,4S)-alpha-(carboxycyclopropyl)-glycine > (1S,3R)-ACPD > L-cysteine sulphinic acid > L-aspartate > L-glutamate. L-(+)-2-Amino-4-phosphonobutyric acid and the ionotropic glutamate receptor agonists N-methyl-D-aspartate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, and kainate failed to activate PLD. (RS)-3,5-dihydroxyphenylglycine (100300 microM), an agonist of mGluRs of the first group, stimulated PLC but inhibited the PLD response elicited by 100 microM (1S,3R)-ACPD. 4. (+)-alpha-Methyl-4-carboxyphenylglycine (0.1-1 mM), a competitive antagonist of mGluRs of the first and second group, elicited a significant PLD response. L-(+)-2-Amino-3-phosphonopropionic acid (1 mM), an antagonist of mGluRs of the first group, inhibited the 100 microM (1S,3R)-ACPD-induced PLC response but produced a robust stimulation of PLD. 5. 12-O-Tetradecanoylphorbol 13-acetic acid and phorbol 12,13-dibutyrate (PDBu), activators of protein kinase C, at 1 microM had a stimulatory effect on mGluRs linked to PLD but depressed (1S,3R)-ACPD-induced phosphoinositide hydrolysis. The protein kinase C inhibitor, staurosporine (1 and 10 microM) reduced PLD activation induced by 1 microM PDBu but not by 100 microM (1S,3R)-ACPD. 6. Our results suggest that PLD-linked mGluRs in rat hippocampus may be distinct from any known mGluR subtype coupled to PLC or adenylyl cyclase. Moreover, they indicate that independent mGluRs coupled to the PLC and PLD pathways exist and that mGluR agonists can stimulate PLD through a PKC-independent mechanism.

Dataset Information

Selectivity and evolutionary divergence of metabotropic glutamate receptors for endogenous ligands and G proteins coupled to phospholipase C or TRP channels.

Publications

Selectivity and evolutionary divergence of metabotropic glutamate receptors for endogenous ligands and G proteins coupled to phospholipase C or TRP channels.

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