Functional organization of PLC signaling microdomains in neurons

doi:10.1016/j.tins.2003.10.013

Trends in Neurosciences

Volume 27, Issue 1, January 2004, Pages 41-47

https://doi.org/10.1016/j.tins.2003.10.013 Get rights and content

Abstract

Our understanding of receptor transduction systems has grown impressively in recent years as a result of intense efforts to characterize signaling molecules and cascades in neurons. A large body of evidence has recently accrued regarding the fast and effective signal transfer that occurs during phosphoinositide signaling. In particular, dissection of the Drosophila phototransduction pathway has enabled a greater understanding of the molecular organization of phospholipase C (PLC) signaling. Supramolecular complexes organize the correct repertoires of receptors, enzymes and ion channels into individual signaling pathways. Such mechanisms involve localization of signaling molecules to sites of action by scaffold and anchoring proteins, ensuring speed and specificity of signal transduction events. However, not all PLC signals nucleate around scaffold proteins, although mechanisms for selectivity and discrimination remain. This article reviews recent advances on the molecular organization and functional consequences of PLC signaling domains, which link membrane receptors to ion channels, including TRP and KCNQ channels.

Section snippets

PLC-mediated signaling to TRP channels: an example of receptor–ion-channel segregation

The sophistication of PLC signaling is best illustrated by the phototransduction cascade in the fruitfly Drosophila 3, 4, 5. This PLCβ-coupled mechanism represents the fastest G_q-protein-signaling pathway known: the absorption of a single photon by rhodopsin is translated into a physiological response (a depolarization) in just 20 ms [6]. Nonetheless, phototransduction in flies is a complex, multiprotein cascade involving many enzymatic processes. First, light signal is transmitted from the Gα_q

PLC-mediated signaling to KCNQ/M channels: an example of receptor segregation

Neural KCNQ/M channels can be shut down by virtually any Gα_q–PLC- or Gα₁₁–PLC-coupled receptor 40, 41. Indeed, all of their putative subunits (KCNQ2–5) – and even the cardiac homolog KCNQ1 – appear to be equally susceptible to suppression by an appropriate Gα_q- or Gα₁₁-linked G-protein-coupled receptor [42]. Nevertheless, there seems to be some functional discrimination between different receptors, at least mechanistically.

Thus, KCNQ/M channels in sympathetic neurons are closed by ACh (the

Concluding remarks: new principles for PLC signaling

Because the PLCβ cascade is utilized by a large numbers of transmembrane receptors and is present in virtually all cells, a central question is how these cells generate receptor-specific signals. From the two examples discussed here, it appears that PLC signaling pathways are tightly coupled, forming architecturally distinct signaling complexes or microdomains. Two strategies also seem to emerge. In the first model, exemplified by the Drosophila phototransduction, the PLC signaling complex

Acknowledgements

Our work was supported by the Centre National de la Recherche Scientifique (CNRS) and by grants from the UK Medical Research Council and the Wellcome Trust.

References (62)

M.J Berridge
Neuronal calcium signaling
Neuron
(1998)
K Scott et al.
Lights out: deactivation of the phototransduction cascade
Trends Biochem. Sci.
(1997)
H Reuss
In vivo analysis of the Drosophila light-sensitive channels, TRP and TRPL
Neuron
(1997)
B.A Niemeyer
The Drosophila light-activated conductance is composed of the two channels TRP and TRPL
Cell
(1996)
X.Z Xu
TRPgamma, a Drosophila TRP-related subunit, forms a regulated cation channel with TRPL
Neuron
(2000)
J.K Acharya
InsP₃ receptor is essential for growth and differentiation but not for vision in Drosophila
Neuron
(1997)
P Raghu
Normal phototransduction in Drosophila photoreceptors lacking an InsP₃ receptor gene
Mol. Cell. Neurosci.
(2000)
P Raghu
Constitutive activity of the light-sensitive channels TRP and TRPL in the Drosophila diacylglycerol kinase mutant, rdgA
Neuron
(2000)
R.C Hardie
Calcium influx via TRP channels is required to maintain PIP₂ levels in Drosophila photoreceptors
Neuron
(2001)
S.J Lee
Light adaptation through phosphoinositide-regulated translocation of Drosophila visual arrestin
Neuron
(2003)

Cited by (71)

Lipid agonism: The PIP<inf>2</inf> paradigm of ligand-gated ion channels
2015, Biochimica et Biophysica Acta - Molecular and Cell Biology of Lipids
The past decade, membrane signaling lipids emerged as major regulators of ion channel function. However, the molecular nature of lipid binding to ion channels remained poorly described due to a lack of structural information and assays to quantify and measure lipid binding in a membrane. How does a lipid–ligand bind to a membrane protein in the plasma membrane, and what does it mean for a lipid to activate or regulate an ion channel? How does lipid binding compare to activation by soluble neurotransmitter? And how does the cell control lipid agonism? This review focuses on lipids and their interactions with membrane proteins, in particular, ion channels. I discuss the intersection of membrane lipid biology and ion channel biophysics. A picture emerges of membrane lipids as bona fide agonists of ligand-gated ion channels. These freely diffusing signals reside in the plasma membrane, bind to the transmembrane domain of protein, and cause a conformational change that allosterically gates an ion channel. The system employs a catalog of diverse signaling lipids ultimately controlled by lipid enzymes and raft localization. I draw upon pharmacology, recent protein structure, and electrophysiological data to understand lipid regulation and define inward rectifying potassium channels (K_ir) as a new class of PIP₂ lipid-gated ion channels.
Three structurally similar odorants trigger distinct signaling pathways in a mouse olfactory neuron
2014, Neuroscience
Citation Excerpt :
U73343, the inactive analog of U73122, did not change H-evoked responses (97 ± 5%, p > 0.3, n = 8). Since cAMP elevation can lead to activation of protein kinase A (PKA) in the AC pathway and PKC is activated by DAG in the PLC pathway (Schild and Restrepo, 1998; Delmas et al., 2004), we examined influences of PKA and PKC on [Ca2+]i transients in Ho-OSNs during odorant-evoked activation by applying an isoquinolinesulfonamide drug H8. H8 is a potent inhibitor of PKA and PKG and shows moderate inhibition to PKC with Ki values of 1.2, 0.48 and 15, respectively (Hidaka et al., 1984).
In the mammalian olfactory system, one olfactory sensory neuron (OSN) expresses a single olfactory receptor gene. By calcium imaging of individual OSNs in intact mouse olfactory turbinates, we observed that a subset of OSNs (Ho-OSNs) located in the most ventral olfactory receptor zone can mediate distinct signaling pathways when activated by structurally similar ligands. Calcium imaging showed that Ho-OSNs were highly sensitive to 2-heptanone, heptaldehyde and cis-4-heptenal. 2-heptanone-evoked intracellular calcium elevation was mediated by cAMP signaling while heptaldehyde triggered the diacylglycerol pathway. An increase of intracellular calcium evoked by cis-4-heptenal was due to a combination of activation mediated by the adenylate cyclase pathway and suppression generated by phospholipase C signaling. Pharmacological studies demonstrated that novel mechanisms were involved in the phospholipase C-mediated intracellular calcium changes. Binary-mixture studies and cross-adaptation data indicate that three odorants acted on the same olfactory receptor. The feature that an olfactory receptor mediates multiple signaling pathways was specific for Ho-OSNs and not established in another population of OSNs characterized. Our study suggests that distinct signaling pathways triggered by ligand-induced conformational changes of an olfactory receptor constitute a complex information process mechanism in olfactory transduction. This study has important implications beyond olfaction in that it provides insights of plasticity and complexity of G-protein-coupled receptor activation and signal transduction.
Purinergic signaling negatively regulates activity of an olfactory receptor in an odorant-dependent manner
2014, Neuroscience
Extracellular purines and pyrimidines are important signaling molecules that mediate diverse biological functions via cell surface purinergic receptors. Although purinergic modulation to olfactory activity has been reported, cell-specific expression and action of purinergic receptors deserve further exploration. We physiologically characterized expression of purinergic receptors in a set of olfactory sensory neurons that are responsive to both acetophenone and benzaldehyde (AB-OSNs). Sparsely distributed in the most ventral olfactory receptor zone, AB-OSNs were activated by P2 purinergic receptor agonists but not by P1 purinergic receptor agonist adenosine. Both P2X-selective agonist α,β-methylene ATP and P2Y-selective agonist uridine 5′-triphosphate (UTP) were stimulatory to AB-OSNs, indicating expression of both P2X and P2Y purinergic receptors in AB-OSNs. Pharmacological characterization of receptor specificity using various P2X and P2Y agonists and antagonists illustrated that P2X1 and P2Y2 receptors played major roles in purinergic signaling in AB-OSNs. Interestingly, the results of purinergic modulation to acetophenone-evoked responses were different from those to benzaldehyde-evoked responses within the same neurons. Activation of P2X1 receptors had more profound inhibitory effects on benzaldehyde-evoked intracellular calcium elevation than on acetophenone-evoked responses within the same neurons, and the reverse was true when P2Y2 receptors were activated. Cross-adaptation data showed that acetophenone and benzaldehyde bound to the same olfactory receptor. Thus, our study has demonstrated that purinergic signaling of P2X and P2Y receptors has different effects on olfactory transduction mediated by a defined olfactory receptor and the consequences of purinergic modulation of olfactory activity might depend on stereotypic structures of the odorant-receptor complex.
Early stress prevents the potentiation of muscarinic excitation by calcium release in adult prefrontal cortex
2014, Biological Psychiatry
Citation Excerpt :
Disruptions in the phospholipase C pathway, activated by Gαq-protein coupled receptors, have been implicated in the pathophysiology of mental illness (93). Here, we present evidence that the experience of early stress dysregulates Gαq-coupled muscarinic signaling and alters the expression of a network of proteins that structurally and/or functionally interact with the IP3 receptor (59–61), including calcineurin (60,62), the L-type Ca2+ channel β2 subunit (63), CD44 (64,65), calpain 8 (60,66), ANKFY1 (65), and AKAP1 (59,90). Peak performance on tasks of executive function is only achieved as the PFC matures in late adolescence (1–6) and brain regions with such protracted development are especially vulnerable to early stress (23).
The experience of early stress contributes to the etiology of several psychiatric disorders and can lead to lasting deficits in working memory and attention. These executive functions require activation of the prefrontal cortex (PFC) by muscarinic M1 acetylcholine (ACh) receptors. Such Gα_q-protein coupled receptors trigger the release of calcium (Ca²⁺) from internal stores and elicit prolonged neuronal excitation.
In brain slices of rat PFC, we employed multiphoton imaging simultaneously with whole-cell electrophysiological recordings to examine potential interactions between ACh-induced Ca²⁺ release and excitatory currents in adulthood, across postnatal development, and following the early stress of repeated maternal separation, a rodent model for depression. We also investigated developmental changes in related genes in these groups.
Acetylcholine-induced Ca²⁺ release potentiates ACh-elicited excitatory currents. In the healthy PFC, this potentiation of muscarinic excitation emerges in young adulthood, when executive function typically reaches maturity. However, the developmental consolidation of muscarinic ACh signaling is abolished in adults with a history of early stress, where ACh responses retain an adolescent phenotype. In prefrontal cortex, these rats show a disruption in the expression of multiple developmentally regulated genes associated with Gα_q and Ca²⁺ signaling. Pharmacologic and ionic manipulations reveal that the enhancement of muscarinic excitation in the healthy adult PFC arises via the electrogenic process of sodium/Ca²⁺ exchange.
This work illustrates a long-lasting disruption in ACh-mediated cortical excitation following early stress and raises the possibility that such cellular mechanisms may disrupt the maturation of executive function.
Dynamic metabolic control of an ion channel
2014, Progress in Molecular Biology and Translational Science
G-protein-coupled receptors mediate responses to external stimuli in various cell types. We are interested in the modulation of KCNQ2/3 potassium channels by the G_q-coupled M₁ muscarinic (acetylcholine) receptor (M₁R). Here, we describe development of a mathematical model that incorporates all known steps along the M₁R signaling cascade and accurately reproduces the macroscopic behavior we observe when KCNQ2/3 currents are inhibited following M₁R activation. G_q protein-coupled receptors of the plasma membrane activate phospholipase C (PLC) which cleaves the minor plasma membrane lipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂) into the second messengers diacylgycerol and inositol 1,4,5-trisphosphate, leading to calcium release, protein kinase C (PKC) activation, and PI(4,5)P₂ depletion. Combining optical and electrical techniques with knowledge of relative abundance of each signaling component has allowed us to develop a kinetic model and determine that (i) M₁R activation and M₁R/Gβ interaction are fast; (ii) Gα_q/Gβ separation and Gα_q/PLC interaction have intermediate time constants; (iii) the amount of activated PLC limits the rate of KCNQ2/3 suppression; (iv) weak PLC activation can elicit robust calcium signals without net PI(4,5)P₂ depletion or KCNQ2/3 channel inhibition; and (v) depletion of PI(4,5)P₂, and not calcium/CaM or PKC-mediated phosphorylation, closes KCNQ2/3 potassium channels, thereby increasing neuronal excitability.
Potential mechanisms of sudden unexpected death in epilepsy
2013, Epilepsy and Behavior
Sudden unexpected death in epilepsy (SUDEP) accounts for 15% of all deaths in people with epilepsy and 50% in refractory epilepsy. The underlying mechanisms are not well understood, but seizure-induced cardiac and respiratory arrests are involved. The cardiovascular and respiratory systems are subject to precise reflex regulation to ensure appropriate oxygen supply under a wide range of circumstances. Barosensory and chemosensory afferents project into the nucleus tractus solitarius (NTS), which relays systemic data to higher brain centers for integration of homeostatic responses in heart rate, peripheral resistance, respiration, and other autonomic reactions. Being the afferent autonomic gatekeeper, NTS plays a critical role in cardiovascular and respiratory regulation. In the course of studying the kainic acid model, we became aware of progressive neuronal loss in the NTS and noted SUDEP-like deaths in rats with frequent convulsions. Increased autonomic susceptibility with inhalation anesthetics was also observed, often seen after impairment of baroreceptor and chemoreceptor reflex loops. Seizure-induced neuron loss in NTS may play a role impairing the integrative functions of NTS resulting in poor homeostatic responses during seizures and leading to SUDEP.
This article is part of a Special Issue entitled “The Future of Translational Epilepsy Research”.

View all citing articles on Scopus

View full text

Trends in Neurosciences

Functional organization of PLC signaling microdomains in neurons

Abstract

Section snippets

PLC-mediated signaling to TRP channels: an example of receptor–ion-channel segregation

PLC-mediated signaling to KCNQ/M channels: an example of receptor segregation

Concluding remarks: new principles for PLC signaling

Acknowledgements

Neuron

Trends Biochem. Sci.

Neuron

Cell

Neuron

Neuron

Mol. Cell. Neurosci.

Neuron

Neuron

Neuron

Neuron

Neuron

Curr. Opin. Neurobiol.

J. Biol. Chem.

Neuron

J. Biol. Chem.

FEBS Lett.

Neuron

Neuron

J. Biol. Chem.

Neuron

Neuron

FEBS Lett.

J. Biol. Chem.

Trends Neurosci.

Neuron

Coupling of catecholamine receptor from one cell with adenylate cyclase from another cell by cell fusion

Proc. Natl. Acad. Sci. U. S. A.

Visual transduction in Drosophila

Annu. Rev. Cell Dev. Biol.

Visual transduction in Drosophila

Nature

A Drosophila mutant defective in extracellular calcium-dependent photoreceptor deactivation and rapid desensitization

Nature

TRP channel proteins and signal transduction

Physiol. Rev.