Constitutive, agonist-accelerated, recycling and lysosomal degradation of GABAB receptors in cortical neurons

Grampp, Thomas; Notz, Valerie; Broll, Ilja; Fischer, Natalie; Benke, Dietmar

doi:10.1016/j.mcn.2008.09.004

Cited by 49 publications

(74 citation statements)

References 22 publications

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“…2C). Therefore, after being internalized, GABA B receptors are recruited to early endosomes, from where they are either recycled via recycling endosomes to be reinserted into the plasma membrane or are degraded in the lysosomes via the late endosomes, consistent with previous findings (14,15,27,28). The process of recycling would account for the plateau phase in the time profiles of surface fluorescence (Fig.…”

Section: Trafficking Of Gaba B Receptor and R2supporting

confidence: 88%

“…Previous studies have proposed that GABA B receptors are very stable on the cell surface (10,11), whereas more recent reports have indicated that GABA B receptors are mobile, being rapidly and constitutively internalized in the absence of agonist in both heterologous expression systems and neurons (12)(13)(14)(15). To date, most studies addressing GABA B receptor trafficking necessarily utilized fixed cells in conjunction with surface receptor biotinylation or C-terminal antibody labeling to monitor receptor subunit mobility.…”

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confidence: 99%

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-Aminobutyric Acid Type B (GABAB) Receptor Internalization Is Regulated by the R2 Subunit

Hannan

Wilkins

Dehghani-Tafti

et al. 2011

Journal of Biological Chemistry

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␥-Aminobutyric acid type B (GABA B ) receptors are important for slow synaptic inhibition in the CNS. The efficacy of inhibition is directly related to the stability of cell surface receptors. For GABA B receptors, heterodimerization between R1 and R2 subunits is critical for cell surface expression and signaling, but how this determines the rate and extent of receptor internalization is unknown. Here, we insert a high affinity ␣-bungarotoxin binding site into the N terminus of the R2 subunit and reveal its dominant role in regulating the internalization of GABA B receptors in live cells. To simultaneously study R1a and R2 trafficking, a new ␣-bungarotoxin binding site-labeling technique was used, allowing ␣-bungarotoxin conjugated to different fluorophores to selectively label R1a and R2 subunits. This approach demonstrated that R1a and R2 are internalized as dimers. In heterologous expression systems and neurons, the rates and extents of internalization for R1aR2 heteromers and R2 homomers are similar, suggesting a regulatory role for R2 in determining cell surface receptor stability. The fast internalization rate of R1a, which has been engineered to exit the endoplasmic reticulum, was slowed to that of R2 by truncating the R1a C-terminal tail or by removing a dileucine motif in its coiled-coil domain. Slowing the rate of internalization by co-assembly with R2 represents a novel role for GPCR heterodimerization whereby R2 subunits, via their C terminus coiled-coil domain, mask a dileucine motif on R1a subunits to determine the surface stability of the GABA B receptor.Metabotropic GABA B 2 receptors mediate a slow and prolonged phase of synaptic inhibition in the CNS. Their importance for neuronal function is evident when they become dysfunctional, which can lead to a range of diseases that includes epilepsy, sleep disorders, stress, depression, and substance abuse (1-3).Native GABA B receptors are considered to function as heterodimers formed from R1 and R2 subunits (4, 5) with the possibility that some higher order oligomeric assemblies (e.g. dimer of dimers) may also retain functionality (6, 7). Heterodimerization of GABA B receptors has profound consequences for their structural and functional properties, impacting on the efficiency of cell surface expression and the linkage between agonist binding and G-protein activation.Functional GABA B receptors require both R1 and R2 to coassemble because an endoplasmic reticulum (ER) retention motif, RSR, in the C-terminal coiled-coil domain of R1 subunits has to be masked by the R2 subunit to ensure surface expression (8, 9). Substitution of the retention motif with ASA allows R1 subunits to exit the ER and travel alone to the cell surface (8). Although the role of R2 in heterodimerization for forward trafficking has been reported, how heterodimerization, and in particular the R2 subunit, affects the cell surface stability and internalization of GABA B receptor subunits remains unresolved.This aspect is important because the cell surface stability and mobility of GA...

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Section: Trafficking Of Gaba B Receptor and R2supporting

confidence: 88%

mentioning

confidence: 99%

-Aminobutyric Acid Type B (GABAB) Receptor Internalization Is Regulated by the R2 Subunit

Hannan

Wilkins

Dehghani-Tafti

et al. 2011

Journal of Biological Chemistry

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“…1C). Agonists accelerate basal endocytosis of GABA B receptors (25). Antagonizing GABA B receptor activity with CGP54626A (2 μM for 10 min) did not attenuate NMDAmediated removal of surface GABA B1b protein (NMDA + CGP54626A: 60.2 ± 9.6% of control, n = 10, P < 0.05; Fig.…”

Section: Nmda Receptorsmentioning

confidence: 85%

“…S2B). Following glutamate or NMDA treatment, a fraction of internalized GABA B1b protein segregated into structures devoid of Rab11-eGFP, possibly indicating GABA B1b protein targeted for degradation (24,25). Preincubation of neurons with dynasore (80 μM for 15 min), a cell-permeable inhibitor of dynamin-dependent endocytosis (26), interfered with the NMDA-mediated removal of surface GABA B1b protein (NMDA: 58.8 ± 5.4% of control, n = 8, P < 0.05; NMDA + dynasore: 105 ± 10% of control, n = 10, P > 0.05; dynasore: 98.4 ± 9.0% of control, n = 9, P > 0.05; Fig.…”

Section: Nmda Receptorsmentioning

confidence: 99%

NMDA receptor-dependent GABA _B receptor internalization via CaMKII phosphorylation of serine 867 in GABA _B1

Guetg

Aziz

Holbro

et al. 2010

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

130

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GABA B receptors are the G-protein-coupled receptors for GABA, the main inhibitory neurotransmitter in the brain. GABA B receptors are abundant on dendritic spines, where they dampen postsynaptic excitability and inhibit Ca 2+ influx through NMDA receptors when activated by spillover of GABA from neighboring GABAergic terminals. Here, we show that an excitatory signaling cascade enables spines to counteract this GABA B -mediated inhibition. We found that NMDA application to cultured hippocampal neurons promotes dynamindependent endocytosis of GABA B receptors. NMDA-dependent internalization of GABA B receptors requires activation of Ca 2+ /Calmodulindependent protein kinase II (CaMKII), which associates with GABA B receptors in vivo and phosphorylates serine 867 (S867) in the intracellular C terminus of the GABA B1 subunit. Blockade of either CaMKII or phosphorylation of S867 renders GABA B receptors refractory to NMDA-mediated internalization. Time-lapse two-photon imaging of organotypic hippocampal slices reveals that activation of NMDA receptors removes GABA B receptors within minutes from the surface of dendritic spines and shafts. NMDA-dependent S867 phosphorylation and internalization is predominantly detectable with the GABA B1b subunit isoform, which is the isoform that clusters with inhibitory effector K + channels in the spines. Consistent with this, NMDA receptor activation in neurons impairs the ability of GABA B receptors to activate K + channels. Thus, our data support that NMDA receptor activity endocytoses postsynaptic GABA B receptors through CaMKIImediated phosphorylation of S867. This provides a means to spare NMDA receptors at individual glutamatergic synapses from reciprocal inhibition through GABA B receptors.γ-aminobutyric acid | spines | trafficking | synaptic plasticity | GABAB

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“…Although GABA B receptor is known to undergo basal endocytosis, it remains controversial whether agonist stimulation facilitates receptor internalization Grampp et al, 2008Grampp et al, , 2007. Thus, some studies attribute the cell surface stability of GABA B receptor to a lack of agonist-induced internalization Perroy et al, 2003), whereas others suggest that this might be due to re-insertion of the receptor into the plasma membrane by an unknown mechanism (Grampp et al, 2008(Grampp et al, , 2007Wilkins et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

GABAB receptor promotes its own surface expression by recruiting a Rap1-dependent signaling cascade

Zhang

Huang

et al. 2015

Journal of Cell Science

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G-protein-coupled receptors (GPCRs) are key players in cell signaling, and their cell surface expression is tightly regulated. For many GPCRs such as β2-AR (β2-adrenergic receptor), receptor activation leads to downregulation of receptor surface expression, a phenomenon that has been extensively characterized. By contrast, some other GPCRs, such as GABA B receptor, remain relatively stable at the cell surface even after prolonged agonist treatment; however, the underlying mechanisms are unclear. Here, we identify the small GTPase Rap1 as a key regulator for promoting GABA B receptor surface expression. Agonist stimulation of GABA B receptor signals through Gαi/o to inhibit Rap1GAPII (also known as Rap1GAP1b, an isoform of Rap1GAP1), thereby activating Rap1 (which has two isoforms, Rap1a and Rap1b) in cultured cerebellar granule neurons (CGNs). The active form of Rap1 is then recruited to GABA B receptor through physical interactions in CGNs. This Rap1-dependent signaling cascade promotes GABA B receptor surface expression by stimulating receptor recycling. Our results uncover a new mechanism regulating GPCR surface expression and also provide a potential explanation for the slow, long-lasting inhibitory action of GABA neurotransmitter.

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Constitutive, agonist-accelerated, recycling and lysosomal degradation of GABAB receptors in cortical neurons

Cited by 49 publications

References 22 publications

-Aminobutyric Acid Type B (GABAB) Receptor Internalization Is Regulated by the R2 Subunit

-Aminobutyric Acid Type B (GABAB) Receptor Internalization Is Regulated by the R2 Subunit

NMDA receptor-dependent GABA _B receptor internalization via CaMKII phosphorylation of serine 867 in GABA _B1

GABAB receptor promotes its own surface expression by recruiting a Rap1-dependent signaling cascade

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Constitutive, agonist-accelerated, recycling and lysosomal degradation of GABAB receptors in cortical neurons

Cited by 49 publications

References 22 publications

-Aminobutyric Acid Type B (GABAB) Receptor Internalization Is Regulated by the R2 Subunit

-Aminobutyric Acid Type B (GABAB) Receptor Internalization Is Regulated by the R2 Subunit

NMDA receptor-dependent GABA B receptor internalization via CaMKII phosphorylation of serine 867 in GABA B1

GABAB receptor promotes its own surface expression by recruiting a Rap1-dependent signaling cascade

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NMDA receptor-dependent GABA _B receptor internalization via CaMKII phosphorylation of serine 867 in GABA _B1