Rab8 Modulates Metabotropic Glutamate Receptor Subtype 1 Intracellular Trafficking and Signaling in a Protein Kinase C-Dependent Manner

Abstract

Metabotropic glutamate receptors (mGluRs) are G protein-coupled receptors (GPCRs) that are activated by glutamate, the primary excitatory neurotransmitter in the CNS. Alterations in glutamate receptor signaling are implicated in neuropathologies such as Alzheimer's disease, ischemia, and Huntington's disease among others. Group 1 mGluRs (mGluR1 and mGluR5) are primarily coupled to G␣ q/11 leading to the activation of phospholipase C and the formation of diacylglycerol and inositol 1,4,5-trisphosphate, which results in the release of intracellular calcium stores and protein kinase C (PKC) activation. Desensitization, endocytosis, and recycling are major mechanisms of GPCR regulation, and the intracellular trafficking of GPCRs is linked to the Rab family of small G proteins. Rab8 is a small GTPase that is specifically involved in the regulation of secretory/recycling vesicles, modulation of the actin cytoskeleton, and cell polarity. Rab8 has been shown to regulate the synaptic delivery of AMPA receptors during long-term potentiation and during constitutive receptor recycling. We show here that Rab8 interacts with the C-terminal tail of mGluR1a in an agonist-dependent manner and plays a role in regulating of mGluR1a signaling and intracellular trafficking in human embryonic kidney 293 cells. Specifically, Rab8 expression attenuates mGluR1a-mediated inositol phosphate formation and calcium release from mouse neurons in a PKC-dependent manner, while increasing cell surface mGluR1a expression via decreased receptor endocytosis. These experiments provide us with an understanding of the role Rabs play in coordinated regulation of mGluR1a and how this impacts mGluR1a signaling.

Numb deficiency in cerebellar Purkinje cells impairs synaptic expression of metabotropic glutamate receptor and motor coordination

“…5 E and F). The down-and up-regulation of mGlu1 expression in response to such agonist challenges was similar to results reported in previous work in other wild-type mice (66)(67)(68). In contrast, synaptic mGlu1 was not changed either 30 min or 180 min after DHPG application to Numb-cKO slices (t = 40 min: 96 ± 8%; t = 190 min: 103 ± 8%; P > 0.05 compared with baseline) (Fig.…”

Metabotropic Glutamate Receptor-1 Contributes to Progression in Triple Negative Breast Cancer

“…Pollock et al [15] first reported a potential mechanistic link between glutamatergic signaling and cancer after observing in a transgenic mouse model that dysregulated mGluR1 activity results in melanoma formation with high penetrance [15]–[17]. Consistent with these observations, pharmacological inhibition of glutamatergic signaling blocks the growth of melanoma cell lines and xenografts [16], [18]–[20], and mGluRs have been implicated as novel drivers of oncogenesis in melanoma and other tumor types, with somatic mutations that alter downstream mGluR1 intracellular localization signaling having been recently reported [21], [22].…”

Diverse Cell Type-Specific Mechanisms Localize G Protein-Coupled Receptors to Caenorhabditis elegans Sensory Cilia

“…G protein-coupled receptors (GPCRs) comprise a large family of transmembrane signaling proteins that directly bind and transduce a range of cues including photons, odorants, neurotransmitters, and peptides (Pierce et al 2002;Kato and Touhara 2009;Demaria and Ngai 2010;Sung and Chuang 2010;Chamero et al 2012;Frooninckx et al 2012;Montell 2012;Bathgate et al 2013). Regulation of GPCR function, including regulation of membrane targeting and trafficking to specific subcellular regions, is a major contributor to the tuning of signaling efficacy and fidelity (e.g., Deretic et al 1995;Ango et al 2000;Xia et al 2003;Esseltine et al 2012;. However, much remains to be understood regarding the mechanisms by which GPCR trafficking and membrane localization are regulated.…”