Receptor Heteromerization Expands the Repertoire of Cannabinoid Signaling in Rodent Neurons

Abstract

A fundamental question in G protein coupled receptor biology is how a single ligand acting at a specific receptor is able to induce a range of signaling that results in a variety of physiological responses. We focused on Type 1 cannabinoid receptor (CB1R) as a model GPCR involved in a variety of processes spanning from analgesia and euphoria to neuronal development, survival and differentiation. We examined receptor dimerization as a possible mechanism underlying expanded signaling responses by a single ligand and focused on interactions between CB1R and delta opioid receptor (DOR). Using co-immunoprecipitation assays as well as analysis of changes in receptor subcellular localization upon co-expression, we show that CB1R and DOR form receptor heteromers. We find that heteromerization affects receptor signaling since the potency of the CB1R ligand to stimulate G-protein activity is increased in the absence of DOR, suggesting that the decrease in CB1R activity in the presence of DOR could, at least in part, be due to heteromerization. We also find that the decrease in activity is associated with enhanced PLC-dependent recruitment of arrestin3 to the CB1R-DOR complex, suggesting that interaction with DOR enhances arrestin-mediated CB1R desensitization. Additionally, presence of DOR facilitates signaling via a new CB1R-mediated anti-apoptotic pathway leading to enhanced neuronal survival. Taken together, these results support a role for CB1R-DOR heteromerization in diversification of endocannabinoid signaling and highlight the importance of heteromer-directed signal trafficking in enhancing the repertoire of GPCR signaling.

G protein-coupled receptor-receptor interactions give integrative dynamics to intercellular communication

“…When the complex forms, for instance, the quaternary structure could display novel specific allosteric sites (Agnati et al, 2008). Furthermore, RM are in the center of two complementary networks of interactions: HMN involving (A) the lipid environment (Gahbauer and Böckmann, 2016), (B) RAMP (Foord and Marshall, 1999), (C) RTK , and (D) membrane channels (Liu et al, 2006a;Gamo et al, 2015) and VMN leading to (E) modulation of the binding sites (Fuxe et al, 1998), (F) modulation of G protein activation (Ferrada et al, 2009), (G) modulation of the signaling cascade, among others, and (H) switching from G protein to β-arrestin signaling (Rashid et al, 2007;Rozenfeld et al, 2012).…”

“…-Modulation of the signaling cascade occurs when the RM recruits a G protein different from those usually associated to the monomers (as in the D 1 -D 2 dimer; Rashid et al, 2007) or when the oligomerization process leads to a switch between G protein and β-arrestin signaling (Rozenfeld et al, 2012), such as, for instance, in the κ-μ and κ-δ opioid heteromers (Le Naour et al, 2014).…”

Molecular Pharmacology ofδ-Opioid Receptors

“…Molecular and structural modeling has since predicted that DOPr homodimers rapidly associate and dissociate through a symmetric interface involving the fourth and/or the fifth TMHs (Filizola and Weinstein, 2002;Provasi et al, 2010;Johnston et al, 2011). In transfected cells, an essential role for the 678 Decreased CB1-mediated signaling, increased DOPr-mediated signaling Altered CB1 localization Bushlin et al (2012), Rozenfeld et al (2012) SNSR-4, sensory neuron-specific receptor subtype 4; SSTR, somatostatin type 4 receptor.…”

Functional diversity on synaptic plasticity mediated by endocannabinoids

“…co-activation of CB1 and m opioid receptors in heterologous expression systems and in rat striatal membranes reduces the potency conveyed by the activation of CB1 receptor alone or m opioid receptor alone [47]. Similar interactions have also been identified between CB1 and d opioid receptors, 'enhancing the repertoire of GPCR (G-protein-coupled receptor) signalling' [48]. Additional downstream targets of the CB1 receptor also include receptor tyrosine kinases and mitogen-activated protein kinases (MAPK), among others [49][50][51].…”