Identification of BiP as a CB₁ Receptor-Interacting Protein That Fine-Tunes Cannabinoid Signaling in the Mouse Brain

Abstract

Cannabinoids, the bioactive constituents of cannabis, exert a wide array of effects on the brain by engaging Type 1 cannabinoid receptor (CB₁R). Accruing evidence supports that cannabinoid action relies on context-dependent factors, such as the biological characteristics of the target cell, suggesting that cell population-intrinsic molecular cues modulate CB₁R-dependent signaling. Here, by using a yeast two-hybrid-based high-throughput screening, we identified BiP as a potential CB₁R-interacting protein. We next found that CB₁R and BiP interact specifically <i>in vitro</i>, and mapped the interaction site within the CB₁R <i>C</i>-terminal (intracellular) domain and the BiP <i>C</i>-terminal (substrate-binding) domain-α. BiP selectively shaped agonist-evoked CB₁R signaling by blocking an "alternative" G_q/11 protein-dependent signaling module while leaving the "classical" G_i/o protein-dependent inhibition of the cAMP pathway unaffected. <i>In situ</i> proximity ligation assays conducted on brain samples from various genetic mouse models of conditional loss or gain of CB₁R expression allowed to map CB₁R-BiP complexes selectively on terminals of GABAergic neurons. Behavioral studies using cannabinoid-treated male BiP^+/- mice supported that CB₁R-BiP complexes modulate cannabinoid-evoked anxiety, one of the most frequent undesired effects of cannabis. Together, by identifying BiP as a CB₁R-interacting protein that controls receptor function in a signaling pathway- and neuron population-selective manner, our findings may help to understand the striking context-dependent actions of cannabis in the brain.<b>SIGNIFICANCE STATEMENT</b> Cannabis use is increasing worldwide, so innovative studies aimed to understand its complex mechanism of neurobiological action are warranted. Here, we found that cannabinoid CB₁ receptor (CB₁R), the primary molecular target of the bioactive constituents of cannabis, interacts specifically with an intracellular protein called BiP. The interaction between CB₁R and BiP occurs selectively on terminals of GABAergic (inhibitory) neurons, and induces a remarkable shift in the CB₁R-associated signaling profile. Behavioral studies conducted in mice support that CB₁R-BiP complexes act as fine-tuners of anxiety, one of the most frequent undesired effects of cannabis use. Our findings open a new conceptual framework to understand the striking context-dependent pharmacological actions of cannabis in the brain.