Identification of BiP as a CB(1) Receptor-Interacting Protein That Fine-Tunes Cannabinoid Signaling in the Mouse Brain

Cannabinoids, the bioactive constituents of cannabis, exert a wide array of effects on the brain by engaging Type 1 cannabinoid receptor (CB(1)R). 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 CB(1)R-dependent signaling. Here, by using a yeast two-hybrid-based high-throughput screening, we identified BiP as a potential CB(1)R-interacting protein. We next found that CB(1)R and BiP interact specifically in vitro, and mapped the interaction site within the CB(1)R C-terminal (intracellular) domain and the BiP C-terminal (substrate-binding) domain-α. BiP selectively shaped agonist-evoked CB(1)R 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. In situ proximity ligation assays conducted on brain samples from various genetic mouse models of conditional loss or gain of CB(1)R expression allowed to map CB(1)R-BiP complexes selectively on terminals of GABAergic neurons. Behavioral studies using cannabinoid-treated male BiP(+/−) mice supported that CB(1)R-BiP complexes modulate cannabinoid-evoked anxiety, one of the most frequent undesired effects of cannabis. Together, by identifying BiP as a CB(1)R-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. SIGNIFICANCE STATEMENT Cannabis use is increasing worldwide, so innovative studies aimed to understand its complex mechanism of neurobiological action are warranted. Here, we found that cannabinoid CB(1) receptor (CB(1)R), the primary molecular target of the bioactive constituents of cannabis, interacts specifically with an intracellular protein called BiP. The interaction between CB(1)R and BiP occurs selectively on terminals of GABAergic (inhibitory) neurons, and induces a remarkable shift in the CB(1)R-associated signaling profile. Behavioral studies conducted in mice support that CB(1)R-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.