Cannabinoid agonists increase the interaction between β-Arrestin 2 and ERK1/2 and upregulate β-Arrestin 2 and 5-HT_2A receptors

We have recently reported that selective cannabinoid 2 (CB₂) receptor agonists upregulate 5-HT_2A receptors by enhancing ERK1/2 signaling in prefrontal cortex (PFCx). Increased activity of cortical 5-HT _2A receptors has been associated with several neuropsychiatric disorders such as anxiety and schizophrenia. Here we examine the mechanisms involved in this enhanced ERK1/2 activation in rat PFCx and in a neuronal cell model. Sprague-Dawley rats treated with a non-selective cannabinoid agonist (CP55940, 50 μg/kg, 7 days, i.p.) showed enhanced co-immunoprecipitation of β-Arrestin 2 and ERK1/2, enhanced pERK protein levels, and enhanced expression of β-Arrestin 2 mRNA and protein levels in PFCx. In a neuronal cell line, we found that selective CB₂ receptor agonists upregulate β-Arrestin 2, an effect that was prevented by selective CB₂ receptor antagonist JTE-907 and CB₂ shRNA lentiviral particles. Additionally, inhibition of clathrin-mediated endocytosis, ERK1/2, and the AP-1 transcription factor also prevented the cannabinoid receptor-induced upregulation of β-Arrestin 2. Our results suggest that sustained activation of CB₂ receptors would enhance β-Arrestin 2 expression possibly contributing to its increased interaction with ERK1/2, thereby driving the upregulation of 5-HT_2A receptors. The CB₂ receptor-mediated upregulation of β-Arrestin 2 would be mediated, at least in part, by an ERK1/2-dependent activation of AP-1. These data could provide the rationale for some of the adverse effects associated with repeated cannabinoid exposure and shed light on some CB₂ receptor agonists that could represent an alternative therapeutic because of their minimal effect on serotonergic neurotransmission.