Paracrine Transactivation of the CB1 Cannabinoid Receptor by AT1 Angiotensin and Other Gq/11 Protein-coupled Receptors

Intracellular signaling systems of G protein-coupled receptors are well established, but their role in paracrine regulation of adjacent cells is generally considered as a tissue-specific mechanism. We have shown previously that AT(1) receptor (AT(1)R) stimulation leads to diacylglycerol lipase-mediated transactivation of co-expressed CB(1)Rs in Chinese hamster ovary cells. In the present study we detected a paracrine effect of the endocannabinoid release from Chinese hamster ovary, COS7, and HEK293 cells during the stimulation of AT(1) angiotensin receptors by determining CB1 cannabinoid receptor activity with bioluminescence resonance energy transfer-based sensors of G protein activation expressed in separate cells. The angiotensin II-induced, paracrine activation of CB1 receptors was visualized by detecting translocation of green fluorescent protein-tagged beta-arrestin2. Mass spectrometry analyses have demonstrated angiotensin II-induced stimulation of 2-arachidonoylglycerol production, whereas no increase of anandamide levels was observed. Stimulation of G(q/11)-coupled M-1, M-3, M-5 muscarinic, V1 vasopressin, alpha(1a) adrenergic, B2 bradykinin receptors, but not G(i/o)-coupled M-2 and M-4 muscarinic receptors, also led to paracrine transactivation of CB1 receptors. These data suggest that, in addition to their retrograde neurotransmitter role, endocannabinoids have much broader paracrine mediator functions during activation of G(q/11)-coupled receptors.