Dual intracellular signaling pathways mediated by the human cannabinoid CB1 receptor

It has long been established that the cannabinoid CB1 receptor transduces s ignals through a pertussis toxin-sensitive G(i)/G(o) inhibitory pathway. Al though there have been reports that the cannabinoid CB, receptor can also m ediate an increase in cyclic AMP levels, in most cases the presence of an a denylyl cyclase costimulant or the use of very high amounts of agonist was necessary. Here, we present evidence for dual coupling of the cannabinoid C B1 receptor to the classical pathway and to a pertussis toxin-insensitive a denylyl cyclase stimulatory pathway initiated with low quantities of agonis t in the absence of any costimulant. Treatment of Chinese hamster ovary (CH O) cells expressing the cannabinoid CB, receptor with the cannabinoid CP 55 ,940, {(-)-cis-3-[2-hydroxy-4-(1,1-dimethyl-heptyl)phenyl]-trans-4-(3-hydro xypropyl) cydohexan-1-ol} resulted in cyclic AMP accumulation in a dose-res ponse manner, an accumulation blocked by the cannabinoid CB1 receptor-speci fic antagonist SR 141716A, {N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-di chlorophenyl)-4-methyl- 1H-pyrazole-3-carboxamide hydrochloride}. In CHO ce lls coexpressing the cannabinoid CB1 receptor and a cyclic AMP response ele ment (CRE)-luciferase reporter gene system, CP 55,940 induced luciferase ex pression by a pathway blocked by the protein kinase A inhibitor N-[2-(p-bro mocinnamylamino)ethyl]-5-isoquinolinesulfonamid hydrochloride (H-89). Under the same conditions the peripheral cannabinoid CB, receptor proved to be i ncapable of inducing cAMP accumulation or luciferase activity. This incapac ity allowed us to study the luciferase activation mediated by CB1/CB2 chime ric constructs, from which we determined that the first and second internal loop regions of the cannabinoid CB, receptor were involved in transducing the pathway leading to luciferase gene expression. (C) 1999 Elsevier Scienc e B.V. All rights reserved.