Abstract
Endocannabinoids are important players in neural development and function. They act via receptors, whose activation inhibits cAMP production. The aim of the paper was to look for calcium- and cAMP-signaling cross-talk mediated by cannabinoid CB(1) receptors (CB(1)R) and to assess the relevance of EF-hand CaM-like calcium sensors in this regard. Using a heterologous expression system, we demonstrated that CB(1)R interacts with calneuron-1 and NCS1 but not with caldendrin. Furthermore, interaction motives were identified in both calcium binding proteins and the receptor, and we showed that the first two sensors competed for binding to the receptor in a Ca(2+)-dependent manner. Assays in neuronal primary cultures showed that, CB(1)R-NCS1 complexes predominate at basal Ca(2+) levels, whereas in the presence of ionomycin, a calcium ionophore, CB(1)R-calneuron-1 complexes were more abundant. Signaling assays following forskolin-induced intracellular cAMP levels showed in mouse striatal neurons that binding of CB(1)R to NCS1 is required for CB(1)R-mediated signaling, while the binding of CB(1)R to calneuron-1 completely blocked G(i)-mediated signaling in response to a selective receptor agonist, arachidonyl-2-chloroethylamide. Calcium levels and interaction with calcium sensors may even lead to apparent Gs coupling after CB(1)R agonist challenge.