Background and purpose: The CB(1) cannabinoid receptor and the beta(2)-adrenoceptor are G protein-coupled receptors (GPCRs) co-expressed in many tissues. The present study examined physical and functional interactions between these receptors in a heterologous expression system and in primary human ocular cells.
Experimental approach: Physical interactions between CB(1) receptors and beta(2)-adrenoceptors were assessed using bioluminescence resonance energy transfer (BRET). Functional interactions between these receptors were evaluated by examining receptor trafficking, as well as extracellular signal-regulated kinase (ERK) and cyclic AMP response element binding protein (CREB) signalling.
Key results: Physical interactions between CB(1) receptors and beta(2)-adrenoceptors were demonstrated using BRET. In human embryonic kidney (HEK) 293H cells, co-expression of beta(2)-adrenoceptors tempered the constitutive activity and increased cell surface expression of CB(1) receptors. Co-expression altered the signalling properties of CB(1 )receptors, resulting in increased Galpha(i)-dependent ERK phosphorylation, but decreased non-Galpha(i)-mediated CREB phosphorylation. The CB(1) receptor inverse agonist AM251 (N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide) attenuated beta(2)-adrenoceptor-pERK signalling in cells expressing both receptors, while the CB(1) receptor neutral antagonist O-2050 ((6aR,10aR)-3-(1-methanesulfonylamino-4-hexyn-6-yl)-6a,7,10,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran) did not. The actions of AM251 and O-2050 were further examined in primary human trabecular meshwork (HTM) cells, which are ocular cells endogenously co-expressing CB(1) receptors and beta(2)-adrenoceptors. In HTM cells, as in HEK 293H cells, AM251 but not O-2050, altered the beta(2)-adrenoceptor-pERK response.
Conclusion and implications: A complex interaction was demonstrated between CB(1) receptors and beta(2)-adrenoceptors in HEK 293H cells. As similar functional interactions were also observed in HTM cells, such interactions may affect the pharmacology of these receptors in tissues where they are endogenously co-expressed.