Abstract

Sphingosine-1-phosphate (S1P) and cannabinoid receptors are G-protein-coupled receptors that mediate the effects of S1P and endocannabinoids, respectively. Cannabinoid receptors also mediate the effects of Δ⁹-tetrahydrocannabinol, the primary psychoactive ingredient in marijuana, whereas S1P receptors contribute to the immunosuppressant effects of 2-amino-2-(2-[4-octylphenyl]ethyl)-1,3-propanediol (FTY720). FTY720 is a sphingosine analog that can prevent renal graft rejections and suppress a variety of autoimmune disorders in animal models and clinical trials. We now report that both FTY720 and sphingosine interact with CB₁ but not CB₂ cannabinoid receptors. FTY720 and sphingosine inhibited the binding of the CB₁-selective antagonist [³H]N-(piperidinyl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide ([³H]SR141716A) and the cannabinoid agonist [³H](–)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4-(3-hydroxypropyl)cyclohexanol ([³H]CP55,940) in a concentration-dependent manner in both CB₁-expressing cell lines and mouse cerebellum. However, these compounds did not significantly alter [³H]CP55,940 binding to CB₂ receptors. In G-protein activation assays, FTY720 and sphingosine inhibited the maximal stimulation of guanosine 5′-O-(3-[³⁵S]thio)triphosphate binding by the cannabinoid agonist R-(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl)methanone mesylate (WIN55,212-2) in a concentration-dependent manner, and this antagonist effect was not mimicked by S1P. FTY720 and sphingosine also inhibited activation of extracellular signal-regulated kinases 1 and 2 and Akt by WIN55,212-2 in intact Chinese hamster ovary (CHO) cells expressing CB₁ receptors and attenuated WIN55,212-2-stimulated internalization of a fluorescence-tagged CB₁ receptor in CHO cells. Moreover, both FTY720 and sphingosine produced rightward shifts in the concentration-effect curves of cannabinoid agonists for G-protein activation, indicating that they act as competitive CB₁ antagonists. These results suggest that the CB₁ receptor could be a novel target of FTY720 and that sphingosine could be an endogenous CB₁ antagonist.