Mol Pharmacol. 2006 Mar 29; [Epub ahead of print]
SPHINGOSINE AND ITS ANALOGUE, THE IMMUNOSUPPRESSANT FTY720, INTERACT WITH THE CB1 CANNABINOID RECEPTOR.
Paugh SW, Cassidy MP, He H, Milstien S, Sim-Selley LJ, Spiegel S, Selley DE.
Virginia Commonwealth University.
Sphingosine-1-phosphate (S1P) and cannabinoid receptors are G-protein-coupled receptors (GPCR) that mediate the effects of S1P and endocannabinoids, respectively. Cannabinoid receptors also mediate the effects of Delta(9)-tetrahydrocannabinol (THC), the primary psychoactive ingredient in marijuana, whereas S1P receptors contribute to the immunosuppressant effects of FTY720 (2-amino-2-(2-[4-octylphenyl]ethyl)-1,3-propanediol). FTY720 is a sphingosine analogue 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 [(3)H]SR141716A and the cannabinoid agonist [(3)H]CP55,940 in a concentration-dependent manner in both CB1-expresssing cell lines and mouse cerebellum. However, these compounds did not significantly alter [(3)H]CP55,940 binding to CB2 receptors. In G-protein activation assays, FTY720 and sphingosine inhibited maximal stimulation of [(35)S]GTPgammaS binding by the cannabinoid agonist 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 (ERK1/2) and Akt by WIN55,212-2 in intact 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. |
