Cristina Sánchez, Daniel Rueda, Bruno Ségui, Ismael Galve-Roperh, Thierry Levade, and Manuel Guzmán

Department of Biochemistry and Molecular Biology I, School of Biology, Complutense University, Madrid, Spain (C.S., D.R., I.G.-R., M.G.); and Institut National de la Santé et de la Recherche Médicale U466, Laboratoire de Biochimie, Centre Hospitalier Universitaire Rangeil, Toulouse, France (B.S., T.L.)
Abstract
Cannabinoids exert most of their effects through the CB₁ receptor. This G protein-coupled receptor signals inhibition of adenylyl cyclase, modulation of ion channels, and stimulation of mitogen- and stress-activated protein kinases. In this article, we report that ⁹-tetrahydrocannabinol (THC), the major active component of marijuana, induces sphingomyelin hydrolysis in primary astrocytes but not in other cells expressing the CB₁ receptor, such as primary neurons, U373 MG astrocytoma cells, and Chinese hamster ovary cells transfected with the CB₁ receptor cDNA. THC-evoked sphingomyelin breakdown in astrocytes was also exerted by the endogenous cannabinoid anandamide and the synthetic cannabinoid HU-210 and was prevented by the selective CB₁ antagonist SR141716. By contrast, the effect of THC was not blocked by pertussis toxin, pointing to a lack of involvement of G_i/o proteins. A role for the adaptor protein FAN in CB₁ receptor-coupled sphingomyelin breakdown is supported by two observations: 1) coimmunoprecipitation experiments show that the binding of FAN to the CB₁ receptor is enhanced by THC and prevented by SR141716; 2) cells expressing a dominant-negative form of FAN are refractory to THC-induced sphingomyelin breakdown. This is the first report showing that a G-protein-coupled receptor induces sphingomyelin hydrolysis through FAN and that the CB₁ cannabinoid receptor may signal independently of G_i/o proteins. 

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