The CB2 cannabinoid receptor signals apoptosis via ceramide-dependent activation of the mitochondrial intrinsic pathway.
Delta9-tetrahydrocannabinol and other cannabinoids exert pro-apoptotic actions in tumor cells via the CB2 cannabinoid receptor. However, the molecular mechanism involved in this effect has remained elusive. Here we used the human leukemia cell line Jurkat-that expresses CB2 as the unique CB receptor-to investigate this mechanism. Our results show that incubation with the selective CB2 antagonist SR144528 abrogated the pro-apoptotic effect of Delta9-tetrahydrocannabinol. Cannabinoid treatment led to a CB2 receptor-dependent stimulation of ceramide biosynthesis and inhibition of this pathway prevented Delta9-tetrahydrocannabinol-induced mitochondrial hypopolarization and cytochrome c release, indicating that ceramide acts at a pre-mitochondrial level. Inhibition of ceramide synthesis de novo also prevented caspase activation and apoptosis. Caspase 8 activation-an event typically related with the extrinsic apoptotic pathway-was also evident in this model. However, activation of this protease was post-mitochondrial since (i) a pan-caspase inhibitor as well as a selective caspase 8 inhibitor were unable to prevent Delta9-tetrahydrocannabinol-induced loss of mitochondrial-membrane transmembrane potential, and (ii) cannabinoid-induced caspase 8 activation was not observed in Bcl-xL over-expressing cells. In summary, results presented here show that CB2 receptor activation signals apoptosis via a ceramide-dependent stimulation of the mitochondrial intrinsic pathway.
Herrera
Blanca
B
Department of Biochemistry and Molecular Biology I, School of Biology, Complutense University, c/José Antonio Novais s/n, 28040 Madrid, Spain.
Carracedo
Arkaitz
A
Diez-Zaera
María
M
Gómez del Pulgar
Teresa
T
Guzmán
Manuel
M
Velasco
Guillermo
G
D017209:Apoptosis / Q000187:drug effects; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D002518:Ceramides / Q000096:biosynthesis / Q000502:physiology*; D045304:Cytochromes c / Q000378:metabolism; D013759:Dronabinol / Q000494:pharmacology*; D006801:Humans; D019169:Jurkat Cells; D008564:Membrane Potentials / Q000187:drug effects; D033681:Mitochondrial Membrane Transport Proteins / Q000502:physiology; D051336:Mitochondrial Membranes / Q000187:drug effects / Q000502:physiology; D043885:Receptor, Cannabinoid, CB2 / Q000187:drug effects* / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D015854:Up-Regulation
D002518:Ceramides; D033681:Mitochondrial Membrane Transport Proteins; D043885:Receptor, Cannabinoid, CB2; D013759:Dronabinol; D045304:Cytochromes c; D020169:Caspases