Cannabinoid-Induced Immunogenic Cell Death of Colorectal Cancer Cells Through De Novo Synthesis of Ceramide Is Partially Mediated by CB2 Receptor

Abstract

Background: Our recent studies have identified a link between sphingolipid metabolites and the induction of a specialized form of regulated cell death termed immunogenic cell death (ICD). We have recently demonstrated that the synthetic cannabinoid (±) 5-epi CP 55,940 (5-epi) stimulates the accumulation of ceramide (Cer), and that inhibition of sphingosine kinase 1 (SphK1) enhances Cer accumulation and ICD-induction in human colorectal cancer (CRC) cell lines. Methods: We employed flow-cytometric, western blot analyses, pharmacological inhibitors of the sphingolipid metabolic pathway and small molecule agonists and antagonists of the CB receptors to further analyze the mechanism by which 5-epi induces Cer accumulation. Results: Herein, and report that 5-epi induces de novo synthesis of Cer primarily through engagement of the cannabinoid receptor 2 (CB2) and depletion of intracellular calcium levels. Moreover, we report that 5-epi stimulates Cer synthesis through dysregulation of the endogenous inhibitor of the de novo Cer pathway, ORMDL3. We also observed a remarkable and specific accumulation of one Cer species, C20:4 Cer, generated predominantly by ceramide synthase 4, as a key factor required for 5-epi-induced ICD. Conclusions: Together, these data indicate that engagement of CB2, by 5-epi, alters regulation of the de novo ceramide synthesis pathway to generate Cer species that mediate ICD.