| Abstrakt: |
Simple Summary: Mounting evidence demonstrates that cannabinoids have anti-cancer properties. The mechanism by which the cannabinoids induce cell death is still unclear. However, increased intracellular production of the sphingolipid, ceramide, seems to be a commonality. We recently demonstrated that a synthetic cannabinoid induced a specialized form of cell death that is known to activate the patient's immune system, termed immunogenic cell death (ICD). Herein, we provide evidence of the mechanism by which synthetic cannabinoids increase ceramide production and demonstrate that ceramide is required for ICD. These findings strengthen the evidence that cannabinoids are effective anti-cancer agents and, importantly, suggest that they may help to recruit the immune system to fight the patient's tumor. 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. [ABSTRACT FROM AUTHOR] |
