Induction of ER stress-mediated apoptosis by ceramide via disruption of ER Ca(2+) homeostasis in human adenoid cystic carcinoma cells

Ceramides are a class of sphingolipids that form the structural component of the cell membrane and also act as second messengers in cell signaling pathways. Emerging results suggest that ceramide induces growth arrest and apoptosis in various human cancer cells. However, the mechanisms underlying its antitumor activity are yet to be identified. Endoplasmic reticulum stress (ER stress), a cellular adaptive response, is believed to initially compensate for damage but can eventually trigger cell death if the stimulus is severe or prolonged. In this study, we investigated whether ceramide induces cell death in human salivary adenoid cystic carcinoma (ACCs) through activation of the apoptotic ER stress. RT-PCR, real-time PCR and western blot demonstrated that exogenous ceramide treatment up-regulated GRP78 and p-eIF2α expression and XBP1 splicing. Moreover, the ceramide synthase inhibitor FB1 abolished ceramide-induced ER stress. Up-regulation of the ER stress-associated apoptosis promoting transcription factor CHOP and p-JNK suggested that the antitumor activity of ceramide is owing to activation of apoptotic ER stress. Mechanistically, [Ca(2+)]ER depletion and SERCA inhibition by ceramide treatment suggested that it induces ER stress by disrupting [Ca(2+)]ER homeostasis. The chemical chaperone TUDCA inhibited ceramide-induced ER stress and cell death. In addition, the downstream metabolite of ceramide, S1P, cannot activate ER stress. These results demonstrated that exogenous ceramide induces cancer cell death through a mechanism involving severe ER stress triggered by the disruption of ER Ca(2+) homeostasis.