Folate Stress Induces Apoptosis via p53-dependent de Novo Ceramide Synthesis and Up-regulation of Ceramide Synthase 6

Abstract

Background: Sphingolipid ceramide regulates cellular responses to stress stimuli. Results: Aldh1l1, the enzyme regulating folate metabolism, leads to CerS6 up-regulation and C 16 -ceramide accumulation in a p53-dependent manner as a proapoptotic signal. Conclusion: Ceramide mediates the cellular response to nongenotoxic folate stress. Significance: We have demonstrated the interaction between two major metabolic pathways, folate and sphingolipids, in regulation of cellular homeostasis.

CerS6 Is a Novel Transcriptional Target of p53 Protein Activated by Non-genotoxic Stress

“…Thus, our previous study demonstrated that CerS6 is elevated in a p53-dependent manner in response to folate stress enzyme ALDH1L1 (28); ALDH1L1, however, induces p53 through metabolic alterations in the absence of DNA damage (33,58). In line with this finding, the treatment of cancer cells with antifolate methotrexate or folate withdrawal, two stimuli inducing alterations in folate, amino acid, and nucleotide metabolism, activated CerS6 in a p53-dependent fashion (28,31). In the present study the transcriptional induction of CerS6 by p53 in the absence of genotoxic stress was further confirmed using two canonical activators of p53, actinomycin D and Nutlin-3, which do not induce DNA damage.…”

“…To eliminate potential impact from endogenous p53 protein on CerS6 promoter, we have also performed luciferase assays in the p53-deficient A549 cell line. In this cell line p53 was silenced by the stable expression of the p53 shRNA, which completely prevented the protein expression (28,33). Similar to p53-proficient A549 cells, strong activation of luciferase was seen in the p53-deficient cells upon co-expression with the p53-expressing vector but not the vector expressing mutant p53 (Fig.…”

“…We previously demonstrated that CerS6 is elevated in response to p53 activation or upon transient transfection of p53 (28). The mechanism of such regulation was not clear as the p53 binding motifs were not found in the CerS6 promoter region.…”

“…Sphingolipids play an important role in both the structural integrity of cellular membranes and as signaling molecules involved in the regulation of major cellular processes such as senescence, survival, and death (26,27). Our previous study suggested that one of the enzymes in sphingolipid biosynthesis, ceramide synthase 6 (CerS6), 4 is regulated by p53 (28). Thus, CerS6 was elevated in several cell lines in response to transient expression of p53 and also in response to folate stress, which is known to activate p53 (29,30).…”

Bcl2L13 is a ceramide synthase inhibitor in glioblastoma

“…Consequently, reduced expression of CerS2 has been shown to be a negative prognostic indicator in breast cancer patients (4). Similarly, CerS6 promotes therapy-induced apoptosis in colon cancer cells (5,6), head and neck squamous cell carcinoma, and lung carcinomas (7,8), and CerS1 acts as a proapoptotic factor in multiple cancer cell lines (9,10).…”