title: Folate stress induces apoptosis via p53-dependent de novo ceramide synthesis and up-regulation of ceramide synthase 6.
abstract: We have investigated the role of ceramide in the cellular adaptation to folate stress induced by Aldh1l1, the enzyme involved in the regulation of folate metabolism. Our previous studies demonstrated that Aldh1l1, similar to folate deficiency, evokes metabolic stress and causes apoptosis in cancer cells. Here we report that the expression of Aldh1l1 in A549 or HCT116 cells results in the elevation of C16-ceramide and a transient up-regulation of ceramide synthase 6 (CerS6) mRNA and protein. Pretreatment with ceramide synthesis inhibitors myriocin and fumonisin B1 or siRNA silencing of CerS6 prevented C16-ceramide accumulation and rescued cells supporting the role of CerS6/C16-ceramide as effectors of Aldh1l1-induced apoptosis. The CerS6 activation by Aldh1l1 and increased ceramide generation were p53-dependent; this effect was ablated in p53-null cells. Furthermore, the expression of wild type p53 but not transcriptionally inactive R175H p53 mutant strongly elevated CerS6. Also, this dominant negative mutant prevented accumulation of CerS6 in response to Aldh1l1, indicating that CerS6 is a transcriptional target of p53. In support of this mechanism, bioinformatics analysis revealed the p53 binding site 3 kb downstream of the CerS6 transcription start. Interestingly, ceramide elevation in response to Aldh1l1 was inhibited by silencing of PUMA, a proapoptotic downstream effector of p53 whereas the transient expression of CerS6 elevated PUMA in a p53-dependent manner indicating reciprocal relationships between ceramide and p53/PUMA pathways. Importantly, folate withdrawal also induced CerS6/C16-ceramide elevation accompanied by p53 accumulation. Overall, these novel findings link folate and de novo ceramide pathways in cellular stress response.
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
authors.forename: L Alexis
authors.initials: LA
authors.lastname: Hoeferlin
authors.forename: Baharan
authors.initials: B
authors.lastname: Fekry
authors.forename: Besim
authors.initials: B
authors.lastname: Ogretmen
authors.forename: Sergey A
authors.initials: SA
authors.lastname: Krupenko
authors.forename: Natalia I
authors.initials: NI
authors.lastname: Krupenko
mesh_terms: D000444:Aldehyde Dehydrogenase / Q000235:genetics / Q000378:metabolism; D019943:Amino Acid Substitution; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000096:biosynthesis / Q000235:genetics; D045744:Cell Line, Tumor; D002518:Ceramides / Q000096:biosynthesis* / Q000235:genetics; D005492:Folic Acid / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000235:genetics; D020125:Mutation, Missense; D000587:Oxidoreductases Acting on CH-NH Group Donors; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics; D020218:Response Elements / Q000235:genetics; D051049:Sphingosine N-Acyltransferase / Q000096:biosynthesis* / Q000235:genetics; D013312:Stress, Physiological; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation / Q000235:genetics; D000099295:Formyltetrahydrofolate Dehydrogenase
chemical_list: D000444:Aldehyde Dehydrogenase; D051017:Apoptosis Regulatory Proteins; D002518:Ceramides; D005492:Folic Acid; D008565:Membrane Proteins; D000587:Oxidoreductases Acting on CH-NH Group Donors; D011518:Proto-Oncogene Proteins; D051049:Sphingosine N-Acyltransferase; D016159:Tumor Suppressor Protein p53; D000099295:Formyltetrahydrofolate Dehydrogenase; C438378:BBC3 protein, human; C495901:TP53 protein, human; C506123:CERS6 protein, human
keywords: Aldh1l1; Apoptosis; CerS6; Ceramide; Folate; PUMA; Signal Transduction; Stress Response; p53