title: Ablation of dihydroceramide desaturase confers resistance to etoposide-induced apoptosis in vitro.
abstract: Sphingolipid biosynthesis is potently upregulated by factors associated with cellular stress, including numerous chemotherapeutics, inflammatory cytokines, and glucocorticoids. Dihydroceramide desaturase 1 (Des1), the third enzyme in the highly conserved pathway driving sphingolipid biosynthesis, introduces the 4,5-trans-double bond that typifies most higher-order sphingolipids. Surprisingly, recent studies have shown that certain chemotherapeutics and other drugs inhibit Des1, giving rise to a number of sphingolipids that lack the characteristic double bond. In order to assess the effect of an altered sphingolipid profile (via Des1 inhibition) on cell function, we generated isogenic mouse embryonic fibroblasts lacking both Des1 alleles. Lipidomic profiling revealed that these cells contained higher levels of dihydroceramide than wild-type fibroblasts and that complex sphingolipids were comprised predominantly of the saturated backbone (e.g. sphinganine vs. sphingosine, dihydrosphingomyelin vs. sphingomyelin, etc.). Des1 ablation activated pro-survival and anabolic signaling intermediates (e.g. Akt/PKB, mTOR, MAPK, etc.) and provided protection from apoptosis caused by etoposide, a chemotherapeutic that induces sphingolipid synthesis by upregulating several sphingolipid biosynthesizing enzymes. These data reveal that the double bond present in most sphingolipids has a profound impact on cell survival pathways, and that the manipulation of Des1 could have important effects on apoptosis.
authors.affiliation: Program in Cardiovascular and Metabolic Diseases, Duke-National University of Singapore Graduate Medical School, Singapore, Singapore. mobin.siddique@duke-nus.edu.sg
authors.forename: Monowarul M
authors.initials: MM
authors.lastname: Siddique
authors.forename: Benjamin T
authors.initials: BT
authors.lastname: Bikman
authors.forename: Liping
authors.initials: L
authors.lastname: Wang
authors.forename: Li
authors.initials: L
authors.lastname: Ying
authors.forename: Erin
authors.initials: E
authors.lastname: Reinhardt
authors.forename: Guanghou
authors.initials: G
authors.lastname: Shui
authors.forename: Markus R
authors.initials: MR
authors.lastname: Wenk
authors.forename: Scott A
authors.initials: SA
authors.lastname: Summers
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D002518:Ceramides / Q000737:chemistry / Q000378:metabolism; D019610:Cytoprotection / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects; D004622:Embryo, Mammalian / Q000166:cytology; D004789:Enzyme Activation / Q000187:drug effects; D005047:Etoposide / Q000494:pharmacology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D017353:Gene Deletion; D020935:MAP Kinase Signaling System / Q000187:drug effects; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D010088:Oxidoreductases / Q000172:deficiency* / Q000378:metabolism*; D054648:Protein Phosphatase 2 / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D013107:Sphingolipids / Q000378:metabolism
chemical_list: D002518:Ceramides; D013107:Sphingolipids; C109343:dihydroceramide; D005047:Etoposide; D010088:Oxidoreductases; C108138:dihydroceramide desaturase; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D054648:Protein Phosphatase 2