title: Coordinated regulation of the orosomucoid-like gene family expression controls de novo ceramide synthesis in mammalian cells.
abstract: The orosomucoid-like (ORMDL) protein family is involved in the regulation of de novo sphingolipid synthesis, calcium homeostasis, and unfolded protein response. Single nucleotide polymorphisms (SNPs) that increase ORMDL3 expression have been associated with various immune/inflammatory diseases, although the pathophysiological mechanisms underlying this association are poorly understood. ORMDL proteins are claimed to be inhibitors of the serine palmitoyltransferase (SPT). However, it is not clear whether individual ORMDL expression levels have an impact on ceramide synthesis. The present study addressed the interaction with and regulation of SPT activity by ORMDLs to clarify their pathophysiological relevance. We have measured ceramide production in HEK293 cells incubated with palmitate as a direct substrate for SPT reaction. Our results showed that a coordinated overexpression of the three isoforms inhibits the enzyme completely, whereas individual ORMDLs are not as effective. Immunoprecipitation and fluorescence resonance energy transfer (FRET) studies showed that mammalian ORMDLs form oligomeric complexes that change conformation depending on cellular sphingolipid levels. Finally, using macrophages as a model, we demonstrate that mammalian cells modify ORMDL genes expression levels coordinately to regulate the de novo ceramide synthesis pathway. In conclusion, we have shown a physiological modulation of SPT activity by general ORMDL expression level regulation. Moreover, because single ORMDL3 protein alteration produces an incomplete inhibition of SPT activity, this work argues against the idea that ORMDL3 pathophysiology could be explained by a simple on/off mechanism on SPT activity.
authors.affiliation: From the Laboratory of Molecular Physiology and Channelopathies, Department of Experimental and Health Sciences, Universitat Pompeu Fabra, 08003 Barcelona, Spain and.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Kiefer
authors.affiliation: From the Laboratory of Molecular Physiology and Channelopathies, Department of Experimental and Health Sciences, Universitat Pompeu Fabra, 08003 Barcelona, Spain and.
authors.forename: Amado
authors.initials: A
authors.lastname: Carreras-Sureda
authors.affiliation: From the Laboratory of Molecular Physiology and Channelopathies, Department of Experimental and Health Sciences, Universitat Pompeu Fabra, 08003 Barcelona, Spain and.
authors.forename: Roberto
authors.initials: R
authors.lastname: García-López
authors.affiliation: From the Laboratory of Molecular Physiology and Channelopathies, Department of Experimental and Health Sciences, Universitat Pompeu Fabra, 08003 Barcelona, Spain and.
authors.forename: Fanny
authors.initials: F
authors.lastname: Rubio-Moscardó
authors.affiliation: Research Unit on Bioactive Molecules (RUBAM), Department of Biomedicinal Chemistry, Institute for Advanced Chemistry of Catalonia (IQAC), 08034 Barcelona, Spain.
authors.forename: Josefina
authors.initials: J
authors.lastname: Casas
authors.affiliation: Research Unit on Bioactive Molecules (RUBAM), Department of Biomedicinal Chemistry, Institute for Advanced Chemistry of Catalonia (IQAC), 08034 Barcelona, Spain.
authors.forename: Gemma
authors.initials: G
authors.lastname: Fabriàs
authors.affiliation: From the Laboratory of Molecular Physiology and Channelopathies, Department of Experimental and Health Sciences, Universitat Pompeu Fabra, 08003 Barcelona, Spain and ruben.vicente@upf.edu.
authors.forename: Rubén
authors.initials: R
authors.lastname: Vicente
mesh_terms: D000818:Animals; D002460:Cell Line; D002518:Ceramides / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D050356:Lipid Metabolism / Q000187:drug effects; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D009961:Orosomucoid / Q000235:genetics / Q000378:metabolism*; D010168:Palmitates / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D051102:Serine C-Palmitoyltransferase / Q000235:genetics / Q000378:metabolism*; D013107:Sphingolipids / Q000378:metabolism
chemical_list: D002518:Ceramides; D008070:Lipopolysaccharides; D009961:Orosomucoid; D010168:Palmitates; D020033:Protein Isoforms; D013107:Sphingolipids; D051102:Serine C-Palmitoyltransferase
keywords: Ceramide; Enzyme Inhibitor; Macrophage; Serine Palmitoyltransferase; Sphingolipid