title: Target metabolomics revealed complementary roles of hexose- and pentose-phosphates in the regulation of carbohydrate-dependent gene expression.
abstract: Carbohydrate response element-binding protein (ChREBP) is a transcription factor that mediates glucose signaling in mammalian liver, leading to the expression of different glycolytic and lipogenic genes, such as pyruvate kinase (L-PK) and fatty acid synthase (FAS). The current model for ChREBP activation in response to sugar phosphates holds that glucose metabolization to xylulose 5-phosphate (X-5-P) triggers the activation of protein phosphatase 2A, which dephosphorylates ChREBP and leads to its nuclear translocation and activation. However, evidence indicates that glucose 6-phosphate (G-6-P) is the most likely signal metabolite for the glucose-induced transcription of these genes. The glucose derivative that is responsible for carbohydrate-dependent gene expression remains to be identified. The difficulties in measuring G-6-P and X-5-P concentrations simultaneously and in changing them independently have hindered such identification. To discriminate between these possibilities, we adapted a liquid chromatography mass spectrometry method to identify and quantify sugar phosphates in human hepatocarcinoma cells (Hep G2) and rat hepatocytes in response to different carbon sources and in the presence/absence of a glucose-6-phosphate dehydrogenase inhibitor. We also used this method to demonstrate that these cells could not metabolize 2-deoxyglucose beyond 2-deoxyglucose-6-phosphate. The simultaneous quantification of sugar phosphates and FAS and L-PK expression levels demonstrated that both X-5-P and G-6-P play a role in the modulation of gene expression. In conclusion, this report presents for the first time a single mechanism that incorporates the effects of X-5-P and G-6-P on the enhancement of the expression of carbohydrate-responsive genes.
authors.affiliation: Faculty of Biology, Department of Biochemistry and Molecular Biology, Universitat de Barcelona, Barcelona, Spain.
authors.forename: Santiago
authors.initials: S
authors.lastname: Diaz-Moralli
authors.forename: Antonio
authors.initials: A
authors.lastname: Ramos-Montoya
authors.forename: Silvia
authors.initials: S
authors.lastname: Marin
authors.forename: Ana
authors.initials: A
authors.lastname: Fernandez-Alvarez
authors.forename: Marta
authors.initials: M
authors.lastname: Casado
authors.forename: Marta
authors.initials: M
authors.lastname: Cascante
mesh_terms: D000818:Animals; D050260:Carbohydrate Metabolism / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D005954:Glucosephosphate Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006600:Hexosephosphates / Q000378:metabolism*; D006801:Humans; D055432:Metabolomics; D010428:Pentosephosphates / Q000378:metabolism*; D051381:Rats
chemical_list: D006600:Hexosephosphates; D010428:Pentosephosphates; D005954:Glucosephosphate Dehydrogenase