Biomedical subjects

Younes Achouri

Publications and source records attributed to Younes Achouri.

6 recordsLinked to original sources

PubMed2006

2-Keto-4-methylthiobutyrate, an intermediate in the methionine salvage pathway, is a good substrate for CtBP1.

In the present work, we have studied the kinetic properties of the catalytic domain of CtBP1, a co-repressor belonging to the d-2-hydroxyacid dehydrogenase family and known to reduce pyruvate in the presence of NADH. CtBP1 acted on a variety of alpha-keto acids, for which it displayed biphasic curves with inhibition at elevated concentrations, as observed with other dehydrogenases of the same family. Based on catalytic efficiencies, the best substrate was 2-keto-4-methylthiobutyrate, an intermediate of the methionine salvage pathway. It was about 20-fold better than 2-ketoisocaproate and glyoxylate, and 80-fold better than pyruvate. From these data we conclude that 2-keto-4-methylthiobutyrate may be an important regulator of CtBP activity, possibly linking gene repression to the activity of the methionine salvage and spermine synthesis pathways.

Alcohol Oxidoreductases↗

PubMed2006

A vHNF1/TCF2-HNF6 cascade regulates the transcription factor network that controls generation of pancreatic precursor cells.

Generation of pancreatic precursor cells in the endoderm is controlled by a network of transcription factors. Hepatocyte nuclear factor-6 (HNF6) is a key player in this network, because it controls the initiation of the expression of pancreatic and duodenal homeobox 1 (Pdx1), the earliest marker of pancreatic precursor cells. To further characterize this network, we have investigated how the expression of HNF6 is controlled in mouse endoderm, by using in vitro and in vivo protein-DNA interaction techniques combined with endoderm electroporation, transgenesis, and gene inactivation in embryos. We delineated Hnf6 regulatory regions that confer expression of a reporter gene in the embryonic endoderm but not in extraembryonic visceral endoderm. HNF6 expression in the embryonic endoderm was found to depend on an intronic enhancer. This enhancer contains functional binding sites for the tissue-specific factors of the forkhead box A and HNF1 families. Among the latter, variant HNF1 (vHNF1)/TCF2, which is expressed before HNF6 in the endoderm, was found to be critical for HNF6 expression. Therefore, the sequential activation of vHNF1, HNF6, and Pdx1 in the endoderm appears to control the generation of pancreatic precursors. This cascade may be used to benchmark in vitro differentiation of pancreatic precursor cells from embryonic stem cells, for cell therapy of diabetes.

Animals↗

PubMed2005

Mutations in phenotypically mild D-2-hydroxyglutaric aciduria.

D-2-hydroxyglutaric aciduria is a neurometabolic disorder with mild and severe phenotypes. Recently, we reported pathogenic mutations in the D-2-hydroxyglutarate dehydrogenase gene as the cause of the severe phenotype of D-2-hydroxyglutaric aciduria in two patients. Here, we report two novel pathogenic mutations in this gene in one patient with a mild presentation and two asymptomatic siblings with D-2-hydroxyglutaric aciduria from two unrelated consanguineous Palestinian families: a splice error (IVS4-2A-->G) and a missense mutation (c.1315A-->G;p.Asn439Asp). Overexpression of this mutant protein showed marked reduction of the enzyme activity.

Alcohol Oxidoreductases↗

PubMed2004

Mutations in the D-2-hydroxyglutarate dehydrogenase gene cause D-2-hydroxyglutaric aciduria.

d-2-hydroxyglutaric aciduria is a neurometabolic disorder with both a mild and a severe phenotype and with unknown etiology. Recently, a novel enzyme, d-2-hydroxyglutarate dehydrogenase, which converts d-2-hydroxyglutarate into 2-ketoglutarate, and its gene were identified. In the genes of two unrelated patients affected with d-2-hydroxyglutaric aciduria, we identified disease-causing mutations. One patient was homozygous for a missense mutation (c.1331T-->C; p.Val444Ala). The other patient was compound heterozygous for a missense mutation (c.440T-->G; p.Ile147Ser) and a splice-site mutation (IVS1-23A-->G) that resulted in a null allele. Overexpression studies in HEK-293 cells of proteins containing the missense mutations showed a marked reduction of d-2-hydroxyglutarate dehydrogenase activity, proving that mutations in the d-2-hydroxyglutarate dehydrogenase gene cause d-2-hydroxyglutaric aciduria.

Alcohol Oxidoreductases↗

PubMed2004

Identification of a dehydrogenase acting on D-2-hydroxyglutarate.

Extracts of frozen rat liver were found to catalyse the formation of 3H2O from DL-2-hydroxy[2-3H]glutarate. Three peaks of enzyme activities were observed on separation by chromatography on DEAE-Sepharose. The first and second peaks corresponded to an enzyme acting on L-2-hydroxyglutarate and the third peak corresponded to an enzyme acting on D-2-hydroxyglutarate, as indicated by competitive inhibition of the detritiation of the racemic radioactive compound by the unlabelled L- and D-isomers respectively. The enzyme acting on the D-form was further characterized. It was independent of NAD or NADP and it converted D-2-hydroxyglutarate into a-ketoglutarate, transferring electrons to artificial electron acceptors. It also oxidized D-lactate, D-malate and meso-tartrate and was stimulated by Zn2+, Co2+ and Mn2+, but not by Mg2+ or Ca2+. Subcellular fractionation indicated that it was present in the mitochondrial fraction. The enzyme was further purified by chromatography on Blue Trisacryl and phenyl-Sepharose, up to a stage where only a few bands were still visible by SDS/PAGE. Among the four candidate polypeptides that were identified by MS, one corresponded to a predicted mitochondrial protein homologous with FAD-dependent D-lactate dehydrogenase. The corresponding human protein was expressed in HEK-293 cells and it was shown to catalyse the detritiation of DL-2-hydroxy[2-3H]glutarate with similar properties as the purified rat enzyme.

Amino Acid Sequence↗

PubMed2002

Sterol regulatory element binding protein-1c expression and action in rat muscles: insulin-like effects on the control of glycolytic and lipogenic enzymes and UCP3 gene expression.

Sterol regulatory element binding protein-1c (SREBP-1c) is a transcription factor that mediates insulin effects on hepatic gene expression. It is itself transcriptionally stimulated by insulin in hepatocytes. Here we show that SREBP-1c mRNA is expressed in adult rat skeletal muscles and that this expression is decreased by diabetes. The regulation of SREBP-1c expression was then assessed in cultures of adult muscle satellite cells. These cells form spontaneously contracting multinucleated myotubes within 7 days of culture. SREBP-1c mRNA is expressed in contracting myotubes. A 4-h treatment with 100 nmol/l insulin increases SREBP-1c expression and nuclear abundance by two- to threefold in myotubes. In cultured myotubes, insulin increases the expression of glycolytic and lipogenic enzyme genes and inhibits the 9-cis retinoic acid-induced UCP3 expression. These effects of insulin are mimicked by adenovirus-mediated expression of a transcriptionally active form of SREBP-1c. We conclude that in skeletal muscles, SREBP-1c expression is sensitive to insulin and can transduce the positive and negative actions of the hormone on specific genes and thus has a pivotal role in long-term muscle insulin sensitivity.

Alitretinoin↗