n-caproylsphingosine and thermozymocidin

Sterol-regulatory element-binding proteins (SREBPs) regulate transcription of genes of lipid metabolism. Ceramide decreases transcriptionally active SREBP levels independently of intracellular cholesterol levels. Mechanisms of the ceramide-mediated decrease of SREBP levels were investigated.. Experiments were performed in Chinese hamster ovary cells. Inhibition of ceramide synthesis with myriocin, cycloserine, or fumonisin decreases levels of transcriptionally active SREBP and reduces SRE-mediated gene transcription. When ceramide synthesis is increased through exogenous sphingosine or inhibition of sphingosine kinase, SRE-mediated gene transcription is increased. The important role of ceramide synthesis in SRE-mediated gene transcription is confirmed in LY-B cells that do not synthesize ceramide de novo. LY-B cells fail to increase SRE-mediated gene transcription in sterol depletion.. Ceramide synthesis correlates with the generation of transcriptionally active SREBP and SRE-mediated gene transcription. Inhibition of ceramide synthesis decreases levels of transcriptionally active SREBP and SRE-mediated gene transcription. It is hypothesized that the process of ongoing ceramide synthesis contributes to the physiological processing of SREBP, perhaps affecting ER-to-Golgi trafficking. Taken together, modification of ceramide synthesis could be a novel target for drug development in the pharmacologic modification of SRE-dependent pathways.

Topics: 1-Deoxynojirimycin; Acyltransferases; Amidohydrolases; Animals; CCAAT-Enhancer-Binding Proteins; Ceramides; CHO Cells; Cholesterol; Cricetinae; Cricetulus; Cycloserine; DNA-Binding Proteins; Enzyme Induction; Fatty Acids, Monounsaturated; Fumonisins; Genes, Reporter; Hydroxymethylglutaryl-CoA Synthase; Morpholines; Myristates; Phosphotransferases (Alcohol Group Acceptor); Propanolamines; RNA Processing, Post-Transcriptional; Serine C-Palmitoyltransferase; Sphingolipids; Sphingosine; Sterol Regulatory Element Binding Protein 1; Transcription Factors; Transcription, Genetic; Transfection

Previous studies have shown that fumonisin B1 (FB1) inhibits ceramide synthase, resulting in accumulation of free sphinganine and sphingosine. Tumor necrosis factor-alpha (TNFalpha) plays an important role in FB1 toxicity and the expression of TNFalpha mRNA in liver and kidney is increased following FB1 exposure in mice. The objective of the current study was to investigate whether these two events (sphingoid bases accumulation and TNFalpha induction) are dependent on each other. An increase in expression of TNFalpha mRNA was detected in LLC-PK1 cells as early as 4 h after FB1 treatment but decreased to the control levels after 8 h. A positive linear correlation was observed between the expression of TNFalpha mRNA and FB1 concentration. Increases of intracellular sphingoid bases were also detected after 4 h of FB1 treatment and progressively increased until 24 h. Exposure of the cells to sphinganine or sphingosine did not significantly alter the expression of TNFalpha. Inhibition of sphingoid base biosynthesis by ISP-1, a specific inhibitor of serine palmitoyltransferase, the first enzyme in de novo sphingolipid biosynthesis, efficiently blocked the accumulation of free sphingoid bases in response to FB1, but it did not prevent the induction of TNFalpha expression. Results indicate that FB1-induced increase in TNFalpha expression is independent of sphingoid base accumulation-induced by ceramide synthase inhibition in LLC-PK1 cells.

Topics: Acyltransferases; Animals; Carboxylic Acids; Cell Line; Ceramides; Enzyme Inhibitors; Fatty Acids, Monounsaturated; Fumonisins; Gene Expression; Kidney; Kinetics; Mitogen-Activated Protein Kinases; Naphthalenes; Oxidoreductases; Protein Kinase C; RNA, Messenger; Serine C-Palmitoyltransferase; Sphingosine; Swine; Tumor Necrosis Factor-alpha