SREBP1c (sterol regulatory element-binding protein 1c) is a metabolic-syndrome-associated transcription factor that controls fatty acid biosynthesis under glucose/insulin stimulation. Oxidative stress increases lipid accumulation, which promotes the generation of reactive oxygen species (ROS). However, we know little about the role of oxidative stress in fatty acid biosynthesis. To clarify the action of oxidative stress in lipid accumulation via SREBP1c, we examined SREBP1c activity in H2O2-treated mammalian cells. We introduced a luciferase reporter plasmid carrying the SREBP1c-binding site into HepG2 or COS-7 cells. With increasing H2O2 dose, SREBP1c transcriptional activity increased in HepG2 cells but declined in COS-7 cells. RT-PCR analysis revealed that mRNA expression of SREBP1c gene or of SREBP1c-regulated genes rose H2O2 dose-dependently in HepG2 cells but dropped in COS-7 cells. Lipid accumulation and levels of the nuclear form of SREBP1c increased in H2O2-stimulated HepG2 cells. ROS may stimulate lipid accumulation in HepG2 cells via SREBP1c activation.

Research into the metabolism of fats may reveal potential targets for developing pharmaceutical approaches to obesity and related disorders. Such research may be limited, however, by the cost and time involved in using mammalian subjects or developing suitable cell lines. To determine whether invertebrates could be used to carry out such research more efficiently, we investigated the ability of Caenorhabditis elegans (C. elegans) to accumulate body fat following the consumption of excess calories and the mechanisms it uses to metabolize fat. C. elegans worms were grown on media containing various sugars and monitored for changes in body fat and expression of sbp-1, a homolog of the mammalian transcription factor SREBP-1c, which facilitates fat storage in mammals. The fat content increased markedly in worms exposed to glucose. In situ analysis of gene expression in transgenic worms carrying the GFP-labeled promoter region of sbp-1 revealed that sbp-1 mRNA was strongly expressed in the intestine. An sbp-1 knockdown caused a reduction in body size, fat storage, and egg-laying activity. RT-PCR analysis revealed a considerable decrease in the expression of fatty acid synthetic genes (including elo-2, fat-2, and fat-5) and a considerable increase of starvation-inducible gene acs-2. Normal egg-laying activity and acs-2 expression were restored on exposure to a polyunsaturated fatty acid. These findings suggest that SBP-1 and SREBP regulate the amount and composition of fat and response to starvation in a similar manner. Thus, C. elegans may be an appropriate subject for studying the metabolism of fats.

A cDNA clone of prostaglandin (PG) E receptor EP 1 subtype (rEP 1 ) was isolated from a rat uterus cDNA library. It encodes 405 amino acid residues with seven transmembrane-spanning domains and couples to Ca 2؉ mobilization. In addition, three cDNA clones encoding a variant form of rEP 1 were isolated. The open reading frame can code a 366-amino acid protein carrying a specific change of 49 amino acids from the middle of transmembrane segment VI to COOH terminus; it possesses a transmembrane segment VII-like structure lacking an intracellular COOH-terminal tail. Southern blot analysis of rat genomic DNA and genomic polymerase chain reaction demonstrated that these cDNAs were derived from a single copy gene. Northern blot analysis and ribonuclease protection assay revealed that both rEP 1 and rEP 1 -variant receptor mRNAs were highly expressed in the kidney. Immunoblot with an antibody directed toward the specific region of rEP 1 -variant receptor showed that rEP 1 -variant receptor protein was expressed in the membrane of the kidney and Chinese hamster ovary (CHO) cells transfected with rEP 1 -variant cDNA. Thus, the rEP 1 -variant receptor is translated from mRNA which is not spliced at nucleotide position 952 in the segment VI transmembrane region. rEP 1 -variant receptor retained the ligand binding activity with affinity and specificity similar to rEP 1 receptor, but lost the coupling of signal transduction systems by itself. However, when rEP 1 -variant receptor was stably co-expressed with rEP 1 receptor in CHO cells, the Ca 2؉ mobilization mediated by EP 1 receptor was significantly suppressed. Furthermore, when rEP 1 -variant receptor was expressed in CHO cells, cAMP formation by activation of endogenous EP 4 receptor was strongly blocked. These results suggest that the rEP 1 -variant receptor may affect the efficiency of signal coupling of PGE receptors and attenuate the action of PGE 2 on tissues. Prostaglandin (PG)1 E 2 is involved in a broad range of pathophysiological actions in diverse tissues through its binding to cell surface PGE receptor (1, 2). PGE receptors are pharmacologically classified into four subtypes, EP 1 , EP 2 , EP 3 , and EP 4 , and the diversity of PGE 2 actions is ascribed to PGE receptor subtypes coupled to different signal transduction pathways. The existence of PGE receptor subtypes has been given substantial support by cloning of cDNAs encoding these four PGE receptor subtypes from various sources and their characterization as GTP-binding protein-coupled receptors (3-6). In addition, several different isoforms of the PGE receptors have also been identified in the bovine, mouse, rabbit, and human EP 3 subtype (7-12). These isoforms, which are produced by alternative RNA splicing events and differ only in their COOHterminal sequences, couple to different GTP-binding proteins to activate different second messenger systems. The pharmacological actions of these subtypes have been well characterized on the basis of their responses to various agonists and antagonists. It has been co...

These findings indicate that both compounds are able to prevent 3T3-L1 differentiation by inhibition of the mitotic clonal expansion and downregulation of the adipogenesis related genes.

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