1,721,138 research outputs found
Lipid-activated nuclear receptors: from gene transcription to the control of cellular metabolism
No full textCellular homeostasis is maintained through a complicated network of signaling, transport and enzymatic events that take place in different compartments of the cell. The result of this composite network determines the cellular behavior in response to environmental challenges. Within this network, many cellular functions are regulated at the transcriptional level and consequently the comprehension of the molecular mechanisms of gene regulation is fundamental to fully understand how the cell reacts to environmental changes. Moreover, it offers an opportunity to find novel targets for the design of better strategies to improve healthy human nutrition and to treat metabolic diseases. In this framework, nuclear receptors have emerged as key regulators of many cellular functions in response to lipid action. In this review, we will discuss the new concepts on the biology of the recently "adopted" nuclear receptors sensing oxysterols (LXR), bile acids (FXR) and fatty acids (PPARs) and their function in the integrated regulation of lipid and glucose metabolism. We will also address the role played by other orphan nuclear receptors, such as FTF, SHP and HNF-4, acting in concert with these lipid-sensing nuclear receptors in the regulation of cellular metabolism
Inhibition of histone deacetylases for the treatment of hyperlipidemias and prevention of atherosclerosis and cardiovascular diseases
No full textThe present invention relates to the use of inhibitors of the histone deacetylases for the preparation of a medicament for the treatment of pathologies caused by increased levels of plasma cholesterol and plasma and hepatic triglycerides. Particularly, the invention relates to the use of said inhibitors for the preparation of a medicament for the treatment of diseases such as hyperlipidaemia, particularly, hypercholesterolaemia, hypertriglyceridaemia, atherosclerosis, cardiovascular and cerebrovascular pathologies, obesity, diabetes metabolic syndromes
Genomic cloning, sequencing and analysis of the hamster cholesterol 7-hydroxylase gene (CYP7)
No full textCholesterol 7 alpha-hydroxylase is the rate limiting enzyme in bile acid biosynthesis and plays an important role in cholesterol homeostasis. The Golden Syrian hamster has been used as an animal model for the study of atherosclerosis and cholesterol gallstone disease. We have screened a lambda DASH II hamster liver genomic library using a rat cDNA as a hybridization probe. A 14-kb genomic clone has been isolated and characterized by restriction mapping and Southern blot hybridization. The clone contained the full-length gene encoding cholesterol 7 alpha-hydroxylase together with an upstream sequence of approximately 5 kb. DNA sequencing and analysis of about 11 kb of the gene revealed that the hamster CYP7 gene consists of six exons and five introns, which have the same structures and sizes as predicted in the rat and human CYP7 genes. The nucleotide and deduced amino acid sequences of the hamster cholesterol 7 alpha-hydroxylase have a high sequence identity of about 90% to the rat and 82% to the human sequences. Particularly, exons 2, 5, and 6 are highly conserved among these species, thus reflecting the presence of some domains that are crucial for the activity of this unique enzyme. The putative cholesterol-binding region, an aromatic amino acid region, and the P450 heme-binding region are completely conserved. Comparison of the 250-bp 5'-flanking sequence to the corresponding region in the rat and human genes revealed a high degree of homology ranging between 71% and 82%. Next to the canonical TATA and CCAAT boxes are many consensus sequences (LF-A1, LF-B1, TGT3) for liver-specific or -enriched transcription factors (HNF4, HNF1, and HNF5, respectively) and an imperfect direct repeat of thyroid hormone responsive element (TRE), which is located between TGT3 and LF-B1. These sequence motifs are completely conserved among the rat, human, and hamster CYP7 genes. Several modified sterol regulatory element (SRE)-like sequences are located in the upstream flanking region and in the first intron. This highly conserved proximal promoter may play important roles in the transcription activity and in the regulation of the CYP7 gene by physiological agents, such as bile acids and steroid/thyroid hormones. This is the first report describing the complete nucleotide sequence and confirming the structure of a CYP7 gen
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Identification of a bile acid response element in the cholesterol 7alpha-hydroxylase gene (CYP7A)
No full textThe transcriptional activity of the cholesterol 7 alpha-hydroxylase gene CYP7A is repressed by bile acids. Taurine conjugates of chenodeoxycholate and deoxycholate, but not cholate and ursodeoxycholate, inhibited the CYP7A promoter/luciferase reporter activity in transient transfection assays in Hep G2 cells. A region from nucleotide (nt) -74 to -55 was found to mediate bile acid response. However, deletion of this bile acid response element (BARE-I) enhanced reporter activity but did not eliminate the bile acid response. This is due to the presence of another BARE-II located in a conserved region between nt -149 and -128. Deletion or mutations of these sequences reduced promoter activity and abolished bile acid repression. This BARE-II shares an identical AGTTCAAG core sequence with BARE-I. Electrophoretic mobility shift assays of BARE-I and BARE-II probes using Hep G2 nuclear extract and the partially purified binding activity of nt -65/-54 DNA-affinity column revealed that the same or a similar nuclear protein might bind to both BAREs. BARE-II is the major BARE involved in the transcriptional repression of the CYP7A gene by hydrophobic bile acid
Effects of bile acids and steroid/thyroid hormones on the expression of cholesterol 7-hydroxylase mRNA and CYP7 gene in HepG2 cells
No full textThe expression of cholesterol 7 alpha-hydroxylase mRNA levels in confluent HepG2 cultures was reduced by tauro- or glyco-conjugates of deoxycholate and chenodeoxycholate, but not by cholate. Ursodeoxycholates, on the other hand, stimulated the mRNA level. The 5'-upstream regions of rat cholesterol 7 alpha-hydroxylase gene (CYP7) were fused to luciferase reporter gene and the constructs, p-3616/Luc, p-224/Luc and p-160/Luc, were transiently transfected into HepG2 cells. Tauro-conjugates of deoxycholate and chenodeoxycholate inhibited the transcriptional activities of the gene constructs in the confluent cells, but not in subconfluent cells. These results reveal that bile acid responsive elements are located in the -160 fragment and also between nt -3616 and -224. Thyroid and steroid hormones stimulated transcriptional activity expressed in the confluent cells and their responsive elements are located upstream of nt -224. It appears that adult phenotypes are responsible for bile acid feedback and hormone response in HepG2 cell
Orphan receptors chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) and retinoid X receptor activate and bind the rat cholesterol 7-hydroxylase gene (CYP7A)
No full textThe cholesterol 7alpha-hydroxylase gene (CYP7A) is transcriptionally regulated by a number of factors, including hormones, bile acids, and diurnal rhythm. Previous studies have identified a region from nucleotides (nt) -74 to -55 of the rat CYP7A promoter that enhanced bile acid repression of the SV40 early promoter, as assayed with a luciferase reporter gene in transiently transfected HepG2 cells. The rat CYP7A promoter/reporter activity was strongly stimulated by cotransfection with an expression plasmid encoding the nuclear hormone receptor chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) in a dose-dependent manner. Site-directed mutagenesis in the region of nt -74 to -55 altered this stimulation. Recombinant COUP-TFII expressed in HepG2 or COS-1 cells were found to bind to nt -74 -55 and nt -149 -128 probes by electrophoretic mobility shift assay (EMSA) and by supershifting the corresponding band with COUP-TFII-specific antibodies. The region of nt -176 -117 was previously mapped as a retinoic acid response region and was found to bind retinoid X receptor (RXR). EMSA supershift assays of wild-type and mutant oligomers using antibody against RXR revealed that the sequences between nt -145 and -134 were important for RXR binding. We conclude that COUP-TFII stimulates the transcriptional activity of the rat CYP7A promoter by binding to the sequences between nt -74 to -54 and nt -149 to -128. RXR may stimulate CYP7A gene transcription by binding to a direct repeat of the hormone response element separated by one nucleotide located at nt -146 -13
Hormonal regulation of the cholesterol 7-hydroxylase gene (CYP7)
No full textThe transcriptional regulation of the rat cholesterol 7 alpha-hydroxylase gene (CYP7) by hormones and signal transduction pathways was studied by transient transfection assay of the promoter activity. HepG2 cells were transfected with deletion mutants of the CYP7 upstream region linked to the luciferase reporter gene. The transcription of CYP7/luciferase chimeric genes was higher in confluent than in subconfluent cultures of HepG2 cells. Glucocorticoid receptors, in the presence of dexamethasone, up-regulated the CYP7 gene through two regions located between -3262 and -2803, and between -344 and -222, respectively. Thyroid hormones did not have any effect on the promoter activity. Insulin inhibited the promoter activity through sequences located between -344 and -222, and abolished the stimulation by dexamethasone. Hence, the insulin effect was dominant over that of glucocorticoids. Treatment of transfected HepG2 cells with phorbol 12-myristate 13-acetate (PMA), a known activator of protein kinase C (PKC), resulted in a time-dependent inhibition of the CYP7 promoter activity. The negative phorbol ester-response sequences were mapped between -344 and -222, and between -200 and -161, respectively. The CYP7 promoter activity was induced nearly 5-fold by all-trans-retinoic acid through sequences in the region from -200 to -129. Finally, cyclic AMP and protein kinase A (PKA) stimulated the expression of the CYP7/luciferase gene through multiple sequences in the distal and proximal regions, and both positive and negative response regions were mapped. Our results revealed that the -416 fragment of the rat CYP7 gene confers the activation by glucocorticoids and retinoic acid, and inhibition by insulin, phorbol esters and cAMP. It appears that this proximal promoter may contain a pleiotropic domain that regulates the effects of multiple signal
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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