1,721,086 research outputs found
Transcriptional Regulation of the Mitochondrial Citrate and Carnitine/Acylcarnitine Transporters: Two Genes Involved in Fatty Acid Biosynthesis and β-oxidation.
No full textTranscriptional regulation of genes involved in fatty acid metabolism is considered the major long-term regulatory mechanism controlling lipid homeostasis. By means of this mechanism, transcription factors, nutrients, hormones and epigenetics control not only fatty acid metabolism, but also many metabolic pathways and cellular functions at the molecular level. The regulation of the expression of many genes at the level of their transcription has already been analyzed. This review focuses on the transcriptional control of two genes involved in fatty acid biosynthesis and oxidation: the citrate carrier (CIC) and the carnitine/ acylcarnitine/carrier (CAC), which are members of the mitochondrial carrier gene family, SLC25. The contribution of tissue-specific and less tissue-specific transcription factors in activating or repressing CIC and CAC gene expression is discussed. The interaction with drugs of some transcription factors, such as PPAR and FOXA1, and how this interaction can be an attractive therapeutic approach, has also been evaluated. Moreover, the mechanism by which the expression of the CIC and CAC genes is modulated by coordinated responses to hormonal and nutritional changes and to epigenetics is highlighte
Functional analysis of the promoter of the mitochondrial phosphate carrier human gene: identification of activator and repressor elements and their transcription factors.
No full textThe phosphate carrier (PiC) catalyses the import of phosphate into mitochondria where it is needed for ATP synthesis. We have analysed the 5′-flanking region of the human PiC gene and found that it has a single transcriptional initiation site and lacks a TATA box. Through deletion analysis of the −1213/−25 nt region, we identified an activation domain (−223/−25) and an inhibition domain (−1017/−814). The most effective promoter activity in transfected HeLa cells corresponded to the region containing putative binding sites for Sp1 (−163/−142; where Sp1 stands for stimulating protein-1) and CREB (−138/−116; where CREB stands for cAMP-response-element-binding protein). These DNA sequences were active in gel-shift assays in the presence of HeLa cell nuclear extracts or recombinant Sp1 and CREB respectively. Forskolin increased PiC promoter activity via the CREB site. Both footprinting and transfection of deletion constructs of the inhibition region (−1017/−814) showed that PiC silencer activity extends over 25 nt (−943/−919), which specifically binds two proteins present in HeLa cell nuclear extracts. These transcription factors were purified by DNA affinity, analysed by MS and identified as p54nrb/NonO (nuclear RNA binding protein) and PSF (protein-associated splicing factor). The PiC silencer region cloned in front of the ferritin promoter conferred a strong inhibition to the heterologous promoter. These findings may provide insight into control of PiC gene expression in different cell types and under different growth conditions. To our knowledge, this is the first study to analyse the regulation of the PiC gene expression in any cell
Role of FOXA and Sp1 in mitochondrial acylcarnitine carrier gene expression in different cell lines
No full textThis study investigates the transcriptional role of the human mitochondrial carnitine/acylcarnitine carrier
(CAC) proximal promoter. Through deletion analysis, an activation domain (334/80 bp) was identified
which contains FOXA and Sp1 active sites. The wild-type (but not mutated) 334/80 bp region of
the CAC gene conferred 74% LUC transgene activity in HepG2 cells, 17% in HEK293 cells and 14% in SK-NSH
cells as compared to that observed with the entire 1503/+3 bp proximal promoter. Overexpression
and silencing of FOXA2 or Sp1 in HepG2 cells enhanced and diminished, respectively, LUC activity, CAC
transcript and CAC protein. In HEK293 and SK-N-SH cells, which do not contain FOXA1-3, LUC activity
was increased by FOXA2 overexpression to a greater extent than in HepG2 cells. Both FOXA2 and Sp1
in HepG2, and only Sp1 in HEK293 and SK-N-SH cells, were found to be bound to the CAC proximal promoter.
These results show that FOXA and Sp1 sites in HepG2 cells and only the Sp1 site in HEK293 and
SK-N-SH cells have a critical role in the transcriptional regulation of the CAC proximal promoter
Elements in support of the 'non-identity' of the PGRMC1 protein with the σ2 receptor
No full textσ2 Receptor subtype is overexpressed in a variety of human tumors, with σ2 agonists showing antiproliferative effects towards tumor cells through multiple pathways that depend both on the tumor cell type and on the molecule type. Therefore, σ2 receptor is an intriguing target for tumor diagnosis and treatment despite the fact that that it has not yet been cloned. One of the last attempts to characterize σ2 receptors led to identify it as the progesterone receptor membrane component 1 (PGRMC1). Although still controversial, such identity appears to have been accepted. We the aim of contributing to solve this controversy, in this work we stably silenced or overexpressed PGRMC1 protein in human MCF7 adenocarcinoma cells. Western blotting analyses were performed to quantify the presence of PGRMC1 protein on each of the three MCF7 cell lines variants, while scatchard analyses with radioligand were performed in order to determine the expression of the σ2 receptors. In order to correlate the antiproliferative effect of σ2 receptor agonist with PGRMC1 density, some σ2 ligands were administered to each of the three MCF7 cells variants. The results suggested that PGRMC1 and σ2 receptors are two different molecular entities
Transcriptional regulation of the human mitochondrial citrate transporter gene
No full textThe mitochondrial citrate carrier (CIC) is a nuclear-encoded protein located in the inner mitochondrial membrane. It exports citrate from mitochondria to the cytosol where it produces acetyl-CoA and NADPH, which are both necessary for fatty acid and sterol biosynthesis. CIC mRNA and CIC protein levels are high in liver, pancreas and kidney.
Recently, we have functionally characterized the promoter of the human CIC gene. Firstly, we found that insulin upregulates and polyunsaturated fatty acids downregulate CIC gene transcription through the SRE/SREBP-1 regulatory system. Then, we assayed the gene reporter activity of CIC promoter deletion fragments and identified three important regions: the proximal promoter from -335 to -20 bp, an activation domain from -1285 to -1017 bp and an inhibitory domain from -742 to -499 bp. In the proximal promoter five active wild-type Sp1-binding elements were present. The DNA demethylating agent 5-aza-2-deoxycytidine (AzaC) and/or trichostatin A (TSA) increased CIC transcript and protein levels as well as Sp1 and acetylated histone binding to the CIC proximal promoter in SK-N-SH cells. Furthermore, Sp1 silencing decreased proximal promoter-driven gene reporter activity as well as CIC expression levels in AzaC- and TSA-treated SK-N-SH cells. In the activation domain a FOXA site was present. The wild-type CIC FOXA site cloned in front of the luciferase promoter conferred gene reporter transcriptional activation, and FOXA overexpression and silencing, respectively, increased and reduced CIC expression. In addition, FOXA1 silencing in INS-1 cells decreased not only CIC mRNA and protein but also the amount of cytosolic citrate and glucose-stimulated insulin secretion. Finally, in the CIC inhibitory domain, we characterized a silencer element of 26 bp that binds the transcriptional factor ZNF224. ZNF224 overexpression decreased LUC activity in cells transfected with a construct containing the CIC silencer, whereas ZNF224 silencing activated reporter transcription in cells transfected with the same construct. Remarkably, ZNF224 and CIC displayed an opposite pattern of expression in fetal tissues. In conclusion, our functional analysis of the CIC gene promoter has led to identify some interesting mechanisms regulating the expression of this gene in different tissues and under various physiological conditions
A key role of the mitochondrial citrate carrier (SLC25A1) in TNFα- and IFNγ-triggered inflammation.
No full textThe chronic induction of inflammation underlies multiple pathological conditions, including metabolic, autoimmune disorders and cancer. The mitochondrial citrate carrier (CIC), encoded by the SLC25A1 gene, promotes the export of citrate from the mitochondria to the cytoplasm, a process that profoundly influences energy balance in the cells. We have previously shown that SLC25A1 is a target gene for lipopolysaccharide signaling and promotes the production of inflammatory mediators. We now demonstrate that SLC25A1 is induced at the transcriptional level by two key pro-inflammatory cytokines, tumor necrosis factor-α (TNFα) and interferon-γ (IFNγ), and such induction involves the activity of the nuclear factor kappa B and STAT1 transcription factors. By studying the down-stream events following SLC25A1 activation during signals that mimic inflammation, we demonstrate that CIC is required for regulating the levels of nitric oxide and of prostaglandins by TNFα or IFNγ. Importantly, we show that the citrate exported from mitochondria via CIC and its downstream metabolic intermediate, acetyl-coenzyme A, are necessary for TNFα or IFNγ to induce nitric oxide and prostaglandin production. These findings provide the first line of evidence that the citrate export pathway, via CIC, is central for cytokine-induced inflammatory signals and shed new light on the relationship between energy metabolism and inflammatio
MEF2C exon α: Role in gene activation and differentiation
No full textMyocyte enhancer factor 2C (MEF2C) belongs to the MEF2 transcription factors. All products of MEF2 genes have a common amino-terminal DNA binding and dimerization domain. All four vertebrate MEF2 gene transcripts are also alternatively spliced. In the present study we identify two novel MEF2C splice variants, named VP and VP2. These variants are generated by the skipping of exon α. The identified α - variants are ubiquitously expressed, although at very low levels compared to the α + variants. The existence of MEF2C α - variants gave us the opportunity to study for the first time the function of exon α. Transactivation experiments show that the presence of exon α induces a reduction of transcription levels. Moreover, α - variants are significantly expressed during neuronal cell differentiation, indicating a putative role of these variants in development. © 2013 Elsevier B.V
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