Purification and characterization of nuclear factors binding to the negative regulatory element D of human apolipoprotein A-II promoter: a negative regulatory effect is reversed by GABP, an Ets-related protein

Interaction between Apo A-II -265T > C polymorphism and dietary total antioxidant capacity on some oxidative stress and inflammatory markers in patients with type 2 diabetes mellitus

This work aims to examine the interaction between apo A2 (Apo A-II) -265T > C SNP and dietary total antioxidant capacity (DTAC) on inflammation and oxidative stress in patients with type 2 diabetes mellitus. The present cross-sectional study included 180 patients (35-65 years) with identified Apo A-II genotype. Dietary intakes were assessed by a FFQ. DTAC was computed using the international databases. IL-18 (IL18), high-sensitivity C-reactive protein (hs-CRP), pentraxin (PTX3), serum total antioxidant capacity (TAC), superoxide dismutase (SOD) activity and 8-isoprostaneF2α (PGF2α) markers were obtained according to standard protocols. General linear model was used to evaluate the interaction. The interaction of gene and DTAC (P_FRAP = 0·039 and P_ORAC = 0·042) on PGF2α level was significant after adjusting for confounders. A significant interaction was observed on IL18 level (P_ORAC = 0·018 and P_FRAP = 0·048) and SOD (P_TEAC = 0·037) in obese patients. Among patients whose DTAC was higher than the median intake, the levels of hs-CRP and PGF2α were significantly higher only in individuals with CC genotype. Serum TAC (P_FRAP = 0·030, P_ORAC = 0·049) and SOD were significantly lower in the CC genotype. There was a favourable relationship between the high-DTAC and SOD (obese: P_TEAC = 0·034, non-obese: P_FRAP = 0·001, P_TRAP < 0·0001, P_TEAC = 0·003 and P_ORAC = 0·001) and PGF2α (non-obese: P_ORAC = 0·024) in T-allele carriers. The rs5082 SNP interacts with DTAC to influence several cardiometabolic risk factors. Also, we found dietary recommendations for antioxidant-rich foods intake might be useful in the prevention of diabetes complications in the T carrier more effectively than the CC genotype. Future large studies are required to confirm these results.

APOA2 -256T>C polymorphism interacts with saturated fatty acids intake to affect anthropometric and hormonal variables in type 2 diabetic patients

Recent studies have established the interaction between APOA2 -256T>C polymorphism and dietary saturated fatty acids intake in relation to obesity on healthy individuals. In the current study, we investigate the effects of this interaction on anthropometric variables and serum levels of leptin and ghrelin in patients with type 2 diabetes. In this cross-sectional study, 737 patients with type 2 diabetes mellitus (290 males and 447 females) were recruited from diabetes clinics in Tehran. The usual dietary intake of all participants during the last year was obtained by validated semiquantitative food frequency questionnaire. APOA2 genotyping was performed by real-time PCR on genomic DNA. No significant relation was obtained by univariate analysis between anthropometric variables and APOA2 genotypes. However, after adjusting for age, gender, physical activity and total energy intake, we identified a significant interaction between APOA2-saturated fatty acids intake and body mass index (BMI). After adjusting for potential confounders, serum levels of ghrelin in CC genotype patients were significantly higher than T allele carriers (p = 0.03), whereas the case with leptin did not reveal a significant difference. The result of this study confirmed the interaction between APOA2 -256T>C polymorphism and SFAs intake with BMI in type 2 diabetic patients. In fact, homozygous patients for the C allele with high saturated fatty acids intake had higher BMI. The APOA2 -256T>C polymorphism was associated with elevated levels of serum ghrelin.

Methylation-sensitive regulation of TMS1/ASC by the Ets factor, GA-binding protein-alpha

Epigenetic silencing involving the aberrant DNA methylation of promoter-associated CpG islands is one mechanism leading to the inactivation of tumor suppressor genes in human cancers. However, the molecular mechanisms underlying this event remains poorly understood. TMS1/ASC is a novel proapoptotic signaling factor that is subject to epigenetic silencing in human breast and other cancers. The TMS1 promoter is embedded within a CpG island that is unmethylated in normal cells and is spanned by three DNase I-hypersensitive sites (HS). Silencing of TMS1 in cancer cells is accompanied by local alterations in histone modification, remodeling of the HS, and hypermethylation of DNA. In this study, we probed the functional significance of the CpG island-specific HS. We identified a methylation-sensitive complex that bound a 55-bp intronic element corresponding to HS2. Affinity chromatography and mass spectrometry identified a component of this complex to be the GA-binding protein (GABP) alpha. Supershift analysis indicated that the GABPalpha binding partner, GABPbeta1, was also present in the complex. The HS2 element conferred a 3-fold enhancement in TMS1 promoter activity, which was dependent on both intact tandem ets binding sites and the presence of GABPalpha/beta1 in trans. GABPalpha was selectively enriched at HS2 in human cells, and its occupancy was inversely correlated with CpG island methylation. Down-regulation of GABPalpha led to a concomitant decrease in TMS1 expression. These data indicate that the intronic HS2 element acts in cis to maintain transcriptional competency at the TMS1 locus and that this activity is mediated by the ets transcription factor, GABPalpha.

The apolipoprotein AII rs5082 variant is associated with reduced risk of coronary artery disease in an Australian male population

Serum high density lipoprotein (HDL) levels are inversely related to the development of coronary artery disease (CAD). Apolipoproteins AI and AII are the major protein constituents of HDL particles. APOAI and APOAII genetic polymorphisms have been proposed to affect transcriptional efficiency of their respective genes, thereby altering serum lipid levels and influencing atherosclerotic disease risk. 556 subjects with angiographically proven CAD (>50% stenosis) and 1109 randomly selected individuals from metropolitan Perth, Western Australia, were included in an association study. APOAI -75G/A (rs670) and APOAII -256T/C (rs5082) polymorphisms were both found to be not associated with plasma HDL levels. In a case-control analysis of 484 male CAD patients and 498 male controls, individuals carrying the 'CC' genotype for the APOAII rs5082 polymorphism had significantly lower risk of CAD than the 'T' allele carriers (OR=0.57, 95% CI 0.39-0.84, p=0.004). The minor 'A' allele of the APOAI rs670 polymorphism was found to be not associated with CAD, contrary to previous reports. We conclude that the APOAII rs5082 polymorphism appears to be cardioprotective in this representative Caucasian Australian population.

Microarray Analysis of VEGF-C Responsive Genes in Human Lymphatic Endothelial Cells

Vascular endothelial growth factor-C (VEGF-C) is considered one of the most important factors influencing lymphatic endothelial cell biology. The goal of this work was to characterize the gene expression response by lymphatic endothelial cells (LECs) to VEGF-C. Primary cultures of human microvascular LECs were exposed to 100 ng/mL VEGF-C for 30 minutes and 6 hours, and their lysates were evaluated by microarray analysis to determine changes in mRNA expression induced by VEGF-C. Characteristic of a response to a growth factor stimulus, the largest number of differentially expressed genes were transcription factors and cell cycle related. A number of genes known to be important in angiogenesis, tumorigenesis and tumor invasion, and the transport of proteins, solutes, and lipids were also affected. Interestingly, a number of genes related to lipid metabolism as well as neurogenesis and neurodegeneration were also responsive to VEGF-C stimulation. Further analysis of these genes may not only provide insight into the molecular mechanisms underlying lymphangiogenesis and associated pathogenesis, but may also identify other important roles of VEGF-C.

Human evidence that the apolipoprotein a-II gene is implicated in visceral fat accumulation and metabolism of triglyceride-rich lipoproteins

BACKGROUND

Apolipoprotein (apo) A-II is a major structural protein of plasma HDLs, but little is known regarding its functions.

METHODS AND RESULTS

To investigate the physiological role of apoA-II in humans, we screened the promoter region of the apoA-II gene for a functional polymorphism and used this polymorphism as a tool in association studies. A common, functional polymorphism in the promoter region of the apoA-II gene, a T to C substitution at position -265, was found. Electrophoretic mobility shift assays demonstrated that the -265T/C polymorphism influences the binding of nuclear proteins, whereas transient transfection studies in human hepatoma cells showed a reduced basal rate of transcription of the -265C allele compared with the -265T allele. The -265C allele was associated with decreased plasma apoA-II concentration and decreased waist circumference in healthy 50-year-old men. In addition, oral fat tolerance tests provided evidence that the -265C allele enhances postprandial metabolism of large VLDLs.

CONCLUSIONS

ApoA-II appears to promote visceral fat accumulation and impair metabolism of large VLDLs.

Ets target genes: past, present and future

Ets is a family of transcription factors present in species ranging from sponges to human. All family members contain an approximately 85 amino acid DNA binding domain, designated the Ets domain. Ets proteins bind to specific purine-rich DNA sequences with a core motif of GGAA/T, and transcriptionally regulate a number of viral and cellular genes. Thus, Ets proteins are an important family of transcription factors that control the expression of genes that are critical for several biological processes, including cellular proliferation, differentiation, development, transformation, and apoptosis. Here, we tabulate genes that are regulated by Ets factors and describe past, present and future strategies for the identification and validation of Ets target genes. Through definition of authentic target genes, we will begin to understand the mechanisms by which Ets factors control normal and abnormal cellular processes.

Cooperative binding of upstream stimulatory factor and hepatic nuclear factor 4 drives the transcription of the human apolipoprotein A-II gene

The activity of the human apoA-II promoter is controlled by a synergistic interaction of the distal enhancer and the proximal promoter. An important role in apoA-II promoter activity is exerted by a transcription factor, designated CIIIB1, which binds to the proximal element AB and the distal elements of the enhancer, K and L. In the present communication we establish that CIIIB1 corresponds to the previously described factor, upstream stimulatory factor (USF) using the following criteria. (a) Purification of CIIIB1 by affinity chromatography provided a heat-stable protein with an apparent molecular mass of 45 kDa that cross-reacted with anti-USF1 and -USF2a antibodies; (b) CIIIB1 bound to the elements AB, K, and L was supershifted by these antibodies; (c) the heterodimer USF1/2a is the predominant form that corresponds to CIIIB1. Cotransfection experiments in HepG2 cells established the functional significance of USF in apoA-II transcription. It was found that the minimal promoter AB was transactivated by USF2a. In addition, all three E-box motifs present in elements AB, K and L are necessary for maximum transactivation by USF2a. A dominant negative form of USF2a inhibits the activity of apoA-II promoter. The USF1/2a heterodimer, which is naturally expressed in the liver, is as efficient as the USF2a homodimer in the transactivation of apoA-II promoter/enhancer constructs. Cotransfection experiments in COS-1 cells showed that hepatic nuclear factor 4 (HNF-4) synergized with USF2a in the transactivation of the apoA-II promoter. In addition, we showed that HNF-4 and USF2a bind to the enhancer cooperatively. This may account for the transcriptional synergism observed between USF and HNF-4 in the transactivation of the apoA-II promoter.

C/EBP factor suppression of inhibition of type II secreted phospholipase A2 promoter in HepG2 cells: possible role of single-strand binding proteins

We previously reported that the type II secreted phospholipase A2 (sPLA2) promoter from positions (-326 to +20) ([-326;+20] promoter) is negatively regulated by two adjacent regulatory elements, C (-210 to -176) and D (-247 to -210). This study examines in greater detail the way in which this negative regulation operates. Successive 5' deletions of the [-326;+20] type II sPLA2 promoter indicated that the region upstream of position -195 inhibits the transcription activity sixfold in HepG2 cells but not in HeLa cells. Although the whole [-326;-176] region decreased the activity of a heterologous thymidine kinase promoter, this effect was orientation and position sensitive. C/EBP beta, C/EBP alpha, and C/EBP delta, which bind to element C, prevented the inhibition of promoter activity. Electrophoretic mobility shift experiments identified the binding of NF1-like proteins to the [-225;-218] site, which overlaps an insulin response-like sequence, 5'-TGTTTTG-3'. This sequence bound a factor which also recognized the promoters of the apolipoproteins C-III and A-II. Substitutions preventing the binding of this factor or the NF1-like proteins did not increase the transcription activity, but substitution in the [-217;-204] sequence blocked the transcription inhibition. This sequence did not bind any double-strand binding factor, but its antisense strand is critical for the binding of single-strand binding proteins to the [-232;-191] region. We therefore suggest that these single-strand binding proteins are involved in the inhibitory mechanism.

The proximal element of the human apolipoprotein A-II promoter increases the enhancer activity of the distal region

We have previously shown that human apolipoprotein A-II (apoA-II) transcription is controlled by a complex set of regulatory elements. In this study, we demonstrate that the distal region of the apoA-II promoter (-911/-614) acts as an enhancer and results in a 6-fold increase in activity when the proximal AB element is inserted between this enhancer and a TATA box. The AB element alone does not display any transcriptional activity. The combination of the proximal AB element and the enhancer is sufficient to activate transcription to the same level as that achieved with the full-length promoter. DNA binding and competition assays, and binding interference experiments allowed us to identify two adjacent binding sites within the AB element. These bind activities designated CIIIB1 and AIIAB3/4, respectively. Mutation on each of these sites showed that the binding site of CIIIB1 within the AB element played a major role in the interaction with the enhancer. Whereas transcriptional activation of other apolipoprotein genes involves the binding of the liver-enriched hepatocyte nuclear factor 4 (HNF4) on their proximal promoter, the present study demonstrates that neither HNF4 nor ApoA-I regulatory protein 1, its antagonistic orphan receptor, was able to bind the AB element. Instead, apoA-II transcription was driven by the interaction of apoA-II enhancer with proximal AB element, which involves an unidentified activity, CIIIB1.

Two regulatory elements of similar structure and placed in tandem account for the repressive activity of the first intron of the human apolipoprotein A-II gene

Recent reports indicate that apolipoprotein (apo) A-II, the second most abundant protein of high-density lipoproteins, plays a crucial role in counteracting the beneficial effect of apo A-I against atherogenesis. Transcription of the human apo A-II gene is controlled by an enhancer comprising 14 regulatory elements located upstream of its promoter whereas the first intron of this gene behaves as a silencer. Here we show that two sequence elements account for the repressive activity of this intron and correspond to negative regulatory elements termed NRE I and NRE II. The activity of intron I and the nuclear proteins binding to NRE I and II are encountered in hepatic cells but not in non-hepatic cells studied here. Both NREs form nucleoprotein complexes of very similar physicochemical characteristics and bind the same or closely related proteins. Site-directed mutagenesis, transient transfection and gel-shift analysis experiments indicate that both NREs exhibit similar structures, being composed of two sites required for maximal activity and optimal binding of transcription factors. Therefore two negative regulatory elements of similar structure and function, placed in tandem, account for the repressive activity of the first intron of the human apo A-II gene. These NREs do not exhibit structural similarity with known NREs of other genes.

Retinoids increase human apolipoprotein A-11 expression through activation of the retinoid X receptor but not the retinoic acid receptor

Considering the link between plasma high-density lipoprotein (HDL) cholesterol levels and a protective effect against coronary artery disease as well as the suggested beneficial effects of retinoids on the production of the major HDL apolipoprotein (apo), apo A-I, the goal of this study was to analyze the influence of retinoids on the expression of apo A-II, the other major HDL protein. Retinoic acid (RA) derivatives have a direct effect on hepatic apo A-II production, since all-trans (at) RA induces apo A-II mRNA levels and apo A-II secretion in primary cultures of human hepatocytes. In the HepG2 human hepatoblastoma cell line, both at-RA and 9-cis RA as well as the retinoid X receptor (RXR)-specific agonist LGD 1069, but not the RA receptor (RAR) agonist ethyl-p-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)-l-pro penyl]-benzoic acid (TTNPB), induce apo A-II mRNA levels. Transient-transfection experiments with a reporter construct driven by the human apo A-II gene promoter indicated that 9-cis RA and at-RA, as well as the RXR agonists LGD 1069 and LG 100268, induced apo A-II gene expression at the transcriptional level. Only minimal effects of the RAR agonist TTNPB were observed on the apo A-II promoter reporter construct. Unilateral deletions and site-directed mutagenesis identified the J site of the apo A-II promoter mediating the responsiveness to RA. This element contains two imperfect half-sites spaced by 1 oligonucleotide. Cotransfection assays in combination with the use of RXR or RAR agonists showed that RXR but not RAR transactivates the apo A-II promoter through this element. By contrast, RAR inhibits the inductive effects of RXR on the apo A-II J site in a dose-dependent fashion. Gel retardation assays demonstrated that RXR homodimers bind, although with a lower affinity than RAR-RXR heterodimers, to the AH-RXR response element. In conclusion, retinoids induce hepatic apo A-II production at the transcriptional level via the interaction of RXR with an element in the J site containing two imperfect half-sites spaced by 1 oligonucleotide, thereby demonstrating an important role of RXR in controlling human lipoprotein metabolism. Since the J site also confers responsiveness of the apo A-II gene to fibrates and fatty acids via the activation of peroxisome proliferator-activated receptor-RXR heterodimers, this site can be considered a plurimetabolic response element.

Fibrates increase human apolipoprotein A-II expression through activation of the peroxisome proliferator-activated receptor

In view of the evidence linking plasma high density lipoprotein (HDL)-cholesterol levels to a protective effect against coronary artery disease and the widespread use of fibrates in the treatment of hyperlipidemia, the goal of this study was to analyze the influence of fibrates on the expression of apolipoprotein (apo) A-II, a major protein constituent of HDL. Administration of fenofibrate (300 mg/d) to 16 patients with coronary artery disease resulted in a marked increase in plasma apo A-II concentrations (0.34 +/- 0.11 to 0.45 +/- 0.17 grams/liter; P < 0.01). This increase in plasma apo A-II was due to a direct effect on hepatic apo A-II production, since fenofibric acid induced apo A-II mRNA levels to 450 and 250% of control levels in primary cultures of human hepatocytes and in human hepatoblastoma HepG2 cells respectively. The induction in apo A-II mRNA levels was followed by an increase in apo A-II secretion in both cell culture systems. Transient transfection experiments of a reporter construct driven by the human apo A-II gene promoter indicated that fenofibrate induced apo A-II gene expression at the transcriptional level. Furthermore, several other peroxisome proliferators, such as the fibrate, Wy-14643, and the fatty acid, eicosatetraynoic acid (ETYA), also induced apo A-II gene transcription. Unilateral deletions and site-directed mutagenesis identified a sequence element located in the J-site of the apo A-II promoter mediating the responsiveness to fibrates and fatty acids. This element contains two imperfect half sites spaced by 1 oligonucleotide similar to a peroxisome proliferator responsive element (PPRE). Cotransfection assays showed that the peroxisome proliferator activated receptor (PPAR) transactivates the apo A-II promoter through this AII-PPRE. Gel retardation assays demonstrated that PPAR binds to the AII-PPRE with an affinity comparable to its binding affinity to the acyl coA oxidase (ACO)-PPRE. In conclusion, in humans fibrates increase plasma apo A-II concentrations by inducing hepatic apo A-II production. Apo A-II expression is regulated at the transcriptional level by fibrates and fatty acids via the interaction of PPAR with the AII-PPRE, thereby demonstrating the pivotal role of PPAR in controlling human lipoprotein metabolism.