Cloning, sequencing and structural analysis of 976 base pairs of the promoter sequence for the rat lipoprotein lipase gene. Comparison with the mouse and human sequences

A Set of Proximal Regulatory Elements Contribute to the Transcriptional Activity of the Human Lipoprotein Lipase Promoter

Lipoprotein lipase (LPL) is a multifunctional protein that catalyzes the hydrolysis of plasma triglycerides, releasing free fatty acids, which play critical roles in the metabolism and transport of lipids. The transcription of LPL in response to cell types and regulatory factors is a complex process that starts with its promoter. In previous studies, several proximal regulatory elements within the human LPL promoter were individually characterized. This study was designed to characterize the effect of 12 proximal regulatory elements as a combined unit on the transcriptional activity of the LPL promoter. The hypothesis was that these proximal regulatory elements collectively result in the optimal transcriptional activity of the human LPL promoter. Full and partial LPL promoter sequences, which contained and excluded the 12 regulatory elements, respectively, were cloned and inserted into a promoterless luciferase reporter vector. The functional activities of these constructs were tested in vitro using a dual-luciferase reporter assay. Our results showed that HEK-293 cells transfected with the full LPL promoter exhibited significantly greater luciferase activity than cells transfected with partial LPL promoters. Our results indicate that the proximal regulatory elements within the LPL promoter, including four TATA boxes, two Oct-1 sites, one CT element, two C/EBPα sites, one SP1 site, and two cis-acting regions (LP-α and LP-β), are essential for its transcriptional activity.

Reduced fetal vitamin D status by maternal undernutrition during discrete gestational windows in sheep

Placental transport of vitamin D and other nutrients (e.g. amino acids, fats and glucose) to the fetus is sensitive to maternal and fetal nutritional cues. We studied the effect of maternal calorific restriction on fetal vitamin D status and the placental expression of genes for nutrient transport [aromatic T-type amino acid transporter-1 (TAT-1); triglyceride hydrolase/lipoprotein uptake facilitator lipoprotein lipase (LPL)] and vitamin D homeostasis [CYP27B1; vitamin D receptor (VDR)], and their association with markers of fetal cardiovascular function and skeletal muscle growth. Pregnant sheep received 100% total metabolizable energy (ME) requirements (control), 40% total ME requirements peri-implantation [PI40, 1-31 days of gestation (dGA)] or 50% total ME requirements in late gestation (L, 104-127 dGA). Fetal, but not maternal, plasma 25-hydroxy-vitamin D (25OHD) concentration was lower in PI40 and L maternal undernutrition groups (P<0.01) compared with the control group at 0.86 gestation. PI40 group placental CYP27B1 messenger RNA (mRNA) levels were increased (P<0.05) compared with the control group. Across all groups, higher fetal plasma 25OHD concentration was associated with higher skeletal muscle myofibre and capillary density (P<0.05). In the placenta, higher VDR mRNA levels were associated with higher TAT-1 (P<0.05) and LPL (P<0.01) mRNA levels. In the PI40 maternal undernutrition group only, reduced fetal plasma 25OHD concentration may be mediated in part by altered placental CYP27B1. The association between placental mRNA levels of VDR and nutrient transport genes suggests a way in which the placenta may integrate nutritional cues in the face of maternal dietary challenges and alter fetal physiology.

The nuclear receptor REV-ERBα is required for the daily balance of carbohydrate and lipid metabolism

Mutations of clock genes can lead to diabetes and obesity. REV-ERBα, a nuclear receptor involved in the circadian clockwork, has been shown to control lipid metabolism. To gain insight into the role of REV-ERBα in energy homeostasis in vivo, we explored daily metabolism of carbohydrates and lipids in chow-fed, unfed, or high-fat-fed Rev-erbα(-/-) mice and their wild-type littermates. Chow-fed Rev-erbα(-/-) mice displayed increased adiposity (2.5-fold) and mild hyperglycemia (∼10%) without insulin resistance. Indirect calorimetry indicates that chow-fed Rev-erbα(-/-) mice utilize more fatty acids during daytime. A 24-h nonfeeding period in Rev-erbα(-/-) animals favors further fatty acid mobilization at the expense of glycogen utilization and gluconeogenesis, without triggering hypoglycemia and hypothermia. High-fat feeding in Rev-erbα(-/-) mice amplified metabolic disturbances, including expression of lipogenic factors. Lipoprotein lipase (Lpl) gene, critical in lipid utilization/storage, is triggered in liver at night and constitutively up-regulated (∼2-fold) in muscle and adipose tissue of Rev-erbα(-/-) mice. We show that CLOCK, up-regulated (2-fold) at night in Rev-erbα(-/-) mice, can transactivate Lpl. Thus, overexpression of Lpl facilitates muscle fatty acid utilization and contributes to fat overload. This study demonstrates the importance of clock-driven Lpl expression in energy balance and highlights circadian disruption as a potential cause for the metabolic syndrome.

GIP increases human adipocyte LPL expression through CREB and TORC2-mediated trans-activation of the LPL gene

GIP (glucose-dependent insulinotropic polypeptide) is a gastrointestinal hormone that regulates pancreatic islet function. Additionally, emerging evidence suggests an important physiological role for GIP in the regulation of adipocyte metabolism. In previous studies on the lipogenic effects of GIP, it was shown to increase adipocyte lipoprotein lipase (LPL) activity in both differentiated 3T3-L1 cells and human adipocytes through a pathway involving activation of protein kinase B (PKB)/Akt. In the current study, we examined the effects of GIP on LPL gene expression. GIP in the presence of insulin increased LPL gene expression in human adipocytes and LPL promoter activity in GIP receptor-expressing HEK-293 cells, and both effects were greatly reduced by the transcription inhibitor actinomycin D. Subsequent studies established that GIP increased phosphorylation of Serine 133 in cAMP-response element binding protein (CREB) and the nuclear localization of cAMP-responsive CREB coactivator 2 (TORC2) through a pathway involving phosphatidylinositol 3-kinase (PI3-K), PKB, and AMP-activated protein kinase (AMPK). However, in the presence of insulin, GIP failed to activate the cAMP/PKA pathway. Knockdown of CREB and TORC2 using RNA interference reduced LPL expression, supporting a functional regulatory role. GIP-induced phospho-CREB and TORC2 were shown to bind to a cAMP-response element (-II) site in the human LPL promoter and GIP increased protein-protein interactions of these two factors. The lipogenic effects of GIP in the presence of insulin are therefore at least partially mediated by upregulation of adipocyte LPL gene transcription through a pathway involving PI3-K/PKB/AMPK-dependent CREB/TORC2 activation.

Identification and characterization of a novel 5 bp deletion in a putative insulin response element in the lipoprotein lipase gene

Our aim was to identify an insulin response element (IRE) in the lipoprotein lipase (LPL) gene. We identified a 19 bp sequence as a putative IRE in LPL non-coding exon 10 using bioinformatics. Upon sequencing the IRE region, a novel 5 bp deletion was identified in Hispanics (N=406) with a carrier frequency of 4.2% but not in non-Hispanic whites (N=604) or Africans. Electrophoretic mobility shift assay revealed binding sites for regulatory factor(s) in muscle cell nuclear extracts with putative IRE sequence. Antibody supershift assay using human aorta smooth muscle cell nuclear extract revealed that Elk-1 specifically binds to putative IRE. TaqMan real-time RT-PCR of the 5 bp deletion, the mutant and wild type cDNA expressed in COS-1 and human muscle cells revealed that the 5 bp deletion was associated with modest reduction in LPL expression. There was also a slight reduction in LPL translation in the deletion mutant. Our data suggest the presence of an IRE in the 3'UTR of the LPL gene.

Dynamics of adipogenic promoter DNA methylation during clonal culture of human adipose stem cells to senescence

Background

Potential therapeutic use of mesenchymal stem cells (MSCs) is likely to require large-scale in vitro expansion of the cells before transplantation. MSCs from adipose tissue can be cultured extensively until senescence. However, little is known on the differentiation potential of adipose stem cells (ASCs) upon extended culture and on associated epigenetic alterations. We examined the adipogenic differentiation potential of clones of human ASCs in early passage culture and upon senescence, and determined whether senescence was associated with changes in adipogenic promoter DNA methylation.

Results

ASC clones cultured to senescence display reduced adipogenic differentiation capacity in vitro, on the basis of limited lipogenesis and reduced transcriptional upregulation of FABP4 and LPL, two adipogenic genes, while LEP and PPARG2 transcription remains unaffected. In undifferentiated senescent cells, PPARG2 and LPL expression is unaltered, whereas LEP and FABP4 transcript levels are increased but not in all clones. Bisulfite sequencing analysis of DNA methylation reveals overall relative stability of LEP, PPARG2, FABP4 and LPL promoter CpG methylation during senescence and upon differentiation. Mosaicism in methylation profiles is maintained between and within ASC clones, and any CpG-specific methylation change detected does not necessarily relate to differentiation potential. One exception to this contention is CpG No. 21 in the LEP promoter, whose senescence-related methylation may impair upregulation of the gene upon adipogenic stimulation.

Conclusion

Senescent ASCs display reduced in vitro differentiation ability and transcriptional activation of adipogenic genes upon differentiation induction. These restrictions, however, cannot in general be attributed to specific changes in DNA methylation at adipogenic promoters. There also seems to be a correlation between CpGs that are hypomethylated and important transcription factor binding sites.

Tumour necrosis factor (TNF)α as a regulator of fat tissue mass in the Mediterranean gilthead sea bream (Sparus aurata L.)

The study was undertaken to analyze the lipolytic effect and transcriptional regulation of tumour necrosis factor (TNF)alpha in gilthead sea bream (Sparus aurata L.). The study was also focused on the transcriptional regulation and analysis of the 5-flanking region of lipoprotein lipase (LPL) in an attempt to identify cis-regulatory elements that would support the TNFalpha-mediated effects. The lipolytic effect of TNFalpha was evidenced by the increased release of glycerol in the culture medium of freshly isolated adipocytes. This observation, in addition to the summer up-regulation of TNFalpha transcripts in liver and mesenteric adipose tissue, supported a key role of TNFalpha as a fish limiting factor of tissue fat mass. Accordingly, TNFalpha expression in liver and mesenteric adipose tissue was reduced by fasting. Furthermore, the up-regulated expression of TNFalpha in the skeletal muscle of older fish can represent an adaptive response to limit the enhanced lipid influx towards muscle. A close positive association between LPL and TNFalpha transcripts supported the contribution of TNFalpha as a part of a regulatory network that exerts an inhibitory tonus upon the expression of LPL, which in turns limits the tissue uptake of fatty acids and the ultimate increase of tissue lipid reservoirs. The precise mechanism for the inhibition of LPL gene expression by TNFalpha remains to be established in fish, but analysis of the 5'-flanking region evidenced the conservation through vertebrate evolution of a functional OCT-1/NF-Y site that would mediate the TNFalpha effects on LPL expression.

Stable CpG hypomethylation of adipogenic promoters in freshly isolated, cultured, and differentiated mesenchymal stem cells from adipose tissue

Mesenchymal stem cells from adipose tissue can differentiate into mesodermal lineages. Differentiation potential, however, varies between clones of adipose stem cells (ASCs), raising the hypothesis that epigenetic differences account for this variability. We report here a bisulfite sequencing analysis of CpG methylation of adipogenic (leptin [LEP], peroxisome proliferator-activated receptor gamma 2 [PPARG2], fatty acid-binding protein 4 [FABP4], and lipoprotein lipase [LPL]) promoters and of nonadipogenic (myogenin [MYOG], CD31, and GAPDH) loci in freshly isolated human ASCs and in cultured ASCs, in relation to gene expression and differentiation potential. Uncultured ASCs display hypomethylated adipogenic promoters, in contrast to myogenic and endothelial loci, which are methylated. Adipogenic promoters exhibit mosaic CpG methylation, on the basis of heterogeneous methylation between cells and of variation in the extent of methylation of a given CpG between donors, and both between and within clonal cell lines. DNA methylation reflects neither transcriptional status nor potential for gene expression upon differentiation. ASC culture preserves hypomethylation of adipogenic promoters; however, between- and within-clone mosaic methylation is detected. Adipogenic differentiation also maintains the overall CpG hypomethylation of LEP, PPARG2, FABP4, and LPL despite demethylation of specific CpGs and transcriptional induction. Furthermore, enhanced methylation at adipogenic loci in primary differentiated cells unrelated to adipogenesis argues for ASC specificity of the hypomethylated state of these loci. Therefore, mosaic hypomethylation of adipogenic promoters may constitute a molecular signature of ASCs, and DNA methylation does not seem to be a determinant of differentiation potential of these cells.

Regulation of lipoprotein lipase activity in rainbow trout (Oncorhynchus mykiss) tissues

Lipoprotein lipase (LPL) is considered as a key enzyme in the lipid deposition and metabolism of many tissues. Information on LPL activity and its regulation in fish remains very scarce. In the present study, we have examined the nutritional regulation of LPL activity by conducting post-feeding and fasting experiments in rainbow trout (Oncorhynchus mykiss). As insulin plays an important role in the nutritional regulation of LPL activity in mammals, the effects of this hormone were tested in vivo by intraperitoneal administration. Moreover, we conducted in vitro studies using fat pads of rainbow trout to better clarify the direct role of insulin and tumor necrosis factor-alpha (TNFalpha) as possible regulators of LPL activity in rainbow trout. LPL activity in adipose tissue increased in response to feeding, 4h after ingestion of food, then decreasing to basal levels at 6h. No clear response was found in either red or white muscles, where LPL values were lower. Moreover, fasting produced a down-regulation of LPL activity in adipose tissue, concomitant with low levels of plasma insulin. While insulin administration stimulated LPL activity of adipose tissue 3h after injection, no response was observed in red or white muscles. Finally, in vitro studies using fat pads revealed that insulin significantly stimulated the proportion of LPL in active conformation at the extracellular level. On the other hand, TNFalpha did not greatly affect LPL activity using this in vitro model. These data indicate that LPL activity is regulated in a tissue-specific manner following food intake, and suggest that insulin is an important regulator of LPL activity in the adipose tissue of rainbow trout.

Regulation of metabolic transcriptional co-activators and transcription factors with acute exercise

Endurance exercise improves insulin sensitivity and increases fat oxidation, which are partly facilitated by the induction of metabolic transcription factors. Next to exercise, increased levels of FFA's also increase the gene expression of transcription factors, hence making it difficult to discern the effects from contractile signals produced during exercise, from those produced by increased circulatory FFA's. We aimed to investigate, in human skeletal muscle, whether acute exercise affects gene expression of metabolic transcriptional co-activators and transcription factors, including PGC-1alpha, PRC, PPARalpha, beta/delta, and gamma and RXR, SREBP-1c and FKHR, and to discern the effect of exercise per se from those of elevated levels of FFA. Two hours of endurance exercise was performed either in the fasted state, or following carbohydrate ingestion prior to and during exercise, thereby blunting the fasting-induced increase in FA availability and oxidation. Of the genes measured, PGC-1alpha and PRC mRNA increased immediately after, while PPARbeta/delta and FKHR mRNA increased 1-4 h after exercise, irrespective of the increases in FFA's. Our results suggest that the induction in vivo of metabolic transcription factors implicated in mitochondrial biogenesis are under the control of inherent signals, (PGC-1alpha, PRC), while those implicated in substrate selection are under the control of associated signals (PPARbeta/delta, FKHR) stimulated from the contracting skeletal muscle that are independent of circulating FFA levels.

A forkhead transcription factor FKHR up-regulates lipoprotein lipase expression in skeletal muscle

Lipoprotein lipase (LPL) plays a role in lipid usage in skeletal muscle by hydrolyzing plasma triglycerides into fatty acids, which are further utilized for beta-oxidation. Lipid usage is stimulated during fasting, diabetes mellitus and exercise, concomitant with enhanced LPL expression in skeletal muscle. Here we show that the forkhead type transcription factor FKHR is strongly induced in skeletal muscle in fasting mice, in mice with streptozotocin-induced diabetes and in mice after treadmill running. Ectopic expression of FKHR enhanced LPL gene expression in C2C12 muscle cells in culture. These results implicate FKHR as an important modulator of lipid metabolism in skeletal muscle.

Lipoprotein lipase: genetics, lipid uptake, and regulation

Lipoprotein lipase (LPL) regulates the plasma levels of triglyceride and HDL. Three aspects are reviewed. 1) Clinical implications of human LPL gene variations: common mutations and their effects on plasma lipids and coronary heart disease are discussed. 2) LPL actions in the nervous system, liver, and heart: the discussion focuses on LPL and tissue lipid uptake. 3) LPL gene regulation: the LPL promoter and its regulatory elements are described.

Lipoprotein lipase: the regulation of tissue specific expression and its role in lipid and energy metabolism

PURPOSE OF REVIEW

The aim of this review is to summarize and discuss recent advances in the understanding of the physiological role of lipoprotein lipase in lipid and energy metabolism.

RECENT FINDINGS

Studies on the transcriptional and the posttranscriptional level of lipoprotein lipase expression have provided new insights into the complex mechanisms that are involved in the regulation of the enzyme. Additionally a large body of evidence from both human studies and animal models suggests that the level of lipoprotein lipase expression in a given tissue is the rate limiting process for the uptake of triglyceride derived fatty acids. Imbalances in the partitioning of fatty acids among peripheral tissues have major metabolic consequences. For example, in mice both decreased lipoprotein lipase activities in adipose tissue and increased activity in muscle are associated with resistance to obesity; lack of lipoprotein lipase activity in macrophages is correlated with a decreased susceptibility to develop atherosclerotic lesions and overexpression of the enzyme in muscle is associated with increased blood glucose levels and insulin resistance.

SUMMARY

Considering the central role of lipoprotein lipase in energy metabolism it is a reasonable goal to discover and develop new drugs that affect the tissue specific expression pattern of the enzyme.

Homocysteine induces protein kinase C activation and stimulates c-Fos and lipoprotein lipase expression in macrophages

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease in human diabetes. Among the multiple factors that may account for the atherogenicity of homocysteine (Hcys) in patients with diabetes, macrophage (Mo) lipoprotein lipase (LPL) has unique features in that it is increased in human diabetes and acts as a proatherogenic factor in the arterial wall. In the present study, we determined the direct regulatory effect of Hcys on Mo LPL gene expression and secretion. Incubation of J774 Mo with Hcys increased, in a time- and dose-dependent manner, LPL mRNA expression and secretion. Induction of LPL gene expression was biphasic, peaking at 1 and 6 h. Whereas Hcys treatment increased protein kinase C (PKC) activity in Mo, pretreatment of Mo with PKC inhibitors totally suppressed Hcys-induced LPL mRNA expression. Hcys also increases the levels of c-fos mRNA in Mo and enhanced nuclear protein binding to the AP-1 sequence of the LPL gene promoter. Overall, these results demonstrate that Hcys stimulates Mo LPL at both the gene and protein levels and that Hcys-induced LPL mRNA expression requires PKC activation. They also suggest a possible role of c-fos in the stimulatory effect of Hcys on Mo LPL mRNA expression. These observations suggest a new mechanism by which Hcys may exert its proatherogenic effects in human diabetes.

Organization of the lipoprotein lipase gene of red sea bream Pagrus major

Lipoprotein lipase (LPL) is a key enzyme of lipid deposition and metabolism. To investigate the mechanism of lipid deposition in fish, as a first step, we have characterized the LPL gene of a marine teleost red sea bream Pagrus major by cDNA and genomic structure analysis. The red sea bream LPL gene encodes 511 amino acids and spans approximately 6.3 kb of the genome. The coding region is organized into ten exons and nine introns. In comparison with the LPL of other animals, the deduced amino acid sequence shows a high degree of similarity with a conservation of functional domains, e.g. catalytic triad, N-glycosylation sites, lipid and heparin binding regions. The 1.1 kb of 5' flanking region contains two CCAAT, sequences homologous to Oct-I site and response elements for hormones including glucocorticoid, insulin and thyroid hormone. The results of the present study will facilitate further study of the function and regulation of the LPL in non-mammalian vertebrates.

cDNA cloning and promoter analysis of rat caspase-9

Caspase-9 is the apex caspase of the mitochondrial pathway of apoptosis, which plays a critical role in apoptotic initiation and progression. However, gene regulation of caspase-9 is largely unknown. This is in part due to the lack of information on the gene promoter. Here we have cloned the full-length cDNA of rat caspase-9 and have isolated promoter regions of this gene. The rat caspase-9 cDNA of 2058 bp predicts a protein of 454 amino acids, which contains a caspase-recruitment domain ('CARD') at the N-terminus and enzymic domains at the C-terminus. The enzyme's active site, with a characteristic motif of QACGG, was also identified. Overall, rat and human caspase-9 have 71% identity. With the cDNA sequence, we subsequently isolated the proximal 5'-flanking regions of rat caspase-9 by the procedure of genomic walking. The 2270 bp genomic segment is 'TATA-less', but contains several GC boxes. Elements binding known transcription factors such as Sp-1, Pit-1, CCAAT-enhancer-binding protein (C/EBP), glucocorticoid receptor and hypoxia-inducible factor 1 (HIF-1) were also identified. When cloned into reporter gene vectors, the genomic segment showed significant promoter activity, indicating that the 5'-flanking regions isolated by genomic walking contain the gene promoter of rat caspase-9. Of significance is that the cloned promoter segments were activated by severe hypoxia, conditions inducing caspase-9 transcription. Thus, the genomic sequences reported here contain not only the basal promoter of rat caspase-9 but also regulatory elements responsive to pathophysiological stimuli including hypoxia.

Lipoprotein lipase activation by red ginseng saponins in hyperlipidemia model animals

The effect of ginseng saponins isolated from red ginseng (a steamed and dried root of Panax ginseng) has been studied in a cyclophosphamide (CPM)-induced hyperlipidemia model in fasted rabbits. In this model, chylomicrons and very low density lipoprotein (VLDL) accumulation was known to occur as a result of reduction in lipoprotein lipase (LPL) activity in the heart and heparin-releasable heart LPL. Oral administration of ginseng saponins at a dose of 0.01 g/kg for 4 weeks was found to reverse the increase in serum triglycerides (TG) and concomitant increase in cholesterol produced by CPM treatment, especially in chylomicrons and VLDL. In addition, ginseng saponins treatment led to a recovery in postheparin plasma LPL activity and heparin-releasable heart LPL activity, which were markedly reduced by CPM treatment. In rats given 15% glycerol/15% fructose solution, postheparin plasma LPL activity declined to two third of normal rats, whereas ginseng saponins reversed it to normal levels. In the present study we first demonstrated that ginseng saponins sustained LPL activity at a normal level or protected LPL activity from being decreased by several factors, resulting in the decrease of serum TG and cholesterol.

Common mutations of the lipoprotein lipase gene and their clinical significance

The accumulation of triglyceride-rich lipoproteins is an independent factor for an increased risk for premature arteriosclerosis. Common mutations in the lipoprotein lipase (LPL) gene are at least in part inherited susceptibility factors involved in the age- and sex-dependent phenotypic expression of hypertriglyceridemia. It can be estimated that about 20% of patients with hypertriglyceridemia are carriers of common LPL gene mutations (Asp9Asn, Asn291Ser, Trp86Arg, Gly188Glu, Pro207Leu, Asp250Asn) associated with the HLP. Genotyping of these LPL gene mutations is recommended especially in patients with high risk for premature arteriosclerosis. A comparably high number of individuals are carriers of common mutations (Ser447X) or silent mutations (Thr361) associated with low favorable lipids.

A corepressor and chicken ovalbumin upstream promoter transcriptional factor proteins modulate peroxisome proliferator-activated receptor-gamma2/retinoid X receptor alpha-activated transcription from the murine lipoprotein lipase promoter

Complex physiological stimuli differentially regulate the tissue-specific transcription of the lipoprotein lipase (LPL) gene. A conserved DNA recognition element (-171 to -149 bp) within the promoter functions as a transcriptional enhancer when bound by the peroxisome proliferator-activated receptor-gamma2 (PPARgamma2)/retinoid X receptor alpha (RXRalpha) heterodimer, but serves as a transcriptional silencer in the presence of unidentified double and single stranded DNA-binding proteins. To address this apparent paradox, the current study examined the effect of two classes of candidate comodulatory proteins, COUP-TF (chicken ovalbumin upstream promoter transcriptional factor) and the corepressor SMRT (silencing mediator of retinoic acid receptor and thyroid receptor). The expression of COUP-TF was detected by Western and Northern blots in a preadipocyte 3T3-L1 cell model during periods corresponding to increased LPL transcription. Cotransfection of COUP-TF expression constructs in the renal epithelial 293T cell line significantly increased transcription from the LPL promoter in synergy with PPARgamma2/RXRalpha heterodimers. The COUP-TFII (ARP-1) protein specifically bound the LPL PPAR recognition element inelectromobility shift assays and interacted directly with the ligand-binding domain of PPARgamma in pull-down experiments. In contrast, cotransfection of SMRT repressed PPARgamma2/ RXRalpha-mediated LPL transcription in the absence or presence of COUP-TFII (ARP-1). The interaction between PPARgamma2 and SMRT localized to the receptor-interactive domain 2 (amino acids 1260-1495) of the SMRT protein based on cotransfection and pull-down assays. These in vitro data indicate that COUP-TF proteins and SMRT modulate PPARgamma-mediated LPL transcription in the 293T cell line.

Cloning, sequencing and characterization of the rat hereditary hemochromatosis promoter: comparison of the human, mouse and rat HFE promoter regions

We have cloned and sequenced 1398bp of the rat HFE gene promoter region. The alignment of the rat promoter HFE sequence with the HFE promoter sequence from human and mouse detected several highly conserved sequences present at orthologous or heterologous positions in the three species. Subsequent analysis of the conserved promoter sequences identified the presence of 10 novel transcription elements present in the promoter regions of the human, mouse and rat HFE genes (GATA, NF-IL6, AP1, AP2, CREB, PEA3, gamma-IRE, GFI1, HNF-3beta, HFH2). Different gel retardation analyses performed with rat-liver nuclear extracts have confirmed the presence of factors binding to some of these transcription elements. This represents the first data concerning the identification of potential transcriptional elements of the HFE promoter in these three species. The expression pattern of the transcription factors corresponding to the novel elements identified in the HFE promoter is consistent with the potential role of the HFE promoter in the transcription regulation and function of the HFE gene. Knowledge of the identified conserved elements in the HFE promoter from human, mouse and rat provides the basis for subsequent in-vitro or in-vivo studies leading to identification of the detailed mechanisms involved in the regulation of the iron metabolism and the design of potential future alternative therapies.

Identification of genetic variation in the human hormone-sensitive lipase gene and 5' sequences: homology of 5' sequences with mouse promoter and identification of potential regulatory elements

Hormone-sensitive lipase (HSL) plays a crucial role in triglyceride hydrolysis in adipose tissue and exhibits cholesterol hydrolase activity in steroidogenic tissue and macrophages. Thus, common genetic variation in the HSL gene could affect both energy metabolism and atherogenesis. Using overlapping single-strand conformational polymorphism analysis (SSCP), a common single base change (T/C) in intron 4 [allele frequency 0.012 (95% CI 0.007-0. 018)] and a variable CA repeat in intron 6 with 9 alleles (heterozygosity index = 0.66) were identified. Sequence of 1.123 kb upstream from the reported 5'UTR (1) which includes intron B, exon B, and 159 bp of the promoter (2) was obtained and a single common nucleotide change, -60C/G [allele frequency 0.052 (95% CI 0.039-0. 064)], identified. Preliminary in vitro studies show that the -60G construct has 38.5% lower luciferase activity compared to the -60C construct (P = 0.035), suggesting a functional change affecting HSL gene expression. The 5' sequence shows 57-59% homology with the mouse promoter with higher homology at potential regulatory motifs. Thus, the 1.7 kb of 5' sequences is well conserved and may play a part in the regulation of HSL gene expression.