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Biomedical subjects

B Staels

Publications and source records attributed to B Staels.

At least 145 records · Page 8Linked to original sources
PubMed1996

Effects of hypolipidemic drugs on the expression of genes involved in high density lipoprotein metabolism in the rat.

Since plasma high density lipoprotein (HDL) concentrations are inversely related to the development of atherosclerosis, induction of HDL after pharmacological treatment is considered of benefit. To study whether currently used hypolipidemic drugs affect HDL metabolism by modulating the expression of genes involved in HDL metabolism, liver and intestinal apolipoprotein (apo) AI, apo-AII and apo-AIV gene expression was evaluated in rats treated with different classes of hypolipidemic drugs, and correlated to the changes in plasma lipid and apolipoprotein concentrations. In rats, the most pronounced hypolipidemic effects were observed after treatment with the fibrates clofibrate and fenofibrate, which lowered plasma lipid, apo-AI and apo-AIV concentrations. This decrease was accompanied by lowered liver apo-AI, apo-AII and apo-AIV mRNA levels. None of the other compounds tested affected plasma cholesterol, whereas probucol and simvastatin decreased plasma triglyceride concentrations. Apo-AI and apo-AII mRNA remained constant after nicotinic acid and probucol, whereas liver apo-AIV mRNA levels decreased. Cholestyramine increased hepatic apo-AI and apo-AII, but not apo-AIV mRNA levels. Simvastatin treatment increased apo-AI mRNA nearly threefold, whereas apo-AII and apo-AIV decreased by more than 50%. Similarly as after cholestyramine, the alteration in hepatic apo-AI mRNA levels did not result in changed plasma apo-AI concentrations. Remarkably, none of the drugs tested significantly affected intestinal apolipoprotein mRNA levels. These results indicate that hypolipidemic drugs may act on plasma lipoprotein metabolism by regulating apolipoprotein gene expression. Further studies in humans and primates are therefore warranted.

Actins↗
PubMed1996

Role of the peroxisome proliferator-activated receptor (PPAR) in mediating the effects of fibrates and fatty acids on gene expression.

The three types of peroxisome proliferator-activated receptors (PPAR), termed alpha, delta (or beta), and gamma, belong to the nuclear receptor superfamily. Although peroxisome proliferators, including fibrates and fatty acids, activate the transcriptional activity of these receptors, only prostaglandin J2 derivatives have been identified as natural ligands of the PPAR gamma subtype that also binds thiazolidinedione antidiabetic agents with high affinity. PPARs heterodimerize with retinoic X receptor (RXR) and alter the transcription of target genes after binding to response elements or PPREs, consisting of a direct repeat of the nuclear receptor hexameric DNA recognition motif (PuGGTCA) spaced by 1 nucleotide (DR-1). Upon activation by fatty acids (FAs) and drugs that affect lipid metabolism, PPARs control the expression of genes implicated in intra- and extracellular lipid metabolism, most notably those involved in peroxisomal beta-oxidation. PPARs partially mediate the inductive effects of fibrates and fatty acids on high density lipoprotein (HDL) cholesterol levels by regulating the transcription of the major HDL apolipoproteins, apoA-I and apoA-II. The hypotriglyceridemic action of fibrates and certain fatty acids also involves PPAR and is constituted of: 1) increased hydrolysis of plasma triglycerides due to induction of LPL and reduction of apoC-III expression; 2) stimulation of cellular fatty acid uptake and conversion to acyl-CoA derivatives due to increased expression of genes for fatty acid transport protein and acyl-CoA synthetase; 3) increased peroxisomal and mitochondrial beta-oxidation; and 4) decreased synthesis of fatty acids and triglycerides and decreased production of very low density lipoprotein (VLDL). Hence, both enhanced catabolism of triglyceride-rich particles and reduced secretion of VLDL particles contribute to the hypolipidemic effect of fibrates and fatty acids. Finally, PPARs appear to be involved in differentiation processes because activation of PPAR gamma 2 triggers adipocyte differentiation and stimulates expression of several genes critical to adipogenesis. It is suggested that PPARs are key messengers responsible for the translation of nutritional and pharmacological stimuli into changes in gene expression and differentiation pathways.

Adipocytes↗
PubMed1996

Lipoprotein lipase in highly vascularized structures of the eye.

Ocular tissues are highly dependent on lipid turnover and metabolism, which requires an uptake mechanism for fatty acids from lipoproteins. We studied the activity and expression of lipoprotein lipase (LPL), which catalyzes the hydrolysis of plasma triglycerides, in different ocular regions. Human and bovine eyes were dissected and various specialized anatomical areas were assayed for LPL activity, mRNA, and immunoreactivity. Variable levels of LPL activity were detected in all structures in human and bovine eyes. LPL activity was much higher in vascularized structures, such as ciliary body, iris, and retina than in avascular eye structures, such as vitreous body, lens, and cornea. In both human and bovine eyes, ciliary body contained the highest LPL lipolytic activity. LPL mRNA was detected by reverse transcription followed by polymerase chain reaction (RT-PCR) in all regions of human eyes. By RT-PCR analysis it was shown that bovine eyes contained high levels of LPL mRNA in ciliary body and iris, lower levels were found in retina, optic nerve, and lens, whereas no LPL mRNA could be found in bovine cornea. RT-PCR data, obtained in bovine eyes, agree with the results obtained by Northern blot experiments, confirming the high levels of LPL mRNA in iris and ciliary body. Immunofluorescence experiments performed on human eye samples indicated that the LPL protein is mostly distributed on the choroides, the choriocapillaris, and on the vessels of ciliary body, iris, optic nerve, and retina. The present study demonstrates that active LPL protein is synthesized, secreted, and located among microvessels in several specialized regions of the eye, and suggests that LPL could be involved in the uptake of fatty acids by the ocular tissues.

Adolescent↗
PubMed1995

Transient increase in obese gene expression after food intake or insulin administration.

Obesity is a disorder of energy balance, indicating a chronic disequilibrium between energy intake and expenditure. Recently, the mouse ob gene, and subsequently its human and rat homologues, have been cloned. The ob gene product, leptin, is expressed exclusively in adipose tissue, and appears to be a signalling factor regulating body-weight homeostasis and energy balance. Because the level of ob gene expression might indicate the size of the adipose depot, we suggest that it is regulated by factors modulating adipose tissue size. Here we show that ob gene exhibits diurnal variation, increasing during the night, after rats start eating. This variation was linked to changes in food intake, as fasting prevented the cyclic variation and decreased ob messenger RNA. Furthermore, refeeding fasted rats restored ob mRNA within 4 hours to levels of fed animals. A single insulin injection in fasted animals increased ob mRNA to levels of fed controls. Experiments to control glucose and insulin independently in animals, and studies in primary adipocytes, showed that insulin regulates ob gene expression directly in rats, regardless of its glucose-lowering effects. Whereas the ob gene product, leptin, has been shown to reduce food intake and increase energy expenditure, our data demonstrate that ob gene expression is increased after food ingestion in rats, perhaps through a direct action of insulin on the adipocyte.

Adipose Tissue↗
PubMed1995

Induction of the acyl-coenzyme A synthetase gene by fibrates and fatty acids is mediated by a peroxisome proliferator response element in the C promoter.

The long-chain acyl-coenzyme A synthetase (ACS) gene gives rise to three transcripts containing different first exons preceded by specific regulatory regions A, B, and C. Exon-specific oligonucleotide hybridization indicated that only A-ACS mRNA is expressed in rat liver. Fibrate administration induced liver C-ACS strongly and A-ACS mRNA to a lesser extent. B-ACS mRNA remained undetectable. In primary rat hepatocytes and Fa-32 hepatoma cells C-ACS mRNA increased after treatment with fenofibric acid, alpha-bromopalmitate, tetradecylthioacetic acid, or alpha-linolenic acid. Nuclear run-on experiments indicated that fenofibric acid and alpha-bromopalmitate act at the transcriptional level. Transient transfections showed a 3.4-, 2.3-, and 2.2-fold induction of C-ACS promoter activity after fenofibric acid, alpha-bromopalmitate, and tetradecylthioacetic acid, respectively. Unilateral deletion and site-directed mutagenesis identified a peroxisome proliferator activator receptor (PPAR)-responsive element (PPRE) mediating the responsiveness to fibrates and fatty acids. This ACS PPRE contains three imperfect half sites spaced by 1 and 3 oligonucleotides and binds PPAR.retinoid X receptor heterodimers in gel retardation assays. In conclusion, the regulation of C-ACS mRNA expression by fibrates and fatty acids is mediated by PPAR.retinoid X receptor heterodimers interacting through a PPRE in the C-ACS promoters. PPAR therefore occupies a key position in the transcriptional control of a pivotal enzyme controlling the channeling of fatty acids into various metabolic pathways.

Animals↗
PubMed1995

Regulation of rat liver apolipoprotein A-I, apolipoprotein A-II and acyl-coenzyme A oxidase gene expression by fibrates and dietary fatty acids.

The regulation by fibrates and dietary fatty acids of the hepatic gene expression of apolipoproteins (apo) A-I and A-II, the major protein constituents of high-density lipoproteins, as well as of acyl-CoA oxidase, the rate-limiting enzyme of the peroxisomal beta-oxidation pathway, was studied in vivo in the rat and in vitro in primary cultures of rat hepatocytes. In primary hepatocytes, different fibrates decreased apo A-I and increased acyl-CoA oxidase mRNA levels, whereas apo A-II mRNA only decreased in level after treatment with fenofibric acid, but not after bezafibrate, gemfibrozil or Wy-14643 treatment. Treatment with fenofibric acid counteracted the increase in apo A-I mRNA levels observed after dexamethasone or all-trans retinoic acid treatment, whereas simultaneous addition of fenofibric acid together with all-trans retinoic acid or dexamethasone resulted in a superinduction of acyl-CoA oxidase mRNA. Addition of the n-3 polyunsaturated fatty acids (PUFAs), docosanohexaenoic acid and eicosanopentaenoic acid, or the fatty acid derivative alpha-bromopalmitate, decreased apo A-I and increased acyl-CoA oxidase mRNA in a dose-dependent and time-dependent manner, whereas apo A-II mRNA did not change significantly. Nuclear run-on experiments demonstrated that fenofibric acid and alpha-bromopalmitate decreased apo A-I and increased acyl-CoA oxidase gene expression at the transcriptional level. When rats were fed isocaloric diets enriched in saturated fat (hydrogenated coconut oil), n-6 PUFAs (safflower oil) or n-3 PUFAs (fish oil), a significant decrease in liver apo A-I and apo A-II mRNA levels was only observed after fish oil feeding. Compared to feeding low fat, liver acyl-CoA oxidase mRNA increased after fat feeding, but this effect was most pronounced (twofold) in rats fed fish oil. Results from these studies indicate that fish oil feeding reduces rat liver apo A-I and apo A-II gene expression, similar to results obtained after feeding fenofibrate. Fibrates and n-3 fatty acids (and the fatty acid derivative, alpha-bromopalmitate) down-regulate apo A-I and induce acyl-CoA oxidase gene expression through a direct transcriptional action on the hepatocyte. In contrast, only fenofibric acid, but not the other fibrates or fatty acids tested, decrease apo A-II gene expression in vitro.

Acyl-CoA Oxidase↗
PubMed1995

Induction of ob gene expression by corticosteroids is accompanied by body weight loss and reduced food intake.

Genetic studies in mice have identified the ob gene product as a potential signaling factor regulating body weight homeostasis and energy balance. It is suggested that modulation of ob gene expression results in changes in body weight and food intake. Glucocorticoids are shown to have important metabolic effects and to modulate food intake and body weight. In order to test the hypothesis that these metabolic effects of glucocorticoids are linked to changes in the expression of the ob gene, ob mRNA levels were evaluated in rats treated with different glucocorticosteroids at catabolic doses and correlated to the kinetics of changes in body weight gain and food intake. Results from time course experiments demonstrate that adipose tissue ob gene expression is rapidly induced by glucocorticosteroids. This induction is followed by a concordant decrease in body weight gain and food consumption. These data suggest that the catabolic effects of corticosteroids on body weight mass and food intake might be mediated by changes in ob expression. Modulation of ob expression may therefore constitute a mechanism through which hormonal, pharmacological, or other factors control body weight homeostasis.

Adipose Tissue↗
PubMed1995

Tissue-specific expression of the human gene for lecithin: cholesterol acyltransferase in transgenic mice alters blood lipids, lipoproteins and lipases towards a less atherogenic profile.

Lecithin:cholesterol acyltransferase (LCAT) is a key enzyme in the reverse cholesterol pathway but its role in lipid metabolism is still unclear. We have generated mice transgenic for a 7-kb genomic DNA fragment comprising the 6 exons and 5 introns of the LCAT gene with 1932 bp of 5' flanking and 908 bp of 3' flanking sequences. One line had integrated about 30 copies and expressed about 40-fold increased LCAT activity in a human test system. The expression showed correct tissue specificity of the human LCAT gene. Increased LCAT activity resulted in a decrease of plasma triacylglycerols below 50% of fasting controls. This reduction was seen in all lipoprotein fractions. Lipoprotein lipase activity did not change significantly, whereas hepatic triacylglycerol lipase increased markedly. Plasma total cholesterol was similar in fasting transgenic and control mice, but low-density lipoprotein and very low-density lipoprotein cholesterol were reduced to about 50%. High-density lipoprotein cholesterol increased about 20%, accompanied by a correspondingly increased size and a higher cholesterol efflux-stimulating activity of transgenic LCAT high-density lipoprotein. Both apolipoprotein A-I and A-II plasma concentrations increased in transgenic mice. Plasma triacylglycerol and cholesteryl ester fatty acid distribution showed an increased proportion of palmitic acid, whereas oleic, linoleic and arachidonic acid decreased, thus resembling more closely the human situation. Overexpression of the human LCAT gene provokes major changes in plasma lipoprotein and apolipoprotein concentrations, resulting in a less atherogenic plasma lipoprotein profile through a reduction in atherogenic and an increase in anti-atherogenic lipoproteins.

Animals↗
PubMed1995

Fibrates downregulate apolipoprotein C-III expression independent of induction of peroxisomal acyl coenzyme A oxidase. A potential mechanism for the hypolipidemic action of fibrates.

Epidemiological and transgenic animal studies have implicated apo C-III as a major determinant of plasma triglyceride metabolism. Since fibrates are very efficient in lowering triglycerides, it was investigated whether fibrates regulate apo C-III gene expression. Different fibrates lowered rat liver apo C-III mRNA levels up to 90% in a dose- and time-dependent manner, whereas intestinal apo C-III mRNA remained constant. This decrease in liver apo C-III mRNA was rapid (1 d) and reversible, since it was restored to control levels within 1 wk after cessation of treatment. In addition, fenofibrate treatment abolished the developmental rise of hepatic apo C-III mRNA observed during the suckling-weaning period. Administration of fibrates to rats induced liver and intestinal expression of the acyl CoA oxidase gene, the rate-limiting enzyme for peroxisomal beta-oxidation of fatty acids. In primary cultures of rat and human hepatocytes, fenofibric acid lowered apo C-III mRNA in a time- and dose-dependent manner. This reduction in apo C-III mRNA levels was accompanied by a decreased secretion of apo C-III in the culture medium of human hepatocytes. In rat hepatocytes fenofibric acid induced acyl CoA oxidase gene expression, whereas acyl CoA oxidase mRNA remained unchanged in human hepatocytes. Nuclear run-on and transient transfection experiments of a reporter construct driven by the human apo C-III gene promoter indicated that fibrates downregulate apo C-III gene expression at the transcriptional level. In conclusion, these studies demonstrate that fibrates decrease rat and human liver apo C-III gene expression. In humans the mechanisms appears to be independent of the induction of peroxisomal enzymes. This downregulation of liver apo C-III gene expression by fibrates may contribute to the hypotriglyceridemic action of these drugs.

Acyl-CoA Oxidase↗
PubMed1995

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.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1994

Negative regulation of the human apolipoprotein A-I promoter by fibrates can be attenuated by the interaction of the peroxisome proliferator-activated receptor with its response element.

Fibrates have been reported to modulate plasma high density lipoprotein cholesterol and apolipoprotein (apo) A-I concentrations. Therefore, the molecular mechanisms underlying the regulation of human apoA-I gene expression by fibrates was investigated. Fenofibrate reduced the expression of a reporter gene driven by the DNA sequences between -192 and +91 (BC-P-chloramphenicol acetyltransferase; CAT) relative to the apoA-I gene transcription start site approximately 3-fold. The sequences involved in the down-regulation of apoA-I gene transcription by fenofibrate were localized between -41 and +91 (P-CAT) relative to the transcription start site. The reduction of the expression of BC-P-CAT was dose-dependent and maximal at 500 microM (20 +/- 7%). Different peroxisome proliferators showed different levels of repression varying from 39 +/- 4% for fenofibrate, 43 +/- 5% for tetradecylthioacetic acid, 48 +/- 4% for bezafibrate, 54 +/- 2% for 5,8,11,14-eicotetraynoic acid, 76 +/- 2% for ciprofibrate, whereas Wy 14643 only marginally inhibited the expression of BC-P-CAT. By contrast, inclusion of sequences between -256 and -192 (ABC-P-CAT) attenuated the repression by fenofibrate. Furthermore, the apoA-IA site (-214 to -192; Awt-P-CAT) could counteract the repression of P-CAT by fenofibrate in the presence of cotransfected mPPAR alpha (peroxisome proliferator-activated receptor). In addition, the acyl-CoA oxidase-peroxisome proliferator response element (PPRE) could substitute the wild-type A-site in blocking the fenofibrate-induced reduction of the apoA-I promoter by mPPAR alpha. The protective effect of PPAR on fenofibrate induced inhibition of apoA-I expression was abolished after mutation of the direct repeat in the A site (Am-P-CAT). Consistent with these functional data only the wild-type, but not the mutated A site bound PPAR/retinoic X receptor heterodimers in gel shift assays. These data suggest that certain peroxisome proliferators can reduce the expression of the apoA-I promoter in a PPAR-independent fashion, through modulation of factors interacting with sequences localized between -41 and +91 of the apoA-I gene transcription initiation site. This inhibitory effect can be overcome when PPAR interacts with a functional PPRE, such as the apoA-I A site or the acyl-CoA oxidase-PPRE.

Animals↗
PubMed1994

Regulation of the peroxisome proliferator-activated receptor alpha gene by glucocorticoids.

This study demonstrates that the expression of the peroxisome proliferator-activated receptor alpha (PPAR alpha) is regulated by glucocorticoid hormones in hepatocytes. Hydrocortisone, dexamethasone, and triamcinolone stimulated PPAR alpha mRNA synthesis in a dose-dependent manner in primary rat hepatocyte cultures. This glucocorticoid stimulation was inhibited by RU 486, a specific glucocorticoid antagonist. Moreover, in contrast to glucocorticoid hormones, the mineralocorticoid aldosterone had only a weak effect, suggesting that the hormonal stimulation of PPAR alpha was mediated by the glucocorticoid receptor. The induction was not prevented by cycloheximide treatment of the hepatocytes, indicating that it was mediated by preexisting glucocorticoid receptor. Finally, the RNA synthesis inhibitor actinomycin D abolished the stimulatory effect of dexamethasone, and nuclear run-on analysis showed an increase of PPAR alpha transcripts after hormonal induction. Thus, the PPAR alpha gene is an early response gene of glucocorticoids that control its expression at the transcriptional level.

Animals↗
PubMed1994

Opposite in vitro and in vivo regulation of hepatic apolipoprotein A-I gene expression by retinoic acid. Absence of effects on apolipoprotein A-II gene expression.

We studied the pharmacological potential of retinoids to modulate apolipoprotein (apo) A-I and apoA-II gene expression and production in vitro in the human cell line HepG2 as well as in primary cultures of adult rat hepatocytes and in vivo in the rat. In HepG2 cells, addition of all-trans retinoic acid (RA) doubled apoA-I mRNA within 24 hours and protein secreted in the culture medium after 48 hours. The induction of apoA-I mRNA by RA was completely blocked by actinomycin D, suggesting that RA acts at the transcriptional level in HepG2 cells. In primary cultures of rat hepatocytes, addition of RA increased apoA-I mRNA in a dose- and time-dependent manner as well as the secretion of apoA-I protein. Similar changes in apoA-I mRNA were observed with 9-cis RA. However, in vivo, hepatic apoA-I mRNA levels decreased after a single administration of RA at 10 mg/kg and remained low after prolonged treatment or at a higher dose, and serum apoA-I concentrations did not change. Furthermore, RA treatment did not substantially affect apoA-II mRNA levels or protein secretion either in vitro or in vivo. As a control, RA receptor-beta mRNA levels increased after RA both in vitro and in vivo. In conclusion, RA treatment selectively induces apoA-I and not apoA-II expression in vitro but not in vivo. These results therefore show additional regulatory effects of RA on apoA-I gene expression in vivo and raise questions about the usefulness of RA in the treatment of atherosclerosis.

Animals↗
PubMed1993

Acyl-CoA synthetase mRNA expression is controlled by fibric-acid derivatives, feeding and liver proliferation.

Several enzymes of the beta-oxidation pathway have been shown to be induced after stimulation with peroxisomal proliferators, including several hypolipidemic drugs. We investigated the regulation of the long-chain-acyl-CoA synthetase (ACS) gene in the liver. Fenofibrate, a hypolipidemic drug and potent peroxisomal proliferator, induced ACS gene expression in several tissues. In liver, large increases in ACS mRNA levels and ACS activity were observed after fenofibrate administration. Adipose tissue ACS mRNA levels and ACS activity were also stimulated upon fibrate treatment but to a lesser extent in comparison with liver ACS mRNA. Kidney ACS mRNA was only weakly induced, except for the highest dose and the longest treatment period, where a strong induction was observed. In contrast to these tissues, heart ACS mRNA and ACS activity remained almost unchanged after fenofibrate treatment. These effects of fenofibrate could be reproduced by other fibrates such as clofibrate. In addition, it is demonstrated that both nutritional composition and liver proliferation trigger ACS gene expression in liver. Consequently, these data suggest that ACS is a highly regulated enzyme with a potentially important control function in lipid metabolism.

Adipose Tissue↗
PubMed1993

Developmental extinction of liver lipoprotein lipase mRNA expression might be regulated by an NF-1-like site.

The molecular mechanism underlying the extinction of lipoprotein lipase (LPL) expression in rat liver during development was investigated. A mouse (BWTG3) and a rat (7777) hepatoma, both of which exhibit characteristics of fetal hepatocytes, were found to contain LPL mRNA, whereas the more differentiated human (Hep G2 and Hep 3B) or rat (Fa32) hepatoma cell lines did not. Somatic cell hybrids between LPL-producing hepatoma cells and non-LPL-producing cells, such as adult rat hepatocytes or fibroblasts, exhibited extinction of LPL gene expression. Assay of expression of nested deletions in the 5' regulatory sequences of the LPL gene in the Hep G2 cell line and in BWTG3 cells localized sequences involved in the suppression of LPL production to a region between -591 and -288 relative to the transcription initiation site. A site with sequence homology to a glucocorticoid responsive element (GRE) was shown not to play an important role in the extinction process. A novel transcription factor, termed RF-1-LPL, was shown to bind to an NF-1-like site in this region. In contrast to neonatal animals, in adult animals an additional protein complex (RF-2-LPL), was formed on the NF-1-like site, suggesting that this sequence might recruit a trans-acting factor involved in the extinction of LPL gene expression in adult rat liver.

Animals↗
PubMed1993

Abundant adrenal-specific transcription of the human P450c21A "pseudogene".

Human adrenal steroid 21-hydroxylase (P450c21) is encoded by the CYP21A1 (21B) gene located in the class III region of the HLA locus. A tandemly duplicated gene designated CYP21A1P (21A), which lies 30 kilobases upstream, contains several point mutations and an 8-base pair deletion so that it cannot encode P450c21 protein; as a result, it is generally considered to be a pseudogene. We previously showed that two additional genes, XA and XB, lie on the opposite strand of DNA overlapping the 3'-ends of the 21A and 21B genes. We have now identified a third pair of duplicated overlapping genes in this locus, termed YA and YB, whose transcriptional orientation is the same as 21A and 21B and opposite to XA and XB. YA transcripts use the 21A promoter, have 5'-ends that are similar to 21B mRNA, and have approximately 10-20% of the abundance of 21B transcripts, but have unique 3'-ends. The YA gene encodes a 7.5-kilobase RNA that overlaps XA completely and a 3.0-kilobase RNA that excludes most of XA. The YB gene appears to be similar in size and organization to YA. The YA and YB genes extend beyond the limit of the duplication in this locus; hence, their cDNAs are distinguishable by differences in their 3'-sequences. YA and YB transcripts are expressed only in the fetal and adult adrenal glands, but their cDNAs do not contain a long open reading frame. Although the function of these genes is not yet clear, the complex genetic organization of three overlapping genes (21/X/Y) appears to be unique among higher eukaryotes. As YA transcription is initiated by the 21A 5'-flanking DNA and includes 21A sequences, the designation of 21A as a "pseudogene" merits reconsideration.

Adrenal Glands↗
PubMed1993

Growth hormone normalizes hepatic lipase in hypothyroid rat liver.

The effects of growth hormone (GH) administration on hepatic lipase (HL) activity and mRNA levels were studied in pair-fed hypothyroid rats. In the hypothyroid state, liver HL mRNA levels and liver and postheparin plasma HL activities were decreased. In hypothyroid rats, GH normalized HL mRNA levels and HL activity in postheparin plasma; GH also increased the activity of HL in the liver, which remained lower than that in controls. These data indicate that at least part of the decrease of HL activity during hypothyroidism is due to the concomitant GH deficiency, and that GH rather than thyroid hormone may regulate HL mRNA levels.

Analysis of Variance↗