Promoter function of the human glucose-6-phosphate dehydrogenase gene depends on two GC boxes that are cell specifically controlled

Myostatin Deficiency Enhances Antioxidant Capacity of Bovine Muscle via the SMAD-AMPK-G6PD Pathway

During exercise, the body’s organs and skeletal muscles produce reactive oxygen species (ROS). Excessive ROS can destroy cellular lipids, sugars, proteins, and nucleotides and lead to cancer. The production of nicotinamide adenine dinucleotide phosphate (NADPH) by the pentose phosphate pathway (PPP) is an auxiliary process of the cellular antioxidant system that supplements the reducing power of glutathione (GSH) to eliminate ROS in the cell. Myostatin (MSTN) is mainly expressed in skeletal muscle and participates in the regulation of skeletal muscle growth and development. Loss of MSTN leads to muscular hypertrophy, and MSTN deficiency upregulates glycolysis. However, the effect of MSTN on the PPP has not been reported. This study investigated the effect of MSTN on muscle antioxidant capacity from a metabolic perspective. We found that reducing MSTN modulates AMP-activated protein kinase (AMPK), a key molecule in cellular energy metabolism that directly regulates glucose metabolism through phosphorylation. Downregulation of MSTN promotes tyrosine modification of glucose-6-phosphate-dehydrogenase (G6PD) by AMPK and is regulated by the Smad signaling pathway. The Smad2/3 complex acts as a transcription factor to inhibit the AMPK expression. These results suggest that reduced MSTN expression inhibits the Smad signaling pathway, promotes AMPK expression, enhances the activity of G6PD enzyme, and enhances the antioxidant capacity of nonenzymatic GSH.

Glucose-6-phosphate dehydrogenase deficiency

Glucose 6-phosphate dehydrogenase (G6PD) deficiency is 1 of the commonest human enzymopathies, caused by inherited mutations of the X-linked gene G6PD. G6PD deficiency makes red cells highly vulnerable to oxidative damage, and therefore susceptible to hemolysis. Over 200 G6PD mutations are known: approximately one-half are polymorphic and therefore common in various populations. Some 500 million persons with any of these mutations are mostly asymptomatic throughout their lifetime; however, any of them may develop acute and sometimes very severe hemolytic anemia when triggered by ingestion of fava beans, by any of a number of drugs (for example, primaquine, rasburicase), or, more rarely, by infection. Approximately one-half of the G6PD mutations are instead sporadic: rare patients with these mutations present with chronic nonspherocytic hemolytic anemia. Almost all G6PD mutations are missense mutations, causing amino acid replacements that entail deficiency of G6PD enzyme activity: they compromise the stability of the protein, the catalytic activity is decreased, or a combination of both mechanisms occurs. Thus, genotype-phenotype correlations have been reasonably well clarified in many cases. G6PD deficiency correlates remarkably, in its geographic distribution, with past/present malaria endemicity: indeed, it is a unique example of an X-linked human polymorphism balanced through protection of heterozygotes from malaria mortality. Acute hemolytic anemia can be managed effectively provided it is promptly diagnosed. Reliable diagnostic procedures are available, with point-of-care tests becoming increasingly important where primaquine and its recently introduced analog tafenoquine are required for the elimination of malaria.

Impaired inflammasome activation and bacterial clearance in G6PD deficiency due to defective NOX/p38 MAPK/AP-1 redox signaling

Glucose-6-phosphate dehydrogenase (G6PD) is the rate-limiting enzyme of the pentose phosphate pathway that modulates cellular redox homeostasis via the regeneration of NADPH. G6PD-deficient cells have a reduced ability to induce the innate immune response, thus increasing host susceptibility to pathogen infections. An important part of the immune response is the activation of the inflammasome. G6PD-deficient peripheral blood mononuclear cells (PBMCs) from patients and human monocytic (THP-1) cells were used as models to investigate whether G6PD modulates inflammasome activation. A decreased expression of IL-1β was observed in both G6PD-deficient PBMCs and PMA-primed G6PD-knockdown (G6PD-kd) THP-1 cells upon lipopolysaccharide (LPS)/adenosine triphosphate (ATP) or LPS/nigericin stimulation. The pro-IL-1β expression of THP-1 cells was decreased by G6PD knockdown at the transcriptional and translational levels in an investigation of the expression of the inflammasome subunits. The phosphorylation of p38 MAPK and downstream c-Fos expression were decreased upon G6PD knockdown, accompanied by decreased AP-1 translocation into the nucleus. Impaired inflammasome activation in G6PD-kd THP-1 cells was mediated by a decrease in the production of reactive oxygen species (ROS) by NOX signaling, while treatment with hydrogen peroxide (H₂O₂) enhanced inflammasome activation in G6PD-kd THP-1 cells. G6PD knockdown decreased Staphylococcus aureus and Escherichia coli clearance in G6PD-kd THP-1 cells and G6PD-deficient PBMCs following inflammasome activation. These findings support the notion that enhanced pathogen susceptibility in G6PD deficiency is, in part, due to an altered redox signaling, which adversely affects inflammasome activation and the bactericidal response.

LPS Down-Regulates Specificity Protein 1 Activity by Activating NF-κB Pathway in Endotoxemic Mice

Background

Specificity protein (Sp) 1 mediates the transcription of a large number of constitutive genes encoding physiological mediators. NF-κB mediates the expression of hundreds of inducible genes encoding pathological mediators. Crosstalk between Sp1 and NF-κB pathways could be pathophysiologically significant, but has not been studied. This study examined the crosstalk between the two pathways and defined the role of NF-κB signaling in LPS-induced down-regulation of Sp1 activity.

Methods and Main Findings

Challenge of wild type mice with samonelia enteritidis LPS (10 mg/kg, i.p.) down-regulated Sp1 binding activity in lungs in a time-dependent manner, which was concomitantly associated with an increased NF-κB activity. LPS down-regulates Sp1 activity by inducing an LPS inducible Sp1-degrading enzyme (LISPDE) activity, which selectively degrades Sp1 protein, resulting in Sp1 down-regulation. Blockade of NF-κB activation in mice deficient in NF-κB p50 gene (NF-κB-KO) suppressed LISPDE activity, prevented Sp1 protein degradation, and reversed the down-regulation of Sp1 DNA binding activity and eNOS expression (an indicator of Sp1 transactivation activity). Inhibition of LISPDE activity using a selective LISPDE inhibitor mimicked the effects of NF-κB blockade. Pretreatment of LPS-challenged WT mice with a selective LISPDE inhibitor increased nuclear Sp1 protein content, restored Sp1 DNA binding activity and reversed eNOS protein down-regulation in lungs. Enhancing tissue level of Sp1 activity by inhibiting NF-κB-mediated Sp1 down-regulation increased tissue level of IL-10 and decreased tissue level of TNF- αin the lungs.

Conclusions

NF-κB signaling mediates LPS-induced down-regulation of Sp1 activity. Activation of NF-κB pathway suppresses Sp1 activity and Sp1-mediated anti-inflammatory signals. Conversely, Sp1 signaling counter-regulates NF-κB-mediated inflammatory response. Crosstalk between NF-κB and Sp1 pathways regulates the balance between pro- and anti-inflammatory cytokines.

Transcriptional and epigenetic basis for restoration of G6PD enzymatic activity in human G6PD-deficient cells

HDAC inhibitors (HDACi) increase transcription of some genes through histone hyperacetylation. To test the hypothesis that HDACi-mediated enhanced transcription might be of therapeutic value for inherited enzyme deficiency disorders, we focused on the glycolytic and pentose phosphate pathways (GPPPs). We show that among the 16 genes of the GPPPs, HDACi selectively enhance transcription of glucose 6-phosphate dehydrogenase (G6PD). This requires enhanced recruitment of the generic transcription factor Sp1, with commensurate recruitment of histone acetyltransferases and deacetylases, increased histone acetylation, and polymerase II recruitment to G6PD. These G6PD-selective transcriptional and epigenetic events result in increased G6PD transcription and ultimately restored enzymatic activity in B cells and erythroid precursor cells from patients with G6PD deficiency, a disorder associated with acute or chronic hemolytic anemia. Therefore, restoration of enzymatic activity in G6PD-deficient nucleated cells is feasible through modulation of G6PD transcription. Our findings also suggest that clinical consequences of pathogenic missense mutations in proteins with enzymatic function can be overcome in some cases by enhancement of the transcriptional output of the affected gene.

Glucose-6-phosphate dehydrogenase deficiency

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common human enzyme defect, being present in more than 400 million people worldwide. The global distribution of this disorder is remarkably similar to that of malaria, lending support to the so-called malaria protection hypothesis. G6PD deficiency is an X-linked, hereditary genetic defect due to mutations in the G6PD gene, which cause functional variants with many biochemical and clinical phenotypes. About 140 mutations have been described: most are single base changes, leading to aminoacid substitutions. The most frequent clinical manifestations of G6PD deficiency are neonatal jaundice, and acute haemolytic anaemia, which is usually triggered by an exogenous agent. Some G6PD variants cause chronic haemolysis, leading to congenital non-spherocytic haemolytic anaemia. The most effective management of G6PD deficiency is to prevent haemolysis by avoiding oxidative stress. Screening programmes for the disorder are undertaken, depending on the prevalence of G6PD deficiency in a particular community.

Characterization of glucose-6-phosphate dehydrogenase deficiency and identification of a novel haplotype 487G>A/IVS5-612(G>C) in the Achang population of Southwestern China

The prevalence of glucose-6-phosphate dehydrogenase (G6PD) deficiency and its gene mutations were studied in the Achang population from Lianghe County in Southwestern China. We found that 7.31% (19 of 260) males and 4.35% (10 of 230) females had G6PD deficiency. The molecular analysis of G6PD gene exons 2-13 was performed by a PCR-DHPLC-Sequencing or PCR-Sequencing. Sixteen independent subjects with G6PD Mahidol (487G>A) and the new polymorphism IVS5-612 (G>C), which combined into a novel haplotype, were identified accounting for 84.2% (16/19). And 100% Achang G6PD Mahidol were linked to the IVS5-612 C. The percentage of G6PD Mahidol in the Achang group is close to that in the Myanmar population (91.3% 73/80), which implies that there are some gene flows between Achang and Myanmar populations. Interestingly, G6PD Canton (1376G>T) and G6PD Kaiping (1388G>A), which were the most common G6PD variants from other ethnic groups in China, were not found in this Achang group, suggesting that there are different G6PD mutation profiles in the Achang group and other ethnic groups in China. Our findings appear to be the first documented report on the G6PD genetics of the AChang people, which will provide important clues to the Achang ethnic group origin and will help prevention and treatment of malaria in this area.

Cloning, characterization and computational analysis of the 5' regulatory region of ovine glucose 6-phosphate dehydrogenase gene

To better understand the structure and the function of ovine glucose 6-phosphate dehydrogenase (G6PD) promoter region, a genome-walking procedure was followed to isolate and sequence a 1628 bp fragment, containing the 5' regulatory region of the G6PD gene. In silico analysis of the sequence showed many conserved blocks and features with other known mammalian G6PD promoter regions. The analysis also revealed the presence of one TATA box, three GC boxes, two E-boxes and several binding sites for Stimulating Protein 1 (Sp1) and Activator Protein 2 (AP2). Moreover, elements involved in the regulation of lipogenesis like USF (Upstream stimulating factor), HSF (Heat Shock Factor), F2F (Prolactin receptor), RAR (Retinoid Acid Receptor), STRE (STress Response Element), RORa (Retinoid related Orphan Receptor alpha), GATA (GATA binding factor), RFX (Regulatory Factor X), SREBP (Sterol Regulatory Element Binding Protein), MEP (Metal Element Protein), CREB (insulin receptor), PRE (Progesterone receptor), and HNF4 (Hepatic Nuclear Factor 4) were detected. The most important regulatory motifs were found to be conserved as compared to those in human and mouse counterparts. However, some differences were noted, likely indicating differences in the transcription regulation of G6PD gene between ruminant and non-ruminant species.

Enhancement of plasmacytoma cell growth by ascorbic acid is mediated via glucose 6-phosphate dehydrogenase

PURPOSE

We investigated the mechanism by which some types of cancer cells grow faster in the presence of ascorbic acid supplementation.

MATERIALS AND METHODS

Adj.PC-5, a mouse plasmacytoma cell, is known to show ascorbic acid-dependent growth and was chosen as a test system. The growth of cancer cells was measured by the colony number on soft agar or the cellular proliferation in suspension culture. The ascorbate level was measured by a high performance liquid chromatography system with an electrochemical detector. Glucose 6-phosphate dehydrogenase was analyzed both on the specific enzyme activity level and on the transcription level by performing Northern blot analysis.

RESULTS

Ascorbyl 2-phosphate among the ascorbate derivatives was the most efficient in stimulating cell growth. The intracellular and extracellular ascorbate concentrations following treatment with either ascorbate or ascorbyl 2-phosphate suggest that the superiority of ascorbyl 2-phosphate for stimulating cell growth may be due to its slow conversion to ascorbate in the culture medium. The steady transformation to ascorbate ensures sustained levels of ascorbate in the culture medium and thereby maximizes the growth stimulatory effect of ascorbate. Ascorbyl 2-phosphate markedly enhanced, in a concentration-and time-dependent manner, mRNA synthesis as well as the enzymatic activity of glucose 6-phosphate dehydrogenase, which is known to be a rate-limiting enzyme in cell growth. On the other hand, simultaneous addition of dehydroisoandrosterone, a well- known inhibitor of glucose 6-phosphate dehydrogenase, to the culture medium abrogated the growth stimulation by ascorbyl 2-phosphate, and it also reduced the glucose 6-phosphate dehydrogenase activity proportionately.

CONCLUSIONS

The results from this study suggest that enhanced glucose 6-phosphate dehydrogenase activity may at least in part explain the stimulation of cell growth by ascorbate or ascorbyl 2-phosphate.

Dietary regulation of expression of glucose-6-phosphate dehydrogenase

The family of enzymes involved in lipogenesis is a model system for understanding how a cell adapts to dietary energy in the form of carbohydrate versus energy in the form of triacylglycerol. Glucose-6-phosphate dehydrogenase (G6PD) is unique in this group of enzymes in that it participates in multiple metabolic pathways: reductive biosynthesis, including lipogenesis; protection from oxidative stress; and cellular growth. G6PD activity is enhanced by dietary carbohydrates and is inhibited by dietary polyunsaturated fats. These changes in G6PD activity are a consequence of changes in the expression of the G6PD gene. Nutrients can regulate the expression of genes at both transcriptional and posttranscriptional steps. Most lipogenic enzymes undergo large changes in the rate of gene transcription in response to dietary changes; however, G6PD is regulated at a step subsequent to transcription. This step is involved in the rate of synthesis of the mature mRNA in the nucleus, specifically regulation of the efficiency of splicing of the nascent G6PD transcript. Understanding the mechanisms by which nutrients alter nuclear posttranscriptional events will help uncover new information on the breadth of mechanisms involved in gene regulation.

Human-mouse comparative sequence analysis of the NEMO gene reveals an alternative promoter within the neighboring G6PD gene

NEMO (NFkappaB essential modulator) is a non-catalytic subunit of the cytokine-dependent IkappaB kinase complex that is involved in activation of the transcription factor NFkappaB. The human NEMO gene maps to Xq28 and is arranged head to head with the proximal G6PD gene. Mutations in NEMO have recently been associated with Incontinentia Pigmenti (Smahi et al., Nature 405 (2000) 466), an X-linked dominant disorder. Three alternative transcripts with different non-coding 5' exons (1a, 1b and 1c) of NEMO have been described. In order to identify regulatory elements that control alternative transcription we have established the complete genomic sequence of the murine orthologs Nemo and G6pdx. Sequence comparison suggests the presence of two alternative promoters for NEMO/Nemo. First, a CpG island is shared by both genes driving expression of the NEMO/Nemo transcripts containing exons 1b and 1c in one direction and the housekeeping gene G6PD/G6pdx in the opposite direction. In contrast to human, an additional variant of exon 1c, named 1c+, was identified in several tissues of the mouse. This larger exon utilizes an alternative donor site located 1594 bp within intron 1c. The putative second promoter for NEMO/Nemo transcripts starting with exon 1a is unidirectional, and not associated with a CpG island. Surprisingly, this promoter is located in the second intron of G6PD/G6pdx. It shows very low basal activity and may be involved in stress/time- and/or tissue-dependent expression of NEMO. To our knowledge, an overlapping gene order similar to the G6PD/NEMO complex has not been described before.

Glucose 6-phosphate dehydrogenase expression is less prone to variegation when driven by its own promoter

The ability to transfer permanently genes into mammalian cells makes retroviruses suitable vectors for the ultimate purpose of treating inherited genetic disease. However, expression of the retrovirally transferred genes is variable (position effect and expression variegation) because retroviruses are highly susceptible to the influence of the host genome sequences which flank the integration site. We have investigated this phenomenon with respect to the human housekeeping enzyme, glucose 6-phosphate dehydrogenase (hG6PD). We have constructed retroviral vectors in which the hG6PD cDNA is driven by either of two conventional retroviral promoters and enhancers from the Moloney Murine Leukemia Virus (MMLV) and the Myeloproliferative Sarcoma Virus (MPSV) long terminal repeats (LTR) or by the hG6PD own promoter replacing most of enhancer and promoter LTR (GRU5). We have compared the activity of retrovirally transferred hG6PD driven by these promoters after retroviral integration in bulk cultures and in individual clones of murine fibroblasts. The level of hG6PD expressed by the hG6PD promoter of GRU5-G6PD was significantly lower than that expressed by conventional retroviral vectors. However, analysis of the single copy clones showed less variation of expression with GRU5-G6PD (coefficient of variation, CV, 35.5%) than with conventional vectors (CV, 58.9%). Thus we have several vectors competent for reliable transfer and expression of hG6PD. The hG6PD promoter provides reproducible expression of hG6PD and limits the variability of expression. This decreased variability is important in order to help ensuring a consistent level of delivery of the needed gene product in future therapeutic protocols.

Nutritional and insulin regulation of leptin gene expression

The leptin and lipogenic enzyme genes contain the common DNA sequences of binding sites for Sp1 proteins. These sites appear to be responsible for glucose/insulin stimulation and polyunsaturated fatty acid suppression. In rat adipose tissue leptin and lipogenic gene expression is similarly regulated by nutritional manipulation. Interestingly, leptin has the ability to down-regulate lipogenic enzyme expression.

Human mutations in glucose 6-phosphate dehydrogenase reflect evolutionary history

Glucose 6-phosphate dehydrogenase (G6PD) is a cytosolic enzyme encoded by a housekeeping X-linked gene whose main function is to produce NADPH, a key electron donor in the defense against oxidizing agents and in reductive biosynthetic reactions. Inherited G6PD deficiency is associated with either episodic hemolytic anemia (triggered by fava beans or other agents) or life-long hemolytic anemia. We show here that an evolutionary analysis is a key to understanding the biology of a housekeeping gene. From the alignment of the amino acid (aa) sequence of 52 glucose 6-phosphate dehydrogenase (G6PD) species from 42 different organisms, we found a striking correlation between the aa replacements that cause G6PD deficiency in humans and the sequence conservation of G6PD: two-thirds of such replacements are in highly and moderately conserved (50-99%) aa; relatively few are in fully conserved aa (where they might be lethal) or in poorly conserved aa, where presumably they simply would not cause G6PD deficiency. This is consistent with the notion that all human mutants have residual enzyme activity and that null mutations are lethal at some stage of development. Comparing the distribution of mutations in a human housekeeping gene with evolutionary conservation is a useful tool for pinpointing amino acid residues important for the stability or the function of the corresponding protein. In view of the current explosive increase in full genome sequencing projects, this tool will become rapidly available for numerous other genes.

Interleukin-9 Regulates NF-κB Activity Through BCL3 Gene Induction

BCL3 encodes a protein with close homology to IκB proteins and interacts with p50 NF-κB homodimers. However, the regulation and transcriptional activity of BCL3 remain ill-defined. We observed here that interleukin-9 (IL-9) and IL-4, but not IL-2 or IL-3, transcriptionally upregulated BCL3 expression in T cells and mast cells. BCL3 induction by IL-9 was detected as soon as 4 hours after stimulation and appeared to be dependent on the Jak/STAT pathway. IL-9 stimulation was associated with an increase in p50 homodimers DNA binding activity, which was mimicked by stableBCL3 expression. This contrasts with tumor necrosis factor (TNF)-dependent NF-κB activation, which occurs earlier, involves p65/p50 dimers, and is dependent on IκB degradation. Moreover, IL-9 stimulation or BCL3 transient transfection similarly inhibited NF-κB–mediated transcription in response to TNF. Taken together, our observations show a new regulatory pathway for the NF-κB transcription factors through STAT-dependent upregulation ofBCL3 gene expression.

Interleukin-9 Regulates NF-κB Activity Through BCL3 Gene Induction

BCL3 encodes a protein with close homology to IκB proteins and interacts with p50 NF-κB homodimers. However, the regulation and transcriptional activity of BCL3 remain ill-defined. We observed here that interleukin-9 (IL-9) and IL-4, but not IL-2 or IL-3, transcriptionally upregulated BCL3 expression in T cells and mast cells. BCL3 induction by IL-9 was detected as soon as 4 hours after stimulation and appeared to be dependent on the Jak/STAT pathway. IL-9 stimulation was associated with an increase in p50 homodimers DNA binding activity, which was mimicked by stableBCL3 expression. This contrasts with tumor necrosis factor (TNF)-dependent NF-κB activation, which occurs earlier, involves p65/p50 dimers, and is dependent on IκB degradation. Moreover, IL-9 stimulation or BCL3 transient transfection similarly inhibited NF-κB–mediated transcription in response to TNF. Taken together, our observations show a new regulatory pathway for the NF-κB transcription factors through STAT-dependent upregulation ofBCL3 gene expression.

Molecular anatomy of the human glucose 6-phosphate dehydrogenase core promoter

The gene encoding glucose 6-phosphate dehydrogenase (G6PD), which plays a pivotal role in cell defense against oxidative stress, is ubiquitously expressed at widely different levels in various tissues; moreover, G6PD expression is regulated by a number of stimuli. In this study we have analyzed the molecular anatomy of the G6PD core promoter. Our results indicate that the G6PD promoter is more complex than previously assumed; G6PD expression is under the control of several elements that are all required for correct promoter functioning and, furthermore, a still unidentified mammalian specific factor is needed.

Regulation of mouse Ah receptor (Ahr) gene basal expression by members of the Sp family of transcription factors

The aromatic hydrocarbon receptor (AHR) is a ligand-activated transcription factor that regulates the expression of several drug-metabolizing enzymes and has been implicated in immunosuppression, teratogenesis, cell-specific hyperplasia, and certain types of malignancies and toxicities. The mouse Ahr gene 5' proximal promoter region, which contains four potential Sp1 motifs, is required for efficient basal expression. Using a fragment spanning the region from nt -174 to +70 of the Ahr promoter, we found that four regions corresponding to four Sp1 sites were protected from DNase I digestion using nuclear extracts from MLE-12 (lung), F9 (embryonal carcinoma), Hepa-1 (hepatoma), and 41-5a (epidermal) cells. The Hepa-1 and F9 cell lines were shown by reverse transcriptase-polymerase chain reaction and Western blot to contain mRNA and protein for Sp1 and Sp3, but not Sp2 and Sp4. In electrophoretic mobility shift assays using oligonucleotide probes corresponding to the four Ahr Sp1 sites, nuclear extracts from Hepa-1 and F9 cells formed complexes that were determined immunologically to contain both Sp1 and Sp3 protein. The two Ahr proximal Sp1 sites (A and B) were shown to bind both Sp1 and Sp3 proteins, whereas the more distal sites (C and D) bound only Sp1. Competition gel shift experiments showed that sites A and B had 10-fold higher affinity for Sp factors than did sites C and D. To determine the transactivation potential of each of the four Ahr Sp1 sites, we fused the Ahr promoter to a luciferase (LUC) reporter gene and transfected the construct into the Drosophila cell line Schneider-2, which contains no Sp1 or Sp1-like factors. Cotransfection of this construct with expression plasmids for each of the Sp factors revealed that Sp3 was approximately 1.6-fold more efficient than Sp1 in Ahr transactivation. Mutation of the four Sp1 sites individually and in combination demonstrated that each site contributes to the overall level of expression of the reporter gene and that interactions between these sites play a minor role in regulation of the Ahr-LUC construct. These results suggest that basal Ahr expression may be regulated by the expression and distribution of Sp1-like factors.

Structural characterization and tissue-specific expression of the mouse glucose-6-phosphate dehydrogenase gene

Glucose-6-phosphate dehydrogenase (G6PD) activity differs among tissues and, in liver, with the dietary state of the mouse. Tissue-specific differences in G6PD activity in adipose tissue, liver, kidney, and heart were associated with similar differences in the amount of G6PD mRNA. Regulation of mRNA amount by dietary fat was only observed in liver. In mice fed a low-fat diet, the relative amounts of G6PD mRNA were 3:1:1:0.38, respectively, in the four tissues. Further, the amount of precursor mRNA for G6PD in liver, kidney, and heart reflected the amount of mature mRNA in these tissues, suggesting differing transcriptional activity. Our S1 nuclease and primer-extension analyses indicated that the same transcriptional start site is used in liver, kidney, and adipose tissue, resulting in a common 5' end of the mRNA in these tissues. Thus, differential regulation is not attributable to alternate promoter usage. A DNase hypersensitivity analysis of the 5' end of the G6PD gene identified three hypersensitive sites (HS): HS 1 and HS 2 were present in all tissues, whereas HS 3 was liver specific. Thus, regulation of G6PD expression involves both dietary and tissue-specific signals that appear to act via different mechanisms.

Structure of the rat methionine adenosyltransferase 2A gene and its promoter

In this study, to understand the regulation of methionine adenosyltransferase (MAT) gene expression, we isolated the rat MAT2A gene encoding MAT alpha2, the catalytic subunit of non-hepatic-type enzyme MAT II and characterized its structural organization and 5'-flanking region. The gene spans approximately 7 kbp and consists of nine exons interrupted by eight introns. The transcription initiation site, as demonstrated by primer extension analysis, is located 123 bp upstream of the translation start codon. Comparison of the structural organization of the rat MAT2A gene to that of the mouse MAT1A gene encoding MAT alpha1, the subunit of liver-type enzymes MAT I and III, shows that the exon structure of two genes is very similar and the insertion sites of all corresponding introns are identical. A canonical TATA box and a GC box, the potential Sp1-binding site, are found 32 bp and 70 bp upstream of the transcription initiation site, respectively. The 5'-flanking region also contains potential recognition sites for various transcription factors including AP-1, AP-2 and NF-IL6 (C/EBPbeta), and a large G+C-rich domain with the characteristics of a CpG island. The 5'-flanking sequence of the rat MAT2A gene has no significant similarity with those of the MAT1A genes. Transient transfection experiments using a luciferase reporter gene showed that the first 820-bp sequence of the 5'-flanking region directed high levels of luciferase activity in cultured rat kidney fibroblast (NRK-49F) and hepatocellular carcinoma (FAA-HTC1) cells, but not in primary rat hepatocytes. Deletion analysis suggested that the first 343 bp of the 5'-flanking region contained cell-type-specific promoter elements of this gene.

Transcription of DmRP140, the gene coding for the second-largest subunit of RNA polymerase II

To analyze transcriptional control regions of Drosophila melanogaster housekeeping genes, we have characterized the promoter of the gene coding for the second-largest subunit of RNA polymerase II (DmRP140). Upstream of DmRP140 the genomic region harbors a gene which is transcribed in the opposite direction (DmRP140up). By determination of the transcription start sites of both genes we found a short non-transcribed intergenic region of 220 bp. Functional analysis of various promoter reportergene constructs by transient transfection of cultured cells revealed that sequences important for transcription of DmRP140 are located in the untranslated leader of the upstream gene. The onset of DmRP140 transcription during embryonic development was studied in transgenic flies using beta-galactosidase as reportergene. To distinguish between the maternally provided DmRP140 transcripts and the embryonically transcribed RNA the offspring of nontransformed females and male transformants was examined. The development of a sensitive detection assay based on a chemiluminescent substrate for beta-galactosidase allowed us to determine the onset of DmRP140 transcription to between 8-10 h after oviposition. Thus, DmRP140 transcription does not start following the transcriptional transition period between 2-3 h of development but occurs much later in embryogenesis coinciding with decreasing DNA synthesis and cell division rates.

High-level regulated expression of the human G6PD gene in transgenic mice

The glucose-6-phosphate dehydrogenase-encoding gene (G6PD) belongs to a group with constitutive expression in all tissues. The regulation of these housekeeping genes is poorly understood, as compared to what is known about many genes whose expression is restricted to a particular tissue or stage of development, and which are often regulated by locus control regions (LCR) able to act over wide distances. In order to identify sequences in human G6PD which are necessary for its expression, we have generated transgenic mice carrying a 20-kb G6PD construct, including only 2.5 kb of upstream and 2.0 kb of downstream flanking sequence. All mice which carried the transgene (TG) expressed it, and the levels of expression detected in a range of tissues from three independent lines of mice were comparable to that of the endogenous murine G6PD. The variation in enzyme activity from tissue to tissue was remarkably similar for both the TG and the endogenous gene, and was shown to be due in both cases to variations in the steady-state mRNA levels.