Effect of peroxisome proliferator-activated receptor alpha on human angiotensinogen promoter

The renin-angiotensin system plays a key role in the regulation of blood pressure. Angiotensinogen (ANG), mainly synthesized in the liver, is the first substrate of renin-angiotensin system. We had previously found that hepatocyte nuclear factor 4 (HNF-4) dramatically activates the human ANG promoter. It is generally known that HNF-4 and peroxisome proliferator-activated receptor alpha (PPARalpha) bind to response elements composed of two core motifs, RG(G/T)TCA, or a closely related sequence separated by 1 nucleotide (DR1 element). To examine whether or not PPARalpha activates the human ANG promoter, we used the reporter gene containing the sequence from -1222 to +44 of the human ANG gene promoter. PPARalpha and RXR heterodimer activated this promoter, and the PPARalpha responsive region was the same site that we had previously mapped as a binding site for HNF-4. Although the human ANG promoter was not induced by PPARalpha ligand bezafibrate in HepG2 cells, this reporter gene was inducible by bezafibrate treatment in HeLa cells, which do not express endogenous HNF-4. We suspected that the high level expression of HNF-4 in HepG2 cells might interfere with the effect of bezafibrate on the human ANG promoter. To confirm this model, we cotransfected HNF-4 expression vector with PPARalpha expression vector into HeLa cells. The bezafibrate-dependent activation of the ANG promoter was inhibited by HNF-4. These results suggest that PPARalpha and HNF-4 competitively affect the human ANG promoter through the C region.     

Localisation of the gene for glycogen storage disease type 1c by homozygosity mapping to 11q.

The microsomal glucose-6-phosphatase (G6Pase) complex regulates the final step in glucose production from glycogenolysis and gluconeogenesis. Glycogen storage disease type 1c (GSD-1c) results from deficient activity of the phosphate/ pyrophosphate transporter of this complex and is associated with neutropenia as well as hepatomegaly and hypoglycaemia. Using three affected subjects from a single highly consanguineous family, we have used homozygosity mapping to localise the gene responsible for GSD-1c to a 10.2 cM region on 11q23.3-24.2. The maximum lod score was 3.12. GSD-1c is therefore distinct from GSD-1a, which has been shown previously to be caused by mutations in the G6Pase gene on chromosome 17.     

Mutation analysis of NR0B2 among 1545 Danish men identifies a novel c.278G>A (p.G93D) variant with reduced functional activity

Variations of the small heterodimer partner (SHP, NR0B2) gene, an atypical nuclear receptor that inhibits transactivation by hepatocyte nuclear factor (HNF)-4alpha, are associated with obesity among Japanese. The purpose of the study was to evaluate the prevalence of SHP variants among obese Danish men. Using combined SSCP and heteroduplex analysis, we analyzed the entire coding region of SHP for variants in a cohort of 750 Danish men with early-onset obesity and genotyped a cohort of 795 nonobese control subjects using PCR-RFLP. Functional analyses of the identified coding region variants were performed in both MIN6-m9 and HepG2 cell lines. A total of five novel variants, including three missense variants (c.100C>G [p.R34G], c.278G>A [p.G93D], and c.415C>A [p.P139H]) and two silent variants (c.65C>T [p.Y22Y] and c.339G>A [p.P113P]) were identified. Moreover, the previously reported c.512G>C [p.G171A] polymorphism was identified. The 171A allele was not associated with obesity (p = 0.07). The 34G, 93D, and 139H-alleles were rare variants, which were found only among obese subjects. Among the four coding region variants, the 93D-allele showed a reduced in vitro inhibition of the HNF-4alpha transactivation of the HNF-1alpha promoter expression when expressed in MIN6-m9 and HepG2 cell lines (p<0.01). In contrast to reported findings among obese Japanese, functional variants are rare among Danish men. A functional 93D variant of SHP was identified in 1 out of 750 obese and in none of 795 nonobese control subjects. Further large-scale population studies are necessary to assess the clinical impact of this rare variant on obesity risk among European subjects.     

Novel alleles at the lymphotoxin alpha (LTalpha) locus mark extended HLA haplotypes in native Africans

Genetic variations at the closely related tumor necrosis factor alpha (TNFalpha or TNF) and lymphotoxin alpha (LTalpha, formerly TNFbeta) loci have been well documented in various human populations, and several haplotypes spanning the MHC class I and class II loci are known to carry specific TNF alleles. Genotyping of the TNFc microsatellite within the first intron of LTalpha in 285 Rwandans and 319 Zambians revealed two predominant alleles, c1 at frequencies of 0.598 and 0.683 and c2 at 0.384 and 0.307, respectively. Overall, the distribution of TNFc genotypes containing the major alleles conformed well to the Hardy-Weinberg equilibrium in both cohorts. Two previously unrecognized minor TNFc alleles were also detected: the first, designated c0, was found in 10 native Africans and was the only allele present in 10 chimpanzees; the second, designated c3, was seen in 6 other African patients. Further genotyping at loci for HLA class I, class II, and for transporters associated with antigen processing, subunit 1 (TAP1) in those 16 individuals suggested a tight, stable extended haplotype involving c0 and 26Asn (LTalpha)-TNF3 (TNF promoter -238A and -308G)-DRB1*1503-DQB1*0602-TAP1.2 (333Val)-TAP1.4 (637Gly). The c3 allele was observed on another extended haplotype with 26Thr (LTalpha)-TNF1 (TNF promoter -238G and -308G)-DQB1*0102-DQB1*0501-TAP1*0101 (333Ile and 637Asp). The c3-tagged haplotype further extended to Cw*15 at the HLA class I C locus, but no specific A or B alleles could be unambiguously assigned. Positive associations between c2 homozygosity and HIV-1 seronegative status in both Rwandans and Zambians (odds ratio = 2.03 and 2.00, p = 0.04 and 0.07, respectively) had little effect on the haplotype assignments. These findings suggest a preferential expansion of the human TNFc dinucleotide (CT/AG) repeat sequence and further imply the existence of two extended MHC lineages that have not been disrupted by recombinations.     

High glucose-6-phosphatase activity in osteoblasts in the metaphysis of femur of growing rats

Glucose-6-phosphatase (G6Pase) activity was examined cytochemically in the metaphysis of femurs of 3- and 7-day-old rats. G6Pase and hexokinase activities were also examined biochemically in the femur and tibia of 3-day-old animals. The reaction product for G6Pase activity was seen in the endoplasmic reticulum and nuclear envelope of all cell types composing the metaphysis. The amount of the reaction product was abundant in osteoblasts, moderate in osteocytes, and moderate to scarce in osteoclasts and capillary endothelial cells. Biochemical G6Pase activity in the bones was higher than that in the brain, submandibular gland, or pancreas of the animals. Hexokinase activity in the bones was not different from that in the submandibular gland, pancreas, or kidney. The activity ratio of G6Pase and hexokinase in the bones (0.603) was greater than that in the submandibular gland, pancreas, or brain and smaller than that in the kidney. Possible physiological significances of the higher G6Pase activity in osteoblasts are discussed.     

Serum and hepatic enzyme activity in rats treated with diethylnitrosamine

Comparative studies of enzyme activities during the dedifferentiation of hepatic cells and through their development into overt hepatomas are few and contradictory. This study was designed to investigate the histochemical, biochemical and morphologic features of the altered liver cells with particular emphasis on the importance and validity of the histoenzymatic behavior of glucose-6-phosphatase (G6Pase) as a marker for the detection of precancerous hepatic cells. Serum and hepatic levels of G6Pase were analyzed and compared with the histoenzymatic behavior of this enzyme. The use of other enzymes, such as adenosine triphosphatase (ATPase) and gamma glutamyl-transpeptidase (GGT) as histochemical markers for malignancy was also tested. The activities of a variety of enzymes commonly used as diagnostic tools were also evaluated in both the liver homogenates and sera of rats treated with 2 mg diethylnitrosamine (DENA)/kg body weight for 2-28 weeks. Using G6Pase as a histoenzymatic marker, precancerous cells appeared after 4 weeks of exposure to DENA in the form of small islets devoid of G6Pase activity. These G6Pase free cells increased in number forming larger islands and finally appeared as tumor nodules after 28 weeks of treatment. The histoenzymatic behavior of ATPase was identical to that of G6Pase. The precancerous cells, as well as the tumor cells appeared devoid of ATPase activity. The application of GGT as a marker, showed significantly increased activity in the altered liver and tumor cells. Increased serum levels of G6Pase were noted after 10 weeks and were greatly elevated in the late stages of the evolution of the precancerous cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cytochemical and biochemical glucose 6-phosphatase activity in skeletal muscle cells of mice

Cytochemical and biochemical glucose 6-phosphatase (G6Pase) activity and fiber type composition were studied in soleus (SOL) and gastrocnemius (GC) muscles of mice. The SOL is a red muscle which contains numerous type I fibers (60%) and relatively few type II fibers (40%). The GC is a white muscle which contains numerous type II fibers (90-100%) and very few type I fibers (0-10%). In the SOL and GC, cytochemical G6Pase activity was localized in the sarcoplasmic reticulum, lateral elements of triads, myonuclear envelope, and in the endoplasmic reticulum and nuclear envelope of endothelial cells. Differential centrifugation showed that G6Pase activity was recovered in the 105,000g pellet (microsomal fraction). Histochemical enzyme activity in type II fibers was slightly higher than that in type I fibers. Biochemical G6Pase activity in the GC was significantly higher than that in the SOL. The possible functional significance of G6Pase in skeletal muscles was discussed.     

Comparative genomics on Wnt3-Wnt9b gene cluster

WNT signals, transduced through Frizzled (FZD) receptors with extracellular WNT-binding domain and cytoplasmic Dishevelled-binding domain, are implicated in carcinogenesis and embryogenesis. WNT3-WNT9B (WNT14B) locus (17q21.31) and WNT3A-WNT9A (WNT14) locus (1q42.13) are paralogous regions within the human genome. Here, the rat Wnt3 and Wnt9b genes were identified and characterized by using bioinformatics. Wnt3 and Wnt9b genes at rat chromosome 10q32.1 were clustered in head-to-head manner with an interval of about 24 kb within AC105632.3 genome sequence. The rat Wnt3 gene, consisting of five exons, encoded a 355-aa protein with N-terminal signal peptide, 24 conserved Cys residues and two Asn-linked glycosylation sites. The rat Wnt9b gene, consisting of four exons, encoded a 359-aa protein with N-terminal signal peptide, 24 conserved Cys residues and one Asn-linked glycosylation site. The rat Wnt3 core promoter showed 80.5% nucleotide identity with human WNT3 core promoter, while rat Wnt9b core promoter showed 45.6% nucleotide identity with human WNT9B core promoter. MYB (c-Myb), ELK1, POU2F1 (OCT1), HNF4A (HNF-4), COMP1, NFYA (NF-Y) and NKX2-5 binding sites were conserved between rat Wnt3 and human WNT3 core promoters. The Wnt3-Wnt9b intergenic conserved region (IGCR), corresponding to nucleotide position 124747-125252 of AC105632.3 genome sequence, showed 85.6% nucleotide identity with human WNT3-WNT9B IGCR. GC content of rat Wnt3-Wnt9b IGCR was 59.5%. Wnt3-Wnt9b IGCR was predicted as regulatory element rather than gene because cDNA or EST derived from Wnt3-Wnt9b IGCR was not identified. This is the first report on the rat Wnt3 and Wnt9b genes as well as on comparative genomics on the Wnt3-Wnt9b gene cluster.     

Molecular genetics of type 1 glycogen storage disease

Glycogen storage disease type 1 (GSD 1) comprises a group of autosomal recessive inherited metabolic disorders caused by deficiency of the microsomal multicomponent glucose-6-phosphatase system. Of the two known transmembrane proteins of the system, malfunction of the catalytic subunit (G6Pase) characterizes GSD 1a. GSD 1 non-a is characterized by defective microsomal glucose-6-phosphate or pyrophosphate/phosphate transport due to mutations in G6PT (glucose-6-phosphate translocase gene) encoding a microsomal transporter protein. Mutations in G6Pase and G6PT account for approximately 80 and approximately 20% of GSD 1 cases, respectively. G6Pase and G6PT work in concert to maintain glucose homeostasis in gluconeogenic organs. Whereas G6Pase is exclusively expressed in gluconeogenic cells, G6PT is ubiquitously expressed and its deficiency generally causes a more severe phenotype. Rapid confirmation of clinically suspected diagnosis of GSD 1, reliable carrier testing, and prenatal diagnosis are facilitated by mutation analyses of the chromosome 11-bound G6PT gene as well as the chromosome 17-bound G6Pase gene.     

Demonstration of glucose-6-phosphatase and peroxisomal catalase activity by ultrastructural cytochemistry in oval cells from livers of carcinogen-treated rats.

Oval cells isolated from livers of carcinogen-treated rats have morphologic and biochemical features of immature hepatocytes but seem to lack glucose-6-phosphatase (G6Pase) activity. The authors reinvestigated this question using histochemical methods for visualization of G6Pase activity by light and electron microscopy and the polyene antibiotic filipin to facilitate the penetration of the substrate. Oval cells that proliferate in the liver of animals receiving a carcinogenic diet (choline-deficient, containing 0.05% ethionine) contained G6Pase activity; 50-60% of nonparenchymal epithelial cells isolated from these livers by centrifugal elutriation contained G6Pase activity; and oval cell cultures displayed intense G6Pase activity at confluence but did not have detectable enzyme activity during exponential growth. These results and the demonstration that clofibrate induces peroxisomal proliferation in cultured oval cells strengthen the view that oval cells (or some subpopulation of cells in this compartment) are part of the hepatocyte lineage.     

Significance of increase in glucose 6-phosphatase activity in brown adipose cells of cold-exposed and starved mice

Cytochemical and biochemical glucose 6-phosphatase (G6Pase) activity was examined in brown adipose tissues of normal, cold-exposed, or starved mice. In addition, G6Pase activity in white adipose tissue and hexokinase activity in brown and white adipose tissues were biochemically measured. In normal animals, the reaction product for G6Pase activity was localized in the endoplasmic reticulum and nuclear envelope of brown adipose cells. The amount of the reaction product increased in cold-exposed or starved animals. Biochemical G6Pase activity (259.7 +/- 48.5 ng Pi/min/mg protein) in brown adipose tissues of normal animals was higher when the value was compared with values of other organs. Biochemical G6Pase and hexokinase activities increased rapidly in brown adipose tissues of cold-exposed animals, and a close relation was found between activities of the two enzymes. In brown adipose tissues of animals starved for 3 days, biochemical G6Pase activity increased, but hexokinase activity did not change. In white adipose tissues of normal, cold-exposed, or starved animals, G6Pase activity was very low, although the enzyme activity increased slightly in animals starved for 3 days. The results show that the high G6Pase activity in brown adipose cells probably relates to thermogenesis in cold-exposed animals and may be concerned with glucose release into the blood in starved animals.     

Metformin-induced suppression of glucose-6-phosphatase expression is independent of insulin signaling in rat hepatoma cells

Metformin is thought to decrease blood glucose levels by reducing hepatic glucose output. To elucidate the pharmacological action of metformin on hepatic glucose production, we examined its effect on the gene expression of glucose-6-phosphatase (G6Pase), a key enzyme of gluconeogenesis, in H4IIE rat hepatoma cell line by RT-PCR and quantitative real-time PCR. Metformin suppressed dexamethasone/cAMP-induced expression of G6Pase mRNA in a dose dependent manner, its maximum effect being observed at 2 mM (79.3% inhibition, P<0.05). Pretreatment with the PI3-kinase inhibitor wortmannin, the MEK-1 inhibitor PD98059 or the protein kinase C inhibitor GF109203X had no effect on suppressed G6Pase expression by metformin. Moreover, metformin did not stimulate Akt phosphorylation. In the present study, we demonstrate that metformin suppresses G6Pase mRNA expression by a mechanism that is independent of the activation of PI3-kinase, Akt, MAP kinase and protein kinase C pathway in hepatocytes.     

An HLA-DRB α-helix motif shared by DR11 and DR8 alleles is implicated in the pluriallelic restriction of peptide-specific T-cell lines

The T-cell recognition of HLA-DR-peptide complexes is generally restricted by the polymorphism of the DRB molecules but pluriallelic restriction has been described. The molecular basis of restriction and promiscuity of such peptide-specific responses is poorly understood. We isolated a panel of T-cell lines specific for the tetanus toxin peptide p2 (TT830-843) exhibiting pluriallelic restriction by DR11 and DR8 alleles. Fine restriction specificity of the T-cell lines was examined in functional assays against DR oligotyped APCs expressing different variants of DR11 and DR8 alleles. Our results show that (a) polymorphisms between serologically related alleles are relevant in terms of restriction of the peptide-specific T-cell response; in some instances, a single amino acid substitution can determine the restriction of a T-cell line; (b) different patterns of restriction are not the result of specific differences in DR-p2 binding as p2 peptide binds to all DR11 and DR8 alleles tested (DRB1^* 1101, -1102, -1103, -1104, 110X, -0801, -0802, -0803, and -0806); and (c) pluriallelic restriction of the peptide-specific T-cell responses correlates with the presence of a DRB1 α-helix motif (67-71-86) shared by some DR11 and DR8 alleles. Possible implications of pluriallelic restriction of peptide-specific T-cell response in autoimmune disorders associated with DR11 and DR8 are discussed.