Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:4.1.1.32 (phosphoenolpyruvate carboxykinase)
 4,204 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

New hepatocyte-like cell lines (mhAT) were derived from the liver of a transgenic mouse expressing SV40 early genes under the direction of the liver-specific antithrombin III gene promoter (ATIII-TSV40). Their differentiated phenotypes were improved and stabilized by the use of liver-specific growth media (arginine-free, glucose-free, or low-fructose/glucose-free medium). The best differentiated lines display a very high level of albumin, transferrin, and L-type pyruvate kinase (L-PK) gene expression that is comparable to that observed in the mouse liver. Abundance of the aldolase B and phosphoenolpyruvate carboxykinase (PEPCK) transcripts varied from 5 to 35% of the in vivo concentrations while abundance of the alpha-fetoprotein and phenylalanine hydroxylase transcripts remained very low. Hormonal (cAMP and insulin) and nutritional (glucose) gene controls of PEPCK and L-PK were, at least partially, conserved. mhAT cells are readily transfectable by the calcium phosphate coprecipitation technique and exhibit a liver-specific pattern of expression of exogenous genes. Thus, mhAT cells seem suitable for the analysis of the regulatory regions involved in the tissue-specific transcription of genes. This work demonstrates, therefore, the great efficiency of targeted carcinogenesis in transgenic mice to create new differentiated cell lines. The availability of various lines of liver-specific cells with different phenotypes will constitute useful tools to establish correlations between expression of trans-acting factors and control of the phenotype.
 ...
PMID:Gene expression in hepatocyte-like lines established by targeted carcinogenesis in transgenic mice. 137 87

Ochratoxin A has a number of toxic effects in mammals, the most notable of which is nephrotoxicity. It is also immunosuppressive, teratogenic and carcinogenic. The biochemical and molecular aspects of its action were first studied in bacteria. The appearance of 'magic spots' (ppGpp and pppGpp) pointed to inhibition of the charging of transfer ribonucleic acids (tRNA) with amino acids. This suggestion was confirmed by the demonstration that ochratoxin A inhibits bacterial, yeast and liver phenylalanyl-tRNA synthetases. The inhibition is competitive to phenylalanine and is reversed by an excess of this amino acid. As a consequence, protein synthesis is inhibited, as shown with hepatoma cells in culture, with Madin Darby canine kidney cells (which are much more sensitive) and in vivo in mouse liver, kidney and spleen, the inhibition being more effective in the latter two organs. An excess of phenylalanine also prevents inhibition of protein synthesis in cell cultures and in vivo. Analogues of ochratoxin A in which phenylalanine has been replaced by other amino acids have similar inhibitory effects on the respective amino acid-specific aminoacyl tRNA synthetases. 4R-Hydroxyochratoxin A, a metabolite of ochratoxin A, has a similar action, whereas ochratoxin alpha (the dihydroisocoumarin moiety) and ochratoxin B (ochratoxin A without chlorine) have no effect. Ochratoxin A might act on other enzymes that use phenylalanine as a substrate. We showed recently that it inhibits phenylalanine hydroxylase. In addition, the phenylalanine moiety of ochratoxin A is partially hydroxylated to tyrosine by incubation with hepatocytes and in vivo. This competitive action with phenylalanine might explain why this amino acid prevents the immuno-suppressive effect of ochratoxin A and partially prevents its teratogenic and nephrotoxic actions. The effect of ochratoxin A on protein synthesis is followed by an inhibition of RNA synthesis, which might affect proteins with a high turnover. Ochratoxin A also lowers the level of phosphoenolpyruvate carboxykinase, a key enzyme in gluconeogenesis; this inhibition is reported to be due to a specific degradation of mRNA that codes for this enzyme. Recently, ochratoxin A was also found to enhance lipid peroxidation both in vitro and in vivo. This inhibition might have an important effect on cell or mitochondrial membranes and be responsible for the effects on mitochondria that have been shown by several authors. Finally, the recent results of Pfohl-Leszkowicz et al. (this volume), who showed the formation of DNA adducts mainly in kidney but also in liver and spleen, explain the DNA single-strand breaks observed previously in mice and rats after acute and chronic treatment.
 ...
PMID:Mechanism of action of ochratoxin A. 182 Mar 32

A series of rat hepatoma cell lines was infected with a recombinant adenovirus bearing the rat albumin promoter. Transcription from this promoter was scored directly and was highest in FAO, the differentiated parent, undetectable in C2, a cell variant that has lost almost all hepatocytic characteristics, and high again in C2-Rev7, a 'revertant' cell line derived from C2 that has regained the ability to produce many proteins characteristic of hepatocytes. The endogenous albumin gene is not transcribed in C2 cells, and at a very low rate in C2-Rev7 cells, which accumulate endogenous albumin mRNA at close to normal amounts. Thus the C2-Rev7 'recovery' of albumin mRNA concentration for the endogenous gene is based mainly on post-transcriptional events while the ability of C2-Rev7 to transcribe the albumin promoter in the viral genome is based on a transcriptional factor(s). We also showed that the C2 phenotype included post-transcriptional effects for other genes: transcription of phenylalanine hydroxylase and phosphoenolpyruvate carboxykinase mRNA sequences continue in C2 at rates equivalent to FAO but these C2 cells have no mRNA for these proteins while FAO does. In addition, C2 cells transcribed certain early adenovirus transcription units (E2 and 4) as well as FAO cells but accumulated E2 mRNAs poorly if at all. The changes that led to the C2-Rev7 cell line produced a return to normal of the ability to accumulate these viral mRNAs. Thus a major event in the C2 to C2-Rev7 transition involves post-transcriptional processes as well as the ability to transcribe the albumin promoter positioned in the virus genome.
 ...
PMID:Hepatoma variants (C2) are defective for transcriptional and post-transcriptional actions from both endogenous and viral genomes. 295 94

Normal adult rat hepatocytes plated on rat tail collagen-coated dishes and fed a chemically defined medium supplemented with epidermal growth factor and dimethylsulfoxide (DMSO) were examined over a 40-d culture period for (a) the amount of albumin secreted; (b) steady-state albumin mRNA levels; (c) steady-state mRNA levels for six other liver-specific genes and three common genes; and (d)transcription of several liver-specific and common genes using isolated nuclei. DMSO-treated hepatocytes in culture for 40 d expressed albumin mRNA at 45% the level of normal liver and five other liver-specific genes at levels ranging from 21% to 72% of those in normal liver. The rate of synthesis of ligandin RNA using nuclei from 40-d hepatocytes in a nascent chain extension assay was 130% of the value obtained for normal liver, indicating that liverlike transcriptional activity for ligandin was maintained in this in vitro culture system. In contrast, the rates of synthesis of albumin and phosphoenolpyruvate carboxykinase (PepCK) mRNAs using nuclei from 40-d hepatocytes were 8% and less than 1%, respectively, and, therefore, were at levels that were much lower than was expected given the steady-state mRNA levels for these two genes. The discrepancy between the steady-state mRNA levels and rates of synthesis of RNA was analyzed, and the results suggest that the albumin and PepCK mRNAs from hepatocytes in culture may be more stable than those from liver. A plateau period for secretion of albumin, expression of albumin, alpha 1-antitrypsin, ligandin, phenylalanine hydroxylase, and PepCK mRNAs, and synthesis of albumin RNA using isolated nuclei was observed from days 6 to 40. The usefulness at a biological and molecular level of a hepatocyte culture system in which liver-specific genes are expressed over a long plateau period is discussed.
 ...
PMID:Persistence of liver-specific messenger RNA in cultured hepatocytes: different regulatory events for different genes. 350 Sep 53

Expression of the phenylalanine hydroxylase gene in livers and kidneys of rodents is activated at birth and is induced by glucocorticoids and cyclic AMP in the liver. Regulatory elements in a 10-kb fragment upstream of the mouse gene have been characterized. The promoter lacks TAATA and CCAAT consensus sequences and shows only extremely weak activity in transitory expression assays with phenylalanine hydroxylase-producing hepatoma cells. No key elements for regulation of promoter activity are localized within 2 kb of upstream sequences. However, a liver-specific DNase I-hypersensitive site at kb -3.5 comprises a tissue-specific and hormone-inducible enhancer. This enhancer contains multiple protein binding sites, including sites for ubiquitous factors (NF1 and AP1), the glucocorticoid receptor, and the hepatocyte-enriched transcription factors hepatocyte nuclear factor 1 (HNF1) and C/EBP. Mutation revealed that the last two sites are critical not only for basal activity but also for obtaining a maximal hormone response. Efficient transcription from the highly inducible promoter shows absolute dependence upon the enhancer at kb - 3.5, which in turn requires HNF1 and C/EBP as well as hormones. The regulatory region of the mouse phenylalanine hydroxylase gene differs totally from that of humans, even though the genes of both species are expressed essentially in the liver. Furthermore, the phenylalanine hydroxylase gene of mice shows an expression pattern very similar to those of the rodent tyrosine aminotransferase and phosphoenolpyruvate carboxykinase genes, yet each shows a different organization of its regulatory region.
 ...
PMID:The activity of the highly inducible mouse phenylalanine hydroxylase gene promoter is dependent upon a tissue-specific, hormone-inducible enhancer. 864 24

Phenylalanine hydroxylase catalyzes the major regulatory step of the phenylalanine degradation pathway. In view of the glucogenic nature of phenylalanine breakdown, and hence its potential contribution to glucose homeostasis, we have investigated the impact of streptozotocin-induced diabetes upon the expression of rat phenylalanine hydroxylase. Northern blot analysis revealed that induction of diabetes was associated with an increase in the in vivo abundance of hepatic phenylalanine hydroxylase-specific mRNA. This increase in mRNA abundance was maintained for at least 8 hr in liver cells isolated from diabetic animals. In contrast, phenylalanine hydroxylase immunoreactivity and enzymic activity decreased, over the 8 hr incubation period, to levels similar to those observed in liver cells from normal animals. These changes were retarded, but not prevented, by the presence of dexamethasone in incubation media. In liver cells from normal animals the abundance of phenylalanine hydroxylase-specific mRNA, immunoreactivity and enzymic activity, were largely insensitive to treatment with dexamethasone and/or glucagon over an 8 hr incubation period. It is concluded that, whereas diabetes-related alterations in phenylalanine hydroxylase-specific mRNA abundance persist after isolation of liver cells, changes in phenylalanine hydroxylase protein abundance do not. Additionally, in contrast to certain other enzymes (e.g. phosphoenolpyruvate carboxykinase) it is not possible to mimic diabetes-related alterations in the expression of phenylalanine hydroxylase, in liver cells from normal animals, by simple hormonal manipulation of incubation media. This implies that other additional factors must also contribute to diabetes-related alterations in hepatic enzyme expression.
 ...
PMID:Differential effects of streptozotocin-induced diabetes on phenylalanine hydroxylase protein and mRNA abundance in isolated rat liver cells. 892 6