Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:4.1.1.32 (phosphoenolpyruvate carboxykinase)
4,204 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transcription of hepatocyte-specific genes requires the interaction of their regulatory regions with several nuclear factors. Among them is the hepatocyte nuclear factor 3 (HNF3) family, composed of the HNF3 alpha, HNF3 beta, and HNF3 gamma proteins, which are expressed in the liver and have very similar fork head DNA binding domains. The regulatory regions of numerous hepatocyte-specific genes contain HNF3 binding sites. We examined the role of HNF3 proteins in the liver-specific phenotype by turning off the HNF3 activity in well-differentiated mhAT3F hepatoma cells. Cells were stably transfected with a vector allowing the synthesis of an HNF3 beta fragment consisting of the fork head DNA binding domain without the transactivating amino- and carboxy-terminal domains. The truncated protein was located in the nuclei of cultured hepatoma cells and competed with endogenous HNF3 proteins for binding to cognate DNA sites. Overproduction of this truncated protein, lacking any transactivating activity, induced a dramatic decrease in the expression of liver-specific genes, including those for albumin, transthyretin, transferrin, phosphoenolpyruvate carboxykinase, and aldolase B, whereas the expression of the L-type pyruvate kinase gene, containing no HNF3 binding sites, was unaltered. Neither were the concentrations of various liver-specific transcription factors (HNF3, HNF1, HNF4, and C/EBP alpha) affected. In partial revertants, with a lower ratio of truncated to full-length endogenous HNF3 proteins, previously extinguished genes were re-expressed. Thus, the transactivating domains of HNF3 proteins are needed for the proper expression of a set of liver-specific genes but not for expression of the genes encoding transcription factors found in differentiated hepatocytes.
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PMID:Overproduction of a truncated hepatocyte nuclear factor 3 protein inhibits expression of liver-specific genes in hepatoma cells. 756 96

Mice homozygous for the targeted deletion of the c/ebp alpha gene, which expresses the CCAAT/enhancer-binding protein alpha (C/EBP alpha), did not store hepatic glycogen and died from hypoglycemia within 8 hours after birth. In these mutant mice, the amounts of glycogen synthase messenger RNA were 50 to 70 percent of normal and the transcriptional induction of the genes for two gluconeogenic enzymes, phosphoenolpyruvate carboxykinase and glucose-6-phosphatase, was delayed. The hepatocytes and adipocytes of the mutant mice failed to accumulate lipid and the expression of the gene for uncoupling protein, the defining marker of brown adipose tissue, was reduced. This study demonstrates that C/EBP alpha is critical for the establishment and maintenance of energy homeostasis in neonates.
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PMID:Impaired energy homeostasis in C/EBP alpha knockout mice. 765 57

Adenosine 3',5'-monophosphate (cAMP) stimulates phosphoenolpyruvate carboxykinase (PEPCK) gene transcription, whereas insulin has the opposite effect. In H4IIE cells, the effect of insulin is dominant since it represses cAMP-stimulated transcription. Discrete cis-acting elements in the PEPCK promoter that serve as an insulin response sequence (IRS) and cAMP response element (CRE) have been identified. Here we show that common proteins can bind both elements, since: (i) an almost identical pattern of protein binding is seen when oligonucleotides representing either the IRS or the CRE are used as the labeled probe in a gel retardation assay and (ii) the unlabeled wild-type, but not mutated, CRE oligonucleotide competes for protein binding to the labeled IRS probe, and vice versa. Six homo- and heterodimer complexes interact with these DNA elements; the complexes are composed of three individual protein species: (a) 42-kDa C/EBP alpha, (b) 30-kDa C/EBP alpha, and (c) an unidentified 20-kDa factor termed p20- CRE/IRS Binding Protein (p20-C/IBP). These proteins have a 30-fold greater affinity for the CRE at room temperature, a difference explained by the rapid dissociation rate of protein bound to the IRS, since the association rate of protein binding to both the IRS and CRE is the same. Protease digestion experiments suggest that the proteins bind to the CRE and IRS in different conformations. The IRS and CRE both function in the context of a heterologous promoter to mediate effects of insulin and cAMP, respectively, but, although the PEPCK IRS and CRE bind common proteins, the PEPCK CRE is not a functional IRS and the PEPCK IRS is not a functional CRE.
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PMID:Potential convergence of insulin and cAMP signal transduction systems at the phosphoenolpyruvate carboxykinase (PEPCK) gene promoter through CCAAT/enhancer binding protein (C/EBP). 798 56

The gene for phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) (PEPCK) is expressed in a tissue-specific manner in the liver, kidney, and adipose tissue and is regulated by hormones including cAMP and insulin. Previous studies have shown that the CCAAT/enhancer-binding protein alpha (C/EBP alpha) binds to several sites on the PEPCK promoter and activates transcription from the promoter in hepatoma cells. Here, we report that a second member of the C/EBP family, C/EBP beta, bound to the same sites on the PEPCK promoter. However, C/EBP beta stimulated transcription primarily through the cAMP-responsive element (CRE), which maps between positions -77 to -94, but not at the more 5'-binding sites. In addition, the nuclear factor-1 site, which is immediately adjacent to the CRE in the PEPCK promoter, was also required for the full response of the promoter to cotransfected C/EBP beta. In gel mobility assays, antibodies to both C/EBP beta and the cAMP regulatory element-binding protein (CREB), but not to C/EBP alpha, "supershifted" DNA-protein complexes formed between a synthetic CRE oligomer and proteins prepared from rat liver nuclei. C/EBP beta mRNA was expressed at low levels in both the periportal and pericentral regions of the liver lobule, whereas expression of the gene for C/EBP alpha was confined to the pericentral region of the liver lobule. PEPCK gene transcription is greatest in the periportal region of the liver. CREB also bound to the CRE and stimulated transcription of a PEPCK-CAT vector in the presence of an expression vector for the catalytic subunit of protein kinase A. C/EBP beta and CREB bound to the CRE with similar affinities, both of which were greater than the affinity of C/EBP alpha. Within 90 min after the administration of dibutyryl cAMP to rats, there was a marked increase in the hepatic concentration of C/EBP beta mRNA and a decrease in the level of mRNA for C/EBP alpha. These studies indicate that C/EBP beta can regulate PEPCK gene transcription by acting through the CRE and that C/EBP beta, together with CREB, may contribute to the cAMP responsiveness of the PEPCK promoter.
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PMID:Relative roles of CCAAT/enhancer-binding protein beta and cAMP regulatory element-binding protein in controlling transcription of the gene for phosphoenolpyruvate carboxykinase (GTP). 809 46

Transcription of the gene for phosphoenolpyruvate carboxykinase (PEPCK) is stimulated by cAMP, the thyroid hormone tri-iodothyronine (T3) and retinoic acid (RA). Regulation of PEPCK transcription by T3 involves two sites in the promoter including a thyroid-hormone-response element (TRE) and a CCAAT-enhancer-binding protein (C/EBP) binding site called P3I. Mutation of either the TRE or P3I eliminates the T3 response. In this study, we examined the role of C/EBPs in the induction of PEPCK transcription by T3 and RA. PEPCK-CAT vectors were transfected into HepG2 cells. Co-transfection of a dominant negative C/EBP eliminated the T3 stimulation indicating that a member of the C/EBP family is required. To determine which C/EBP isoform was required, Gal4 fusion proteins were created that contained the Gal4 DNA-binding domain ligated to the transcriptional activation domain of C/EBP alpha, C/EBP beta or the cAMP-responsive-element-binding protein. A Gal4 DNA-binding site was introduced into the P3(I) site of the PEPCK-CAT vector. Only co-transfection of the Gal4-C/EBP alpha vector was able to restore T3 responsiveness to the PEPCK-CAT vector. The T3 and RA receptors are members of the nuclear receptor superfamily and bind to repeats of the AGGTCA motif. We found that the RA receptor can bind to sequences within the PEPCK-TRE and contribute to RA responsiveness of the PEPCK gene. However, the RA induction of PEPCK transcription was found to be independent of C/EBPs, further demonstrating the specificity of the involvement of C/EBP alpha in the T3 effect.
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PMID:CCAAT-enhancer-binding protein alpha (C/EBP alpha) is required for the thyroid hormone but not the retinoic acid induction of phosphoenolpyruvate carboxykinase (PEPCK) gene transcription. 907 82

The liver-enriched transcription factor C/EBP alpha has been implicated in the regulation of numerous liver-specific genes. It was previously reported that mice carrying a homozygous null mutation at the c/ebp alpha locus died as neonates due to the absence of hepatic glycogen and the resulting hypoglycemia. However, the lethal phenotype precluded further analysis of the role of C/EBP alpha in hepatic gene regulation in adult mice. To circumvent this problem, we constructed a conditional knockout allele of c/ebp alpha by using the Cre/loxP recombination system. Homozygous c/ebp-loxP mice, (c/ebp alpha(fl/fl);fl, flanked by loxP sites) were found to be indistinguishable from their wild-type counterparts. However, when Cre recombinase was delivered to hepatocytes of adult c/ebp alpha(fl/fl) mice by infusion of a recombinant adenovirus carrying the cre gene, more than 80% of the c/ebp alpha(fl/fl) genes were deleted specifically in liver and C/EBP alpha expression was reduced by 90%. This condition resulted in a reduced level of bilirubin UDP-glucuronosyltransferase expression in the liver. After several days, the knockout mice developed severe jaundice due to an increase in unconjugated serum bilirubin. The expression of genes encoding phosphoenolpyruvate carboxykinase, glycogen synthase, and factor IX was also strongly reduced in adult conditional-knockout animals, while the expression of transferrin, apolipoprotein B, and insulin-like growth factor I genes was not affected. These results establish C/EBP alpha as an essential transcriptional regulator of genes encoding enzymes involved in bilirubin detoxification and gluconeogenesis in adult mouse liver.
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PMID:Disruption of the c/ebp alpha gene in adult mouse liver. 931 60

Dietary n-3 polyunsaturated fatty acids (n-3 PUFAs) limit abdominal fat depot hypertrophy. This could be due to regulation of the expression of proteins involved in adipose tissue metabolism. We investigated in vivo whether fatty acid synthase (FAS), hormone-sensitive lipase (HSL), lipoprotein lipase (LPL), phosphoenolpyruvate carboxykinase (PEPCK), CCAAT/enhancer binding protein alpha (C/EBP alpha), and leptin mRNA levels are affected in retroperitoneal (RP) and subcutaneous adipose tissues (SC) of rats fed n-3 PUFAs. For 4 weeks rats were fed high fat diets (20% fat) containing n-3 PUFAs given as eicosapentaenoic acid (EPA group), docosahexaenoic acid (DHA group), a mixture of these two fatty acids (MIX group), or native fish oil (FO group). A control group was fed with lard plus olive oil (LOO group). Final mean fat cell weight in RP ranged according to: LOO > or = EPA > or = DHA = FO = MIX. There was no difference in fat cell size of SC when comparing the LOO and MIX groups. The fatty acid compositions of RP and SC were similar and resemble that of dietary fat within each experimental group. In RP and compared to the LOO group, FAS, HSL, PEPCK, LPL, C/EBP alpha, and leptin mRNA levels decreased although not significantly in the EPA group, and were 40-75% lower in the DHA and MIX groups. mRNA levels were positively correlated to fat cell size in RP. In contrast, n-3 PUFAs had no effect on gene expression in SC. We conclude that n-3 PUFAs and mainly 22:6n-3 affect gene expression in a site-dependent manner in white adipose tissues via possible antiadipogenic effects.
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PMID:Site-specific regulation of gene expression by n-3 polyunsaturated fatty acids in rat white adipose tissues. 937 19

The CCAAT/enhancer-binding protein alpha (C/EBP) is a transcription factor that trans-activates a number of metabolically important genes. Previous work has demonstrated that C/EBPalpha and C/EBPbeta have the potential to mediate the cAMP responsiveness of phosphoenolpyruvate carboxykinase (PEPCK) in liver cells. However, these studies used GAL4 fusion proteins and artificial promoter-reporter gene vectors in transfection experiments; as a result, these studies only indicated that both isoforms had the potential to mediate the hormonal response and not which isoform actually participated in vivo. To address this issue, we produced hepatoma cell lines that stably expressed either a dominant negative inhibitor or antisense RNA for these two main liver C/EBP isoforms. Inhibition of all C/EBP isoforms via expression of the dominant negative protein eliminated cAMP responsiveness, and reduced glucocorticoid responsiveness, of the endogenous PEPCK gene in hepatoma cells. Antisense directed against C/EBPalpha mRNA, which reduced C/EBPalpha protein levels by nearly 80%, also significantly reduced the cAMP responsiveness of the endogenous PEPCK promoter, whereas antisense directed against C/EBPbeta was without effect. There was no major alteration in cAMP signaling in the C/EBPalpha antisense cells, as cAMP induction of the C/EBPbeta gene was similar to that in wild-type H4IIE cells. These data suggest that the alpha-isoform of C/EBP is specifically utilized for mediating the cAMP responsiveness of the PEPCK gene.
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PMID:Hormonal regulation of the phosphoenolpyruvate carboxykinase gene. Role of specific CCAAT/enhancer-binding protein isoforms. 1068 69

The X gene product of the human hepatitis B virus (HBx), a major factor responsible for hepatitis and hepatocellular carcinoma, modulates transactivation by a variety of transcription factors. Herein, expression of the phosphoenolpyruvate carboxykinase (PEPCK) gene was found to be regulated transcriptionally by HBx through two distinct promoter regions. The cAMP response element (CRE)-1 site within the proximal promoter region mediated the HBx-induced transactivation of the PEPCK gene through C/EBP alpha and ATF-2. A retinoid X receptor (RXR) response element within the distal promoter region also contributed to the HBx-induced transactivation. Consistent with these results, HBx directly interacted with RXR, and the interaction interfaces were localized to the transactivation domain of HBx and the ligand binding domain of RXR.
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PMID:Direct binding of hepatitis B virus X protein and retinoid X receptor contributes to phosphoenolpyruvate carboxykinase gene transactivation. 1104 64

The cytosolic form of the phosphoenolpyruvate carboxykinase (PEPCK-C) gene is selectively expressed in several tissues, primarily in the liver, kidney, and adipose tissue. The transcription of the gene is reciprocally regulated by glucocorticoids in these tissues. It is induced in the liver and kidney but repressed in the white adipose tissue. To elucidate which adipocyte-specific transcription factors participate in the repression of the gene, DNase I footprinting analyses of nuclear proteins from 3T3-F442A adipocytes and transient transfection experiments in NIH3T3 cells were utilized. Glucocorticoid treatment slightly reduced the nuclear C/EBP alpha concentration but prominently diminished the binding of adipocyte-derived nuclear proteins to CCAAT/enhancer-binding protein (C/EBP) recognition sites, without affecting the binding to nuclear receptor sites in the PEPCK-C gene promoter. Of members of the C/EBP family of transcription factors, C/EBP alpha was the strongest trans-activator of the PEPCK-C gene promoter in the NIH3T3 cell line. The glucocorticoid receptor (GR), in the presence of its hormone ligand, inhibited the activation of the PEPCK-C gene promoter by C/EBP alpha or C/EBP beta but not by the adipocyte-specific peroxisome proliferator-activated receptor gamma 2. This inhibition effect was similar using the wild type or mutant GR and did not depend on GR binding to the DNA. The glucocorticoid response unit (GRU) in the PEPCK-C gene promoter (-2000 to +73) restrained C/EBP alpha-mediated trans-activation, because mutation of each single GRU element increased this activation by 3-4-fold. This series of GRU mutations were repressed by wild type GR to the same percent as was the nonmutated PEPCK-C gene promoter. In contrast, the repression by mutant GR depended on the intact AF1 site in the gene promoter, whereby mutation of the AF1 element abolished the repression.
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PMID:Glucocorticoids repress transcription of phosphoenolpyruvate carboxykinase (GTP) gene in adipocytes by inhibiting its C/EBP-mediated activation. 1256 Mar 25


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