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Manes NP, El-Maghrabi MR. The kinase activity of human brain 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase is regulated via inhibition by phosphoenolpyruvate. Arch Biochem Biophys 2005; 438:125-36. [PMID: 15896703 DOI: 10.1016/j.abb.2005.04.011] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2004] [Revised: 04/14/2005] [Accepted: 04/14/2005] [Indexed: 12/31/2022]
Abstract
The two enzymatic activities of the highly conserved catalytic core of 6PF2K/Fru-2,6-P(2)ase are thought to be reciprocally regulated by the amino- and carboxy-terminal regions unique to each isoform. In this study, we describe the recombinant expression, purification, and kinetic characterization of two human brain 6PF2K/Fru-2,6-P(2)ase splice variants, HBP1 and HBP2. Interestingly, both lack an arginine which is highly conserved among other tissue isoforms, and which is understood to be critical to the fructose-2,6-bisphosphatase mechanism. As a result, the phosphatase activity of both HBP isoforms is negligible, but we found that it could be recovered by restoration of the arginine by site directed mutagenesis. We also found that AMP activated protein kinase and protein kinases A, B, and C catalyzed the phosphorylation of Ser-460 of HBP1, and that in addition both isoforms are phosphorylated at a second, as yet undetermined site by protein kinase C. However, none of the phosphorylations had any effect on the intrinsic kinetic characteristics of either enzymatic activity, and neither did point mutation (mimicking phosphorylation), deletion, and alternative-splice modification of the HBP1 carboxy-terminal region. Instead, these phosphorylations and mutations decreased the sensitivity of the 6PF2K to a potent allosteric inhibitor, phosphoenolpyruvate, which appears to be the major regulatory mechanism.
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Affiliation(s)
- Nathan P Manes
- Department of Physiology and Biophysics, Stony Brook University, NY 11794-8661, USA
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2
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El-Maghrabi MR, Noto F, Wu N, Manes N. 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase: suiting structure to need, in a family of tissue-specific enzymes. Curr Opin Clin Nutr Metab Care 2001; 4:411-8. [PMID: 11568503 DOI: 10.1097/00075197-200109000-00012] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The present review addresses recent advances in research into a family of bifunctional enzymes that are responsible for the twofold task of synthesizing and hydrolyzing fructose-2,6-bisphosphate (Fru-2,6-P2), which in turn regulates the rate of glycolysis in most cells. The structure of the synthetic kinase, conjoined at its carboxyl-terminus to the phosphatase, is very highly conserved throughout evolution and differentiation, with isotypic expression arising from highly variable amino-terminal and carboxyl-terminal regulatory domains. These domains, which frequently contain protein-kinase-catalyzed phosphorylation motifs, are responsible for the widely divergent kinetics observed in various tissues and species, and for the hormonal modulation that alters intracellular levels of Fru-2,6-P2. The present review discusses recent advances in relating structure to function, and the identification of new pathways of transcriptional regulation of this important family of regulatory enzymes.
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Affiliation(s)
- M R El-Maghrabi
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, New York 11794-8661, USA.
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3
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McFarlan SC, Zhang Q, Miksicek RJ, Lange AJ. Characterization of an intronic hormone response element of the rat liver/skeletal muscle 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase gene. Mol Cell Endocrinol 1997; 129:219-27. [PMID: 9202405 DOI: 10.1016/s0303-7207(97)00069-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The glucocorticoid response element of the rat liver/skeletal muscle 6- phosphofructo-2-kinase/fructose-2,6-bisphosphatase gene was characterized. The element is composed of two tandem hormone receptor binding sites separated by 12 base pairs. Addition of dexamethasone to HeLa cells transiently transfected with a chloramphenicol acetyl transferase (CAT) reporter plasmid containing the hormone response element and cotransfected with glucocorticoid receptor stimulated transcription 24-fold in an orientation- and position-independent manner. Deletion or mutation of essential G/C pairs of the distal binding site abolished hormone-stimulated CAT activity, whereas deletion or mutation of the proximal binding site decreased the hormone-stimulated response only slightly. Mutation of both distal and proximal binding sites resulted in complete loss of hormone-stimulated CAT activity. Experiments carried out using testosterone and progesterone with their respective receptors revealed qualitatively similar results to those seen with glucocorticoid. Binding of glucocorticoid receptor or androgen receptor DNA binding domains to the hormone response element, visualized by gel mobility shift, was unaffected in the proximal binding site mutant, markedly decreased in the distal binding site mutant, and abolished in the double mutant. In gel mobility shift analysis of separate distal and proximal binding sites, only the native distal site demonstrated high affinity binding to glucocorticoid and androgen receptor DNA binding domains. The results demonstrate that this element is responsible for glucocorticoid, androgen, and progesterone stimulation of transcription of the 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase gene and that the distal receptor binding site is dominant.
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Affiliation(s)
- S C McFarlan
- Department of Biochemistry, School of Medicine, University of Minnesota, Minneapolis 55455, USA
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4
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Casado M, Boscá L, Martín-Sanz P. Differential regulation of the expression of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase and pyruvate kinase by cyclic adenosine 3',5'-monophosphate in fetal and adult hepatocytes. J Cell Physiol 1995; 165:630-8. [PMID: 7593243 DOI: 10.1002/jcp.1041650322] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Incubation of fetal hepatocytes from 21-day-old rats with permeant derivatives of cyclic AMP (cAMP) or glucagon, increased the mRNA levels of 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase (PFK-2/FBPase-2), L-pyruvate kinase (L-PK) and phosphoenolpyruvate carboxykinase (PEPCK). Contrary to this behavior, adult hepatocytes exhibited a decrease in the PFK-2/FBPase-2 and L-PK mRNA levels when incubated under equivalent experimental conditions. Dexamethasone also increased the PFK-2/FBPase-2 mRNA levels and costimulation of fetal hepatocytes with dexamethasone and a permeant analogue of cyclic AMP enhanced the levels of PFK-2/FBPase-2 mRNA, a situation opposite to that exhibited by adult hepatocytes. Treatment of the hepatocytes with transcriptional and translational inhibitors also produced differential responses in both types of cells. The PFK-2/FBPase-2 mRNA in fetal hepatocytes was more stable than in the adult cells. These results suggest that specific transcriptional factors and regulatory pathways differentially operate in fetal and adult hepatocytes in the control of the responses of carbohydrate metabolism to cAMP.
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Affiliation(s)
- M Casado
- Instituto de Bioquímica (CSIC-UCM), Facultad de Farmacia, Madrid, Spain
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5
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Lemaigre FP, Rousseau GG. Transcriptional control of genes that regulate glycolysis and gluconeogenesis in adult liver. Biochem J 1994; 303 ( Pt 1):1-14. [PMID: 7945228 PMCID: PMC1137548 DOI: 10.1042/bj3030001] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- F P Lemaigre
- Hormone and Metabolic Research Unit, University of Louvain Medical School, Brussels, Belgium
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6
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Rosa J, Ventura F, Tauler A, Bartrons R. Regulation of hepatic 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase gene expression by glucagon. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(18)41563-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
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7
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Espinet C, Vargas AM, el-Maghrabi MR, Lange AJ, Pilkis SJ. Expression of the liver 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase mRNA in FAO-1 cells. Biochem J 1993; 293 ( Pt 1):173-9. [PMID: 8392331 PMCID: PMC1134336 DOI: 10.1042/bj2930173] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The hormonal regulation of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase gene expression was studied in the rat hepatoma cell line FAO-1. Both 6-phosphofructo-2-kinase and fructose-2,6-bisphosphatase activities were detected in FAO-1 cells, at 68% of the levels found in rat liver. Northern blot analysis showed that FAO-1 cells, like rat liver, contained a predominant species of bifunctional enzyme mRNA, which is 2.2 kb in size. A sensitive RNAase protection assay revealed the presence in FAO-1 cells of an additional mRNA species, which is generated when transcription is initiated from the skeletal muscle promoter of the rat liver/skeletal muscle gene. The liver/skeletal muscle mRNA ratio in FAO-1 cells was 10:1, which is similar to that observed in rat liver. In contrast, in another rat hepatoma cell line, FTO-2B, only the skeletal muscle mRNA was detected. Insulin and dexamethasone induced the liver bifunctional enzyme mRNA in FAO-1 cells by 2-4-fold and 10-20-fold respectively in a concentration- and time-dependent manner, and their effects were antagonized by cyclic AMP. Transcription of the gene in FAO-1 cells, measured by nuclear run-on assays, was also enhanced by dexamethasone and insulin. It is concluded that the FAO-1 cell line is similar to liver with respect to both the preferential use of the liver promoter of the gene and its regulation by hormones, and is therefore an excellent model for the study of the hepatic expression of this gene.
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Affiliation(s)
- C Espinet
- Department of Physiology and Biophysics, SUNY, Stony Brook 11794
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8
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Clore JN, Stillman JS, Helm ST, Blackard WG. Evidence for dissociation of gluconeogenesis stimulated by non-esterified fatty acids and changes in fructose 2,6-bisphosphate in cultured rat hepatocytes. Biochem J 1992; 288 ( Pt 1):145-8. [PMID: 1445259 PMCID: PMC1132091 DOI: 10.1042/bj2880145] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
In order to examine the role of fructose 2,6-bisphosphate (Fru-2,6-P2) in non-esterified-fatty-acid-stimulated gluconeogenesis, Fru-2,6-P2 levels were measured in cultured rat hepatocytes under conditions mimicking the fasted state. After addition of either 1.5 mM-palmitate or 10 nM-glucagon, [U-14C]lactate incorporation into glucose increased 2-fold, but only glucagon suppressed Fru-2,6-P2. Prevention of palmitate oxidation with a carnitine palmitoyltransferase-I inhibitor (2-bromopalmitate) diminished glucose production and Fru-2,6-P2 levels. Addition of exogenous glucose to the media increased Fru-2,6-P2 in a dose-related manner, which was further augmented by addition of palmitate. When Fru-2,6-P2 levels were examined in cells cultured under conditions mimicking the fed state (significantly higher basal Fru-2,6-P2 levels and lower glucose production), palmitate oxidation was associated with a significant fall in Fru-2,6-P2. In conclusion, the present studies have demonstrated a dissociation between fatty-acid-stimulated gluconeogenesis and changes in Fru-2,6-P2 in cultured rat hepatocytes. Further experiments suggest that the accumulation of intracellular hexose 6-phosphate as a result of fatty-acid-stimulated gluconeogenesis masks a putative inhibitory effect of fatty acids on Fru-2,6-P2 concentrations.
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Affiliation(s)
- J N Clore
- Medical College of Virginia/Virginia Commonwealth University, Richmond 23298
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9
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Regulation of gene expression of rat skeletal muscle/liver 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. Isolation and characterization of a glucocorticoid response element in the first intron of the gene. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)49588-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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10
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Rosa JL, Tauler A, Lange AJ, Pilkis SJ, Bartrons R. Transcriptional and posttranscriptional regulation of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase during liver regeneration. Proc Natl Acad Sci U S A 1992; 89:3746-50. [PMID: 1315037 PMCID: PMC525567 DOI: 10.1073/pnas.89.9.3746] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The control of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2; EC 2.7.1.105/3.1.3.46) gene expression during liver regeneration was studied. The level of PFK-2/FBPase-2 mRNA decreased to about 5% of the control value 6 hr after partial hepatectomy. Thereafter the mRNA increased to a maximum at 48 hr and returned to normal levels by 96 hr. In sham-operated animals, only a small increase was observed during the first 4 hr. The mRNA was recognized by a 299-base-pair liver-specific cDNA probe but not by a muscle-specific probe. The time course of mRNA modulation was well correlated with PFK-2/FBPase-2 activity and with the amount of bifunctional enzyme protein determined by immunoblotting with an antibody raised against the N-terminal decapeptide of liver PFK-2/FBPase-2. No alteration in the degradation rate of PFK-2/FBPase-2 mRNA was noted after partial hepatectomy. The modulation of PFK-2/FBPase-2 gene expression during liver regeneration involved changes in the transcription rate. The rate decreased by 50% at 6 hr after liver resection. The rate increased thereafter to a maximum at 72 hr and then returned to control values by 96 hr. The transcription rate of albumin did not change, whereas that of phosphoenolpyruvate carboxykinase increased 12-fold at 6 hr. These results show that PFK-2/FBPase-2 gene transcription is specifically regulated and that this regulation is in part responsible for the alterations in hepatic metabolism seen in regenerating liver.
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Affiliation(s)
- J L Rosa
- Departament de Ciències Fisiològiques Humanes i de la Nutrició, Universitat de Barcelona, Spain
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11
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Lin K, Li L, Correia J, Pilkis S. Glu327 is part of a catalytic triad in rat liver fructose-2,6-bisphosphatase. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)50463-x] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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12
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Martín-Sanz P, Cascales M, Boscá L. Characterization of 6-phosphofructo-2-kinase from foetal-rat liver. Biochem J 1992; 281 ( Pt 2):457-63. [PMID: 1310598 PMCID: PMC1130707 DOI: 10.1042/bj2810457] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Foetal and adult liver 6-phosphofructo-2-kinase (PFK-2) were purified by identical protocols. The native molecular masses of both enzymes were determined by gel filtration and were 89.1 and 100.0 kDa respectively. No differences were found in SDS/PAGE in 10%-acrylamide gel (55 kDa per subunit). The kinetic properties displayed by both enzymes were similar, except for the sensitivity to inhibition by sn-glycerol 3-phosphate. Foetal PFK-2 was a good substrate for phosphorylation by cyclic AMP-dependent protein kinase and protein kinase C, whereas the adult enzyme was phosphorylated only by cyclic AMP-dependent protein kinase. However, the phosphorylation affected only the kinetic properties of the adult enzyme, suggesting the presence in both enzymes of different sites of phosphorylation by cyclic AMP-dependent protein kinase. These differences in primary structure were consistent with the distinct chromatographic profiles of the phosphopeptides after digestion of the protein with CNBr. Western-blot analysis with antibodies specific for the N-terminal region of the liver-type PFK-2 poorly recognized the foetal enzyme, suggesting that both enzymes differ at least in the N-terminal sequence.
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Affiliation(s)
- P Martín-Sanz
- Facultad de Farmacia, Universidad Complutense, Madrid, Spain
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13
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Lange AJ, el-Maghrabi MR, Pilkis SJ. Isolation of bovine liver 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase cDNA: bovine liver and heart forms of the enzyme are separate gene products. Arch Biochem Biophys 1991; 290:258-63. [PMID: 1654864 DOI: 10.1016/0003-9861(91)90617-r] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In order to ascertain whether the heart and liver forms of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase were products of two different genes or arose via alternative splicing of a single gene, the bovine liver cDNA of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase was isolated from a lambda gt10 phage library and its sequence compared with that of bovine heart cDNA. The deduced amino acid sequence of the bovine liver cDNA was also compared with the amino acid sequence of the human and rat liver phosphofructo-2-kinase/fructose-2,6-bisphosphatase enzyme. The bovine liver cDNA codes for a protein that has 81.6% amino acid identity with the bovine heart form and 97.0 and 98.3% identity with the rat and human liver forms of the enzyme, respectively. Comparison of the nucleotide sequences of the two bovine cDNAs and their deduced amino acid sequences demonstrates that while there is conservation of the active sites of liver/muscle and heart 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases they are encoded by different genes.
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Affiliation(s)
- A J Lange
- Department of Physiology and Biophysics, State University of New York, Stony Brook 11794-8661
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14
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Affiliation(s)
- R M O'Brien
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical School, Nashville, TN 37232-0615
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15
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O'Brien RM, Bonovich MT, Forest CD, Granner DK. Signal transduction convergence: phorbol esters and insulin inhibit phosphoenolpyruvate carboxykinase gene transcription through the same 10-base-pair sequence. Proc Natl Acad Sci U S A 1991; 88:6580-4. [PMID: 1650476 PMCID: PMC52130 DOI: 10.1073/pnas.88.15.6580] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Phosphoenolpyruvate carboxykinase (PEPCK) governs the rate-limiting step in gluconeogenesis. Glucocorticoids and cAMP increase PEPCK gene transcription and gluconeogenesis, whereas insulin and phorbol esters have the opposite effect. Insulin and phorbol esters are dominant, since they prevent cAMP and glucocorticoid-stimulated transcription. Basal promoter elements and hormone response elements for cAMP, glucocorticoids, and insulin have been defined in previous studies. By using stable transfectants containing a variety of different PEPCK-chloramphenicol acetyltransferase fusion gene constructs, a phorbol ester response sequence, located between positions -437 and -402 relative to the transcription start site, was identified. This region coincides with the insulin response sequence that has recently been defined in the PEPCK promoter. Using a vector containing various wild-type and mutated sequences of this region ligated to the heterologous thymidine kinase promoter, we delineated the boundaries of both elements to the 10 base pairs between positions -416 through -407. Thus, although it has been previously shown that insulin and phorbol esters repress PEPCK gene transcription through distinct pathways, the final target of insulin and phorbol ester action is the same DNA element.
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Affiliation(s)
- R M O'Brien
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical School, Nashville, TN 37232-0615
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16
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Cifuentes ME, Espinet C, Lange AJ, Pilkis SJ, Hod Y. Hormonal control of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase gene expression in rat hepatoma cells. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)52330-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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17
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Hepatic 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. Use of site-directed mutagenesis to evaluate the roles of His-258 and His-392 in catalysis. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(18)55442-9] [Citation(s) in RCA: 61] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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18
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Kummel L, Pilkis SJ. Multihormonal regulation of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase gene expression in primary cultures of rat hepatocytes. Biochem Biophys Res Commun 1990; 169:406-13. [PMID: 1694072 DOI: 10.1016/0006-291x(90)90346-o] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In the absence of hormone, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase mRNA rapidly declined to undetectable levels in primary cultures of rat hepatocytes. Dexamethasone increased mRNA levels and this effect was blocked by actinomycin D or cycloheximide. Insulin or thyroxine had no effect but potentiated the dexamethasone induction. Dibutyryl cyclic AMP decreased the stimulatory effect of dexamethasone at early times but after 24 hours the cyclic nucleotide increased mRNA levels compared with dexamethasone alone. It was concluded that expression of the bifunctional enzyme gene in hepatocytes is under a complex multihormonal control. Glucocorticoids are the most important transcriptional factor and their effect requires ongoing protein synthesis.
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Affiliation(s)
- L Kummel
- Department of Physiology and Biophysics, SUNY, Stony Brook 11794-8661
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19
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20
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Bazan JF, Fletterick RJ, Pilkis SJ. Evolution of a bifunctional enzyme: 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. Proc Natl Acad Sci U S A 1989; 86:9642-6. [PMID: 2557623 PMCID: PMC298557 DOI: 10.1073/pnas.86.24.9642] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The bifunctional rat liver enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (ATP:D-fructose-6-phosphate 2-phosphotransferase/D-fructose-2,6-bisphosphate 2-phosphohydrolase, EC 2.7.1.105/EC 3.1.3.46) is constructed of two independent catalytic domains. We present evidence that the kinase and bisphosphatase halves of the bifunctional enzyme are, respectively, structurally similar to the glycolytic enzymes 6-phosphofructo-1-kinase and phosphoglycerate mutase. Computer-assisted modeling of the C-terminal bisphosphatase domain reveals a hydrophobic core and active site residue constellation equivalent to the yeast mutase structure; structural differences map to length-variable, surface-located loops. Sequence patterns derived from the structural alignment of mutases and the bisphosphatase further detect a significant similarity to a family of acid phosphatases. The N-terminal kinase domain, in turn, is predicted to form a nucleotide-binding fold that is analogous to a segment of 6-phosphofructo-1-kinase, suggesting that these unrelated enzymes bind fructose 6-phosphate and ATP substrates in a similar geometry. This analysis indicates that the bifunctional enzyme is the likely product of gene fusion of kinase and mutase/phosphatase catalytic units.
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Affiliation(s)
- J F Bazan
- Department of Biochemistry and Biophysics, University of California, San Francisco 94143
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