Differential expression of the genes for the mitochondrial and cytosolic forms of phosphoenolpyruvate carboxykinase

Differential expression of glucose metabolism-related genes and AMP-activated protein kinases in crop tissue of male and female pigeons (Columba livia domestica) during the incubation and chick-rearing periods

The objective of this study was to explore the carbohydrate contents of crop milk, insulin and glucose concentrations in serum and the expression patterns of AMP-activated protein kinases (AMPKs) and genes related to glucose metabolism in pigeon crops during the breeding period. Crop milk was collected from squabs of rearing Day 1 (R1) to R6. Contents of total sugar and reducing sugar increased to the maximum levels at R6 (p < 0.05). Forty-two pairs of adult pigeons were allotted to seven groups by different breeding stages, and their crops and serum were sampled. No significant differences were found in either insulin or glucose levels in serum. The glucose transporter 2 gene level was the greatest at R15 in females, whereas it was at R7 in males. However, sodium-dependent glucose transporters 1 expression in both sexes decreased from incubation Day 17 (I17) to R7. In females, glucokinase expression peaked at R1, and at R1 and R7 in males. Pyruvate kinase mRNA levels peaked at R7 in females and at R15 males. The mRNA abundance of fructose-1,6-bisphosphatase 1 in both sexes and glucose-6-phosphatase in females decreased after I10. While phosphoenolpyruvate carboxykinase 1 expression decreased after I17 (p < 0.05). Protein levels of AMPKα in crops were minimized at R1 (p < 0.05). In females, expression of AMPKα1 and AMPKα2 was inhibited at I17 and R1 (p < 0.05). In males, AMPKα1 expression was decreased at R7 (p < 0.05) and AMPKα2 was reduced at I10 and R1. pAMPK expression was the lowest at I17 in females, and it was at R7 and R25 in males. Conclusively, glycolysis in pigeon crops was enhanced during chick-rearing, while gluconeogenesis was significantly inhibited. The stability of the insulin level suggests that it was probably not involved in the regulation of glucose metabolism in crop tissues.

Changes in hepatic glucose and lipid metabolism-related parameters in domestic pigeon (Columba livia) during incubation and chick rearing

This study aimed to evaluate the hepatic glucose and lipid metabolism-related parameters of adult male and female White King pigeons (Columba livia) during incubation and chick rearing. At day 4 (I4), 10 (I10) and 17 (I17) of incubation and day 1 (R1), 7 (R7), 15 (R15) and 25 (R25) of chick rearing, livers were sampled from six pigeons for each sex. Glycogen and fat contents, activities of glycolytic enzymes (hexokinase, HK; 6-phosphofructokinase, 6-PFK), and genes expressions of key enzymes involved in glycolysis (pyruvate kinase, PK; glucokinase, GK), gluconeogenesis (phosphoenolpyruvate carboxykinase cytosolic, PCK1; fructose-1,6-bisphosphatase, FBP1; glucose-6-phosphatase, G6Pase), fatty acid synthesis (fatty acid synthase, FAS; acetyl-CoA carboxylase, ACC) and fatty acid β-oxidation (carnitine palmitoyltransferase 1, CPT1; acyl-CoA 1, ACO) were measured. In male and female pigeon livers, glycogen content and HK activity dramatically increased after I17 and after R1, respectively; expressions of FBP1 and G6Pase genes were maximized at R15; activity of 6-PFK and expressions of PK and CPT1 genes were highest at R7; fat content and expressions of FAS and ACC genes steeply increased from I10 to R1. In females, hepatic expressions of GK and PCK1 genes were greatest at R7 and I17, respectively; however, in males, both of them were maximized at R15. Hepatic expression of ACO gene was significantly enhanced at R1 compared to I17 and R7 in males, whereas it was notably up-regulated at I17 and R7 in females. Furthermore, expressions of PCK1, GK, FAS and ACC genes were in significant relation to fat content in the livers of female pigeons, while fat content in male pigeons was highly correlated with expression of PCK1, ACC, CPT1 and ACO genes. In conclusion, regulations of glucose and lipid metabolic processes were enhanced in parent pigeon livers from terminal phases of incubation to mid phase of chick rearing with sexual effects.

Embryonic protein undernutrition by albumen removal programs the hepatic amino acid and glucose metabolism during the perinatal period in an avian model

Different animal models have been used to study the effects of prenatal protein undernutrition and the mechanisms by which these occur. In mammals, the maternal diet is manipulated, exerting both direct nutritional and indirect hormonal effects. Chicken embryos develop independent from the hen in the egg. Therefore, in the chicken, the direct effects of protein deficiency by albumen removal early during incubation can be examined. Prenatal protein undernutrition was established in layer-type eggs by the partial replacement of albumen by saline at embryonic day 1 (albumen-deprived group), compared to a mock-treated sham and a non-treated control group. At hatch, survival of the albumen-deprived group was lower compared to the control and sham group due to increased early mortality by the manipulation. No treatment differences in yolk-free body weight or yolk weight could be detected. The water content of the yolk was reduced, whereas the water content of the carcass was increased in the albumen-deprived group, compared to the control group, indicating less uptake of nutrients from the yolk. At embryonic day 16, 20 and at hatch, plasma triiodothyronine (T₃), corticosterone, lactate or glucose concentrations and hepatic glycogen content were not affected by treatment. At embryonic day 20, the plasma thyroxine (T₄) concentrations of the albumen-deprived embryos was reduced compared to the control group, indicating a decreased metabolic rate. Screening for differential protein expression in the liver at hatch using two-dimensional difference gel electrophoresis revealed not only changed abundance of proteins important for amino acid metabolism, but also of enzymes related to energy and glucose metabolism. Interestingly, GLUT1, a glucose transporter, and PCK2 and FBP1, two out of three regulatory enzymes of the gluconeogenesis were dysregulated. No parallel differences in gene expressions causing the differences in protein abundance could be detected pointing to post-transcriptional or post-translational regulation of the observed differences.

Aryl hydrocarbon receptor activation by dioxin targets phosphoenolpyruvate carboxykinase (PEPCK) for ADP-ribosylation via 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible poly(ADP-ribose) polymerase (TiPARP)

Effects of the environmental toxin and carcinogen 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) include a wasting syndrome associated with decreased gluconeogenesis. TCDD is a potent activator of the aryl hydrocarbon receptor (AHR), a ligand activated transcription factor. The relationship between gene activation by the AHR and TCDD toxicities is not well understood. We recently identified a pathway by which the AHR target gene TiPARP (TCDD-inducible poly(ADP-ribose) polymerase) contributes to TCDD suppression of transcription of phosphoenolpyruvate carboxykinase (PEPCK), a key regulator of gluconeogenesis, by consuming NAD(+) and decreasing Sirtuin 1 activation of the peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α), a transcriptional activator of PEPCK. We report here that TCDD-induced TiPARP also targets PEPCK for ADP-ribosylation. Both cytosolic and mitochondrial forms of PEPCK were found to undergo ADP-ribosylation. Unexpectedly, AHR suppression also enhanced ADP-ribosylation and did so by a poly(ADP-ribose) polymerase-independent mechanism. This report 1) identifies ADP-ribosylation as a new posttranslational modification for PEPCK, 2) describes a pathway by which transcriptional induction of TiPARP by the AHR can lead to a downstream posttranslational change in a TCDD target protein (PEPCK), and 3) reveals that the AHR exerts complex, previously unidentified modulatory effects on ADP-ribosylation.

Cloning and reporter analysis of human mitochondrial phosphoenolpyruvate carboxykinase gene promoter

Phosphoenolpyruvate carboxykinase (PEPCK) is one of the key regulatory enzymes in gluconeogenesis. In human liver, PEPCK is about equally distributed in both cytosol (PEPCK-1) and mitochondria (PEPCK-2). The human pepck2 gene and cDNA have been reported, but the cloning of the promoter region of the pepck2 gene has not been elucidated yet. We isolated and characterized human genomic P1-artificial chromosome (PAC) clones carrying the human pepck2 gene promoter. The oligocapping method revealed that the transcriptional start point (tsp) of the human pepck2 gene is located at 97 bp upstream of the first adenine residue of the translation start site. We also determined the nucleotide sequence to 1819 bp upstream of tsp. Sequence analysis of this region revealed that it contained several potential regulatory elements, including five GC boxes and three CCAAT boxes. Reporter analysis using transient transfection with firefly luciferase synthetic gene indicated 5' flanking region up to 822 bp, and 317 bp upstream of tsp had transcriptional activity. These results suggest that these regions of the human pepck2 gene play an important role for its expression.

Cloning and characterization of bovine cytosolic and mitochondrial PEPCK during transition to lactation

The cytosolic (C) and mitochondrial (M) forms of phosphoenolpyruvate carboxykinase (PEPCK; EC 4.1.1.32) are encoded by two different nuclear genes in mouse, human, and chicken. Our objective was to clone the two forms of PEPCK for bovine and determine their expression during the immediate periparturient interval in dairy cows. Bovine PEPCK-C cDNA contains 2,592 nucleotides and contains 84% similarity to the coding sequence of human PEPCK-C cDNA. A 449-nt partial clone of the 3' end of PEPCK-M is 76% similar to the corresponding sequence of human PEPCK-M. The coding sequence of bovine PEPCK-C and coding sequence of the partial PEPCK-M clone were 58% similar but the similarities in the 3'-untranslated regions were negligible. Northern blot analysis revealed single transcripts of 2.85 and 2.35 kb for PEPCK-C and PEPCK-M, respectively. The transition to lactation did not alter PEPCK-M transcript expression, but expression of PEPCK-C mRNA was transiently increased during early lactation, indicating that enhanced hepatic gluconeogenesis during this period may be tied to enhanced capacity for cytosolic rather than mitochondrial formation of phosphoenolpyruvate.

Changes in mRNA expression for gluconeogenic enzymes in liver of dairy cattle during the transition to lactation

The objective of this study was to profile phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate carboxylase (PC) mRNA expression in the liver of dairy cattle during the peripartum transition and determine changes in abundance of these mRNA in response to protein fed during the prepartum period. Thirty-eight multiparous Holstein cows were fed diets containing either 12% crude protein (CP) and 26% rumen undegradable protein (RUP), 16% CP and 26% RUP, 16% CP and 33% RUP, or 16% CP and 40% RUP on a dry-matter basis beginning 28 d before expected calving. After calving, all cows were fed a common diet through 56 d in milk (DIM). Northern analysis of RNA from liver biopsy samples obtained on days -28, -14, +1, +28, and +56 relative to calving indicated that PC and PEPCK mRNA expression were responsive to onset of lactation but not to prepartum protein or RUP concentration. Abundance of PEPCK mRNA was similar at -28, -14, and +1 DIM but was elevated by +28 and +56 DIM relative to precalving levels. Liver PC mRNA abundance was elevated on +1 DIM, remained elevated through 28 DIM, and declined to precalving levels by 56 DIM. The activity of PC enzyme was correlated (r2 = 0.89) with PC mRNA abundance. The data demonstrate increased abundance of PC mRNA during the early transition period followed by increased abundance of PEPCK mRNA during the postpartum period and suggest increased potential metabolism of lactate, pyruvate, and amino acids that contribute to the liver pyruvate pool.

Human mitochondrial phosphoenolpyruvate carboxykinase 2 gene. Structure, chromosomal localization and tissue-specific expression

The mitochodrial (mt) phosphoenolpyruvate carboxykinase 2 (PCK2) gene was isolated by screening a human genomic library with a rat cytosolic (cy) PCK1 cDNA probe comprising sequences from exons 2-9 and by PCR amplification of human genomic DNA spanning consecutive exons with known primer pairs from mtPCK2 cDNA containing sequences from two putative neighbouring exons. The mtPCK2 gene spans approx. 10 kb and consists of ten exons and nine introns. All exon-intron junction sequences match the classical GT/AG rule. Northern blot analysis of poly(A)+ and total RNA from various tissues revealed one mRNA species of approx. 2.4 kb. The gene is expressed in a variety of human tissues, mainly in liver, kidney, pancreas, intestine and fibroblasts. In contrast with the cytosolic isoenzyme, the mitochondrial form might not have a purely gluconeogenic function. The mtPCK2 gene maps to chromosome 14q11.2-q12, in contrast with the cyPCK1 gene located on 20q13.2-q13.31.

Involvement of HNF-1 in the regulation of phosphoenolpyruvate carboxykinase gene expression in the kidney

The cytosolic form of phosphoenolpyruvate carboxykinase (GTP) (PEPCK) gene is differentially expressed in several tissues. A specific set of regulatory elements in the promoter are responsible for the control of PEPCK gene transcription and, in turn, determine its distinct metabolic role in each tissue. DNase I footprinting analysis of the PEPCK promoter, using nuclear proteins from tissues which express the gene for PEPCK, and transient expression assays in renal cell lines have demonstrated that the HNF-1 recognition motif (P2) in the PEPCK promoter characterizes kidney-specific expression. This site is required also for the response to acidosis. Since the P2 site is not involved in the expression of the PEPCK gene in the liver, we propose that its critical role in the kidney stems from a combination of abundance of HNF-1 together with low concentrations of members of the C/EBP family in this tissue.

The promoter regulatory regions of the genes for the cytosolic form of phosphoenolpyruvate carboxykinase (GTP) from the chicken and the rat have different species-specific roles in gluconeogenesis

Hepatic expression of the gene for phosphoenolpyruvate carboxykinase (GTP) (PEPCK-C) (EC 4.1.1.32) in birds occurs prior to birth and decreases to negligible levels before hatching, whereas in mammals the gene for PEPCK-C in the liver is expressed at birth and is active throughout the life of the animal. The administration of cyclic AMP to adult chickens results in the induction of transcription of the gene for PEPCK-C and the transient accumulation of PEPCK-C mRNA in the liver. DNase I footprint analysis of 330 bp of the avian PEPCK-C promoter immediately 5' of the start-site of transcription indicated the presence of several protein binding domains, purified CAAT/enhancer binding protein alpha, cAMP regulatory element binding protein and nuclear factor-1 bound to these regions of the promoter. Sequences corresponding to an hepatic nuclear factor-1 binding domain and to the insulin response sequence, previously identified in the rat PEPCK-C promoter, were also found in the chicken PEPCK-C promoter. Co-transfection of an expression vector for CAAT/enhancer binding protein alpha or CAAT/enhancer binding protein beta markedly stimulated transcription from both the chicken and rat PEPCK-C promoters in human hepatoma cells. Sequences involved in the regulation of gene transcription by cyclic AMP and insulin were found to reside between -210 and +1 of the avian PEPCK-C promoter. In general, transcription from the avian promoter was more sensitive to inhibition by insulin than was noted for the rat PEPCK-C promoter, which may explain in part the lack of expression of the gene for PEPCK-C in the livers of adult birds.

Regulation of phosphoenolpyruvate carboxykinase (GTP) gene expression

Phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) (PEPCK) is a key enzyme in the synthesis of glucose in the liver and kidney and of glyceride-glycerol in white adipose tissue and the small intestine. The gene for the cytosolic form of PEPCK (PEPCK-C) is acutely regulated by a variety of dietary and hormonal signals, which result in alteration of synthesis of the enzyme. Major factors that increase PEPCK-C gene expression include cyclic AMP, glucocorticoids, and thyroid hormone, whereas insulin inhibits this process. PEPCK-C is absent in fetal liver but appears at birth, concomitant with the capacity for gluconeogenesis. Regulatory elements that control transcription of the PEPCK-C gene in liver, kidney, and adipose tissue have been delineated, and many of the transcription factors that bind to these elements have been identified. Transgenic mice have been especially useful in elucidating the physiological roles of specific sequence elements in the PEPCK-C gene promoter and in demonstrating the key role played at these sites by the isoforms of CAAT/enhancer binding protein in patterning of PEPCK-C gene expression during the perinatal period. The PEPCK-C gene provides a model for the metabolic control of gene transcription.

Identification of differentially expressed genes during hepatocytes development and characterization of their prenatal hormonal induction

Upon birth, the liver acquires new functions as a result of the initiation of expression of key enzymes. One example is the initiation of gluconeogenesis which depends on the induced appearance of phosphoenolpyruvate carboxykinase (P-pyruvate-CK) at birth. To characterize other genes that undergo such regulation, a differential screening was performed on a cDNA library from well-differentiated hepatoma cells. The pattern of tissue-specific and developmental-specific expression was determined for seven genes. Three clones, out of which two encode for the known genes alcohol dehydrogenase class I (ADH) and phenylalanine 4-monooxygenase (PAH) and a new gene (clone 116-3), exhibited a pattern of expression similar to that of the P-pyruvate-CK gene, i.e. their expression was liver and kidney specific and induced in the liver upon birth. Determination of the sequence of clone 116-3 revealed that it belonged to the UDP-glucuronosyltransferases type 2 (UGT2) family and thus was named UGT2B-rH4. To examine whether expression of the various genes could be prematurely induced by hormones in the fetal liver, either high levels of cAMP or low levels of insulin were induced in utero. The results demonstrated that cAMP induced a marked expression only of the genes for P-pyruvate-CK and ADH but not of those for PAH or UGT2B-rH4, while insulin deficiency induced premature expression of all four genes. We suggest that a set of genes whose expression is specifically induced in the liver upon birth can be prematurely induced by the hormones in utero.

Subcellular localization of PEPCK and metabolism of gluconeogenic substrains of renal cell lines

The two gluconeogenic substrains of renal epithelial cells, LLC-PK1-FBPase+ and OKGNG+, have been shown to differ markedly in their metabolism of lactate and pyruvate. OKGNG+ cells consumed lactate as well as pyruvate at high rates in contrast to LLC-PK1-FBPase+ cells, which failed to take up or utilize lactate. (Aminooxy)acetate (AOA), an inhibitor of transamination reactions, was used to further delineate these differences. Lactate consumption of OKGNG+ cells was significantly inhibited by AOA, whereas pyruvate consumption by LLC-PK1-FBPase+ cells was slightly stimulated. Growth of OKGNG+ cultures, however, could be achieved on lactate in the presence of AOA. From these results it was concluded that the cell strains might differ in the subcellular distribution of phosphoenolpyruvate carboxykinase (PEPCK). LLC-PK1-FBPase+ cells may express both mitochondrial and cytosolic PEPCK isoenzymes, whereas OKGNG+ cells express only the mitochondrial isoenzyme. This was tested by directly assaying PEPCK activity in subcellular fractions of the cells. In OKGNG+ cells PEPCK activity fractionated with the mitochondrial marker glutamate dehydrogenase; however, in LLC-PK1-FBPase+ cells two-thirds of PEPCK activity was found in the cytosol. In LLC-PK1-FBPase+ cells, PEPCK activity increased twofold on incubation in acidic culture medium (pH 6.9) for 18 h, in contrast to the PEPCK activity in OKGNG+ cells. Northern blot analysis using cDNA probes specific for the mitochondrial and cytosolic PEPCK mRNAs confirmed the enzyme activity data. In LLC-PK1-FBPase+ cells strong expression of cytosolic PEPCK mRNA was observed, whereas in OKGNG+ cells only very low levels could be detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Significant amounts of glycogen are synthesized from 3-carbon compounds in astroglial primary cultures from mice with participation of the mitochondrial phosphoenolpyruvate carboxykinase isoenzyme

The incorporation was studied of the gluconeogenic substrates lactate, alanine, aspartate and glutamate into glycogen of astroglial primary cultures derived from mouse brain. The incorporation was inhibited by 3-mercaptopicolinate, an inhibitor of one of the characteristic gluconeogenic enzymes, phosphoenolpyruvate carboxykinase. Only the mitochondrial isoenzyme of phosphoenolpyruvate carboxykinase was detectable in the astroglial primary cultures. After the incubation of glucose-starved cells with medium containing a mixture of [6-3H]glucose and [U-14C]glucose, the newly synthesized glycogen showed a 3H/14C ratio which was approximately 15% less than the isotope ratio for the medium. The decrease of the isotope ratio was not significantly inhibited by 3-mercaptopicolinate, indicating a cycling of approximately 15% of the glucose to the level of the triose phosphates before its incorporation into astroglial glycogen. During the initial phase of glycogen resynthesis, the contribution of the gluconeogenic substrates appeared to be higher. This was in agreement with the accumulation of fructose 2,6-bisphosphate during refeeding. A participation of gluconeogenic substrates in glycogen metabolism was also detectable when the glycogen content was not changing significantly.

Transcriptional regulation of the phosphoenolpyruvate carboxykinase gene by cooperation between hepatic nuclear factors

To study the transcriptional regulation of the liver gluconeogenic phenotype, the underdifferentiated mouse Hepa-1c1c7 (Hepa) hepatoma cell line was used. These cells mimicked the fetal liver by appreciably expressing the alpha-fetoprotein and albumin genes but not the phosphoenolpyruvate carboxykinase (PEPCK) gene. Unlike the fetal liver, however, Hepa cells failed to express the early-expressed factors hepatocyte nuclear factor 1 alpha (HNF-1 alpha) and HNF-4 and the late-expressed factor C/EBP alpha, thereby providing a suitable system for examining possible cooperation between these factors in the transcriptional regulation of the PEPCK gene. Transient transfection assays of a chimeric PEPCK-chloramphenicol acetyltransferase construct showed a residual PEPCK promoter activity in the Hepa cell line, which was slightly stimulated by cotransfection with a single transcription factor from either the C/EBP family or HNF-1 alpha but not at all affected by cotransfection of HNF-4. In contrast, cotransfection of the PEPCK construct with members from the C/EBP family plus HNF-1 alpha resulted in a synergistic stimulation of the PEPCK promoter activity. This synergistic effect depended on the presence in the PEPCK promoter region of the HNF-1 recognition sequence and on the presence of two C/EBP recognition sequences. The results demonstrate a requirement for coexistence and cooperation between early and late liver-enriched transcription factors in the transcriptional regulation of the PEPCK gene. In addition, the results suggest redundancy between members of the C/EBP family of transcription factors in the regulation of PEPCK gene expression.

Transcriptional regulation of the phosphoenolpyruvate carboxykinase gene by cooperation between hepatic nuclear factors

To study the transcriptional regulation of the liver gluconeogenic phenotype, the underdifferentiated mouse Hepa-1c1c7 (Hepa) hepatoma cell line was used. These cells mimicked the fetal liver by appreciably expressing the alpha-fetoprotein and albumin genes but not the phosphoenolpyruvate carboxykinase (PEPCK) gene. Unlike the fetal liver, however, Hepa cells failed to express the early-expressed factors hepatocyte nuclear factor 1 alpha (HNF-1 alpha) and HNF-4 and the late-expressed factor C/EBP alpha, thereby providing a suitable system for examining possible cooperation between these factors in the transcriptional regulation of the PEPCK gene. Transient transfection assays of a chimeric PEPCK-chloramphenicol acetyltransferase construct showed a residual PEPCK promoter activity in the Hepa cell line, which was slightly stimulated by cotransfection with a single transcription factor from either the C/EBP family or HNF-1 alpha but not at all affected by cotransfection of HNF-4. In contrast, cotransfection of the PEPCK construct with members from the C/EBP family plus HNF-1 alpha resulted in a synergistic stimulation of the PEPCK promoter activity. This synergistic effect depended on the presence in the PEPCK promoter region of the HNF-1 recognition sequence and on the presence of two C/EBP recognition sequences. The results demonstrate a requirement for coexistence and cooperation between early and late liver-enriched transcription factors in the transcriptional regulation of the PEPCK gene. In addition, the results suggest redundancy between members of the C/EBP family of transcription factors in the regulation of PEPCK gene expression.

Novel marine alkaloids from the tunicate Eudistoma sp. are potent regulators of cellular growth and differentiation and affect cAMP-mediated processes

Six novel alkaloids that contain a fused tetracyclic pyrido[2,3,4-kl]acridine ring system were purified recently from the Red Sea purple tunicate Eudistoma sp. Evaluation of the effects of these alkaloids on cultured neuroblastoma and fibroblast cells revealed that they possess potent growth regulatory properties, and affect cell shape and adhesion. In mouse neuroblastoma cells, the Eudistoma alkaloids inhibited cell proliferation and induced a process of differentiation during which the cells flattened onto the surface, increased considerably in size, and extended long neurites. In hamster fibroblasts the alkaloids slowed down cell multiplication, and caused an exceptional cell flattening or elongation. In a virus-transformed derivative of the hamster fibroblasts the alkaloids restored many aspects of normal cell growth and morphology. In addition, several of the alkaloids mimicked the effects of cAMP analogs on two well-characterized cAMP-mediated processes involved in hepatic glucose metabolism--inhibition of pyruvate kinase (PK) activity and induction of mRNA for phosphoenolpyruvate carboxykinase (PEPCK). All these effects suggest that the Eudistoma alkaloids may act on the cAMP signaling system. However, a single application of these compounds was sufficient to completely block cell multiplication and to induce and sustain differentiation and "reverse transformation". Furthermore, these effects were not readily reversible following removal of the drugs. In contrast, a single application of agents that mimic or elevate cAMP induced a transient response that waned with time in culture, and the effects induced by constant elevation of cAMP reverse rapidly following drug removal. We propose that the Eudistoma alkaloids cause growth inhibition, differentiation, and reverse transformation by modifying the activity state of proteins that are involved in the regulation of cell shape and adhesion and serve as a target for the cAMP and/or other second messenger systems.

Liver-specific expression of a phosphoenolpyruvate carboxykinase-neo gene in genetically modified chickens

In order to investigate the potential of the avian liver for the expression of recombinant proteins in vivo, replication-competent retroviral vectors were used to introduce a recombinant rat phosphoenolpyruvate carboxykinase promoter-driven neomycin resistance gene (PEPCKneo) into early Line 11 Leghorn embryos. After hatching, these birds possessed apparently intact PEPCKneo sequences in most tissues examined, however, the neo protein was expressed preferentially in the liver (up to .45% of total cellular protein). Therefore, the tissue specificity of the PEPCK promoter from the rat was retained in the chicken, although hormone responsiveness was not observed. Retroviral vectors used to transmit the genes were more stable during passage in either fibroblast cells or in the animal if the inserted genes were oriented in the same (sense) direction as the viral genome. After Geneticin drug selection in cultured cells, PEPCKneo mRNA was the predominant recombinant species observed on Northern blots, whereas embryos expressed mostly the RNA species originating in the retroviral long terminal repeats. The results demonstrate the potential usefulness of liver-specific gene expression in chickens, as well as the transcriptional effects observed when a foreign promoter is introduced into the replication-competent vector.

Differential regulation of the rat phosphoenolpyruvate carboxykinase gene expression in several tissues of transgenic mice

The selective expression of a unique copy gene in several mammalian tissues has been approached by studying the regulatory sequences needed to control expression of the rat phosphoenolpyruvate carboxykinase (PEPCK) gene in transgenic mice. A transgene containing the entire PEPCK gene, including 2.2 kb of the 5'-flanking region and 0.5 kb of the 3'-flanking region, exhibits tissue-specific expression in the liver, kidney, and adipose tissue, as well as the hormonal and developmental regulation inherent to endogenous gene expression. Deletions of the 5'-flanking region of the gene have shown the need for sequences downstream of position -540 of the PEPCK gene for expression in the liver and sequences downstream of position -362 for expression in the kidney. Additional sequences upstream of position -540 (up to -2200) are required for expression in adipose tissue. In addition, the region containing the glucocorticoid-responsive elements of the gene used by the kidney was identified. This same sequence was found to be needed specifically for developmental regulation of gene expression in the kidney and, together with upstream sequences, in the intestine. The apparently distinct sequence requirements in the various tissues indicate that the tissues use different mechanisms for expression of the same gene.

Differential regulation of the rat phosphoenolpyruvate carboxykinase gene expression in several tissues of transgenic mice

The selective expression of a unique copy gene in several mammalian tissues has been approached by studying the regulatory sequences needed to control expression of the rat phosphoenolpyruvate carboxykinase (PEPCK) gene in transgenic mice. A transgene containing the entire PEPCK gene, including 2.2 kb of the 5'-flanking region and 0.5 kb of the 3'-flanking region, exhibits tissue-specific expression in the liver, kidney, and adipose tissue, as well as the hormonal and developmental regulation inherent to endogenous gene expression. Deletions of the 5'-flanking region of the gene have shown the need for sequences downstream of position -540 of the PEPCK gene for expression in the liver and sequences downstream of position -362 for expression in the kidney. Additional sequences upstream of position -540 (up to -2200) are required for expression in adipose tissue. In addition, the region containing the glucocorticoid-responsive elements of the gene used by the kidney was identified. This same sequence was found to be needed specifically for developmental regulation of gene expression in the kidney and, together with upstream sequences, in the intestine. The apparently distinct sequence requirements in the various tissues indicate that the tissues use different mechanisms for expression of the same gene.

Induction of phosphoenolpyruvate carboxykinase gene expression by retinoic acid in an adult rat hepatocyte line

Regulation of expression of the phosphoenolpyruvate carboxykinase (PEPCK) gene was examined in an adult rat hepatocyte line, RALA255-10G, that was immortalized with an SV40 temperature-sensitive (ts) A mutant. These hepatocytes express a transformed phenotype at the permissive temperature (33 degrees C) but a differentiated liver phenotype at the nonpermissive temperature (40 degrees C). We have shown previously that RALA255-10G cells express only low levels of liver-specific genes such as albumin and tyrosine aminotransferase at 33 degrees C. In the present study, we demonstrated that at 33 degrees C, PEPCK synthesis and mRNA expression could be detected only in the simultaneous presence of dexamethasone (DEX), retinoic acid, and dibutyryl-cAMP (Bt2cAMP). At 40 degrees C, PEPCK synthesis and mRNA expression were demonstrated in the presence of Bt2cAMP alone, but not in the presence of either DEX or retinoic acid. However, at 40 degrees C, PEPCK gene expression was stimulated by the combination of DEX plus retinoic acid; additionally, DEX and retinoic acid potentiated the Bt2cAMP-mediated PEPCK induction. In RALA255-10G cells, optimal PEPCK gene expression required the simultaneous presence of DEX, retinoic acid, and Bt2cAMP; DEX had to be present at all times. Triiodothyronine (T3) also potentiated the Bt2cAMP-mediated PEPCK gene expression but failed to increase further the induction by DEX/retinoic acid/Bt2cAMP. By performing nuclear runoff assays, we demonstrated that the PEPCK gene transcription rate in the absence or presence of inducing agents was closely related to the levels of the corresponding mRNAs.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmentally regulated interactions of liver nuclear factors with the rat phosphoenolpyruvate carboxykinase promoter

A sequential pattern of interactions of trans-acting factors in rat liver with the phosphoenolpyruvate carboxykinase promoter during late development was observed. A liver-enriched factor, possibly AF1, interacted with the promoter in fetal liver, whereas a factor with the characteristics of C/EBP bound the promoter after birth with the onset of the gene expression.

Developmentally regulated interactions of liver nuclear factors with the rat phosphoenolpyruvate carboxykinase promoter

A sequential pattern of interactions of trans-acting factors in rat liver with the phosphoenolpyruvate carboxykinase promoter during late development was observed. A liver-enriched factor, possibly AF1, interacted with the promoter in fetal liver, whereas a factor with the characteristics of C/EBP bound the promoter after birth with the onset of the gene expression.

Fuel selection and carbon flux during the starved-to-fed transition

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Separate cis-regulatory elements confer expression of phosphoenolpyruvate carboxykinase (GTP) gene in different cell lines

The gene encoding cytosolic phosphoenolpyruvate carboxykinase (GTP) [PEPCK; GTP:oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.32], a key enzyme in gluconeogenesis and glyceroneogenesis, is expressed in tissues that arise from different embryonal origins: the gluconeogenic liver arises from endoderm, whereas the gluconeogenic kidney cortex and glyceroneogenic adipose tissue arise from the mesoderm. To identify the cis-regulatory elements conferring the differential gene expression, PEPCK chimeric genes were transfected into two rat hepatoma cell lines (H4IIEC3 and HTC-M1.1) and mouse adipocytes (3T3F442A), which express the endogenous gene, and into myoblasts and preadipocytes, which do not express it. The results demonstrate that 597 base pairs of the 5' flanking region of the PEPCK gene are sufficient to confer cell-specific gene expression in the PEPCK-expressing hepatoma cells and adipocytes. However, different elements within this 597-base-pair region enhance the gene expression in the hepatoma cells (endoderm) and adipocytes (mesoderm). In the hepatocytes, expression is conferred by two elements--one 5' of position -362 and the other 3' of position -98 with respect to the transcription start site. The region in between these two elements (from -362 to -98), which seems to inhibit the gene expression in the hepatocytes, confers enhanced expression in the adipocytes. Moreover, the distal positive regulatory element of the hepatocytes seems to be orientation and PEPCK promoter dependent. In contrast, the positive regulatory element of the adipocytes seems to act as a more typical enhancer. These results suggest that separate cis-regulatory elements confer cell-specific expression of the PEPCK gene.