Disease relevance of Pck1

• Overexpression of constitutively active Ras (V61) (or Raf-1 (RafCAAX)) partially represses PEPCK transcription in hepatoma cells [1].
• The gene for cytosolic phosphoenolpyruvate carboxykinase (GTP) [GTP:oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.32] from the rat was isolated from a recombinant library containing the rat genome in phage lambda Charon 4A [2].
• Chloramphenicol acetyltransferase activity was enhanced when the DNA fragment encompassing the upstream HS site was linked to various lengths of the PEPCK promoter or to the heterologous simian virus 40 promoter [3].
• A chimeric gene was constructed in which a 620-base pair fragment of the 5'-end of the PEPCK gene (including 547 base pairs of 5'-flanking sequence) was ligated to the herpes simplex virus thymidine kinase (TK) structural gene [4].
• The amino acid sequence of phosphoenolpyruvate carboxykinase was deduced from the mRNA sequence and confirmed by fast atom bombardment mass spectrometric analysis of peptides generated with trypsin and Staphylococcus aureus V8 protease [5].

Psychiatry related information on Pck1

• In young animals, food deprivation also: (i) reduced liver GK and PK, (ii) increased kidney PEPCK, (iii) decreased muscle PEPCK and (iv) decreased kidney PDH [6].

High impact information on Pck1

• Regulation of phosphoenolpyruvate carboxykinase (GTP) gene expression [7].
• PEPCK-C is absent in fetal liver but appears at birth, concomitant with the capacity for gluconeogenesis [7].
• 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 [7].
• 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 [7].
• Glucocorticoid exposure in late gestation permanently programs rat hepatic phosphoenolpyruvate carboxykinase and glucocorticoid receptor expression and causes glucose intolerance in adult offspring [8].

Chemical compound and disease context of Pck1

• Treatment of ob/ob mice with 30 mg/kg b.i.d. A-769662 decreased hepatic expression of PEPCK, G6Pase, and FAS, lowered plasma glucose by 40%, reduced body weight gain and significantly decreased both plasma and liver triglyceride levels [9].
• However, it replicated the effects of hyperglycemia on Glc-6-Pase and PEPCK gene expression and resulted in a 75% increase in the in vivo flux through Glc-6-Pase (total glucose output) [10].
• Insulin pulses less effective than continuous insulin in inhibiting PEPCK mRNA levels stimulated by cAMP and dexamethasone in perifused hepatoma cells [11].
• To test whether this explains the repression of hepatic phosphoenolpyruvate carboxykinase (PEPCK) by insulin we measured intracellular cAMP, cAMP-dependent protein kinase, mRNAPEPCK, and PEPCK gene transcription in cultured Reuber H4IIE hepatoma cells treated with forskolin with and without insulin [12].
• Effects of 6- and 8-substituted analogs of adenosine 3':5'-monophosphate on phosphoenolpyruvate carboxykinase and tyrosine aminotransferase in hepatoma cell cultures [13].

Biological context of Pck1

• Phosphoenolpyruvate carboxykinase (PEPCK) catalyzes the first committed step in hepatic gluconeogenesis [1].
• Insulin regulation of phosphoenolpyruvate carboxykinase gene expression does not require activation of the Ras/mitogen-activated protein kinase signaling pathway [14].
• The influence of the enhancer of split- and hairy-related protein-2 (SHARP-2) transcriptional repressor on the expression of rat phosphoenolpyruvate carboxykinase (PEPCK) gene was examined [15].
• Finally, when a SHARP-2 expression plasmid was transiently transfected with various reporter plasmids into MH1C1 cells, the promoter activity of a PEPCK reporter plasmid was specifically decreased [15].
• We suggest that this protein factor binds to DNA within the HS site and interacts with the proximal promoter region to control tissue-specific high-level expression of the PEPCK gene [3].

Anatomical context of Pck1

• The adenovirus-mediated overexpression of SHARP-2 in H4IIE cells and primary cultured rat hepatocytes led to a decrease in the levels of PEPCK mRNA [15].
• Phosphoenolpyruvate carboxykinase from the cytosol of rat liver has 13 cysteines, at least one of which is known to be very reactive and essential for catalytic activity (Carlson, G. M., Colombo, G., and Lardy, H. A. (1978) Biochemistry 17, 5329-5338) [16].
• There was no relationship between the number of copies of the PEPCK-TK gene integrated in the various cell lines and either the basal level of TK activity or its inducibility of Bt2cAMP [4].
• Here we show that the PUFA docosahexaenoic acid (DHA) stimulates PEPCK mRNA in glucose-deprived adipose tissue explants from fed rats and in 3T3-F442A differentiated adipocytes [17].
• Evidence for selective induction of phosphoenolpyruvate carboxykinase gene expression by unsaturated and nonmetabolized fatty acids in adipocytes [17].

Associations of Pck1 with chemical compounds

• Using the structurally and mechanistically distinct phosphatidylinositol 3-kinase (PI 3-kinase) inhibitors, wortmannin and LY 294002, we provide further evidence supporting a role for PI 3-kinase activation in the regulation of PEPCK gene transcription by insulin [14].
• When H4IIE cells were treated with epigallocatechin gallate, a green tea constituent, an increase in SHARP-2 mRNA levels and a decrease in PEPCK mRNA levels were observed [15].
• To determine whether altered production or activity of phosphoenolpyruvate carboxykinase or pyruvate kinase was responsible for the reduced glucose synthesis, their mRNA, protein levels and enzyme activities were measured [18].
• Primary hepatocytes co-cultured with lipopolysaccharide-stimulated Kupffer cells or cultured with a combination of IL-1beta and IL-10 displayed reduced levels of phosphoenolpyruvate carboxykinase mRNA, protein and enzyme activity [18].
• A 47-base pair region of the PEPCK promoter was identified which was essential for stimulation by dibutyryl cAMP [19].

Physical interactions of Pck1

• It is suggested that phosphoenolpyruvate carboxykinase rather than amino acid transport is the key pacemaker reaction in the long-term incubation since the direction and magnitude of the response for glucocorticoid and glucagon stimulation of glucose production is the same whether alanine or lactate is used as the 3-carbon precursor [20].
• We have reported that both the IGFBP-1 and PEPCK IRSs bind hepatocyte nuclear factor-3 (HNF-3) proteins [1] [21].

Regulatory relationships of Pck1

• Third, insulin cannot activate p42/p44 MAP kinase in the presence of cAMP even though cAMP-induced PEPCK gene transcription is inhibited by insulin [1].
• SREBP-1c and Sp1 interact to regulate transcription of the gene for phosphoenolpyruvate carboxykinase (GTP) in the liver [22].
• Glucagon and glucocorticoids stimulate PEPCK gene transcription, whereas insulin has a dominant inhibitory effect [1].
• Kupffer cell cytokines interleukin-1beta and interleukin-10 combine to inhibit phosphoenolpyruvate carboxykinase and gluconeogenesis in cultured hepatocytes [18].
• However, PEPCK mRNA is not always reduced in proliferating cells since treatment of serum-starved cells with epidermal growth factor stimulated entry into the cell cycle but did not affect PEPCK mRNA levels [23].

Other interactions of Pck1

• In contrast, three distinct agents, all of which prevent activation of p42/p44 mitogen-activated protein (MAP) kinase, have no effect on the regulation of PEPCK transcription by insulin [1].
• Based on these findings, we conclude that SHARP-2 is a potential repressor of PEPCK gene expression [15].
• Insulin and phorbol esters inhibit basal PEPCK transcription and antagonize the induction of PEPCK gene expression by glucocorticoids and glucagon (or its second messenger cAMP) [14].
• Although phorbol esters activate MAP kinase and mimic the effects of insulin on PEPCK gene transcription, inhibition of MEK has no effect on phorbol ester inhibition of PEPCK gene transcription [14].
• Epidermal growth factor receptor tyrosine kinase inhibition is not protective in PCK rats [24].

Analytical, diagnostic and therapeutic context of Pck1

• In situ hybridization demonstrated expression of PEPCK mRNA only in the medullary rays in controls [25].
• After NH4Cl, PEPCK mRNA was expressed throughout the cortex, confirming the RT-PCR results [25].
• Surgical biopsies of liver from patients undergoing partial hepatectomies and parenchymal hepatocytes derived from the biopsies were used to assay glucokinase, hexokinase and phosphoenolpyruvate carboxykinase activities [26].
• Phosphoenolpyruvate carboxykinase could be detected among the polypeptides synthesized and quantitated by immunoprecipitation with a monospecific antibody followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis [27].
• The 3'-untranslated region of phosphoenolpyruvate carboxykinase mRNA as a potential target was used to select RNA-binding protein(s) from rat liver by the use of gel retardation assays [28].

References