Role of fructose 2,6-bisphosphate in the stimulation of glycolysis by anoxia in isolated hepatocytes

Hue, Louis

doi:10.1042/bj2060359

Cited by 71 publications

(39 citation statements)

References 29 publications

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“…These kinetic properties make the HTC cell enzyme resemble the heart PFK-2 more than liver PFK-2. This might explain why HTC cell Fru(2,6)P2 concentration was not decreased by anoxia and ethanol [6] which, in liver, are thought to inhibit PFK-2 through an increase in sn-glycerol 3-phosphate [18,191. One could argue that the absence of inactivation of HTC cell PFK-2 by cyclic-AMP-dependent protein kinase could result from the fact that the HTC cell enzyme was already in a fully phosphorylated form.…”

Section: Kinetic Properties Of Pfk-2mentioning

confidence: 99%

Rat hepatoma (HTC) cell 6‐phosphofructo‐2‐kinase differs from that in liver and can be separated from fructose‐2,6‐bisphosphatase

Loiseau¹,

Rider²,

Foret³

et al. 1988

European Journal of Biochemistry

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6-Phosphofructo-2-kinase was purified from rat liver and hepatoma (HTC) cells. The HTC cell enzyme had kinetic properties different from those of the liver enzyme (more sensitive to inhibition by citrate and not inhibited by sn-glycerol3-phosphate) and was not a substrate of the cyclic-AMP-dependent protein kinase. Unlike the liver enzyme, which is bifunctional and phosphorylated by fructose 2,6-[2-32P]bisphosphate, the HTC cell enzyme contained no detectable fructose-2,6-bisphosphatase activity and phosphorylation by fructose 2,6-[2-32P]-bisphosphate could not be detected. HTC cell fructose-2,6-bisphosphatase could be separated from 6-phosphofructo-2-kinase activity by purification. Antibodies raised against liver 6-phosphofructo-2-kinase did not precipitate HTC cell fructose-2,6-bisphosphatase whose kinetic properties were completely different from those of the liver enzyme.Fructose 2,6-bisphosphate, Fru(2,6)P2, is an intracellular regulatory molecule that controls glycolysis in mammalian tissues by integrating hormonal and metabolic signals. These signals act through 6-phosphofructo-2-kinase (PFK-2) and fructose-2,6-bisphosphatase (FBPase-2), which catalyze the synthesis and degradation of Fru(2,6)P2, respectively. Both activities are catalysed by a single protein composed of two identical subunits, each of which bears the two catalytic sites. The liver bifunctional enzyme can be phosphorylated on a serine residue by the cyclic-AMP-dependent protein kinase which inactivates PFK-2 and activates FBPase-2. Experimental evidence supports the existence of several PFK-2/FBPase-2 isozymes, which differ from each other in kinetic properties, FBPase-2 content and phosphorylation by protein kinases. (For recent reviews, see [I, 21.) Compared to normal cells, many tumour cells display a high glycolytic rate which is maintained even under aerobic conditions. Recent work has shown that Fru(2,6)P2 might be involved in this phenomenon [3 -61. In addition, several agents or conditions such as cyclic AMP, adenosine, ethanol, and anoxia, which are known to decrease Fru(2,6)P2 concentration in hepatocytes [l, 21, are without effect on this regulator in hepatoma (HTC) cells [6]. This might result from abnormal properties of HTC cell PFK-2. The purpose of this work was to compare PFK-2 from liver and HTC cells. Our results show the two enzymes differ in many respects, but, most of all, in their FBPase-2 content. In HTC cells, FBPase-

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Section: Kinetic Properties Of Pfk-2mentioning

confidence: 99%

Rat hepatoma (HTC) cell 6‐phosphofructo‐2‐kinase differs from that in liver and can be separated from fructose‐2,6‐bisphosphatase

Loiseau¹,

Rider²,

Foret³

et al. 1988

European Journal of Biochemistry

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“…However, ATP depletion also leads to increases in intracellular AMP and adenosine (10,12). Because adenine, adenosine, and some of their thiolated or methylated derivates also inhibit autophagic protein degradation (8,9,35,36), the posibility should be considered that at least part of the autophagy-inhibitory effect of ATP depletion might be mediated by adenosine or AMP, perhaps through AMPK.…”

Section: Effect Of Aicar On the Intracellular Atp Concentration-mentioning

confidence: 99%

Inhibition of Hepatocytic Autophagy by Adenosine, Aminoimidazole-4-carboxamide Riboside, and N 6-Mercaptopurine Riboside

Samari

Seglen

1998

Journal of Biological Chemistry

141

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To examine the role of AMP-activated protein kinase (AMPK; EC 2.7.1.109) in the regulation of autophagy, rat hepatocytes were incubated with the AMPK proactivators, adenosine, 5-amino-4-imidazole carboxamide riboside (AICAR), or N 6 -mercaptopurine riboside. Autophagic activity was inhibited by all three nucleosides, AICAR and N 6 -mercaptopurine riboside being more potent (IC 50 ‫؍‬ 0.3 mM) than adenosine (IC 50 ‫؍‬ 1 mM). 2-Deoxycoformycin, an adenosine deaminase (EC 3.5.4.4) inhibitor, increased the potency of adenosine 5-fold, suggesting that the effectiveness of adenosine as an autophagy inhibitor was curtailed by its intracellular deamination. 5-Iodotubercidin, an adenosine kinase (EC 2.7.1.20) inhibitor, abolished the effects of all three nucleosides, indicating that they needed to be phosphorylated to inhibit autophagy. A 5-iodotubercidin-suppressible phosphorylation of AICAR to 5-aminoimidazole-4-carboxamide riboside monophosphate was confirmed by chromatographic analysis. AICAR, up to 0.4 mM, had no significant effect on intracellular ATP concentrations. Because activated AMPK phosphorylates and inactivates 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase (EC 1.1.1.88), the rate-limiting enzyme in cholesterol synthesis, the strong inhibition of hepatocytic cholesterol synthesis by all three nucleosides confirmed their ability to activate AMPK under the conditions used. Lovastatin and simvastatin, inhibitors of HMG-CoA reductase, strongly suppressed cholesterol synthesis while having no effect on autophagic activity, suggesting that AMPK inhibits autophagy independently of its effects on HMG-CoA reductase and cholesterol metabolism.Numerous biochemical processes are involved in the maintenance and support of cell function and cellular growth. These processes need to be coordinated not only relative to each other but also in relation to the metabolic energy available to the cell. The coordination is generally thought to be effectuated in a diffuse fashion by the adenine nucleotides (AMP, ADP, and ATP), which are both carriers of energy (ATP and ADP) and capable of serving as direct regulators of the activity of many enzymes. Although the cellular energy metabolism is too complex to be described by a manageable algorithm, the activities of most metabolic pathways have been found to correlate reasonably well, positively or negatively, with the overall cellular energy state as embodied e.g. in the concept of "energy charge"In recent years, the enzyme AMP-activated protein kinase (AMPK) 1 (EC 2.7.1.109) has been emerging as a "master switch" that mediates at least part of the coordination between energy state and metabolism (2). The activity of this enzyme is regulated in a complex fashion by adenine nucleotides as well as by an upstream kinase (itself activated by AMP) and becomes active when the AMP level is high relative to ATP. Activated AMPK in turn shuts down energy-requiring pathways like fatty acid and cholesterol synthesis through phosphorylation and inactivation of the pertinent key enzymes while...

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“…Correspondence to G. Mieskes Under some conditions (e. g. anoxia) the increased glycolytic flux cannot be explained by the stimulation of CAMP-dependent protein kinase or by an increase of fructose-2,6-bisphosphate, a potent activator of 6-phosphofructo-lkinase [7]. Garrison et al [8,91 have reported that treatment of hepatocytes with catecholamines, vasopressin, angiotensin I1 or the calcium ionophore A23187 results in a Ca2+-dependent increase of the phosphorylation state of pyruvate kinase.…”

mentioning

confidence: 99%

Are calcium‐dependent protein kinases involved in the regulation of glycolytic/gluconeogenetic enzymes?

Mieskes

Kuduz

Söling

1987

European Journal of Biochemistry

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Changes in glycolytic flux have been observed in liver under conditions where effects of cAMP seem unlikely. We have, therefore, studied the phosphorylation of four enzymes involved in the regulation of glycolysis and gluconeogenesis (6-phosphofructo-1-kinase from rat liver and rabbit muscle; pyruvate kinase, 6-phosphofructo-2-kinase and fructose-l,6-bisphosphatase from rat liver) by defined concentrations of two CAMP-independent protein kinases: Ca2 +/calmodulin-dependent protein kinase and Ca2 +/phospholipid-dependent protein kinase (protein kinase C). The results were compared with those obtained with the catalytic subunit of CAMP-dependent protein kinase. The following results were obtained.1. Ca2 +/calmodulin-dependent protein kinase phosphorylates 6-phosphofructo-1-kinase and L-type pyruvate kinase at a slightly lower rate as compared to CAMP-dependent protein kinase.2. 6-Phosphofructo-1-kinase is phosphorylated by the two kinases at a single identical position. There is no additive phosphorylation. The final stoichiometry is 2 mol phosphate/mol tetramer. The same holds for L-type pyruvate kinase except that the stoichiometry with either kinase or both kinases together is 4 mol phosphate/mol tetramer .3. Rabbit muscle 6-phosphofructo-1-kinase is phosphorylated by CAMP-dependent protein kinase but not by Ca2 +/calmodulin-dependent protein kinase.4. Fructose-1,6-bisphosphatase from rat but not from rabbit liver is phosphorylated at the same position but at a markedly lower rate by Ca2+/calmodulin-dependent protein kinase when compared to the phosphorylation by CAMP-dependent protein kinase.5. 6-Phosphofructo-2-kinase is phosphorylated by Ca2 +/calmodulin-dependent protein kinase only at a negligible rate.6. Protein kinase C does not seem to be involved in the regulation of the enzymes examined: only 6-phosphofructo-2-kinase became phosphorylated to a significant degree. In contrast to the phosphorylation by CAMP-dependent protein kinase, this phosphorylation is not associated with a change of enzyme activity. This agrees with our observation that the sites of phosphorylation by the two kinases are different.The results indicate that Ca2 +/calmodulin-dependent protein kinase but not protein kinase C could be involved in the regulation of hepatic glycolytic flux under conditions where changes in the activity of CAMP-dependent protein kinase seem unlikely.One possible mechanism for the regulation of glycolysis/ gluconeogenesis is the covalent modification of rate-limiting enzymes by phosphorylation/dephosphorylation. For pyruvate kinase and the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (rat liver), the regulatory role of reversible phosphorylation/dephosphorylation is now well established [l -31. This contrasts with 6-phosphofructo-1-kinase and fructose-l,6-bisphosphatase for which the physiological role of this modification remains largely unclear [4 -61.

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Role of fructose 2,6-bisphosphate in the stimulation of glycolysis by anoxia in isolated hepatocytes

Cited by 71 publications

References 29 publications

Rat hepatoma (HTC) cell 6‐phosphofructo‐2‐kinase differs from that in liver and can be separated from fructose‐2,6‐bisphosphatase

Rat hepatoma (HTC) cell 6‐phosphofructo‐2‐kinase differs from that in liver and can be separated from fructose‐2,6‐bisphosphatase

Inhibition of Hepatocytic Autophagy by Adenosine, Aminoimidazole-4-carboxamide Riboside, and N 6-Mercaptopurine Riboside

Are calcium‐dependent protein kinases involved in the regulation of glycolytic/gluconeogenetic enzymes?

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