Molecular Coordination of Hepatic Glucose Metabolism by the 6-Phosphofructo-2-Kinase/Fructose-2,6- Bisphosphatase:Glucokinase Complex

Smith, William E.; Langer, Sara; Wu, Chaodong; Baltrusch, Simone; Okar, David A.

doi:10.1210/me.2006-0356

Cited by 30 publications

(33 citation statements)

References 35 publications

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“…Consistent with this hypothesis, we demonstrated in this study that ectopic expression of PFKFB3 in the nucleus did not have a significant effect on total cell glycolysis but rather stimulated cellular proliferation. We should emphasize, however, that our findings should not be interpreted as an argument against the well established role for Fru-2,6-BP in the regulation of glycolysis (43,(45)(46)(47)(48)(49)(50). We suspect that Fru-2,6-BP may be primarily involved in the regulation of glycolysis in normal non-proliferating cells such as neurons and hepatocytes, whereas, in transformed cells, Fru-2,6-BP may serve a dual function in glycolysis and cell cycle regulation.…”

Section: Discussionmentioning

confidence: 54%

Nuclear Targeting of 6-Phosphofructo-2-kinase (PFKFB3) Increases Proliferation via Cyclin-dependent Kinases

Yalçin

Clem

Simmons

et al. 2009

Journal of Biological Chemistry

199

175

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The regulation of metabolism and growth must be tightly coupled to guarantee the efficient use of energy and anabolic substrates throughout the cell cycle. Fructose 2,6-bisphosphate (Fru-2,6-BP) is an allosteric activator of 6-phosphofructo-1-kinase (PFK-1), a rate-limiting enzyme and essential control point in glycolysis. The concentration of Fru-2,6-BP in mammalian cells is set by four 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (PFKFB1-4), which interconvert fructose 6-phosphate and Fru-2,6-BP. The relative functions of the PFKFB3 and PFKFB4 enzymes are of particular interest because they are activated in human cancers and increased by mitogens and low oxygen. We examined the cellular localization of PFKFB3 and PFKFB4 and unexpectedly found that whereas PFKFB4 localized to the cytoplasm (i.e. the site of glycolysis), PFKFB3 localized to the nucleus. We then overexpressed PFKFB3 and observed no change in glucose metabolism but rather a marked increase in cell proliferation. These effects on proliferation were completely abrogated by mutating either the active site or nuclear localization residues of PFKFB3, demonstrating a requirement for nuclear delivery of Fru-2,6-BP. Using protein array analyses, we then found that ectopic expression of PFKFB3 increased the expression of several key cell cycle proteins, including cyclin-dependent kinase (Cdk)-1, Cdc25C, and cyclin D3 and decreased the expression of the cell cycle inhibitor p27, a universal inhibitor of Cdk-1 and the cell cycle. We also observed that the addition of Fru-2,6-BP to HeLa cell lysates increased the phosphorylation of the Cdk-specific Thr-187 site of p27. Taken together, these observations demonstrate an unexpected role for PFKFB3 in nuclear signaling and indicate that Fru-2,6-BP may couple the activation of glucose metabolism with cell proliferation.Neoplastic transformation and growth require a massive increase in glucose uptake and glycolytic flux not only for energy production but also for the synthesis of nucleic acids, amino acids, and fatty acids. A central control point of glycolysis is the negative allosteric regulation of a rate-limiting enzyme, phosphofructokinase-1 (PFK-1), 2 by ATP (i.e. the Pasteur effect) (1, 2). When intracellular ATP production exceeds usage, ATP inhibits PFK-1 and glycolytic flux. Fructose 2,6-bisphosphate (Fru-2,6-BP) is a potent allosteric activator of PFK-1 that overrides this inhibitory influence of ATP on PFK-1, allowing forward flux of the entire pathway (3-5).The steady-state cellular concentration of Fru-2,6-BP is dependent on the activities of bifunctional 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (PFKFB), which are encoded by four independent genes (PFKFB1-4) (6, 7). The PFKFB3 mRNA is distinguished by the presence of multiple copies of an AUUUA instability motif in its 3Ј-untranslated region and the PFKFB3 protein product has a high kinase:phosphatase activity ratio (740:1) (8). PFKFB3 mRNA is overexpressed by rapidly proliferating transformed cells and the PFKFB3 protein is high...

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Section: Discussionmentioning

confidence: 54%

Nuclear Targeting of 6-Phosphofructo-2-kinase (PFKFB3) Increases Proliferation via Cyclin-dependent Kinases

Yalçin

Clem

Simmons

et al. 2009

Journal of Biological Chemistry

199

175

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“…To investigate the function of TIGAR at the outer mitochondrial membrane, we considered previous studies that identified the binding between the bisphosphatase domain of PFK2/ FBPase and glucokinase (27)(28)(29), a member of the HK family expressed mainly in the liver, pancreas, gut, and brain (5). Because TIGAR resembles the bisphosphatase domain of PFK2/ FBPase (16,17), we reasoned that TIGAR might form a complex with HK family members.…”

Section: Resultsmentioning

confidence: 99%

“…Previous studies have suggested that binding to PFK2/FBPase enhances the activity of glucokinase (27,31,32), and so we examined the effect of TIGAR on HK activity under normoxic and hypoxic conditions. Although HK2 depletion by siRNA strongly reduced HK activity in both conditions, a clear reduction in HK activity was also seen after siRNA depletion of TIGAR (Fig.…”

Section: Resultsmentioning

confidence: 99%

Mitochondrial localization of TIGAR under hypoxia stimulates HK2 and lowers ROS and cell death

Cheung

Ludwig

Vousden

2012

Proc. Natl. Acad. Sci. U.S.A.

207

168

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The p53-inducible protein TIGAR (Tp53-induced Glycolysis and Apoptosis Regulator) functions as a fructose-2,6-bisphosphatase (Fru-2,6-BPase), and through promotion of the pentose phosphate pathway, increases NADPH production to help limit reactive oxygen species (ROS). Here, we show that under hypoxia, a fraction of TIGAR protein relocalized to mitochondria and formed a complex with hexokinase 2 (HK2), resulting in an increase in HK2 activity. Mitochondrial localization of TIGAR depended on mitochondrial HK2 and hypoxia-inducible factor 1 (HIF1α) activity. The ability of TIGAR to function as a Fru-2,6-BPase was independent of HK2 binding and mitochondrial localization, although both of these activities can contribute to the full activity of TIGAR in limiting mitochondrial ROS levels and protecting from cell death.cancer metabolism | glycolysis | oxidative stress | low oxygen T he uptake and metabolism of glucose is fundamental for energy production and supporting various anabolic pathways that produce the macromolecules required for cell growth and proliferation. Flux through the different metabolic pathways can be modulated in response to varying growth conditions and demands, as seen in cancer cells, which adopt high rates of aerobic glycolysis that is characterized by extensive glucose uptake and high levels of lactate production (1).Glycolysis can be regulated by changes in the expression or activity of enzymes that catalyze various steps of the pathways. Allosteric regulation or covalent modification of many metabolic enzymes has been described, and the concentration of the active enzyme can also be controlled through changes in transcription, splicing, or protein stability. The subcellular localization of some glycolytic enzymes has also been shown to play an important role in regulating their functions (2, 3). In the first step of glucose metabolism, hexokinases (HK) generate glucose-6-phosphate, which can then be further used through glycolysis to produce energy, diverted into the pentose phosphate pathway (PPP) to produce NADPH and anabolic intermediates or converted to glycogen for storage. HK2 is thought to play a key role in promoting anabolic pathways and is frequently overexpressed in cancers (4). Both HK1 and HK2 show cytoplasmic and-through interaction with voltage-dependent anion-selective channel (VDAC)-mitochondrial localization. The presence of HK at the mitochondria provides a close proximity to intramitochondrial ATP production, which helps to couple glycolysis and oxidative phosphorylation (5). This mitochondrial HK also helps to limit mitochondrial reactive oxygen species (ROS) production by maintaining local ADP levels (6). Furthermore, mitochondrial HK2 can directly inhibit apoptosis through regulation of the mitochondrial permeability transition pore that, in part, reflects the ability to block the recruitment of proapoptotic proteins such as Bax and Bak (7-11). The interaction of HK2 with the phosphoprotein PEA15 is also required for protection from apoptosis under hypoxia (12).Severa...

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“…A tentative hypothesis is that, in the absence of phosphorylation of Ser-32, glucokinase can bind to PFK2 and facilitate formation of fructose-2,6-P 2 through either inhibition of the bisphosphatase, because glucokinase binds to the bisphosphatase domain (8), or channelling involving phosphoglucoisomerase. A further possibility is that glucokinase may increase the kinase activity of PFK2 as suggested from a study on liver homogenates (38). The higher cell content of fructose-2,6-P 2 with titrated glucokinase overexpression in hepatocytes from fa/fa compared with Fa/?…”

Section: Discussionmentioning

confidence: 98%

Contributions of glucokinase and phosphofructokinase-2/fructose bisphosphatase-2 to the elevated glycolysis in hepatocytes from Zuckerfa/farats

Payne

Arden

Lange³

et al. 2007

American Journal of Physiology-Regulatory, Integrative and Comp

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The insulin-resistant Zucker fa/fa rat has elevated hepatic glycolysis and activities of glucokinase and phosphofructokinase-2/fructose bisphosphatase-2 (PFK2). The latter catalyzes the formation and degradation of fructose-2,6-bisphosphate (fructose-2,6-P 2) and is a glucokinasebinding protein. The contributions of glucokinase and PFK2 to the elevated glycolysis in fa/fa hepatocytes were determined by overexpressing these enzymes individually or in combination. Metabolic control analysis was used to determine enzyme coefficients on glycolysis and metabolite concentrations. Glucokinase had a high control coefficient on glycolysis in all hormonal conditions tested, whereas PFK2 had significant control only in the presence of glucagon, which phosphorylates PFK2 and suppresses glycolysis. Despite the high control strength of glucokinase, the elevated glycolysis in fa/fa hepatocytes could not be explained by the elevated glucokinase activity alone. In hepatocytes from fa/fa rats, glucokinase translocation between the nucleus and the cytoplasm was refractory to glucose but responsive to glucagon. Expression of a kinase-active PFK2 variant reversed the glucagon effect on glucokinase translocation and glucose phosphorylation, confirming the role for PFK2 in sequestering glucokinase in the cytoplasm. Glucokinase had a high control on glucose-6-phosphate content; however, like PFK2, it had a relative modest effect on the fructose-2,6-P2 content. However, combined overexpression of glucokinase and PFK2 had a synergistic effect on fructose-2,6-P2 levels, suggesting that interaction of these enzymes may be a prerequisite for formation of fructose-2,6-P2. Cumulatively, this study provides support for coordinate roles for glucokinase and PFK2 in the elevated hepatic glycolysis in fa/fa rats. liver; glucose metabolism; fructose-2,6-bisphosphate THE BIFUNCTIONAL ENZYME 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK2) catalyzes both the formation of fructose-2,6-bisphosphate (fructose-2,6-P 2 ) and its degradation (26,27,35). Fructose-2,6-P 2 is a regulator of glycolysis because it is a potent activator of phosphofructokinase-1 and inhibitor of fructose-1,6-bisphosphatase-1. Various tissue-specific isoforms of PFK2 encoded by four genes are expressed in mammals. They differ in their relative kinase and bisphosphatase activities and also in their regulatory mechanisms (36). The liver isoform is regulated by phosphorylation of a serine residue at the NH 2 terminus (Ser-32) by cAMP-dependent protein kinase, which leads to an increase in the bisphosphatase-to-kinase activity ratio. This mechanism accounts for the lowering of fructose-2,6-P 2 and inhibition of glycolysis caused by glucagon (26).Recent studies by Baltrusch et al. (8) showed that PFK2 binds to glucokinase through the bisphosphatase domain. Putative roles for this heterodimeric interaction have been proposed for both the hepatocyte and pancreatic ␤-cells, which express different isoforms of PFK2 (8,31,34). In pancreatic ␤-cells, binding of PFK2 activates gluc...

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Molecular Coordination of Hepatic Glucose Metabolism by the 6-Phosphofructo-2-Kinase/Fructose-2,6- Bisphosphatase:Glucokinase Complex

Cited by 30 publications

References 35 publications

Nuclear Targeting of 6-Phosphofructo-2-kinase (PFKFB3) Increases Proliferation via Cyclin-dependent Kinases

Nuclear Targeting of 6-Phosphofructo-2-kinase (PFKFB3) Increases Proliferation via Cyclin-dependent Kinases

Mitochondrial localization of TIGAR under hypoxia stimulates HK2 and lowers ROS and cell death

Contributions of glucokinase and phosphofructokinase-2/fructose bisphosphatase-2 to the elevated glycolysis in hepatocytes from Zuckerfa/farats

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