Hormonal stimulation of mitochondrial pyruvate carboxylation in filipin-treated hepatocytes

Allan, Elizabeth; Chisholm, A B; Titheradge, Michael A.

doi:10.1042/bj2120417

Cited by 31 publications

(21 citation statements)

References 36 publications

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“…The value obtained, 0.86 at 3 mM-Pyr ( In these experiments we did not determine the elasticity coefficients of the Pyr-transport system to Pyrm and Pyr, in the presence of glucagon. However, since glucagon exerts a stimulatory effect on Pyr transport (Adam & Haynes, 1969;Halestrap, 1978;Allan et al, 1983), the elasticity coefficients of the Pyr-transport system to Pyre and Pyrm will also be high in the presence of the hormone.…”

Section: Resultsmentioning

confidence: 97%

Control of gluconeogenesis in rat liver cells. Flux control coefficients of the enzymes in the gluconeogenic pathway in the absence and presence of glucagon

Groen¹,

Roermund²,

Vervoorn³

et al. 1986

Biochemical Journal

168

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We have used control analysis to quantify the distribution of control in the gluconeogenic pathway in liver cells from starved rats. Lactate and pyruvate were used as gluconeogenic substrates. The flux control coefficients of the various enzymes in the gluconeogenic pathway were calculated from the elasticity coefficients of the enzymes towards their substrates and products and the fluxes through the different branches in the pathway. The elasticity coefficients were either calculated from gamma/Keq. ratios (where gamma is the mass-action ratio and Keq. is the equilibrium constant) and enzyme-kinetic data or measured experimentally. It is concluded that the gluconeogenic enzyme pyruvate carboxylase and the glycolytic enzyme pyruvate kinase play a central role in control of gluconeogenesis. If pyruvate kinase is inactive, gluconeogenic flux from lactate is largely controlled by pyruvate carboxylase. The low elasticity coefficient of pyruvate carboxylase towards its product oxaloacetate minimizes control by steps in the gluconeogenic pathway located after pyruvate carboxylase. This situation occurs when maximal gluconeogenic flux is required, i.e. in the presence of glucagon. In the absence of the hormone, when pyruvate kinase is active, control of gluconeogenesis is distributed among many steps, including pyruvate carboxylase, pyruvate kinase, fructose-1,6-bisphosphatase and also steps outside the classic gluconeogenic pathway such as the adenine-nucleotide translocator.

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Section: Resultsmentioning

confidence: 97%

Control of gluconeogenesis in rat liver cells. Flux control coefficients of the enzymes in the gluconeogenic pathway in the absence and presence of glucagon

Groen¹,

Roermund²,

Vervoorn³

et al. 1986

Biochemical Journal

168

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“…For these studies, U251 cells retrovirally infected with constructs encoding non-targeted shRNA or an shRNA targeting beclin 1 were permeabilized with filipin I (5 mM) (a sterol-binding agent that disrupts caveolae to permeabilize the cell 17 ), then incubated with pyruvate (0 or 25 mM) for 2 days beginning 3 days after TMZ exposure (0 or 100 mM, 3 h), after which ATP levels and the percentage of cells undergoing micronucleation were examined. As shown in Figure 5d, ATP levels were not significantly increased by permeabilization or incubation of shNeg control cells with pyruvate, although consistent with data shown in Figure 3c, TMZ exposure increased ATP levels approximately three-to six-fold in the absence or presence of pyruvate.…”

Section: Resultsmentioning

confidence: 99%

DNA damaging agent-induced autophagy produces a cytoprotective adenosine triphosphate surge in malignant glioma cells

et al. 2006

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Although autophagy enhances cell survival in nutrient-deprived cells by increasing adenosine triphosphate (ATP) production, it remains unclear if autophagy functions similarly in cells treated with cytotoxic chemotherapy agents. To address this issue, we measured both the ability of DNA damaging agents (Temozolomide, and Etoposide) to induce an autophagy-dependent production of ATP, and the effects of modulation of autophagy on drug-induced cell death. Both drugs induced an autophagyassociated increase in ATP production in multiple glioma cell lines. The drug-induced ATP surge could not be blocked by glucose starvation, but could be blocked by preincubation with the autophagy inhibitor 3-methyladenine (3-MA), an siRNA targeting beclin 1, or the mitochondrial inhibitor oligomycin. Inhibition of autophagy-induced ATP production increased nonapoptotic cell death associated with micronucleation, while restoration of the 3-MA-inhibited ATP surge by addition of pyruvate suppressed cell death. These results show that DNA damaging agents induce an autophagy-associated ATP surge that protects cells and may contribute to drug resistance. Autophagy is a process by which subcellular constituents are degraded in autophagosomes/autolysosomes in response to stress. 1 Whereas growth factors enhance the ability of metazoan cells to take up extracelluar nutrients and suppress autophagy, deprivation of either growth factors or extracellular nutrients leads to decreased nutrient uptake and derepression of autophagy. The catabolic autophagy process is believed to allow starving cells to support adenosine triphosphate (ATP) production and avoid cell death. 2,3 The autophagic process is regulated by both class I and class III phosphatidylinositol 3-kinase (PI3K) pathways. 2,4,5 Mammalian target of Rapamycin (mTOR) functions downstream of the class-I PI3K/Akt, and is a key negative regulator of autophagy. In this role, mTOR serves as a metabolic sensor that coordinates crosstalk between nutrient availability and autophagy. 6,7 In contrast, class III PI3K positively regulates autophagy. The formation of a preautophagosomal isolation membrane that encloses cytoplasmic cargo is positively regulated by phosphatidylinositol 3-phosphate, the products of class III PI3K phosphorylation. 4 It has also been suggested that the trafficking of autophagosomes is regulated by class III PI3Ks, 4,5 an idea supported by the observation that 3-methyladenine (3-MA), which inhibits class III PI3K activity, also inhibits autophagosome formation and is widely used as an autophagy inhibitor. 5 It is also known that autophagy is induced in cancer cells derived from tissues such as breast, colon, prostate and brain in response to a variety of anticancer therapies. 3,8 However, autophagy in response to these drugs can produce different outcomes, in some cases promoting cell adaptation and survival similar to what is seen in nutrient deprived cells, while in other cases, inducing programmed cell death type. The role of drug-induced autophagy in cell death or surv...

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“…ATP was determined by using firefly luciferin-luciferase [27]. Other assays Cellular pyruvate carboxylation was assayed essentially as described in [28], except that (a) liver cells were preincubated in Krebs buffer [17] containing 2% bovine serum albumin, 10 mM-lactate and 1 mM-pyruvate for 20 min, and (b) saponin (200 ,tg/ml) was used to permeabilize the cells. PEPCK was assayed at 37°C in the physiological direction in extracts of isolated liver cells as previously described [29,30].…”

Section: Vol 242mentioning

confidence: 99%

“…1), even though glucagon is thought to inhibit flux through pyruvate kinase substantially (reviewed in [40]). A variety of experimental approaches have implicated pyruvate carboxylation as an important controlling step in gluconeogenesis from lactate and pyruvate ( [28], [41] and references therein); this step could therefore be proposed as a plausible locus for the action of endotoxin. Table 1, however, shows that endotoxin treatment not only inhibits gluconeogenesis from substrates (lactate plus pyruvate, alanine) which require pyruvate carboxylase for their conversion into glucose, but also inhibits that from substrates (asparagine, proline, glutamine) which do not (Scheme 1).…”

Section: Site Of Inhibition Of Gluconeogenesis By Endotoxinmentioning

confidence: 99%

The characteristics and site of inhibition of gluconeogenesis in rat liver cells by bacterial endotoxin. Stimulation of phosphofructokinase-1

Knowles¹,

McCabe²,

Beevers³

et al. 1987

Biochemical Journal

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The characteristics and site of inhibition of gluconeogenesis by endotoxin were investigated in liver cells isolated from control and endotoxin-treated rats. Endotoxin treatment was associated with inhibition (40-50%) of gluconeogenesis from lactate plus pyruvate over a range of concentrations of substrate and of oleate and with or without glucose or glucagon. Similar inhibition was observed with asparagine, proline, glutamine, alanine and a substrate mixture, but not with glycerol, glyceraldehyde, dihydroxyacetone or endogenous substrates. There was no change in cellular ATP content or in the rates of ketogenesis or ureogenesis from asparagine, proline or glutamine. Other effects on isotopic fluxes, metabolite contents, enzyme activities and control coefficients were consistent with the suggestion that the effects of endotoxin on gluconeogenesis are exerted at the level of phosphofructokinase-1, and not at phosphoenolpyruvate carboxykinase, pyruvate kinase, pyruvate carboxylase or glucokinase.

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Hormonal stimulation of mitochondrial pyruvate carboxylation in filipin-treated hepatocytes

Cited by 31 publications

References 36 publications

Control of gluconeogenesis in rat liver cells. Flux control coefficients of the enzymes in the gluconeogenic pathway in the absence and presence of glucagon

Control of gluconeogenesis in rat liver cells. Flux control coefficients of the enzymes in the gluconeogenic pathway in the absence and presence of glucagon

DNA damaging agent-induced autophagy produces a cytoprotective adenosine triphosphate surge in malignant glioma cells

The characteristics and site of inhibition of gluconeogenesis in rat liver cells by bacterial endotoxin. Stimulation of phosphofructokinase-1

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