Regulation of glucose-6-P dehydrogenase activity in primary rat hepatocyte cultures

Winberry, L; Nakayama, Roderick; Wolfe, Ronald G.; Holten, Darold

doi:10.1016/0006-291x(80)91418-7

Cited by 28 publications

(10 citation statements)

References 20 publications

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“…This observation is consistent with the suggestion that the individual enzymes of lipogenesis are coordinately regulated when responding to physiological stimuli [14,21]. Recently, Winberry et al [22] reported that the activity of glucose-6-phosphate dehydrogenase increased with time when primary rat hepatocyte cultures were maintained for up to eight days. Our data indicate that such a phenomenon also exists for malic enzyme, acetyl-CoA carboxylase, and fatty acid synthetase.…”

Section: Discussionsupporting

confidence: 90%

“…Evidence also exists indicating that long-term changes in the activities of several lipogenic enzymes reflect changes in the rates of synthesis of the enzymes [l 1,22,25,26,38]. Our present results using inhibitors of protein synthesis suggest that the induction of the lipogenic enzymes due to the addition of fructose to the culture medium is a reflection of the synthesis of these proteins.…”

Section: Discussionsupporting

confidence: 63%

“…Using immunochemical techniques, we had previously demonstrated that the induction of ATP-citrate lyase activity by insulin in cultured hepatocytes was the result of an increase in the rate of synthesis of the enzyme [ll]. Further evidence that the induction of lipogenic enzymes is the result of increased enzyme protein synthesis has been presented by Winberry et al [22] for glucose-6-phosphate dehydrogenase, and for acetyl-CoA carboxylase and fatty acid synthetase in chick liver by Fischer and Goodridge [25]. Gompertz and Greenbaum [26] reported that thyroxine stimulated lipogenesis in rat liver slices along with an increase in the formation of oleic acid.…”

Section: Discussionmentioning

confidence: 99%

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Induction of Lipogenic Enzymes in Primary Cultures of Rat Hepatocytes

Spence

Pitot

2005

European Journal of Biochemistry

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Using primary cultures of adult rat hepatocytes, the regulation of the following lipogenic enzymes was studied: glucose-6-phosphate dehydrogenase, malic enzyme, ATP-citrate lyase, acetyl-CoA carboxylase, fatty acid synthetase, and stearoyl-CoA desaturase. The addition to the culture medium of either insulin or triiodothyronine produced a 2-3-fold increase in each of the individual enzyme activities whereas glucagon slightly decreased enzyme activities. The addition to the medium of 8-bromoguanosine 3,'5'-monophosphate had no effect on any of the enzyme activities unless glucose was also added to the culture medium. Glucose addition alone to the culture medium was without any effect; however, glucose enhanced the stimulation of enzyme activity due to insulin. The addition of fructose or glycerol, even in the absence of insulin, increased the activities of each of the enzymes studied 2-3-fold. The increases in enzyme activity brought about by insulin or fructose were apparently the result of de n o w enzyme synthesis, as indicated by the observation that the increases were not noted in the presence of cordycepin or cycloheximide. Immunoprecipitation of ATP-citrate lyase from hepatocytes pulselabeled with [3H]leucine indicated that the induction of this enzyme in response to the addition of fructose or glycerol to the culture medium was the result of an increase in the rate of synthesis of the enzyme. These results indicate that the activity and synthesis of individual enzymes involved in lipogenesis are increased in response to the metabolism of carbohydrate independently in part from hormonal effects.Hepatic fatty acid synthesis is known to be regulated in response to the hormonal and nutritional state of the animal (see reviews, [1,2]). Dietary fructose has been shown to be as effective as glucose in increasing the hepatic production of fatty acids despite its weak action on insulin secretion [3]. Furthermore, Baker et al. [4] reported that dietary fructose, but not glucose, stimulated lipogenesis in diabetic rats. A number of enzymes involved in lipogenesis including ATPcitrate lyase [5,6], acetyl-CoA carboxylase [5,7], fatty acid synthetase [7,8] and stearoyl-CoA desaturase [9] have been induced in livers of diabetic rats by feeding fructose or glycerol.Based upon these and related observations, it has been suggested that the increase in fatty acid synthesis observed following carbohydrate feeding is the result of a buildup of carbohydrate metabolites [3,.Recently, we have presented evidence indicating that the synthesis of glucokinase is regulated in response to the breakdown of carbohydrates and that this regulation may be mediated via cGMP [lo]. It is intriguing to speculate that a common system of regulation may be responsible for the control of metabolic pathways which respond similarly to physiological stimuli. In this report, the regulation of the following lipogenic enzymes was studied using primary cultures of adult rat hepatocytes: glucose-6-phosphate de-

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Section: Discussionsupporting

confidence: 90%

Section: Discussionsupporting

confidence: 63%

Section: Discussionmentioning

confidence: 99%

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Induction of Lipogenic Enzymes in Primary Cultures of Rat Hepatocytes

Spence

Pitot

2005

European Journal of Biochemistry

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“…Using these cells, we showed that insulin induced G6PDH and malic enzyme (35). Recently Winberry et al also reported induction of G6PDH by insulin in cul tured liver cells (36). But neither study provided information on the relation between induction of G6PDH and the regulation of lipogenesis.…”

Section: The Biosynthesismentioning

confidence: 97%

Hormonal Regulations of Glucose-6-Phosphate Dehydrogenase and Lipogenesis in Primary Cultures of Rat Hepatocytes1

Nakamura

Yoshimoto

Aoyama

et al. 1982

The Journal of Biochemistry

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In primary cultured monolayer hepatocytes of adult rats, insulin (1 x 10(-8) M) induced glucose-6-phosphate dehydrogenase [EC 1.1.1.49, G6PDH] several fold in 48 h. It also induced lipogenesis, measured as [1-14C]acetate incorporation in 2 h, in these cells. Of the various lipids, triglycerides and phospholipids were induced markedly, while cholesterol and its esters were not induced. The increase of G6PDH and lipogenesis were parallel. Glucagon, dibutyryl cyclic AMP, triiodothyronine, dexamethasone, epinephrine, isoproterenol, and dibutyryl cyclic GMP were also tested under similar conditions, but none of them caused significant induction of G6PDH or lipogenesis. Use of anti-G6PDH serum showed that induction of G6PDH by insulin was due to increase in the amount of enzyme protein. Insulin was found to increase the rate of synthesis of G6PDH about 3-fold. SDS-polyacrylamide gel electrophoresis of the immunoprecipitable protein revealed that besides G6PDH another radioactive fraction (Mr 37,000) was increased by insulin. This suggests that complete synthesis of G6PDH protein is slowed down in primary cultured hepatocytes and that an apparent nascent peptide of the enzyme accumulates. Although on long-term treatment (48 h), glucagon and dibutyryl cyclic AMP had no effect on lipogenesis, when added with [14C]acetate for 2 h they strongly inhibited lipogenesis. Significant inhibition of lipogenesis by short-term treatment with glucagon was seen even in cells with a high capacity for lipogenesis induced by long-term treatment with insulin. Insulin again stimulated lipogenesis in short-term treatment, but its effect was slight. It is concluded from these results that insulin exerts long-term stimulation of lipogenesis by inducing enzymes related to lipogenesis including G6PDH as well as causing slight stimulation by enhancing supply of substrate for lipogenesis. Glucagon seems to play a minor role in long-term control, but it causes short-term inhibition of lipogenesis.

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“…Conflicting results have been reported by several laboratories using cultured hepatocytes to study G6PDH regulation. Winberry et al (1980) and Kurtz & Wells (1981) have observed that the glucocorticoids and insulin each increased G6PDH activity individually, and when present together they had no additive effect. Nakamura et al (1982), on the other hand, reported that the glucocorticoids had no effect on basal or insulin-stimulated G6PDH activity.…”

mentioning

confidence: 97%

The effect of ethanol, alone and in combination with the glucocorticoids and insulin, on glucose-6-phosphate dehydrogenase synthesis and mRNA in primary cultures of hepatocytes

Stumpo¹,

Kletzien²

1985

Biochemical Journal

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The hormonal regulation of the relative rate of synthesis and mRNA of glucose-6-phosphate dehydrogenase (G6PDH; EC 1.1.1.49) was studied in primary cultures of adult-rat liver parenchymal cells maintained in a chemically defined medium. Maintenance of hepatocytes from starved animals in a culture medium devoid of any hormones resulted in a 4-fold increase in the relative rate of G6PDH synthesis in 48 h. Parallel cultures treated with glucocorticoids alone exhibited a rate of G6PDH synthesis comparable with that in the control cultures, whereas insulin alone caused a 6.5-fold increase in the rate of synthesis in 48 h. However, if the cultures were treated with glucocorticoids and insulin simultaneously, a 13-fold increase in the rate of synthesis was observed. The effect of ethanol, alone and in combination with the hormones, on the relative rate of G6PDH synthesis was studied also. Ethanol alone caused an 8-fold increase in the rate of synthesis in 48 h, whereas the combination of ethanol, glucocorticoid and insulin caused a 25-fold increase. The amount of functional mRNA encoding G6PDH, as measured in a cell-free translation system, was compared with enzyme activity and relative rate of enzyme synthesis. The increases in G6PDH activity and relative rate of synthesis in primary cultures of hepatocytes treated with ethanol, alone and in combination with the glucocorticoids and insulin, were paralleled by comparable increases in G6PDH mRNA. The results of this study show that the glucocorticoids acted in a permissive manner to amplify the insulin stimulation of G6PDH synthesis and that insulin, glucocorticoids and ethanol interact to stimulate synthesis of G6PDH primarily by increasing the concentration of functional G6PDH mRNA.

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Regulation of glucose-6-P dehydrogenase activity in primary rat hepatocyte cultures

Cited by 28 publications

References 20 publications

Induction of Lipogenic Enzymes in Primary Cultures of Rat Hepatocytes

Induction of Lipogenic Enzymes in Primary Cultures of Rat Hepatocytes

Hormonal Regulations of Glucose-6-Phosphate Dehydrogenase and Lipogenesis in Primary Cultures of Rat Hepatocytes1

The effect of ethanol, alone and in combination with the glucocorticoids and insulin, on glucose-6-phosphate dehydrogenase synthesis and mRNA in primary cultures of hepatocytes

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