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

Abstract

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.

Hormonal regulation of malic enzyme and glucose‐6‐phosphate‐dehydrogenase expression in fetal brown‐adipocyte primary cultures under non‐proliferative conditions

“…These results agree with those reported for adult rat-hepatocyte primary cultures where neither adrenaline nor isoproterenol suppressed the induction of Glc6P dehydrogenase by insulin [24]. The lack of effect of noradrenaline on the suppression of the induction of Glc6P dehydrogenase by insulin in fetal brown adipocytes contrasted with the inhibitory effect observed on malic-enzyme protein content and specific activity after 6 d of culture.…”

Elevation of Glucose 6-Phosphate Dehydrogenase Activity Induced by Amplified Insulin Response in Low Glutathione Levels in Rat Liver

“…G6PD was reported to be induced several fold in the presence of 10 −8  M insulin in primary cultured hepatocytes [7]. Using cultured hepatocytes in the present study, G6PD activity was amplified through a range of insulin concentrations from 10 −10 to 10 −6  M, and the activity was further augmented by GSH deficiency caused by BSO.…”

Primary culture, cellular stress and differentiated function

“…In addition to its rapid metabolic effects on isolated cells, insulin enhances the relatively slow lipogenesis in ,&ort term rat hepatocyte primary cultures [92,93], the action requiring continuing RNA synthesis following a 24-h lag period after cell isolation [92,94]. A similar latent period was observed with %he stimulation of lipogenesis by triiodothyronine in primary cultures of chick embryo hepatocytes [25].…”