Lowering glucose depletes a thapsigargin-sensitive calcium pool and inhibits transcription of the S14 gene.

Abstract

S14 is a nuclear protein that is rapidly and synergistically induced by glucose and thyroid hormone, and the level of it's messenger RNA correlates with hepatocyte and adipocyte lipogenesis. We previously reported that the calcium ionophore A23187 markedly inhibits the carbohydrate response of the S14 gene without inhibiting glucose metabolism. Because the calcium ionophore not only increased intracellular cytosolic free calcium but also depletes intracellular calcium stores, we examined which of these two possibilities accounts for the regulation of S14 gene transcription. We found that increasing cytosolic calcium with arginine vasopressin is insufficient to inhibit S14 gene transcription. Furthermore, reduction of intracellular calcium by addition of EGTA to medium containing A23187 leads to further inhibition of S14 transcription. Measurement of intracellular free calcium in indo-1-loaded hepatocytes showed no significant changes induced by high glucose. These results suggested that depletion of an intracellular pool of calcium by A23187 causes the inhibition of S14 transcription. Addition of thapsigargin, which depletes intracellular calcium pools by inhibition of endoplasmic reticulum Ca2+-ATPase, led to significant inhibition of glucose-regulated S14 transcription. Lastly, continuous incubation in 5.5 mM glucose depletes the thapsigargin-sensitive calcium pool. These studies imply that the ability of glucose to induce S14 transcription is related to a thapsigargin-sensitive calcium pool, and depletion of this pool by lowering glucose inhibits S14 transcription.

A Gonadotropin‐Releasing Hormone Insensitive, Thapsigargin‐Sensitive Ca2+ Store Reduces Basal Gonadotropin Exocytosis and Gene Expression: Comparison with Agonist‐Sensitive Ca2+ Stores

“…Results from the present study provide insight into the functional complexity of the relationship between Ca 2+ and the long‐term release, storage and production of GTH‐II protein, as well as GTH‐II‐ β mRNA levels. Depletion of Ca 2+ in Tg‐sensitive stores caused the emptying of stored GTH‐II and a decrease in GTH‐II‐ β mRNA levels at 12 h and 24 h. Similar to the present study, Tg has also been reported to reduce the transcription of the glucose‐sensitive S14 gene in hepatocytes (58). It is thus tempting to attribute the long‐term decrease in cellular GTH‐II content observed following Tg treatment to its effect on GTH‐II‐ β mRNA levels and a drop in protein synthesis.…”

Signaling pathways between the plasma membrane and endoplasmic reticulum calcium stores

“…Thus, the status of Ca 2 + pools can influence the expression of genes involved in regulating cell growth, and the activity of growth-regulating genes in turn can influence the size and status of endoplasmic reticulum Ca 2 + pools. In recent years, other instances of either activation [108] or inhibition [109] of gene expression clearly linked to depletion of endoplasmic reticulum Ca 2 + have been reported. These findings raise the general question of the role of intracellular Ca 2 + storage in the response to other Ca 2 + -mobilizing stimuli, whether pharmacological (ionophores, SERCA inhibitors) or physiological (phospholipase C-linked agonists).…”

"Spot 14" Protein: A Metabolic Integrator in Normal and Neoplastic Cells

“…The precise identity of the accessory factor for the S14 CHORE has yet to be established. The effect of carbohydrate on S14 gene regulation involves both protein phosphorylation (51), and the maintenance of a specific intracellular calcium pool that signals for reduced transcription (52), indicating further complexity of the regulatory system.…”

“…Work described from the authors' laboratory was supported by NIH grant (to W.B.K.). Mariash C 1996 Insulin increases the processing efficiency of messenger ribonucleic acid-S14 nuclear precursor. Opposing effects of glucagon and triiodothyronine on hepatic levels of messenger ribonucleic acid S14 and the dependence of such effects on circadian factors.…”