Glucocorticoid receptor properties and glucocorticoid regulation of glutamine synthetase activity in sensitive C6 and resistant C6H glial cells

Glucocorticoid receptor properties and glucocorticoid regulation of glutamine synthetase activity... The relationship between induction of glutamine synthetase activity by dexamethasone and binding of the steroid to cytosolic glucocorticoid receptors was examined in sensitive C6 and resistant C6H glial cell cultures. Glutamine synthetase activity increased 3–4‐fold when C6 cultures were exposed to 7.6 × 10−6 M dexamethasone. This inductive response was reversible, dose‐dependent (ED50 ∼ 2 × 10−8 M), required de novo protein and RNA synthesis, and was elicited only by glucocorticoid steroids. Progesterone, but not epicortisol, antagonized the dexamethasone‐induced enzyme increase. In contrast, only a slight inductive effect was observed in dexamethasone‐treated C6H cells. Competitive binding assays demonstrated that specific binding of (3H)‐dexa‐methasone to cytosolic receptors was also dose‐dependent. The ED50 was ∼ 10−8 M for both C6 and C6H cells. Scatchard analysis revealed that each C6 cell contained ∼10,800 receptor sites and that the equilibrium dissociation constant (Kd) was 4.5 × 10−9 M. Each C6H cell possessed ∼ 12,200 sites, and the Kd was 6.7 × 10−9 M. Unlabeled dexamethasone and cortisol (but not epicortisol) competed effectively with (3H)‐dexamethasone for binding to cytosolic receptor sites and nuclear sites of both cell types. These results suggest that induction of glutamine synthetase activity in dexamethasone‐treated C6 cells is a glucocorticoid‐directed response. Since C6H cells are refractory in this regard but contain functional cytosolic receptors which interact with cell nuclei, the basis for their resistance appears to involve some step beyond these cellular processes. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Neuroscience Research Wiley

Glucocorticoid receptor properties and glucocorticoid regulation of glutamine synthetase activity in sensitive C6 and resistant C6H glial cells

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Publisher
Wiley
Copyright
Copyright © 1981 Alan R. Liss, Inc.
ISSN
0360-4012
eISSN
1097-4547
D.O.I.
10.1002/jnr.490060108
Publisher site
See Article on Publisher Site

Abstract

The relationship between induction of glutamine synthetase activity by dexamethasone and binding of the steroid to cytosolic glucocorticoid receptors was examined in sensitive C6 and resistant C6H glial cell cultures. Glutamine synthetase activity increased 3–4‐fold when C6 cultures were exposed to 7.6 × 10−6 M dexamethasone. This inductive response was reversible, dose‐dependent (ED50 ∼ 2 × 10−8 M), required de novo protein and RNA synthesis, and was elicited only by glucocorticoid steroids. Progesterone, but not epicortisol, antagonized the dexamethasone‐induced enzyme increase. In contrast, only a slight inductive effect was observed in dexamethasone‐treated C6H cells. Competitive binding assays demonstrated that specific binding of (3H)‐dexa‐methasone to cytosolic receptors was also dose‐dependent. The ED50 was ∼ 10−8 M for both C6 and C6H cells. Scatchard analysis revealed that each C6 cell contained ∼10,800 receptor sites and that the equilibrium dissociation constant (Kd) was 4.5 × 10−9 M. Each C6H cell possessed ∼ 12,200 sites, and the Kd was 6.7 × 10−9 M. Unlabeled dexamethasone and cortisol (but not epicortisol) competed effectively with (3H)‐dexamethasone for binding to cytosolic receptor sites and nuclear sites of both cell types. These results suggest that induction of glutamine synthetase activity in dexamethasone‐treated C6 cells is a glucocorticoid‐directed response. Since C6H cells are refractory in this regard but contain functional cytosolic receptors which interact with cell nuclei, the basis for their resistance appears to involve some step beyond these cellular processes.

Journal

Journal of Neuroscience ResearchWiley

Published: Jan 1, 1981

References

  • Effect of hydrocortisone on cell morphology in C6 cells
    Berliner, Berliner; Bennett, Bennett; de Vellis, de Vellis
  • Glutamine synthetase localization in cortisol‐induced chick embryo retinas
    Norenberg, Norenberg; Dutt, Dutt; Reif‐Lehrer, Reif‐Lehrer
  • Glucocorticoid stimulation of glutamine synthetase production in cultured rat glioma cells
    Pishak, Pishak; Phillips, Phillips
  • The attractions of proteins for small molecules and ions
    Scatchard, Scatchard

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