Differential effects of chelating agents on cytosolic glucocorticoid receptor stability and nuclear binding in vitro

The action of calcitonin on the TM4 Sertoli cell line and on rat Sertoli cell-enriched cultures

The effects of synthetic salmon calcitonin on primary Sertoli cell-enriched cultures and on an established cell line (TM4 cells, derived from immature mouse Sertoli cells) were studied. Synthetic salmon calcitonin stimulated the conversion of [3H]adenine to [3H]cyclic AMP in both cell systems. In addition, this peptide stimulated the secretion of rABP in primary Sertoli cell-enriched cultures prepared from rat testis. Calcitonin also increased the total concentration of both androgen and estrogen receptors in TM4 cells. Because cAMP analogs decreased androgen and estrogen receptor concentrations, the effect of calcitonin on sex steroid receptors may not be mediated by its effect on cyclic AMP in these cells. The possibility that the action of synthetic salmon calcitonin on the receptors might be mediated by a change in cellular Ca2+ was investigated. Lowering extracellular Ca2+ concentrations from 1.5 mM to less than 0.01 mM markedly reduced the concentration of androgen and estrogen receptors; restoration of Ca2+ to 1.5 mM returned receptor levels to normal. When the receptor concentrations were decreased by lowering extracellular Ca2+ concentrations to 0.5 mM, treatment with the calcium ionophore, A23187, restored receptor levels to normal. Although the calcium channel blocker, verapamil, decreased receptor levels, calcitonin partially counteracted its effect. Trifluoperazine, an inhibitor of calmodulin, also diminished androgen and estrogen receptor, levels in the cytosol of TM4 cells. It was concluded that calcitonin stimulates the formation of cyclic AMP and the secretion of rABP by Sertoli cells. This peptide also increases the concentration of androgen and estrogen receptors, possibly by a mechanism that is, in part, Ca2+ -mediated. These results, along with those on Leydig cells, suggest that calcitonin could be a regulator of testicular function.

Effects of metal ions and chelating agents on in vitro stability of glucocorticoid receptors in brain cytosol

In vitro studies in a variety of tissues and cell types suggest that glucocorticoid receptor binding capacity is not static and that binding sites are subject to up- and down-regulatory mechanisms. The interpretation of such studies, however, is often complicated by factors affecting the stability of the receptor. This situation is particularly acute in the absence of ligand because of the increased lability of the unoccupied receptor. Studies reported here investigate effects of various metal ions and chelating agents on the stability of unoccupied [3H]dexamethasone binding sites in whole mouse brain cytosol. Variation in the ionic strength of cytosol, as created by the additions of various monovalent cations (Li+, Na+, K+, Rb+ and Cs+), was found to be an important factor affecting the increased stability of the receptor in vitro. Additions of divalent (Mg++, Ca++, Ba++, and Mn++) and trivalent (La , Cr and Al ) cations to cytosol, however, were generally found to produce a dose-dependent decrease in the stability of the unoccupied receptor. Additions of the chelating agents EDTA, EGTA and 1,10-phenanthroline to cytosol, resulted in differential, and sometimes complex, dose-dependent effects on receptor stability. The complex effects of various combinations of cations and the chelator EDTA were also investigated.