Transformation of the glucocorticoid receptor in the cell-free cytosol of the neural retina of the chick embryo: changes in the size and charge of the receptor complex during transformation suggest a multistage process

Rapid accumulation of cyclic GMP near activated vitamin D receptors

The mechanisms of early calcitriol (1 alpha,25-dihydroxycholecalciferol) effects, including its receptor activation process as well as its "nongenomic" effects, are poorly understood. Calcitriol causes a rapid accumulation of cGMP, dependent on the presence of normal vitamin D receptors (VDRs). We recently developed an immunocytology method based on rapid microwave fixation suitable to detect the locations of agonist-induced intracellular cGMP accumulation. With the same technique we found that calcitriol induces stepwise and rapid reorganization of VDRs. Here we used this technique to study the subcellular compartmentalization of cGMP accumulation after exposure of cells to various steroid-related agonists and to study the spatial relationship between cGMP accumulation and VDRs. Calcitriol (10 nM) within 15 sec caused clumping of VDRs and accumulation of cGMP around VDR clumps; thereafter (up to 5 min), the cGMP accumulation surrounded VDRs throughout their stepwise reorganization. In fibroblasts from subjects with mutations affecting VDR function, we found disruptions of the calcitriol-induced patterns of cGMP accumulation analogous to the disruptions of VDR reorganization. The colocalization of cGMP accumulation with reorganizing VDRs at early moments after calcitriol addition indicates transduction of the cGMP increase by VDRs inside the cell, rather than by components in the plasma membrane. Other steroid-related agonists caused compartmentalized and sequential changes in cGMP accumulation that seemed specific for each class of agonist. Our findings suggest that compartmentalized cGMP accumulation is an early and common step during activation of steroid-related receptors.

Immunocytology with microwave-fixed fibroblasts shows 1 alpha,25-dihydroxyvitamin D3-dependent rapid and estrogen-dependent slow reorganization of vitamin D receptors

Prior studies have given no evidence for regulation of vitamin D receptor (VDR) compartmentalization or subcellular organization. Microwave fixation (9-15 s) and an indirect immunodetection system of avidin-biotin enhancement and phycoerythrin fluorophore resulted in sufficient spatial and temporal resolution to allow analysis of these processes. We studied cultured fibroblasts from normals or from patients with four different types of hereditary defect compromising VDR function (mutant cells). Compartmentalization of VDRs in the absence of 1,25-dihydroxyvitamin D3 (calcitriol) was regulated by serum or estrogen. VDRs were mainly cytoplasmic in cells cultured without serum and phenol red, but VDRs were mainly intranuclear after addition of serum or an estrogen to cells for at least 18 h (slow regulation). Calcitriol initiated a rapid and multistep process (rapid regulation) of reorganization in a portion of VDRs: clumping within 15-45 s, alignment of clumps along fibrils within 30-45 s, perinuclear accumulation of clumps within 45-90 s, and intranuclear accumulation of clumps within 1-3 min. We found similar rapid effects of calcitriol on VDRs in various other types of cultured cells. These sequential VDR pattern changes showed calcitriol dose dependency and calcitriol analogue specificity characteristic for the VDR. In mutant fibroblasts VDR pattern changes after calcitriol were absent or severely disturbed at selected steps. Treatment of normal cells with wheat germ agglutinin, which blocks protein transport through nuclear pores, also blocked calcitriol-dependent translocation of VDRs. We conclude that immunocytology after microwave fixation provides evidence for regulation of VDR organization and localization.

Glucocorticoid receptor binding to calf thymus DNA. 2. Role of a DNA-binding activity factor in receptor heterogeneity and a multistep mechanism of receptor activation

In the preceding paper [Cavanaugh, A. H., & Simons, S. S., Jr. (1990) Biochemistry (preceding paper in this issue)], we characterized an apparently identical factor in the cytosol and the nuclear extract of HTC cells that is required for the DNA binding of approximately 43% of the activated receptor-glucocorticoid complexes. In the present study, both those activated complexes that are influenced by this factor and the role of this factor in the process of activation are examined. We find that sodium arsenite inhibits only the DNA binding of those complexes that require factor. Conversely, methyl methane-thiolsulfonate inhibits the DNA binding of only those complexes that are independent of factor. These results provide direct chemical evidence for two populations of activated complexes. Double-reciprocal plots revealed that the increase in DNA binding with endogenous factor occurred by recruiting new complexes for DNA binding as opposed to increasing the binding affinity of existing complexes. These results further suggest that factor associates only with the receptor-steroid complex and does not additionally interact with DNA. A saturable association of factor with complexes was indicated since the amount of available factor in cytosolic solutions decreased after activation of the complexes. Sodium molybdate is known to inhibit the activation of HTC cell receptor-steroid complexes. When factor was added to complexes that had been subjected to activating conditions in the presence of the inhibitor sodium molybdate, no increased DNA binding was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that 5 S intermediate state in glucocorticoid receptor transformation contains hsp90 in addition to the steroid-binding protein

Previous studies have shown that the exposure of molybdate-stabilized nontransformed glucocorticoid receptor (GR) of the chick embryonic neural retina to 0.4 M KCl dissociated the 9.5 S complex to a 5 S GR complex, which is an intermediate state in GR transformation. The present study was designed to characterize the 5 S GR complex. It shows that molybdate-stabilized nontransformed 9.5 S GR complex and 5 S GR interact with monoclonal antibodies (MAb) directed against 90 kDa heat shock protein (hsp90), as evidenced by the increase in the sedimentation velocity of these GR-complexes. Electrofocusing of the partially purified molybdate-stabilized nontransformed GR, prepared from [32P]-labeled neural retinas, and of the 5 S GR (derived from molybdate-stabilized preparation) showed that nontransformed GR complex, which has an apparent pI (pI') value of 5.0 +/- 0.2, and 5 S GR, which was resolved in a major peak with a pI' value of 5.8, are phosphorylated. Partially purified 5 S GR, cleared of molybdate and exposed to 25 degrees C, was resolved by electrofocusing into two phosphorylated fractions, one with a pI' value of 6.5, representing the monomeric GR form and the other with a pI' value of 5.1, apparently representing the acidic hsp90. The dissociation of hsp90 from the molybdate-cleared 5 S heterodimer seems to account for the decrease in the negative net charge of 5 S GR from pI' 6.5. Monomeric GR, derived from a molybdate-cleared, partially purified GR preparation, by the exposure to 25 degrees C, did not retain glucocorticoid-binding activity. Molybdate-stabilized 5 S GR was apparently re-assembled into the oligomeric nontransformed state when the salt concentration was reduced. This phenomenon was evident under the low-salt conditions of electrofocusing, by the shift in pI' value of GR from 5.8 to 5.0; and in glycerol density gradients containing 0.15 M KCl, by the shift in the sedimentation of the GR complex from 5 S to 9.5 S.

Analysis of glucocorticoid receptor subspecies binding to DNA-cellulose and isolated nuclei

Conversion of the glucocorticoid receptor into a DNA-binding protein results in the generation of several distinct receptor subspecies (peaks A-E) which can be resolved by anion exchange chromatography. In vitro, the fraction of the receptor population (approx. 40%) which gains a capacity to bind DNA-cellulose is preferentially transformed into the peak A species by a process that was enhanced by the presence of KCl. At 0.4 M KCl, virtually all of the DNA-binding receptor was in the peak A form. Isolated nuclei also exhibit a receptor binding profile similar to that observed with DNA-cellulose.