Resolution of steroid binding heterogeneity by Fourier-derived affinity spectrum analysis (FASA)

Modeling of the separation of the enantiomers of 1-phenyl-1-propanol on cellulose tribenzoate

The competitive adsorption isotherms of rac-1-phenyl-1-propanol on cellulose tribenzoate were measured by competitive frontal analysis. The experimental data were fitted to four different isotherm models: Langmuir, Bilangmuir, Langmuir-Freundlich, and Tóth. The fittings of the experimental data to all four models were satisfactory. It was excellent in the case of the Langmuir-Freundlich and the Tóth models. Overloaded elution profiles calculated with the Tóth isotherm were in good agreement with the experimental profiles in all the different experimental conditions investigated. This work extends to the case of binary mixtures the equivalence between the general rate and the lumped pore diffusion models already demonstrated for pure compounds when the ratio between the Stanton and the Biot numbers exceeds 5. The adsorption energy distribution for the Tóth isotherm was also calculated.

Development and characterization of monoclonal antibodies specific for the murine thyrotropin receptor

We have characterized 10 monoclonal antibodies (Mabs) to recombinant murine thyrotropin receptor extracellular domain (mTSHR-ecd). Affinity purified mTSHR-ecd (amino acids 22-415), expressed in a baculovirus-insect cell system, was refolded in vitro and used to hyperimmunize female Balb/c mice. Spleens were removed 10 days after a final boost of 25 microg mTSHR-ecd intraperitoneally and intravenously, and the cells were fused to SP-2 cells and cloned. Hybridoma supernatants were screened by enzyme-linked immunosorbent assay (ELISA) with folded mTSHR-ecd antigen. Ten of 18 higher affinity hybridomas were selected at random and ascites fluids prepared. Nine of the monoclonals were of IgG 1 isotype, and one was IgM. Five Mabs (M3, M4, M5, M6, and M9) inhibited the binding of 125I-TSH to functional hTSHR expressed on Chinese hamster ovary (CHO) cells, and four (M1, M3, M5, and M9) blocked the TSH-stimulated generation of cyclic adenosine monophosphate (cAMP), using the same cells. The remaining Mabs appeared to be neutral in their interaction with native TSHR. The Mabs were also compared for their reactivity to mTSHR-ecd under folding (ELISA) and unfolding (reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis [SDS-PAGE]) conditions. Most Mabs demonstrated reactivity to both conformational (folded) and linear (unfolded) forms of mTSHR-ecd, suggesting that they were generated primarily against linear epitopes although one Mab (M4) showed affinity for only folded antigen indicating a preference for a conformational epitope. Mapping the Mab epitopes using 26 overlapping peptides spanning the human (h)TSHR-ecd showed that 6 bound peptide 397-415, 1 bound peptide 352-371, and 1 peptide 22-41. These epitope mapped Mabs to the mTSHR-ecd, both receptor blocking and receptor neutral, will provide further insight into the structure-function of the TSHR ectodomain.

Characterization of soluble, disulfide bond-stabilized, prokaryotically expressed human thyrotropin receptor ectodomain

To study the interaction of TSH receptor (TSHR) autoantibodies with receptor protein; it is necessary first to express the receptor in the proper conformation including the formation of correct disulfide bridges. However, the reducing environment of the Escherichia coli (E. coli) cytoplasm prevents the generation of protein disulfide bonds and limits the solubility and immunoreactivity of recombinant human TSHR (hTSHR) products. To circumvent these limitations, hTSHR complementary DNA encoding the extracellular domain (hTSHR-ecd; amino acids 21-415) was inserted into the vector pGEX-2TK by directional cloning and used to transform the thioredoxin reductase mutant strain of E. coli (Ad494), which allowed formation of disulfide bonds in the cytoplasm. After induction, the expressed soluble hTSHR-ecd fusion protein was detected by Western blot analysis using a monoclonal antibody directed against hTSHR amino acids 21-35. This showed that over 50% of the expressed hTSHR-ecd was soluble in contrast to expression in a wild-type E. coli (strain alpha F'), where the majority of the recombinant receptor was insoluble. The soluble recombinant receptor was affinity purified and characterized. Under nonreducing SDS-PAGE conditions, the soluble hTSHR-ecd migrated as refolded, disulfide bond-stabilized, multimeric species, whose formation was independent of fusion partner protein. This product was found to be biologically active as evidenced by the inhibition of the binding of 125I-TSH to the full-length hTSHR expressed in transfected CHO cells and was used to develop a competitive capture enzyme-linked immunosorbent assay for mapping of hTSHR antibody epitopes. Hence, hTSHR-ecd produced in bacteria with a thioredoxin reductase mutation was found to be highly soluble and biologically relevant.

Steroid receptors in the rat hippocampus: a note to the methodology of their binding assay

Mineralocorticoid (MR) and glucocorticoid (GR) receptors in the rat hippocampus are linked to several cognitive functions of the animal and seem to play an important role in the response to various stressors. Their assessment by binding experiments brings about problems associated with their intracellular compartmentalization, and in particular with the separation of the bound and free ligands. Adrenalectomy 24 h before sacrificing is commonly used to clear the circulating adrenal steroids, and to facilitate their dissociation from hippocampal MR and GR. We have successful attempted to use dialysis to these purposes and thus, to avoid a potential surgical stress. Without dialysis, only GR can be measured in the cytosol from intact rats, while the corresponding pellet contains MR as a component of the cell nuclei. The bound ligand fraction was separated by filtration on polyethyleneimine pretreated glass fiber filters as suggested earlier. The method has clear-cut preferences compared to any alternative used up to now. Discrimination between the two receptor types can be optimally achieved in a cross-displacement experiment in which two labeled ligands possessing various affinities to individual receptors (in our case: corticosterone and aldosterone, or their synthetic analogs) are displaced with the two corresponding nonlabelled ligands from their receptors. Computations can be carried out with LIGAND software which yield accurate values of binding parameters.

Multiple receptor populations: binding isotherms and their numerical analysis

This paper reviews present models and methods of parameter estimation in relationships describing receptor-ligand interactions in equilibrium, as used in the author's laboratory. The state-of-the-art and the present experience can be summarized as follows: 1) Binding isotherms (relationships of bound and free/total ligand concentrations) are superpositions of several elementary terms describing the ligand binding to individual binding sites (receptors) present in the biological material investigated. The "nonspecific binding" is usually represented by a linear term. 2) The elementary terms are most frequently described by a rectangular hyperbola, Hill (power) function, or a rational function (binding of several ligand molecules to one molecule of receptor). Heterologous displacement requires specific functions which, however, can be transformed into one of the elementary terms. 3) Parameters (binding capacities, dissociation constants, Hill coefficients, etc.) can most reliably be estimated by nonlinear regression methods. However, these methods frequently fail to yield physically relevant values if initial estimates are far from "real" values, or if the data are strongly scattered. Some of the available routines (e.g., LIGAND) offer manifold tools to solve these difficulties. 4) The "affinity spectrum", a relationship between binding capacities and equilibrium constants, shows the presence of individual binding sites in the binding system in question. The spectrum can be constructed either by Fourier analysis, or by a stepwise procedure (computation of binding capacity for several dissociation constants). The former way of analysis is demanding; software tools are rare. 5) The "STEP" routine based on Hill/Scatchard linearization routines yields profiles similar to affinity spectra, but offers, in addition, values of Hill coefficients of individual binding populations. Values obtained can be used as initial estimates for nonlinear regression. 6) Selection of a suitable model, its testing, numerical procedures, statistical estimates, etc. frequently entail severe difficulties which are approached in the available software packages in different ways, none of them is usually optimal.

Growth-promoting effects of progesterone in a human endometrial cancer cell line (Ishikawa-Var I)

Significant growth responses to progesterone of human endometrial adenocarcinoma cells (Ishikawa-Var I) were observed under in vitro culture conditions. Progesterone affected both the rate of exponential proliferation and cell population densities after the exponential phase. In the presence of the hormone, the doubling time of exponentially proliferating cells was reduced from 44 to 35.6 h and cell densities were increased by as much as 2-3 times over those of controls during approx. 2 weeks in culture. The effects of progesterone on cell population growth were dose dependent. Estradiol (10(-8) M) and testosterone (10(-6) M) did not affect cell densities and the effects of dexamethasone (10(-6) M) were small. In contrast, both progesterone and estradiol stimulated colony formation under anchorage-independent conditions in soft agar. These results suggest the possibility that growth of sensitive cell clones in endometrial tumors could be enhanced in some patients during adjuvant progestin therapy.

Altered estrogen receptor system in estrogen-unresponsive human endometrial adenocarcinoma cells

Previous studies from our laboratories demonstrated that cells from a human endometrial adenocarcinoma cell line (Ishikawa) responded to estradiol whereas cells from another endometrial cancer line (HEC-50) did not. In an attempt to identify factors responsible for the observed estrogen insensitivity we compared the characteristics of the estradiol receptor (ER) systems in Ishikawa and HEC-50 cells. Saturation analyses of cytosolic estrogen binders were performed over a 0.1-70 nM range of [3H]estradiol concentrations. Equilibrium dissociation constants and number of binding sites were determined by graphic analysis of Scatchard plots or computed by applying Fourier-derived affinity spectrum analysis (FASA) of the binding data. No significant differences were noted in the dissociation constants (Kd approx. 0.6 nM) or number of binding sites (approx. 6-10 fmol/mg protein) for the single binder that could be evaluated by the graphic method in cytosol from the two cell lines. However, 2 binders in Ishikawa cells (Kd approx. 0.2 and 6 nM) could be detected by the FASA method; the higher affinity binder in HEC-50 cells could not be clearly demonstrated. Structural differences in the specific estrogen binders which might distinguish HEC-50 from Ishikawa cells or normal endometrial tissue were investigated by using the anti-ER monoclonal antibody JS 34/32. Interaction of the antibody with [3H]estradiol binders of estrogen-responsive cells and tissue was evident from the formation of labeled complexes that were shown to sediment faster in glycerol density gradients and could be immunoprecipitated with Protein A attached to Sepharose beads. In contrast, the antibody did not recognize labeled specific binders in the HEC-50 cells. Furthermore, [3H]estradiol receptors in Ishikawa cells could be transformed into a species that exhibited increased hydrophilicity, evident from its binding to DNA-cellulose, whereas binders from HEC-50 could not. These results indicate that the lack of responsiveness of HEC-50 cells to estrogens might be due to structural or functional alterations in the ER protein resulting in a loss of its capability to undergo estrogen-directed conformational changes required for biological activity.