Simple methods for production and characterization of rabbit antibodies to human breast tumor estrogen receptors

Steroid hormone receptors

In the three decades since the original discovery of receptors for steroid hormones, much has been learned about the biochemical processes by which these regulatory agents exert their effects in target tissues. The intracellular receptor proteins are potential transcription factors, needed for optimal gene expression in hormone-dependent cells. They are present in an inactive form until association with the hormone converts them to a functional state that can react with target genes. Transformation of the receptor protein to the nuclear binding form appears to involve the removal of both macromolecular and micromolecular factors that act to keep the receptor form reacting with DNA. Much of the native receptor is present in the nucleus, loosely bound and readily extractable, but for some and possibly all steroid hormones, some receptor is in the cytoplasm, perhaps in equilibrium with a nuclear pool. Methods have been developed for the stabilization, purification, and characterization of receptor proteins, and through cloning and sequencing of their cDNAs, primary structures for these receptors are now known. This has led to the recognition of structural similarities among the family of receptors for the different steroid hormones and to the identification of regions in the protein molecule responsible for the various aspects of their function. Monoclonal antibodies recognizing specific molecular domains are available for most receptors. Despite the knowledge that has been acquired, many important questions remain unsolved. How does association with the steroid remove factors keeping the receptor protein in its native state, and how does binding of the transformed receptor to the response element in the promoter region enhance gene transcription? Once it has converted the receptor to the nuclear binding state, is there a further role for the steroid in modulating transcription? Still not entirely clear is the involvement of phosphorylation and/or dephosphorylation in hormone binding, receptor transformation, and transcriptional activation. Less vital to basic understanding but important in the overall picture is whether the native receptors for gonadal hormones are entirely confined to the nucleus or whether there is an intracellular distribution equilibrium. With the effort now being devoted to this field, and with the application of new experimental techniques, especially those of molecular biology, our understanding of receptor function is progressing rapidly. The precise mechanism of steroid hormone action should soon be completely established.

Nuclear binding of the estrogen receptor: a potential predictor for hormone response in metastatic breast cancer

We have previously described an in vitro immunohistochemical test employing anti-receptor antibodies, for demonstrating the nuclear binding characteristics of estrogen receptors (ER) in breast carcinomas. Based on a retrospective analysis of twenty-five patients with estrogen receptor-positive (ER+) breast cancer who were treated with hormone therapy and whose clinical responses were evaluable, we were able to demonstrate that this test may be valuable to predict which, among the ER+ tumors (whether or not they are progesterone receptor positive, PR+), are likely to respond to hormone therapy and which may fail. While tumors in which ER exhibited abnormalities in nuclear binding behavior (ligand-independent nuclear binding or no nuclear binding) failed hormone therapy (16 out of 19 patients), those in which nuclear binding of ER appeared normal (ligand-dependent) in the in vitro test, responded to hormone therapy (5/6 patients). While our previous report dealt with the procedural details, specificity of the reagents, and the design of the study, this report addresses the clinical aspects of this study and response correlation.

Nuclear location of hormone-free estrogen receptors by monoclonal antibodies could be a tissue-fixation dependent artifact

The 'two-step' model proposed by Jensen and his collaborators for explaining estrogen action conceptualized hormone-free estrogen receptors (ER) to be cytoplasmic, and hormone-filled, transformed ER to be nuclear. Applying monoclonal antibodies which recognized epitopes in ER and formaldehyde-fixed tissues, King et al demonstrated exclusively nuclear staining in target tissues utilizing immunoperoxidase technique. Recently these antibodies have become commercially available enabling other investigators to conduct studies. In this report, using these monoclonal antibodies we have demonstrated that a change in the concentration of formaldehyde alters the staining pattern yielding cytoplasmic instead of nuclear staining in calf uterus, MCF-7 cells, and ER(+) human breast cancer. In addition, neutralization of the antibody activity was not achieved with freshly prepared ER(+) cytosols. Formaldehyde-treated cytosols were essential. These results ought to caution investigators in determining in vivo location of antigens based on the staining pattern obtained in fixed tissues. Furthermore, this effect of formaldehyde on estrogen receptors may be applicable to other steroid hormone receptors.

Hormone receptor assays: clinical usefulness in the management of carcinoma of the breast

The revision of the subcellular model of hormone action is described, with an incorporation of potential autocrine mechanisms. A general overview of available assay methodologies considers the major disadvantages of earlier methods and describes in detail the current methodologies (sucrose gradient analysis, dextran-coated charcoal assays, ER-EIA, ERICA). A major concern with clinical correlations of response to hormone receptor levels is the quality assurance of the multicentric programs. Results from national and international programs are considered. The clinical correlations are divided into four major categories: (1) the response to hormone deprivation (oophorectomy or adrenalectomy), (2) the development of specific agents which exploit receptor mechanisms (antiestrogens) or inhibit steroid biosynthesis (aminoglutehimide), (3) the rates of recurrence of tumors following mastectomy, and (4) the correlation of hormone receptors with current adjuvant therapies.

An update on the immunohistochemical localization of estrogen receptors in mammary carcinomas utilizing polyclonal anti-receptor antibodies

An immunohistochemical (IF) method utilizing polyclonal antibodies to cytoplasmic estrogen receptors (ER) and a tissue processing procedure which allows in situ precipitation of cytoplasmic ER without denaturation of antigenic sites were first described in this journal. In this report we present data on the immunohistochemical classification of 153 cases of human breast carcinomas (123 frozen sections, 28 cytological specimens) as ER-positive (IF+) or ER-negative (IF-). Results on correlation between the biochemical vs immunohistochemical assessment of the ER status and the relationship between quantity of ER and the proportion of IF+/IF- tumor cells are presented. In addition, a procedure which has been successfully applied to study in vitro translocation of cytoplasmic ER in cryostat sections of human breast carcinomas is described. A positive correlation between ER translocatability and status of progesterone receptors (PR) was obvious. All biochemical and immunohistochemical data are collectively reviewed and the question of whether the antibodies are detecting Type I ER is examined.

Immunochemical studies of estrogen receptors

Fusion of splenic lymphocytes from Lewis rats, immunized with affinity-purified estrogen receptor from the cytosol of MCF-7 human breast cancer cells, with two different mouse myeloma lines, has provided 13 monoclonal hybridoma lines secreting antiestrophilin antibodies, each of which (with one possible exception) recognizes a different antigenic determinant in the human receptor molecule. Of this library of monoclonal antibodies, some react with estrophilin from all sources tested, some react with mammalian but not avian receptors, whereas one preparation appears specific for estrophilin from primate sources. By proteolytic digestion under controlled conditions with mercury-deactivated papain, chymotrypsin, and trypsin, respectively, it is possible to remove sequentially the determinants recognized by one, two or three of the monoclonal antibodies, leaving the epitopes for the six remaining antibodies investigated on the steroid-binding portion of the receptor. The proteolytic fragment containing the epitope most readily removed (by mercuripapain) also contains the DNA-binding domain of the activated receptor molecule. Immunocytochemical staining, using the peroxidase procedure with various monoclonal antibody preparations, of frozen sections of human breast cancer tissue, fixed in ethanol or in picric acid-formaldehyde reagent, shows clearly that the majority of the native receptor, which appears in the cytosol after tissue homogenization, is actually localized within the nuclear compartment in the intact cell. The immunocytochemical technique also permits the identification of mixed populations of receptor-containing and non-containing cells in human breast cancers.

A comparative study of electrophoretic mobilities of [3H]-estradiol and monohydroxytamoxifen binding components in the cytosols of human breast carcinomas and sera of healthy adult females

Cytosols from human breast carcinomas rich in estrogen receptors (ER) were examined for the presence of [3H]-estradiol (E2) and [3H]-monohydroxytamoxifen (OH-TX) binding components. Polyacrylamide gel electrophoresis was used to examine the comparative anodal mobilities of ER-[3H]-E2 and ER-[3H]-OH-TX complexes, and also to identify any cytosol or serum component that may exhibit preferential high affinity to OH-TX. We have demonstrated that [3H]-OH-TX binds ER with high affinity and the anodal mobility of ER-[3H]-OH-TX complexes is identical to that of ER-[3H]-E2 complexes. We were unable to identify an antiestrogen-specific component in ER-positive or ER-negative cytosols or in sera of healthy adult females. A serum component exhibiting a higher affinity to [3H]-OH-TX and [3H]-DES than to [3H]-E2 has been identified in all the female sera examined, but this binding is of high capacity and is unsaturable by a 1000-fold molar excess of unlabeled E2 or antiestrogens. The electrophoretic mobility of this component is comparable to that of serum albumin.

Translocation of cytoplasmic estrogen receptors to the nucleus: immunohistochemical demonstration utilizing rabbit antibodies to estrogen receptors of mammary carcinomas

Rabbit antibodies to cytoplasmic estrogen receptors (ER) of human breast carcinoma were utilized for investigating steroid-triggered in-vitro translocation of cytoplasmic ER to the nuclear compartment of the estrogen target cells. The immunofluorescent method (IF) previously described (S Raam et al., Eur J Cancer Clin Oncol 18: 1-12, 1982) was employed for immunohistochemical localization of ER. Four cases of normal endometrium, two cancers of the endometrium, and MCF-7 human breast cancer cells were maintained in a steroid free medium and exposed at 37 degrees C for two hours to growth medium alone (control) or to 2.5, 25 or 250 nanomoles of estradiol (E2), diethylstilbestrol (DES), or monohydroxytamoxifen (OH-TX). At the end of the incubation period the cells were processed for intracellular localization of ER. Complete traslocation of IF from the cytoplasm to the nuclear compartment was evident in all normal endometrial cells exposed to E2, DES or OH-TX for two hours. While cells from the endometrial cancer 'S', like the normal cells, translocated IF to the nucleus, cells of another cancer ('KLE') failed to translocate when exposed to E2 or OH-TX. Partial translocation was evident in 'KLE' cells exposed to DES. In MCF-7 cells grown in the absence of E2, IF was exclusively cytoplasmic. When these cells were exposed to the hormones, 50% showed a complete transfer of IF to the nucleus; in 40% a delayed response was evident; 10% failed to translocate. The results revealed the suitability of anti-ER antibodies for investigating the intracellular dynamics of ER in target cells responding to estrogens or antiestrogens.

Immunohistochemical localization of estrogen receptors in human mammary carcinoma using antibodies to the receptor protein

An immunofluorescent method has been developed for localizing estrogen receptors (ER) in frozen sections of human breast cancer biopsies which utilizes the biochemically well-characterized antibodies to the cytoplasmic ER of human breast cancer produced in rabbits. Frozen sections of sixteen breast cancer biopsies, in which the receptor content has been quantified using dextran-coated charcoal assay (DCC technique), were used to study the localization of ER. Two aspects of ER detection, namely "estrogen-binding" and ability to react with the homologous antibodies, have been analyzed and the results compared with those of DCC technique. Fluorescent labelled estrogen method (F.E2) of Pertschuk was utilized to detect the distribution of estrogen binding proteins and the indirect immunofluorescent (IM-AR) method using anti-receptor antibodies to assess the antigenic sites of the receptor protein. In addition to the comparison of the results of three techniques, DCC, IM-AR and F.E2, for ER detection, a procedure for processing the frozen sections, which enables the study of estrogen binding characteristic as well as the antigenic reactivity of the receptor molecules, is described.