Regulation of epidermal growth factor receptor by progestins and glucocorticoids in human breast cancer cell lines

Functions of dehydroepiandrosterone in relation to breast cancer

Although DHEA sulfate (DS) is the most abundant steroid in the circulation, breast fluid contains an approximately 80-fold greater concentration than serum. Transport of DS into cells requires organic anion transporting polypeptides (OATPs), which are specific for cell type, cell location, and substrate, but may have a broader specificity for housekeeping functions. Specific classes, which may be modified by soluble factors including neutral steroids, have been identified in the breast. After transport, DS may be cleaved to DHEA by ubiquitous sulfatases, which may be modified by the cell milieu, or DHEA may enter by diffusion. Synthesis from cholesterol does not occur because CYP17B12 and cytochrome b5 are lacking in breast tissues. Case-control studies reveal a positive association of serum DS with risk of breast cancer. The association is even greater with DHEA, particularly in postmenopausal women with HR + invasive tumors. Metabolites of DHEA, androstenedione and testosterone, are associated with breast cancer but DHEA is likely to have an independent role as well. Mechanisms by which DHEA may promote breast cancer relate to its effect in increasing circulating IGF-I, by inhibiting the suppressive effect of glucocorticoids, and by promoting retention of pre-adipocytes with aromatase activity. In addition, DHEA may interact with the G-protein coupled receptor GPER for stimulation of miR-21 and subsequent activation of the MAPK pathway. DHEA also has antitumor properties that relate to stimulation of immunity, suppression of inflammation, and elevation of adipose tissue adiponectin synthesis. The net effect may depend on the which factors predominate.

Systems pharmacology of mifepristone (RU486) reveals its 47 hub targets and network: comprehensive analysis and pharmacological focus on FAK-Src-Paxillin complex

Mifepristone (RU486), a synthetic steroid compound used as an abortifacient drug, has received considerable attention to its anticancer activity recently. To explore the possibility of using mifepristone as a cancer metastasis chemopreventive, we performed a systems pharmacology analysis of mifepristone-related molecules in the present study. Data were collected by using Natural Language Processing (NLP) and 513 mifepristone-related genes were dug out and classified functionally using a gene ontology (GO) hierarchy, followed by KEGG pathway enrichment analysis. Potential signal pathways and targets involved in cancer were obtained by integrative network analysis. Total thirty-three proteins were involved in focal adhesion-the key signaling pathway associated with cancer metastasis. Molecular and cellular assays further demonstrated that mifepristone had the ability to prevent breast cancer cells from migration and interfere with their adhesion to endothelial cells. Moreover, mifepristone inhibited the expression of focal adhesion kinase (FAK), paxillin, and the formation of FAK/Src/Paxillin complex, which are correlated with cell adhesion and migration. This study set a good example to identify chemotherapeutic potential seamlessly from systems pharmacology to cellular pharmacology, and the revealed hub genes may be the promising targets for cancer metastasis chemoprevention.

Glucocorticoid receptor and breast cancer

Stress enhances glucocorticoid (GC) synthesis, which alters inflammation and immune responses, as well as cellular proliferation and apoptosis in a number of tissues. Increasingly, stress has been associated with cancer progression, and in particular in breast cancer. Consequently, an operational glucocorticoid receptor system in breast tissue influences breast cancer development. In this review, we summarize the data on the GC/GR system in normal and tumoral breast tissue. We also review the molecular mechanisms by which GCs control apoptosis and proliferation in breast cancer models and how GCs alter the chemotherapy of breast cancer treatment when used in combination. Finally, we discuss the participation of GR in breast tumorigenesis under hormone replacement therapy.

The glucocorticoid receptor signalling in breast cancer

Glucocorticoids (GCs) are provided as co-medication with chemotherapy in breast cancer, albeit several lines of evidence indicate that their use may have diverse effects and in fact may inhibit chemosensitivity. The molecular basis of GC-induced resistance to chemotherapy in breast cancer remains poorly defined. Recent researchers, in an attempt to clarify some aspects of the underlying pathways, provide convincing evidence that GCs induce effects that are dependent upon the glucocorticoid-receptor (GR)-mediated transcriptional regulation of specific genes known to play key roles in cellular/tissue functions, including growth, apoptosis, differentiation, metastasis and cell survival. In this review, we focus on how GC-induced chemoresistance in breast cancer is mediated by the GR, unravelling the molecular interplay of GR signalling with other signalling cascades prevalent in breast cancer. We also include a detailed description of GR structure and function, summarizing data gained during recent years into the mechanism(s) of the cross-talk between the GR and other signalling cascades and secondary messengers, via which GCs exert their pleiotropic effects.

The effect of megestrol acetate on growth of HepG2 cells in vitro and in vivo

PURPOSE

Hepatocellular carcinoma (HCC) is generally considered as a sex hormone-dependent tumor, and hormonal therapy has been proposed as a strategy for the treatment of HCC. The aim of the study is to investigate the effect of megestrol acetate, a synthetic progesteronal agent, on growth of HepG2 cells in vitro and in vivo.

EXPERIMENTAL DESIGN

Cell growth in vitro was assessed by a colormetric method, and cell growth in vivo was assessed by tumor volumetrics.

RESULTS

Megestrol acetate was shown to inhibit the growth of HepG2 cells in vitro in dose- and time-dependent manners with an IC (50) of 260 microm (24-h incubation). The growth of HepG2 cell-transplanted tumors in nude mice was also inhibited by i.p. injection of megestrol acetate (10 mg/kg/day). The tumor volumes of the megestrol acetate-treated group regressed to 59% of controls by week 6 and to 41% of controls by week 13. Apoptosis following G(1) arrest was observed in megestrol acetate-treated cells and may be a mechanism through which megestrol acetate inhibits HepG2 cells. Megestrol acetate was also demonstrated to have a beneficial effect on the weight gain of tumor-bearing nude mice, and the mean weight of the megestrol acetate-treated animals was higher than that of controls from week 4 of the treatment period, and the differences were statistically significant in week 5 and 6 (P < 0.05, compared with controls). No significant survival advantage was, however, demonstrated in the treatment group.

CONCLUSIONS

This study showed that megestrol acetate inhibited the growth of HepG2 cells grown in vitro and in vivo. These data provide useful information for clinical study of megestrol acetate for the treatment of HCC.

Glucocorticoid and mineralocorticoid cross-talk with progesterone receptor to induce focal adhesion and growth inhibition in breast cancer cells

Progesterone receptor (PR), glucocorticoid receptor, and mineralocorticoid receptor belong to a subfamily of nuclear receptor superfamily with similar sequence and structural characteristics. Many reports have documented glucocorticoid-like effects of progesterone in various tissues. This study addresses the issue of cross-talk between corticosteroids and PR using PR-transfected MDA-MB-231 cells ABC28 and vector-transfected control cells CTC15. At physiological concentrations, dexamethasone, cortisol, and aldosterone mimic the effects of progesterone by inducing significant growth inhibition, cell spreading, and focal adhesions in PR-positive ABC28 cells. These hormones also induce progesterone-like effects in increasing the expression of p21(CIP1/WAF1) protein and decreasing the level of phospho-p42/p44 mAPK. Two lines of evidence suggest that these effects are mediated by cross-talk with PR. First, these compounds do not exhibit the same progesterone-like effects in PR-negative CTC15 cells. Second, PR blocker ZK98299 abolishes their effect on cell spreading and focal adhesion in ABC28 cells. The cross-talk is corticosteroid specific because estradiol and thyroid hormone triiodothyronine have no effect on PR-transfected cells ABC28. It is also interesting to note that dexamethasone induces a small but detectable increase of focal adhesions and limited growth stimulation in vector-transfected cells CTC15. In contrast, progesterone exhibits no detectable effect on CTC15 cells. This study provides evidence that glucocorticoid and mineralocorticoid cross-talk with PR to produce progesterone-like effects in breast cancer cells. Glucocorticoid receptor and PR share some overlapping activity in mediating focal adhesion but not in regulating cell proliferation.

The glucocorticoid receptor represses the positive autoregulation of the trout estrogen receptor gene by preventing the enhancer effect of a C/EBPbeta-like protein

Stress and cortisol are known to have negative effects on vitellogenesis in oviparous species. This provides a physiological context in which to explore in more detail the molecular mechanisms involved in transcriptional interferences between two steroids receptors, the estradiol receptor (ER) and the glucocorticoid receptor (GR). We have previously shown that the cortisol inhibitory effect on rainbow trout (rt) vitellogenesis is the result of a repression of the estradiol-induced ER-positive autoregulation by activated GR. In the present study, we demonstrate that the GR repression involves a proximal region of the rtER promoter that is unable to bind GR. This inhibition is counteracted in part by the orphan receptor COUP-TF1 that has been previously shown to cooperate with ERs on the same promoter. A detailed analysis allowed us to identify a C/EBPbeta-like protein that is implicated in both the maximal stimulatory effect of estradiol and the GR repression. Indeed, GR, through its DNA-binding domain, suppresses the binding of C/EBPbeta on the rtER promoter by protein-protein interactions and thereby prevents the enhancer effect of this transcription factor.

Transcriptional interference between glucocorticoid receptor and estradiol receptor mediates the inhibitory effect of cortisol on fish vitellogenesis

In oviparous species, the synthesis of vitellogenin (Vg) takes place in the liver according to a strictly estrogen-dependent mechanism that first involves an up-regulation of the estrogen receptor (ER) by its own ligand. However, reports from the literature indicate that in trout stress or cortisol may cause a reduction of cytosolic E2-binding sites in the liver and a decrease in plasma Vg levels. To investigate the mechanisms underlying these effects, in vivo and in vitro experiments were designed in rainbow trout (Oncorhynchus mykiss). The results demonstrate that cortisol implanted into maturing females caused a marked decrease of rainbow trout ER (rtER) and rainbow trout Vg (rtVg) mRNA levels in the liver. In vitro experiments on hepatocyte aggregates also showed that dexamethasone (Dex) caused a strong decrease in the basal and E2-stimulated rtER mRNA and to a lesser extent rtVg mRNA. These effects were specific as no other hormones were able to mimic the inhibitory action of Dex. A study of rtER mRNA stability indicated that the effects of glucocorticoids are likely to take place at the transcriptional level. This was further indicated by transfection experiments in CHO-K(1) cells, which showed that rainbow trout glucocorticoid receptor (rtGR) strongly inhibited the E2-stimulated transcriptional activity of the rtER promoter. Taken together, these results indicate that the rtGR exerts a transcriptional interference on the expression of the rtER that may explain some of the negative effects of stress or cortisol on vitellogenesis.

Progestin regulation of 11beta-hydroxysteroid dehydrogenase expression in T-47D human breast cancer cells

This study examined the enzymatic characteristics and steroid regulation of the glucocorticoid-metabolizing enzyme 11beta-hydroxysteroid dehydrogenase (11beta-HSD) in the human breast cancer cell line T-47D. In cell homogenates, exogenous NAD significantly increased the conversion of corticosterone to 11-dehydrocorticosterone, while NADP was ineffective. There was no conversion of 11-dehydrocorticosterone to corticosterone either with NADH or NADPH demonstrating the lack of reductase activity. In keeping with these results, RT-PCR analysis indicated a mRNA for 11beta-HSD2 in T-47D cells, while 11beta-HSD1 mRNA levels were undetectable. In T-47D cells treated for 24 h with medroxyprogesterone acetate (MPA), 11beta-HSD catalytic activity was elevated 11-fold, while estrone (E(1)), estradiol (E(2)) and the synthetic glucocorticoid dexamethasone (DEX) were ineffective. The antiprogestin mifepristone (RU486) acted as a pure antagonist of the progestin-enhanced 11beta-HSD activity, but did not exert any agonistic effects of its own. In addition, RT-PCR analysis demonstrated that MPA was a potent inducer of 11beta-HSD2 gene expression, increasing the steady-state levels of 11beta-HSD2 mRNA. Taken together, these results demonstrate that 11beta-HSD2 is the 11beta-HSD isoform expressed by T-47D cells under steady-state conditions and suggest the existence of a previously undocumented mechanism of action of progestins in breast cancer cells.

Expression of epidermal growth factor receptor mRNA and protein in primary breast carcinomas

The expression of epidermal growth factor receptor (EGFR) mRNA and protein has been determined in a group of breast carcinomas and compared to oestrogen and progesterone receptor (ER, PgR) status, as well as pathological features. In situ hybridization using a digoxigenin-labelled oligonucleotide probe was applied to formalin-fixed paraffin-embedded sections, and immunohistochemistry was used to determine EGFR protein. EGFR mRNA was detected in 66% of carcinomas with a third having labelling similar to normal breast tissue, 22% heterogeneous weak to strong labelling, and 11% strong labelling. EGFR protein was detected in 36% and these tumours had a strong correlation to lack of ER and high histological grade. The presence of EGFR protein was strongly correlated with more intense labelling for EGFR mRNA (p < 0.0001). This contrasted with normal breast in which both EGFR protein and mRNA were present with varying degrees in both tumours and a normal breast control. The ER-/PgR- carcinomas showed the full range of EGFR mRNA labelling. It is postulated that oestrogen or oestrogen regulated proteins are involved in regulation of EGFR mRNA and protein. In a proportion of tumours lacking steroid receptors regulation is lost, leading to EGFR overexpression.

A single in vivo administration of bombesin antagonist RC-3095 reduces the levels and mRNA expression of epidermal growth factor receptors in MXT mouse mammary cancers

Epidermal growth factor (EGF) and its receptors (EGFR) play important roles in tumorigenesis. In various experimental cancers, treatment with antagonists of bombesin/gastrin-releasing peptide (BN/GRP) produces a reduction in EGFRs, concomitant to inhibition of tumor growth. To investigate the mechanisms involved, we monitored concentrations of BN/GRP antagonist RC-3095 in serum of mice, rats, and hamsters given a single subcutaneous or intravenous injection of this analog. In parallel studies, we measured levels and mRNA expression of EGFRs in estrogen-dependent and independent MXT mouse mammary cancers, following a single subcutaneous administration of RC-3095 to tumor-bearing mice. Peak values of RC-3095 in serum were detected 2 min after intravenous or 15 min after subcutaneous injection. The levels of RC-3095 declined rapidly and became undetectable after 3-5 hr. In the estrogen-dependent MXT tumors, the concentration of EGF receptors was reduced by about 60% 6 hr following injection and returned to original level after 24 hr. Levels of mRNA for EGFR fell parallel with the receptor number and were nearly normal after 24 hr. In the hormone-independent MXT cancers, the number of EGFRs decreased progressively, becoming undetectable 6 hr after injection of RC-3095, and returned to normal values at 24 hr, but EGFR mRNA levels remained lower for 48 hr. Thus, in spite of rapid elimination from serum, BN/GRP antagonist RC-3095 can induce a prolonged decrease in levels and mRNA expression of EGFRs. These findings may explain how single daily injections of BN/GRP antagonists can maintain tumor growth inhibition.

Transcriptional activities of estrogen and glucocorticoid receptors are functionally integrated at the AP-1 response element

Estrogens and glucocorticoids often act in opposition to regulate physiological responses. We investigated whether this might reflect the opposing actions of hormone-bound receptors on target genes regulated by the AP-1 response element. We performed a series of transfection experiments in which transcriptional activation, mediated by the AP-1 response element, was reflected in reporter gene activity. As previously described, we found that estrogens stimulate, whereas the glucocorticoid dexamethasone (Dex) inhibits, transcription through a model promoter from the collagenase gene (-73 to +63). This promoter bears a consensus AP-1 response element. When HeLa cells were treated with both estradiol and Dex, the steroids counteracted each other's transcriptional effects. The amount of transfected estrogen and glucocorticoid receptors (ER and GR) determined the extent to which Dex blunted estrogen stimulation or estrogen prevented Dex inhibition. The ER/GR interaction was observed both in the presence of estradiol and tamoxifen, which has previously been shown to have estrogen-like action at an AP-1 response element. The AP-1 family member c-Jun enhanced Dex inhibition and estradiol stimulation of transcriptional activation. c-Fos potentiated the effect of cotransfected c-Jun on estradiol stimulation but not Dex inhibition. The pattern of steroid responses was retained in the presence of the c-Jun activator phorbol 12-myristate 13-acetate. However, estradiol stimulation was lost in the presence of the c-Jun activator tumor necrosis factor-alpha. The ER/GR/AP-1 response element interaction was present, not only in a cell line originally derived from a uterine cervical adenocarcinoma (HeLa), but also in a cell line derived from the hypothalamus (GT1-1). Lastly, both progesterone receptor types A and B also interacted with the ER at the AP-1 site. These data indicate that opposing steroid influences can be mediated at the level of transcription through the AP-1 site and suggest that the integration of hormone action at this response element may underlie some of the opposing actions of estrogens and glucocorticoids or progestins on physiological responses.

Inverse regulation of oestrogen receptor and epidermal growth factor receptor gene expression in MCF-7 breast cancer cells treated with phorbol ester

In human breast cancer cell lines, an inverse relationship exists between the basal levels of oestrogen receptor (ER) and epidermal growth factor receptor (EGF-R) gene expression. In addition, the tumour-promoting phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA) inhibits ER and stimulates EGF-R expression in MCF-7 breast cancer cells. This study aimed to define further the potential mechanisms involved in the modulation of ER and EGF-R gene expression by TPA. ER mRNA levels were reduced after 3 h and declined to 30% of control between 12 and 72 h after exposure to 10 nM TPA. This decrease in mRNA levels was preceded by an apparent fall in ER transcription rate. There was no effect on the stability of ER mRNA following pretreatment for 3-24 h with TPA, supporting the conclusion that the fall in ER mRNA levels was predominantly due to a decrease in ER transcription rate. Levels of EGF-R mRNA increased 10-fold by 12 h due predominantly to an increased transcription rate. The TPA-induced decrease in ER mRNA was unaffected by the simultaneous administration of the protein synthesis inhibitor cycloheximide, whereas the increase in EGF-R mRNA was inhibited by co-incubation with cycloheximide. These data indicate a requirement for continuing protein synthesis for the TPA effect on EGF-R but not on ER mRNA levels. Because the modulation of ER and EGF-R gene expression by TPA is likely to involve the protein kinase C (PKC) signal transduction pathway, the effects of other known activators of PKC were investigated. The non-phorboid tumour promoter mezerein modulated ER (an 80% decrease) and EGF-R (a 20-fold increase) mRNA levels in a similar manner to TPA. In contrast, neither 1,2-dioctanoyl-sn-glycerol (DiC8) nor 1-oleoyl-2-acetyl-sn-glycerol (OAG), both permeant analogues of the endogenous physiological activators of PKC, affected ER and EGF-R mRNA levels. These latter results were not due to a lack of efficacy because a single administration of DiC8 was as effective as TPA in inducing c-fos mRNA at 30 min. However DiC8 was less active in the later induction of c-myc mRNA. These data demonstrate reciprocal regulation of ER and EGF-R gene expression by TPA, involving effects on transcriptional events, which appear to be mediated by sustained activation of PKC.

Effect of a cytotoxic analog of LH-RH (T-98) on the growth of estrogen-dependent MXT mouse mammary cancers: correlations between growth characteristics and EGF receptor content of tumors

Female BDF mice bearing estrogen-dependent MXT mouse mammary cancers were treated for 4 weeks with a cytotoxic analog of luteinizing hormone-releasing hormone (LH-RH). T-98 (agonist [D-Lys6]LH-RH linked to glutaryl-2(hydroxymethyl)anthraquinone). The effects of T-98 were compared to those of equimolar amounts of the cytotoxic moiety 2-(hydroxymethyl)anthraquinone hemiglutarate (G-HMAQ) and carrier LH-RH agonist [D-Lys6]LH-RH. Both T-98 and [D-Lys6]LH-RH significantly inhibited the growth of MXT cancers, but G-HMAQ had only a minor non-significant effect. Cytotoxic analog T-98 and the carrier [D-Lys6]LH-RH had similar inhibitory hormonal activities on the pituitary-gonadal axis, but T-98 caused a larger reduction in tumor volume and decreased proliferation characteristics such as mitotic activity and AgNOR numbers in tumor cells to a greater extent than the carrier. Tumor inhibition by T-98, [D-Lys6]LH-RH, and ovariectomy was connected with a significant decrease in binding capacity of EGF receptors in tumor cell membranes. The concentration of EGF receptors remained high in tumors that continued to enlarge in spite of treatment and in all control untreated tumors, even those of small size. Thus, the changes in EGF receptors are likely to be the result of the therapy. Treatment with T-98 caused a greater reduction in the binding capacity of EGF receptors in tumors than [D-Lys6]LH-RH. This could explain the higher inhibitory effect of the cytotoxic analog on tumor growth. Since radiolabeled T-98 was shown to accumulate in MXT cancers 3 hours after a subcutaneous injection, this indicates that specific targeting might play a role in the antitumor effect exerted by this cytotoxic analog.

Relationship between receptors for epidermal growth factor and steroid hormones in normal, dysplastic and neoplastic canine mammary tissues

The concentrations of receptors for epidermal growth factor (EGF-R), oestrogen (ER) and progesterone (PR) were measured in 108 samples from canine mammary tumours and 132 samples of normal mammary tissue removed surgically from 84 bitches. The history and clinical signs were also recorded. Binding sites of high affinity were detected in 70 per cent of both types of tissue and no significant variations in EGF-R concentrations or positivity were observed with the histology, location, size or number of mammary tumours or the age of the animal. A significant direct correlation (P = 0.002) was observed between the concentrations of ER and EGF-R only in malignant tumours. The concentrations of EGF-R were significantly correlated (P = 0.04) in normal mammary tissues adjacent to and distant from the lesions, but not between normal tissue and tumour tissue. No significant differences were observed in the expression of EGF-R in normal and neoplastic tissues from the same bitches. The direct correlation between the concentrations of EGF-R and ER in malignant tumours could be related to an oestrogen-dependent expression of EGF-R or to a similar pattern of regulation of the receptors.

Expression of receptors for epidermal growth factor and insulin-like growth factor I by ZR-75-1 human breast cancer cell variants is inversely related: the effect of steroid hormones on insulin-like growth factor I receptor expression

We have investigated the expression of insulin-like growth factor I receptors (IGFR) by the ZR-75-1 human breast cancer cell line and tamoxifen-resistant (ZR-75-9a1) and oestrogen-independent (ZR-PR-LT) variants. ZR-75-1 cells expressed 6633+/-953 receptors per cell,(K(d) 0.24+/-0.06 nM). IGFR expression was reduced in ZR-75-9a1 cells (1180+/-614 receptors per cell, K(d) 0.13+/-0.05) and increased in the ZR-PR-LT cell line (18 430+/-3210 receptors per cell, K(d) 0.24+/-17). A comparison of these data with previously published findings for epidermal growth factor receptor (EGFR) expression by these cell lines revealed that IGFR and EGFR expression are inversely related in the variant lines whereas ZR-75-1 cells express similar numbers of both receptors. Since the changes in IGFR expression observed are associated with changes in steroid hormone receptor status, we also investigated the effects of oestradiol, the synthetic progestin ORG 2058 and dexamethasone on IGFR expression. Oestradiol increased IGFR expression only in the ZR-75-1 cell line. Low concentrations of ORG 2058 increased IGFR levels in the two cell lines positive for progesterone receptor (ZR-75-1 and ZR-PR-LT). High concentrations of ORG 2058 increased IGFR expression in all cell lines, as did dexamethasone. These data suggest that EGFR and IGFR expression may be linked in breast cancer, and that EGFR/IGFR ratios in breast cancer may be a more sensitive prognostic indicator than EGFR expression alone. Regardless of basal IGFR expression by the cell studied, ORG 2058 increased IGFR expression, possibly via both the progesterone and glucocorticoid receptors.

Oestrogen receptor: a stable phenotype in breast cancer

Oestrogen receptor (ER) expression in breast cancer is regarded as a phenotype that may change during the natural history of the disease or during endocrine therapy. It has been suggested that in up to 70% of tumours that show acquired resistance the mechanism may be changed in ER status from positive to negative. This paper proposes an alternative hypothesis that ER expression in a stable phenotype in breast cancer. The paper reviews the literature on ER expression during the natural history of breast cancer in patients and also presents data on the effect of endocrine therapy on ER expression. If the alternative hypothesis is true it has important implications for treatment from chemoprevention to acquired endocrine resistance in advanced disease. Equally, if the hypothesis is true, attempts to develop laboratory models of endocrine resistance where ER-positive tumours become ER negative need to be re-evaluated.

The antiglucocorticoid action of mifepristone

Glucocorticoid hormones influence the physiological activity of almost all cell types in the mammal. This is accomplished via a soluble receptor that, in the presence of an appropriate steroid, modifies the activity of RNA polymerase by binding to the site where different factors assemble for the initiation of cell transcription. The development of antiglucocorticoids has permitted the molecular elucidation of a number of underlying events. Contrary to the classical view, it is now clear that the affinity, stability and activability of the glucocorticoid receptor in the presence of a steroid are cell- and/or tissue-dependent events. The antiglucocorticoid RU 38486 can even activate transcription by binding to sites distinct from those that process transactivation by the agonist. Furthermore, glucocorticoids can sometimes activate the mineralocorticoid receptor, whereas mineralocorticoids can bind the glucocorticoid receptor. Since mifepristone is devoid of adverse toxicity, it has been used for the paraclinical diagnosis of the hypothalamus-pituitary-adrenal axis in normal volunteers, subjects with disorders of the behaviour, and the treatment of Cushing's disease. However, the whole spectrum of cell-specific processes that are antagonized by RU 38486 suggests wide ranging possibilities in the eventual application of antigluco-corticoids.

Mechanisms of action of endocrine treatment in breast cancer

Endocrine treatment plays an important role in the therapy of breast cancer. While the basic mechanisms are understood, additional mechanisms may be of importance to their action and they may also contribute to the mechanism(s) of acquired resistance. Currently, several novel drugs are entering into clinical trials. Observations of the absence or presence of cross resistance to novel 'pure' steroidal antiestrogens and the non-steroidal tamoxifen may add important information to our understanding of the mechanisms of action of both classes of drugs. Similarly, exploration of different aromatase inhibitors in sequence or concert, as well as the combining of different endocrine treatment options may be warranted. Additionally, alterations in different biochemical parameters such as growth factors should not only be carefully explored in relation to treatment options but should also be followed during the course of treatment to asess alterations over time and in relation to the development of drug resistance.

The induction of apoptosis in human mammary luminal epithelial cells by expression of activated c-neu and its abrogation by glucocorticoids

The effects of expressing neu-T, a mutated constitutively activated form of c-neu, have been examined in the non-transformed conditionally immortalised human mammary luminal epithelial cell line, HB4a. A variant cell line, N4.1, which expressed neu-T, showed evidence of transformation, including partial loss of growth factor dependence and acquisition of anchorage-independent growth, but failed to give rise to tumours in nude mice, indicating that expression of neu-T alone was probably insufficient to cause tumorigenic progression to a full malignant phenotype. During characterisation of the N4.1 cell line, it was observed that under conditions of serum deprivation, it underwent apoptotic cell death, as demonstrated by light microscopy, flow cytometry and DNA gel electrophoresis. The induction of apoptotic cell death in the N4.1 cell line by serum deprivation was abrogated specifically by the addition of steroids with glucocorticoid activity but not any peptide growth factors studied. This study shows the induction of apoptosis by serum deprivation, and its abrogation by glucocorticoids occurring in human mammary luminal epithelial cells transformed by expression of neu-T, and implicates the involvement of receptor protein tyrosine kinases in an apoptotic signalling pathway in this cell type.

Prolactin and epidermal growth factor regulation of the proliferation, morphogenesis, and functional differentiation of normal rat mammary epithelial cells in three dimensional primary culture

The epithelial cell-specific effects of prolactin and epidermal growth factor (EGF) on the development of normal rat mammary epithelial cells (MEC) were evaluated using a three dimensional primary culture model developed in our laboratory. Non-milk-producing MEC were isolated as spherical end bud-like mammary epithelial organoids (MEO) from pubescent virgin female rats. The cultured MEO developed into elaborate multilobular and lobuloductal alveolar organoids composed of cytologically and functionally differentiated MEC. Prolactin (0.01-10 micrograms/ml) and EGF (1-100 ng/ml) were each required for induction of cell growth, extensive alveolar, as well as multilobular branching morphogenesis, and casein accumulation. MEO cultured without prolactin for 14 days remained sensitive to the mitogenic, morphogenic, and lactogenic effects of prolactin upon subsequent exposure. Similarly, cells cultured in the absence of EGF remained sensitive to the mitogenic and lactogenic effects of EGF, but were less responsive to its morphogenic effects when it was added on day 14 of a 21-day culture period. If exposure to prolactin was terminated after the first week, the magnitude of the mitogenic and lactogenic effects, but not the morphogenic response was decreased. Removal of EGF on day 7 also reduced the mitogenic response, but did not have any effect on the magnitude of the lactogenic or morphogenic responses. These studies demonstrate that physiologically relevant development of normal MEC can be induced in culture and that this model system can be used to study the mechanisms by which prolactin and EGF regulate the complex developmental pathways operative in the mammary gland.

Changes in oestrogen, progesterone and epidermal growth factor receptor concentrations and affinities during the oestrous cycle in the normal mammary gland and uterus of dogs

Changes in the concentrations and affinities of receptors for oestrogen (ER), progesterone (PR) and epidermal growth factor (EGF-R) were studied in mammary glands of healthy bitches with regard to age, the location in the mammary chain and the stage of the oestrous cycle. Uterus was used as the reference tissue for the evaluation of steroid receptors. Mammary and uterine samples from 7 healthy bitches were taken at five stages of the oestrous cycle in such a way that all the locations in the mammary chain were represented at each stage of the cycle (10 samples/dog). ER, PR and EGF-R were detected by biochemical assays using increasing concentrations of tritiated (steroids) or iodinated (EGF) ligands. A significant direct correlation was found between the ER and PR concentrations for mammary and uterine samples. No significant correlation was found between the steroid receptors and EGF-R concentrations. Mammary ER concentrations were significantly higher in bitches of 5 years of age or older than in younger ones; in posterior glands (4th and 5th pairs) than in anterior glands; and in the mid-luteal phase. Mammary PR did not vary significantly with age or location but was significantly lower in the early luteal phase than in other phases. A similar decrease in PR concentrations was observed in the uterus during the early luteal phase and uterine ER and PR concentrations were very low in the mid-luteal phase. Mammary EGF-R were not significantly higher in the early or mid-luteal phase than in pro-oestrus or anoestrus. The differences observed between the uterine and mammary steroid receptor concentrations during the oestrous cycle could be due to different mechanisms for regulating steroid receptor expression in the two tissues. Mammary EGF-R concentrations may be linked, as in other species, to cellular proliferation and/or to the serum progesterone concentrations.

Dual immunocytochemical analysis of oestrogen and epidermal growth factor receptors in human breast cancer

Recent studies have demonstrated a consistent inverse relationship between oestrogen receptor (ER) and epidermal growth factor receptor (EGFR) levels in female human breast cancer. Serial cross-section studies have suggested that separate populations of ER+/EGFR- and ER-/EGFR+ cancer cells exist in tumours deemed by immunocytochemical assay (ICA) to be positive for both. We have developed a dual ICA that is able to stain for both ER and EGFR on a single 5 microns frozen section sample of breast tissue. Twenty-two samples of female human breast cancer tissue that exhibited positivity for ER and EGFR by ER-ICA using the H222 monoclonal antibody and EGFR-ICA using the EGFR1 monoclonal antibody underwent the dual ICA. There was a significant correlation in receptor positivity between the single and dual assays for both ER (rs = 0.801, P < 0.001) and EGFR (rs = 0.831, P < 0.001). Individual cancer cells exhibited one of three staining patterns: nuclear staining only (ER+/EGFR-), membrane-associated and cytoplasmic staining only (ER-/EGFR+) or no staining (ER-/EGFR-). No cancer cells exhibited both nuclear and membrane/cytoplasmic staining. This is the first description of a simultaneous dual immunocytochemical assay system for ER and EGFR in clinical breast cancer specimens. The results suggest that ER and EGFR expression are mutually exclusive within an individual breast cancer cell in vivo with separate populations of ER+/EGFR- cells, ER-/EGFR+ cells and ER-/EGFR- cells coexisting.

Steroid regulation of oncofetal fibronectin expression in human cytotrophoblasts

Oncofetal fibronectin (onfFN) is a uniquely glycosylated form of FN suggested to play a critical role in uterine/placental adherence during pregnancy. In the present study we have examined steroid regulation of onfFN in highly purified preparations (> or = 95%) of cytotrophoblasts isolated from human term placentas. Based on immunoassays, relative to controls, treatment of cytotrophoblasts with 10(-6) M medroxyprogesterone acetate (MPA) down-regulated media levels of onfFN 25, 53, 59, and 62% on days 1, 2, 3 and 4, respectively. The pattern of steroid regulation and levels of total FN were nearly identical to that of onfFN suggesting that chronic steroid treatment regulates synthesis of FN and not its oncofetal glycosylation. MPA treatment induced a 2-fold stimulation in media levels of hCG indicating that increased placental function was associated with steroid-mediated changes in FN expression. Steroid specificity experiments demonstrated that MPA, cortisol, and dexamethasone were potent inhibitors of onfFN expression whereas estradiol (E2), deoxycorticosterone, testosterone, progesterone, and the synthetic progestin OD-14, were not. This suggested that glucocorticoids and not progestins may be the physiologic regulators of placental FN expression and that MPA may mediate its matrix-modifying activity through a glucocorticoid-like mechanism. Treatment of cells with dexamethasone (10(-7) M) did not affect the levels of total protein synthesis or the release of human placental lactogen to the culture medium. This indicated that steroid-mediated down-regulation of onfFN expression in cytotrophoblasts did not result from a general reduction of protein synthesis. Based on densitometric scanning of Western blots, MPA and dexamethasone treatments down-regulated media levels of onfFN 70% relative to control levels. Northern blotting revealed that MPA and dexamethasone mediated a 60-90% reduction in steady state levels of FN mRNA in the presence or absence of E2. Our in vitro model may provide a unique system to evaluate steroidal effects on extracellular matrix (ECM) protein expression. In addition, we suggest that steroids may critically regulate placental ECM protein synthesis, and thus affect trophoblast/uterine adherence throughout pregnancy and expulsion of the placenta and membranes following delivery of the fetus.

Effect of treatment with LHRH analogs containing cytotoxic radicals on the binding characteristics of receptors for luteinizing-hormone-releasing hormone in MXT mouse mammary carcinoma

Binding capacities and apparent dissociation constants of receptors for luteinizing-hormone-releasing hormone (LHRH) were investigated in estrogen-independent MXT mammary cancers of untreated mice and after in vivo treatment with agonistic or antagonistic analogs of LHRH containing cytotoxic radicals: AJ-04 (agonist [D-Lys6]LHRH linked to methotrexate), T-98-([D-Lys6]LHRH coupled to glutaryl-2-(hydroxmethyl)anthraquinone (G-HMAQ)) and T-121/B (LHRH antagonist T-147 containing two residues of G-HMAQ), which induced tumor growth inhibition. The effects were compared to LHRH agonist [D-Trp6]LHRH and carriers [D-Lys6]LHRH, LHRH antagonist T-147, as well as to methotrexate, G-HMAQ and surgical bilateral overiectomy. Analysis of the binding data revealed that in control tumors the interaction of 125I-[D-TRP6]LHRH was consistent with the presence of one class of saturable, specific, noncooperative, high-affinity and low-capacity binding sites. Chronic treatment of mice bearing MXT tumors with LHRH analogs AJ-04 and T-121/B carrying cytotoxic radicals, but not with T-98 produced significant down-regulation of membrane receptors for LHRH. The largest decrease in dissociation binding constant and Bmax of receptors for LHRH was also found in animals treated with T-121/B. Specific, high affinity binding of 125I-labelled epidermal growth factor (EGF) was detected in the membranes from control and treated MXT tumors. Treatment with cytotoxic LHRH analogs, AJ-04, T-98 and especially with T-121/B, reduced maximal binding capacity of EGF receptors. Our results indicate that LHRH analogs carrying cytotoxic radicals retain their hormonal activity and inhibit tumor growth while inducing down-regulation of LHRH receptors. In addition, probably both components of the cytotoxic LHRH analog, peptide carriers and cytotoxic radicals, reduce the binding capacity of EGF receptors, which might be useful in the treatment of breast cancer.

Growth inhibition of estrogen independent MXT mouse mammary carcinomas in mice treated with an agonist or antagonist of LH-RH, an analog of somatostatin, or a combination

Female BDF1 mice inoculated with MXT (3.2) estrogen independent mouse mammary carcinoma were treated for three weeks with microcapsules of the luteinizing hormone-releasing hormone (LH-RH) agonist [D-Trp6]LH-RH, the antagonist SB-75, the somatostatin analog RC-160, or combinations. The lack of estrogen dependence of the tumor was proved by bilateral surgical ovariectomy, which had no effect. In two experiments, treatment with 25 micrograms/day doses of each analog alone resulted in a significant inhibition of tumor growth as shown by a 40-53% inhibition of tumor volumes, 38-43% decrease in tumor weights, and histological signs of tumor regression. However, the combination of SB-75 or [D-Trp6]LH-RH with somatostatin analog RC-160 caused greater reduction of tumor volume (68 and 61%) or tumor weights (59 and 56%), than single analogs, and histologically the occurrence of apoptosis and decrease in AgNOR numbers was more pronounced in the groups receiving combination therapy. Specific binding sites for [D-Trp6]LH-RH, EGF, and IGF-I were demonstrated in the tumor membranes. The binding capacity of LH-RH receptors was decreased by treatment with the analogs, the greatest down-regulation being caused by combination therapy. A significant decrease in EGF binding capacity was observed after treatment with the LH-RH analogs, alone or especially in combination with somatostatin analog RC-160. The combination of these analogs also caused a reduction in IGF-I receptors. The finding that LH-RH agonists and antagonists and somatostatin analogs inhibit the growth of estrogen independent mammary tumors, and that combinations are more effective than single analogs, might be of practical importance in human breast cancer therapy.

EGF receptor regulation in normal mouse mammary gland

Estrogen (E), progesterone (P), and epidermal growth factor (EGF) are known to regulate growth and development of the normal mammary gland, and it is possible that EGF may interact with E and/or P. Estrogen (ER), progesterone (PR), and EGF receptors (EGF-R) have been detected in both mammary epithelial and stromal cells, and the relative roles of the various cells types in hormone-dependent growth regulation are not known. The present studies were undertaken to determine if E and/or P influence EGF action by exerting a regulatory effect on EGF-R levels and which cell types are affected. The comparative effects of ovariectomy and hormone treatments on EGF-R levels were examined in immature, pubertal 5-week-old and sexually mature 10-week-old female mice. EGF-R were characterized as a single class of high affinity sites and EGF-R concentration was 2-fold higher in glands of 5-week-old mice. Ovariectomy had no significant effect on EGF-R concentration in either age group, and treatment with E and/or P had no effect on EGF-R levels in either epithelial or stromal cells in 5-week-old mice. In contrast, E+P treatment caused a 2-fold increase in receptor concentration in 10-week-old mice in the mammary epithelium. Thus it appears that the developmental state of the gland may determine the nature and extent of the interaction of of EGF, E, and P.

Modulation of tumor cell susceptibility to cytokine-induced cell death by hormones, growth factors, and cell density

The mechanisms controlling "spontaneous" cellular death rates in normal and tumorigenic tissues are largely unknown. An important parameter in this respect is the susceptibility of the target cell to induction of the lytic pathway by appropriate signals. In the present article it is demonstrated in a serum-free in vitro system that the susceptibility of human tumor cells (TC) to induction of lysis by cytokine signals generated during interaction of TC with elutriated human monocytes (MO) is a highly dynamic parameter subject to modulation by hormones, growth factors, and tumor cell density. It was found that growth stimulatory signals such as insulin, and especially epidermal growth factor (EGF), increase lytic susceptibility, whereas hydrocortisone, which does not exert significant growth modulatory effects in these examples, protects TC against the induction of lysis. Increasing TC density above confluence dramatically enhances lytic susceptibility, suggesting interactions between TC to be involved in the induction of their death. In conjunction with previous data demonstrating the insusceptibility of TC, which are forced out of the cell cycle into the quiescent state (G0), the hypothesis is put forward that growth stimulatory factors increase a TC's lytic susceptibility by preventing its transit from G1 to G0 in response to growth inhibitory signals generated during MO/TC interaction. The data support the concept that TC susceptibility to the induction of cell death is a consequence of simultaneously activated growth stimulatory and growth inhibitory signalling pathways.

Progestins in breast cancer treatment. A review

The two most widely used synthetic progestins in breast cancer treatment, medroxyprogesterone acetate (MPA) and megestrol acetate (MA), are reviewed with regard to pharmacological, endocrinological and clinical aspects. In high oral doses as second- or first-line endocrine therapy in advanced breast cancer, they give a similar response rate as tamoxifen (TAM) and aminoglutethimide (AG). The mechanism of action is probably complex. Considerable changes in serum levels of different hormones are induced by progestin treatment. The decrease of serum estrone sulfate (E1S) may be part of the therapeutic mechanism. Some studies suggest that the two drugs, MPA and MA, have a different mode of action, and possibly a low cross resistance. Randomized studies using the two progestins with a cross-over design may answer these questions. Further studies on the influence of progestin on different receptors and growth factors are warranted. To determine the most effective clinical dose of the two progestins, studies with increasing therapeutic doses are needed.

Progestins both stimulate and inhibit breast cancer cell cycle progression while increasing expression of transforming growth factor alpha, epidermal growth factor receptor, c-fos, and c-myc genes

This study documents a biphasic change in the rate of cell cycle progression and proliferation of T-47D human breast cancer cells treated with synthetic progestins, consisting of an initial transient acceleration in transit through G1, followed by cell cycle arrest and growth inhibition. Both components of the response were mediated via the progesterone receptor. The data are consistent with a model in which the action of progestins is to accelerate cells already progressing through G1, which are then arrested early in G1 after completing a round of replication, as are cells initially in other phases of the cell cycle. Such acceleration implies that progestins act on genes or gene products which are rate limiting for cell cycle progression. Increased production of epidermal growth factor and transforming growth factor alpha, putative autocrine growth factors in breast cancer cells, does not appear to account for the initial response to progestins, since although the mRNA abundance for these growth factors is rapidly induced by progestins, cells treated with epidermal growth factor or transforming growth factor alpha did not enter S phase until 5 to 6 h later than those stimulated by progestin. The proto-oncogenes c-fos and c-myc were rapidly but transiently induced by progestin treatment, paralleling the well-known response of these genes to mitogenic signals in other cell types. The progestin antagonist RU 486 inhibited progestin regulation of both cell cycle progression and c-myc expression, suggesting that this proto-oncogene may participate in growth modulation by progestins.

Progestins both stimulate and inhibit breast cancer cell cycle progression while increasing expression of transforming growth factor alpha, epidermal growth factor receptor, c-fos, and c-myc genes

This study documents a biphasic change in the rate of cell cycle progression and proliferation of T-47D human breast cancer cells treated with synthetic progestins, consisting of an initial transient acceleration in transit through G1, followed by cell cycle arrest and growth inhibition. Both components of the response were mediated via the progesterone receptor. The data are consistent with a model in which the action of progestins is to accelerate cells already progressing through G1, which are then arrested early in G1 after completing a round of replication, as are cells initially in other phases of the cell cycle. Such acceleration implies that progestins act on genes or gene products which are rate limiting for cell cycle progression. Increased production of epidermal growth factor and transforming growth factor alpha, putative autocrine growth factors in breast cancer cells, does not appear to account for the initial response to progestins, since although the mRNA abundance for these growth factors is rapidly induced by progestins, cells treated with epidermal growth factor or transforming growth factor alpha did not enter S phase until 5 to 6 h later than those stimulated by progestin. The proto-oncogenes c-fos and c-myc were rapidly but transiently induced by progestin treatment, paralleling the well-known response of these genes to mitogenic signals in other cell types. The progestin antagonist RU 486 inhibited progestin regulation of both cell cycle progression and c-myc expression, suggesting that this proto-oncogene may participate in growth modulation by progestins.

Glucocorticoid receptors in human malignancies: a review

The present knowledge of the human glucocorticoid receptor (hGCR) in primary malignancies is reviewed. It is concluded that hGCR is present in a large number of these tissues; in all tissue specimens of lymphoid malignancies and in varying fractions of the different solid tumors. The hGCR functions as a hormone dependent, specific enhancer interacting protein in mediating the considerable effects of glucocorticoids on growth regulation, both through stimulation and inhibition of expression of the target genes, including other transcription regulation systems. The processes of receptor activation and regulation, as well as the effects of glucocorticoids, are tissue-specific. Subjects for future research are proposed: Establishment of more cell lines and animal models to extend investigation beyond the present concentration on only a few cell lines, especially CEM-C7, application of 'dynamic' assays to cells obtained from patients, in an attempt to predict development of glucocorticoid resistance, and further investigation of the relationships among GCR and growth factors and oncogenes.

Mechanisms of 4-hydroxytamoxifen anti-growth factor activity in breast cancer cells: alterations of growth factor receptor binding sites and tyrosine kinase activity

We previously demonstrated that antiestrogen 4-hydroxytamoxifen (OH-Tam) blocks the mitogenic activity of growth factors in breast cancer. We now investigate this mechanism by evaluating how OH-Tam affects growth factor binding and receptor tyrosine kinase activity. We show here that OH-Tam has an opposite effect on epidermal growth factor (EGF) and insulin-like growth factor-1 (IGF-1) binding in estrogen receptor (ER) positive cells. A decrease in IGF-1 binding sites may explain the reduced IGF-I mitogenic effect, whereas an increase in high affinity EGF binding associated with a decrease in in vitro receptor autophosphorylation rather favors the possibility of an alteration in EGF receptor tyrosine kinase activity. We conclude that OH-Tam may prevent growth factor action in ER+ cells both by modulating the concentration of growth factor binding sites and by altering growth factor receptor functionality.

Steroid hormone receptor gene expression in human breast cancer cells: inverse relationship between oestrogen and glucocorticoid receptor messenger RNA levels

The relative expression in human breast cancer cells of messenger ribonucleic acids (mRNA) encoding different steroid hormone receptors is unknown. Accordingly, mRNA levels in total RNA extracted from 13 human breast cancer cell lines were measured by Northern analysis employing complementary DNA probes for the human oestrogen (ER), progesterone (PR), androgen (AR), vitamin D3 (VDR) and glucocorticoid receptors (GR). The 7 ER+ lines expressed a single 6.4 kilobases (kb) ER mRNA. Interestingly, low concentrations of ER mRNA were detected in the ER- cell lines, MDA-MB-330 and BT 20. PR mRNA, predominantly a 13.5 kb species, was expressed in the 6 lines known to be ER+, PR+ by radioligand binding; however, one ER+ cell line, MDA-MB-134, failed to express PR mRNA. A 10.5 kb AR mRNA was expressed at significantly higher levels in ER+ than ER- cell lines. All cell lines expressed a single 4.6 kb mRNA for VDR and a single 7.4 kb mRNA for GR. ER and PR mRNA levels were positively correlated (p = 0.011) and each was positively correlated with androgen receptor (AR) mRNA levels (p less than or equal to 0.009). ER, PR and AR mRNAs were negatively associated with GR levels (p less than or equal to 0.012), while ER and AR mRNA levels were negatively correlated with mRNA for the epidermal growth factor receptor. In contrast, levels of VDR mRNA were unrelated to the concentration of any other steroid receptor mRNA. Our data demonstrate the coordinate expression of ER, PR and AR genes, and an inverse relationship between sex steroid hormone receptor and GR gene expression in human breast cancer cell lines.

Inverse relationship between estrogen receptor and epidermal growth factor receptor mRNA levels in human breast cancer cell lines

Epidermal growth factor receptors (EGF-R) are present in a number of human breast cancer cell lines and tumor biopsies. Furthermore, it has been suggested that EGF-R levels are higher in estrogen receptor negative (ER-) than in ER+ human breast tumors and that EGF-R status may be a prognostic indicator in breast cancer. The present study was undertaken to establish whether there is a quantitative relationship between EGF-R and ER mRNA concentrations in a series of 10 well-characterized human breast cancer cell lines. All cell lines expressed detectable quantities of EGF-R mRNA by Northern analysis but the relative abundance of EGF-R mRNA varied more than 50-fold. Two transcripts corresponding to the 10.5- and 5.8-kb mRNAs described in other cell types were present but in different relative proportions in different cell lines. When these lines were divided into an ER+ and an ER- group based on their ability to bind estradiol, ER- cell lines were shown to express significantly higher concentrations of EGF-R mRNA than did ER+ cell lines (p less than 0.005). Furthermore, linear-regression analysis revealed a significant inverse relationship between ER and EGF-R mRNA concentrations both within the group of 10 human breast cancer cell lines as a whole (r = 0.66) and within the 6 functionally ER + lines (r = 0.77). This demonstration of a significant (p less than 0.005) inverse relationship between the concentrations of ER and EGF-R mRNAs in ER + cell lines raises the possibility of reciprocal regulation of the expression of these genes in human breast cancer.