Progestin action and progesterone receptor structure in human breast cancer: a review

Luteolin inhibits progestin-dependent angiogenesis, stem cell-like characteristics, and growth of human breast cancer xenografts

PURPOSE

Clinical trials and epidemiological evidence have shown that combined estrogen/progestin hormone replacement therapy, but not estrogen therapy alone, increases breast cancer risk in post-menopausal women. Previously we have shown that natural and synthetic progestins, including the widely used synthetic progestin medroxyprogesterone acetate (MPA), increase production of a potent angiogenic factor, vascular endothelial growth factor (VEGF), in human breast cancer cells, potentially providing an explanation for progestin's mechanism of action. Here, we tested the effects of luteolin (LU), a flavonoid commonly found in fruits and vegetables, on inhibiting progestin-dependent VEGF induction and angiogenesis in human breast cancer cells, inhibiting stem cell-like characteristics, as well as breast cancer cell xenograft tumor growth in vivo and expression of angiogenesis markers.

METHODS

Viability of both T47-D and BT-474 cells was measured using sulforhodamine B assays. Enzyme-linked immunosorbent assays were used to monitor VEGF secretion from breast cancer cells. Progestin-dependent xenograft tumor growth was used to determine LU effects in vivo. CD31 immunohistochemistry was used to determine blood-vessel density in xenograft tumors. CD44 expression, aldehyde dehydrogenase activity, and mammosphere-formation assays were used to monitor stem cell-like characteristics of breast cancer cells.

RESULTS

Luteolin treatment reduced breast cancer cell viability, progestin-dependent VEGF secretion from breast cancer cells, and growth of MPA-dependent human breast cancer cell xenograft tumors in nude mice. LU treatment also decreased xenograft tumor VEGF expression and blood-vessel density. Furthermore, LU blocked MPA-induced acquisition of stem cell-like properties by breast cancer cells.

CONCLUSIONS

Luteolin effectively blocks progestin-dependent human breast cancer tumor growth and the stem cell-like phenotype in human breast cancer cells.

Progestin modulates the lipid profile and sensitivity of breast cancer cells to docetaxel

Progestins induce lipid accumulation in progesterone receptor (PR)-positive breast cancer cells. We speculated that progestin-induced alterations in lipid biology confer resistance to chemotherapy. To examine the biology of lipid loaded breast cancer cells, we used a model of progestin-induced lipid synthesis. T47D (PR-positive) and MDA-MB-231 (PR-negative) cell lines were used to study progestin response. Oil red O staining of T47D cells treated with progestin showed lipid droplet formation was PR dependent, glucose dependent and reduced sensitivity to docetaxel. This protection was not observed in PR-negative MDA-MB-231 cells. Progestin treatment induced stearoyl CoA desaturase-1 (SCD-1) enzyme expression and chemical inhibition of SCD-1 diminished lipid droplets and cell viability, suggesting the importance of lipid stores in cancer cell survival. Gas chromatography/mass spectroscopy analysis of phospholipids from progestin-treated T47D cells revealed an increase in unsaturated fatty acids, with oleic acid as most abundant. Cells surviving docetaxel treatment also contained more oleic acid in phospholipids, suggesting altered membrane fluidity as a potential mechanism of chemoresistance mediated in part by SCD-1. Lastly, intact docetaxel molecules were present within progestin induced lipid droplets, suggesting a protective quenching effect of intracellular lipid droplets. Our studies suggest the metabolic adaptations produced by progestin provide novel metabolic targets for future combinatorial therapies for progestin-responsive breast cancers.

Expression profiling of human breast cancers and gene regulation by progesterone receptors

Even the first expression profiling studies of breast cancers have generated new insights. They suggest for example, that information about tumor aggressiveness, prognosis, metastatic potential, or treatment outcome is encoded in, and can be deduced from, the primary tumor. On the other hand no clinical genomic array data have yet been published that deal with hormonal aspects of breast tumorigenesis, tumor progression, or therapeutics. Rather, studies have focused on experimental model systems. We review below the currently published data on array profiling in clinical breast cancer, then describe our studies in breast cancer cell lines and xenograft models dealing with progesterone receptors (PRs) and the role of progesterone. We demonstrate that the two PR isoforms, PR-A and PR-B, have mostly nonoverlapping molecular signatures when liganded by progesterone, with PR-B the more active form. Additionally, we document the surprising finding that unliganded PRs can regulate gene transcription, with PR-A the more active form. In ovariectomized mice supplemented with estradiol but lacking measurable progesterone, PR-B-expressing tumors grow to twice the size of PR-A-expressing ones. We conclude that in breast cancers, PRs are more than simple markers of estrogen receptor function. Rather, presence of PRs and the ratio of the two isoforms directly influence tumor phenotype, even in the absence of ligand.

Estrogen mitogenic action. I. Demonstration of estrogen-dependent MTW9/PL2 carcinogen-induced rat mammary tumor cell growth in serum-supplemented culture and technical implications

The MTW9/PL cell line was established by our laboratory in culture from the carcinogen-induced hormone-responsive MT-W9A rat mammary tumor of a Wistar-Furth (W/Fu) rat. This tumor formed estrogen, androgen, and progesterone responsive tumors in W/Fu rats (Sirbasku, D. A., Cancer Res. 38:1154-1165; 1978). It was later used to derive the MTW9/PL2 cell population which was also estrogen-responsive in vivo (Danielpour, D., et al., In Vitro Cell. Dev. Biol. 24:42-52; 1988). In the study presented here, we describe serum-supplemented culture conditions in which the MTW9/PL2 cells demonstrate > or = 80-fold steroid hormone growth responses. All sera used were steroid hormone-depleted by charcoal-dextran treatment at 34 degrees C. The studies were done with horse serum as well as serum from other mammalian species. The growth of the MTW9/PL2 cells was biphasic in response to hormone-depleted serum. Concentrations of < or = 5% (v/v) promoted optimum growth. Above this concentration, serum was inhibitory. Concentrations > or = 40% (v/v) inhibited growth altogether. Addition of 1.0 x 10(-13)-1.0 x 10(-8) M 17beta,-estradiol (E2) reversed the inhibition completely. At 1.0 x 10(-8) M, estrone, estriol and diethylstilbestrol promoted growth as well as E2. Testosterone and dihydrotestosterone promoted growth only at > or = 10(-7) M. Progesterone was effective only at > or = 10(-6) M. Cortisol was ineffective. Labeled-hormone-binding analysis and Western immunoblotting documented that MTW9/PL2 cells had estrogen and progesterone receptors but not androgen or cortisol receptors. Estrogen treatment of MTW9/PL2 cells induced a concentration and time dependent increase in progesterone receptors. We conclude (1) the MTW9/PL2 population is the first highly steroid hormone-responsive rat mammary tumor cell line to be established in culture from a carcinogen-induced tumor, and (2) sera from a number of species including horse, rat and human contain an inhibitor which mediates estrogen sensitive MTW9/PL2 cell growth in culture.

BCAR1, a human homologue of the adapter protein p130Cas, and antiestrogen resistance in breast cancer cells

BACKGROUND

Treatment of breast cancer with the antiestrogen tamoxifen is effective in approximately one half of the patients with estrogen receptor-positive disease, but tumors recur frequently because of the development of metastases that are resistant to tamoxifen. We have previously shown that mutagenesis of human estrogen-dependent ZR-75-1 breast cancer cells by insertion of a defective retrovirus genome caused the cells to become antiestrogen resistant. In this study, we isolated and characterized the crucial gene at the breast cancer antiestrogen resistance 1 (BCAR1) locus.

METHODS/RESULTS

Transfer of the BCAR1 locus from retrovirus-mutated, antiestrogen-resistant cells to estrogen-dependent ZR-75-1 cells by cell fusion conferred an antiestrogen-resistant phenotype on the recipient cells. The complete coding sequence of BCAR1 was isolated by use of exon-trapping and complementary DNA (cDNA) library screening. Sequence analysis of human BCAR1 cDNA predicted a protein of 870 amino acids that was strongly homologous to rat p130Cas-adapter protein. Genomic analysis revealed that BCAR1 consists of seven exons and is located at chromosome 16q23.1. BCAR1 transcripts were detected in multiple human tissues and were similar in size to transcripts produced by retrovirus-mutated ZR-75-1 cells. Transfection of BCAR1 cDNA into ZR-75-1 cells again resulted in sustained cell proliferation in the presence of antiestrogens, confirming that BCAR1 was the responsible gene in the locus.

CONCLUSIONS

Overexpression of the BCAR1 gene confers antiestrogen resistance on human ZR-75-1 breast cancer cells. Overexpression of BCAR1 in retrovirus-mutated cells appears to result from activation of the gene's promoter. The isolation and characterization of this gene open new avenues to elucidating mechanisms by which the growth of human breast cancer becomes independent of estrogen.

Effects of antiprogestins on the rate of proliferation of breast cancer cells

We have examined the influence of progestins (progesterone, R5020) and antiprogestins (RU486, ZK98299, Org 31710 and Org 31806) on the rate of proliferation of wild type T47D cells cultured in whole fetal bovine serum (FBS) or in single charcoal stripped fetal bovine serum (SSFBS). All of the progesterone antagonists RU486, ZK98299 and two novel antiprogestins Org 31710 and Org 31806 inhibited cell proliferation when cells were cultured in FBS. In contrast, all of the antiprogestins with the exception of ZK98299 enhanced cell growth when cells were cultured in SSFBS. This stimulatory effect of RU486 was observed only at a high concentration of the ligand (1 microM). The effect of R5020, however, was concentration independent. The number of cells in the presence of RU486 was approximately 600% followed by R5020 approximately 400% above control values after a 28 day culturing period. In contrast, when the cells were grown in the presence of medium containing non-stripped whole serum, RU486 inhibited the extent of cell proliferation by 45%. Estradiol (E2) stimulated the rate of proliferation in cells cultured in SSFBS. Similar to when cells were cultured in whole serum, the antiprogestins inhibited cell growth in E2-supplemented SSFBS. Detection of the growth enhancement effects of progesterone receptor (PR) ligands such as RU486 and R5020 on the cells grown in charcoal-stripped medium appear to require the removal of E2 by charcoal stripping of the serum.

Relationship of PS2 with response to tamoxifen therapy in patients with recurrent breast cancer

PS2, an oestrogen-inducible protein, was measured in the cytosol of 230 primary tumours from patients who were subjected to first-line tamoxifen therapy for advanced disease without prior adjuvant therapy with tamoxifen. PS2 correlated positively with oestrogen receptor (ER, P < 0.01) and progesterone receptor content (PgR, P < 0.001), and with the length of progression-free survival (PFS, P = 0.05). Although not statistically significant, higher levels of PS2 (> or = 10 ng mg-1 protein) were also associated with increased probability of response to tamoxifen treatment and a longer total post-relapse survival (PRS). ER, PgR, menopausal status, site of disease and prior adjuvant chemotherapy were all associated with response to tamoxifen therapy and with PFS. In multivariate analysis for PFS, low levels of ER and PgR, visceral metastasis, a disease-free interval of less than 1 year and prior adjuvant chemotherapy were all significantly associated with an increased probability of a rapid disease progression after start of tamoxifen therapy. In the subset of 83 tumours with intermediate levels of ER and PgR (both > or = 10, but not both > or = 75 fmol mg-1 protein), PS2 was positively related with the length of PFS (P < 0.01) and PRS (P < 0.05). PS2 remained the strongest factor in multivariate analysis for PFS (P < 0.01) in this ER/PgR intermediate subgroup, but was not of predictive value in univariate or multivariate analysis for both PFS and PRS in tumours classified as ER/PgR low or high (> or = 75 fmol mg-1 protein). It is concluded that PS2 status may be used as a parameter, additional to ER and PgR, for better refinement of prediction of response to tamoxifen treatment in advanced breast cancer patients especially with intermediate ER/PgR levels in their primary tumour.

Progestogen use and decreased risk of breast cancer in a cohort study of premenopausal women with benign breast disease

A cohort study of 1,150 premenopausal French women with benign breast disease diagnosed in two breast clinics between 1976 and 1979 was carried out to analyse the relationship between progestogen use and the risk of breast cancer. The follow-up accumulated 12,462 person-years. The risk of breast cancer was estimated using a Poisson regression analysis on person-time data and the proportional hazards model. In the latter analysis, cumulated progestogen use and age were considered as time-varying covariables and adjustment was performed on the main risk factors for breast cancer. Neither overall progestogen use nor the duration of use was found to be significantly associated with the risk of breast cancer. When progestogens were classified into two categories according to their hormonal potency (19-nortestosterone derivatives vs other progestogens), 19-nortestosterone derivative use was found to be significantly associated with a lower risk of breast cancer. In the adjusted model, the corresponding risk of breast cancer was 0.48 (95% confidence interval 0.25-0.90). In addition, there was a linear trend in the decrease of the relative risk of breast cancer with the duration of use (P = 0.02). These results do not support the hypothesis that progestogens might increase the breast cancer risk. They suggest, instead, that treatment with 19-nortestosterone derivatives might have a beneficial effect on the risk of breast cancer in women with benign breast disease.

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.

William L. McGuire Memorial Symposium. Estrogen and progestin effects in human breast carcinogenesis

The influences of estrogen and progestin on human mammary neoplasia are reviewed with a view to identifying what is known about their effects. Estrogens promote growth of established cancer and pharmacological levels of progestins induce remission. In vivo, highest proliferation of histologically normal mammary epithelium occurs in the progestogenic phase of the menstrual cycle or under the progestogenic influence of oral contraceptives. Little additional hard data exist to indicate whether progestins promote or inhibit human mammary carcinogenesis. Effects on proliferation, steroid receptor content and development are discussed together with interpretation of epidemiological data on risk factors that have hormonal components. Progestins may not be the benign or beneficial agents previously supposed, and there are virtually no data to suggest that they are antiestrogenic. It is hypothesized that carcinogenesis may be accompanied by increased sensitivity to estrogen, which provides a growth advantage to the tumor by maximizing use of the low estrogen concentrations encountered in the postmenopausal state.

Comparative effect of embryonic mouse fibroblasts (Balb/c-3T3) on the proliferation of hormone-dependent (T-47D) and hormone-independent (MDA-MB-231) human breast cancer cell lines

The effects of cellular extracts (CE) and conditioned medium (CM) of embryonic mouse BALB/c-3T3 (clone A 31) cells on the proliferation and DNA content of hormone-dependent T-47D and hormone-independent MDA-MB-231 breast cancer cell lines were explored. After 6 days of culture, CE and CM provoke an intense proliferative effect in T-47D cells which correlates with DNA content. In contrast, in the MDA-MB-231 cells a significant inhibitory effect was observed. For both CE and CM the action was dose-dependent. In the T-47D cells, the CM can abolish the inhibitory effect provoked by the potent antiestrogen ICI 164,384. It is concluded that mouse embryonic BALB/c-3T3 cells contain factors which can stimulate or inhibit the growth of human mammary cancer cells.

Analysis by DNA polymerase alpha activity of human breast tumour proliferation and the effect of endocrine therapy

Cytosols of human breast tumours have been assayed for DNA dependent DNA polymerase alpha activity. DNA polymerase alpha activity in benign tumours was found to be significantly lower than in untreated malignant tumours. Biopsy samples removed surgically before and after endocrine therapy showed reduced DNA polymerase alpha activity in 6 out of 9 patients treated with 4-hydroxyandrostenedione, and in 6 out of 7 patients treated with MPA. DNA polymerase alpha activity in malignant breast tumours was higher in oestrogen receptor negative than oestrogen receptor positive tumours.

Influence of tamoxifen-medroxyprogesterone sequential therapy on estrogen and progesterone receptor contents of breast cancer

The influence of tamoxifen (TAM) and medroxyprogesterone acetate (MPA) sequential administration on the estrogen receptor (ER) and progesterone receptor (PR) contents of breast cancer was studied in 68 patients with operable breast cancer. TAM was used as a primer of PR induction in order to enhance the effects of MPA. Half of the patients (n = 34) were preoperatively treated with TAM (20 mg/day for 7 days) and sequentially with MPA (1200 mg/day for 17 (median) days). ER and PR of surgical specimens were assayed by enzyme immunoassay and the results were compared with those obtained from the other half of the patients (n = 34), who had not received any treatment before surgery. TAM-MPA treatment significantly lowered PR in the cytosol regardless of the menopausal status. On the other hand, TAM-MPA treatment significantly lowered ER in the cytosol only in the postmenopausals but not in the premenopausals. These results demonstrate that reduction of ER provoked by TAM-MPA treatment is dependent on menopausal status.

Difference between R5020 and the antiprogestin RU486 in antiproliferative effects on human breast cancer cells

We have compared the effects of the progestin R5020 and the antiprogestin RU486 on the growth of the MCF-7 and T47D breast cancer cell lines. Differences between the two compounds were demonstrated in several parameters. 1. Estradiol was required for the efficient inhibition of cell growth of both lines by R5020 but not by RU486. Therefore in the total absence of estrogen (phenol-red free medium), the effects of the two drugs on cell growth were dissociated, RU486 remaining inhibitory while R5020 was inactive. 2. The proteins secreted by cells were differently affected, since R5020 induced a 48K protein and decreased the production of the estrogen-regulated 52K protein, while RU486 had no effect on these two parameters. 3. The morphology of cells treated by R5020 was more altered in the presence of estradiol than in its absence, while that of cells treated by RU486 was not affected whether or not estradiol was present. 4. There was a greater reduction of estrogen receptor sites in MCF-7 cells produced by R5020 than by RU486. Even though the two drugs appear to act through the same progesterone receptor and to inhibit total protein secretion, it is likely that they exert their antiproliferative effects on cultured breast cancer cells by different mechanisms. R5020 antagonizes the stimulation produced by estradiol. RU486 by contrast exerts a more direct progesterone receptor mediated inhibitory effect requiring no synergism by estradiol and therefore does not act through a partial progestin activity.

Antiestrogen action of progesterone in breast tissue

In normal breast, estrogen stimulates growth of the ductal system, while lobular development depends on progesterone. Thus, estrogen and progesterone, when secreted in an adequate balance, permit the complete and proper development of the mammary gland. Progesterone may also have an antagonistic activity against estradiol, mediated through a decrease in the replenishment of the estrogen receptor, and also through increased 17 beta-hydroxysteroid dehydrogenase which leads to accelerated metabolism of estradiol to estrone in the target organ. Thus, it can be inferred that long periods of luteal phase defect leading to an unopposed estrogen effect on the breast might promote breast carcinogenesis.

Cloning of the chicken progesterone receptor

Monospecific antibodies directed against the chicken progesterone receptor (PR) form B were used to screen a randomly primed phage lambda gt11 cDNA expression library prepared from size-fractionated chicken oviduct mRNA. Two independent immunoreactive clones, lambda cPR1 and lambda cPR2, were isolated. Antibodies selected from anti-PR form B antiserum on matrices of lambda cPR1 and lambda cPR2 fusion proteins detected two proteins on electrophoretic immunoblots of crude and purified PR preparations. These proteins had the same apparent molecular weights as did PR forms A and B crosslinked with the tritiated progestin R 5020. Thus, lambda cPR1 and lambda cPR2 fusion proteins contain epitopes present in both PR forms A and B. A cDNA clone, lambda cPR3, containing the inserts of both lambda cPR1 and lambda cPR2, was isolated from a randomly primed lambda gt10 oviduct cDNA library, indicating that both cDNA inserts were derived from the same oviduct mRNA. Additional evidence that these cDNAs correspond to PR mRNA was provided by sequencing the lambda cPR3 cDNA insert, since it was found to encode the sequence of three tryptic peptides prepared from purified PR form B. A fourth and a fifth cDNA clone, lambda cPR4 and lambda cPR5, were sequentially isolated from the same lambda gt10 cDNA library beginning with a probe derived from the 3' end of the lambda cPR3 insert. Partial DNA sequencing of lambda cPR4 and lambda cPR5 revealed the presence of a sequence coding for a cysteine-rich domain that is strikingly homologous to the amino acid sequences present in the putative DNA-binding domain of the human and chicken estrogen receptors, human glucocorticoid receptor, and v-erbA gene product of the avian erythroblastosis virus.