Adaptation of the human breast cancer cell line MCF-7 to serum free medium culture on extracellular matrix

Molecular characterization of the microsomal tamoxifen binding site

Tamoxifen is a selective estrogen receptor modulator widely used for the prophylactic treatment of breast cancer. In addition to the estrogen receptor (ER), tamoxifen binds with high affinity to the microsomal antiestrogen binding site (AEBS), which is involved in ER-independent effects of tamoxifen. In the present study, we investigate the modulation of the biosynthesis of cholesterol in tumor cell lines by AEBS ligands. As a consequence of the treatment with the antitumoral drugs tamoxifen or PBPE, a selective AEBS ligand, we show that tumor cells produced a significant concentration- and time-dependent accumulation of cholesterol precursors. Sterols have been purified by HPLC and gas chromatography, and their chemical structures determined by mass spectrometric analysis. The major metabolites identified were 5alpha-cholest-8-en-3beta-ol for tamoxifen treatment and 5alpha-cholest-8-en-3beta-ol and cholesta-5,7-dien-3beta-ol, for PBPE treatment, suggesting that these AEBS ligands affect at least two enzymatic steps: the 3beta-hydroxysterol-Delta8-Delta7-isomerase and the 3beta-hydroxysterol-Delta7-reductase. Steroidal antiestrogens such as ICI 182,780 and RU 58,668 did not affect these enzymatic steps, because they do not bind to the AEBS. Transient co-expression of human 3beta-hydroxysterol-Delta8-Delta7-isomerase and 3beta-hydroxysterol-Delta7-reductase and immunoprecipitation experiments showed that both enzymes were required to reconstitute the AEBS in mammalian cells. Altogether, these data provide strong evidence that the AEBS is a hetero-oligomeric complex including 3beta-hydroxysterol-Delta8-Delta7-isomerase and the 3beta-hydroxysterol-Delta7-reductase as subunits that are necessary and sufficient for tamoxifen binding in mammary cells. Furthermore, because selective AEBS ligands are antitumoral compounds, these data suggest a link between cholesterol metabolism at a post-lanosterol step and tumor growth control. These data afford both the identification of the AEBS and give new insight into a novel molecular mechanism of action for drugs of clinical value.

Expression of the interleukin-6 gene is constitutive and not regulated by estrogen in rat vascular smooth muscle cells in culture

Vascular smooth muscle cells (SMC) are major constituents of the medial layer of blood vessels and are involved in the development of atherosclerotic plaque. SMC secrete copious IL-6 under basal conditions that can be increased by cytokines such as tumor necrosis factor-alpha and interleukin-1beta (IL-1beta). The goal of our studies was to define the role of estrogen in IL-6 production by SMC. In a first series of experiments, the expression of specific messenger RNAs as well as the production of IL-6 bioactivity by rat SMC in culture could be demonstrated in basal and IL-1-stimulated conditions, but was unaffected by estrogen treatment. Different constructs containing deleted or mutated fragments of the human IL-6 promoter driving luciferase or chloramphenicol acetyltransferase reporter gene were then transiently transfected in these cells. A significant basal activity that was increased 2- to 4-fold after IL-1beta stimulation was observed with the total IL-6 promoter. Deletion analysis indicated that the -158/+11 region containing activator protein-1 and cAMP response element sites was apparently the minimal region of IL-6 promoter to confer both constitutive and IL-1-inducible activities. Site-directed mutagenesis experiments suggest that basal activity is dependent upon the promoter sequence -158 to -112 containing the nuclear factor (NF)-IL6(-153) and Sp1 sites, whereas IL-1beta stimulation would depend on the residual -112 nucleotides containing NF-IL6(-75) and NF-kappaB sites. In contrast to the down-regulation of IL-6 expression by estrogen described in osteoblasts, ethinyl estradiol as well as 17beta-estradiol did not influence stimulated IL-6 activity in our experimental conditions whatever the construct tested, even when either estrogen receptor alpha or beta was overexpressed. Thus, the atheroprotective properties of estrogen are probably not mediated through the regulation of IL-6 production by SMC.

Melatonin blocks the stimulatory effects of prolactin on human breast cancer cell growth in culture

Melatonin (aMT) appears to be a potentially important oncostatic substance that can block the mitogenic effects of tumour-promoting hormones and growth factors such as oestradiol and epidermal growth factor, in vitro. In the present study, we examined the possibility that aMT would also inhibit the stimulatory effects of the tumour-promoter prolactin (PRL) on MCF-7 and ZR75-1 human breast cancer cell (HBC) growth under 5% charcoal-stripped fetal bovine serum culture conditions. Human PRL (10-100 ng ml-1) stimulated the rate of MCF-7 and ZR-75-1 HBC growth up to 2-fold above that of untreated controls. Melatonin, at concentrations between 10(-12) M and 10(-5)M, diminished and at physiological levels completely abolished PRL's mitogenic activity, but had no effect on growth in the absence of PRL. The mitogenic effects of human growth hormone (hGH), a PRL-related hormone, and also of several monoclonal antibodies (MAbs) against the PRL receptor (PRLR), were also abrogated by physiological concentrations of aMT. Additionally, aMT blocked the enhancement of MAb mitogenic activity induced by a second 'cross-linking' antibody (CLA). These findings indicate that aMT interrupts the PRLR-mediated growth signal in HBC and suggest that the oncostatic activity of aMT may also be linked with an antagonism of PRL's actions.

Antiproliferative effect of phorbol esters on MCF-7 human breast adenocarcinoma cells: relationship with enhanced expression of transforming growth-factor-beta 1

In human breast carcinoma MCF-7 cells, phorbol diesters inhibit proliferation and induce cell maturation. We have recently reported that exogenous TGF-beta 1 reverses the resistance of a breast adenocarcinoma MCF-7 subline (MCF-7:RPh-4) to these phorbol ester effects. Here, we investigated the involvement of TGF-beta 1 in the PKC-mediated inhibition of breast-cancer cell proliferation. Parental MCF-7-conditioned medium contained a 20-fold higher transforming activity on NRK-49F fibroblasts than the TPA-resistant subline. TPA increased TGF-beta activity in MCF-7 conditioned medium. MCF-7 cells also expressed more TGF-beta 1 mRNA than the resistant subline. TPA induced a dose-dependent increase in TGF-beta 1 mRNA levels that paralleled the inhibitory effect on MCF-7 proliferation. The lower level of TGF-beta mRNA expression in TPA resistant subline was not modified after addition of TPA, but was significantly increased in the presence of exogenous TGF-beta 1. These data argue in favor of a role of endogenous TGF-beta 1 in the maturation process induced by protein kinase C activation.

The growth response of BG-1 ovarian carcinoma cells to estradiol, 4OH-tamoxifen, and tamoxifen: evidence for intrinsic antiestrogen activation

The influence of estrogen (E) and antiestrogen (AES) on the in vitro growth of BG-1 ovarian carcinoma cells, which express steroid receptors was examined (K. R. Geisinger, T. E. Kute, M. J. Pettenati, C. E. Welander, Y. Dennard, L. A. Collins, and M. E. Berens, Characterization of a human ovarian carcinoma cell line with estrogen and progesterone receptors, Cancer 63, 280-288, 1989). All determinations were simultaneously referenced under similar conditions to MCF-7 cells, a well-established cell line for modeling hormonal responses in breast cancer. In "complete" media containing fetal calf serum (FCS, 10%), MCF-7 cell numbers increased approximately 7 x in 7 days, remaining at this level Days 8-15. In contrast, BG-1 cells achieved similar numbers by Day 7, but showed apparent exponential growth over Days 8-15 to 15-20 x. Phenol red-free media containing 10% FCS (less than 20 pg estradiol (E2)/ml by RIA) was used to assess responses to E and AES. Growth of both MCF-7 and BG-1 cells slowed in E-free media. E2 (10 nM) stimulated the growth of both cell lines, yet was responsible for exponential increases during Days 8-15 only in BG-1 cell numbers (50-70 x). The metabolically active AES (4OH-tamoxifen, 50 nM) reduced E2-stimulated MCF-7 growth to 3-4 x, while tamoxifen (50 nM) had no effect. Rescue with 10 microM E2 fully overcame the AES inhibition of MCF-7 proliferation. In contrast, BG-1 cells experienced significant E2-stimulated growth reductions in the presence of either 4OH-tamoxifen or tamoxifen. E2 was observed to rescue BG-1 cells from both of these antagonists. We conclude that BG-1 ovarian carcinoma cells respond in vitro to E and AES. Moreover, by virtue of responses to tamoxifen, BG-1 cells may have an intrinsic capacity to hydroxylate tamoxifen to its active metabolite. This property of ovarian carcinoma cells might be worth exploiting in the design of more effective combination chemotherapy regimens.

Dissociation between protein kinase C content and biological responsiveness to phorbol esters in tumor promoter-sensitive (MCF-7) and resistant (RPh-4) cells

A cell line (RPh-4) insensitive to the effects of phorbol esters has been isolated from MCF-7 human breast cancer cells. The growth pattern of RPh-4 cells in the presence of 50 ng/mL (80 nM) 12-O-tetradecanoylphorbol 13-acetate (TPA) is similar to that of parental MCF-7 cells in the absence of TPA. While phorbol esters inhibit MCF-7 cell proliferation and increase cell volume and protein content, no such effects are observed in RPh-4 cells. TPA affects MCF-7 but not RPh-4 cell cycle in two ways: a G1 block and a delayed passage through G2 phase. Profound alterations in protein kinase C content and activity are observed in RPh-4 versus MCF-7 cells, i.e. (i) a dramatic decline in the cellular enzyme content; (ii) a loss of the capacity to translocate upon acute TPA stimulation for the remainder enzyme; and (iii) a lack of stimulation by phorbol esters of the endogenous Mr 28,000 substrate. However, these striking changes are only transient and rapidly reverse when RPh-4 cells are subcultured in TPA-free medium, with a 60% and an almost total recovery, respectively, after 15 days and 3 months. By contrast, a much lower rate of reversion is observed in terms of cell growth responsiveness to TPA with a total insensitivity to phorbol ester after 80 days and a 50% inhibition of RPh-4 cell proliferation after 3.5 months. Our data clearly demonstrate an apparent dissociation between the cellular protein kinase C content and the biological responsiveness to phorbol ester in the variant RPh-4 cells. Moreover, they suggest that the Mr 28,000 protein phosphorylation event is not directly related to the cell growth arrest induced by phorbol esters in MCF-7 cells.

Effects of differentiation-inducing agents on maturation of human MCF-7 breast cancer cells

The effects of the differentiation inducing agents (DIAS), sodium butyrate (NaBu), retinoic acid (RA), dimethylformamide (DMF), hexamethylene bisacetamide (HMBA), forskolin, and 12-O-tetradecanoylphorbol-13-acetate (TPA), on the growth, morphology, and estrogen receptor (ER) content and epithelial membrane antigen (EMA) expression on a serumless human breast cancer cell line (MCF-7) were compared. All these agents reversibly caused a concentration-dependent growth inhibition in monolayers and markedly reduced colony-forming efficiency in soft agar. A twofold increase in doubling time was obtained with RA (1 microM), but cell replication ceased with NaBu (1 mM), forskolin (50 microM), DMF (1%), HMBA (5 mM), and TPA (8 nM). Total growth arrest induced by these last compounds was preceded by an accumulation of cells in G0/G1 phase observed at 24 h by flow cytometry and accompanied by a change in cell morphology as seen by light and electronic microscopy. An increase in cell volume and the presence of lipid droplets was noted in treated cells that were spread out, as compared with controls. The acquisition of a more mature phenotype was confirmed by an increased expression of EMA monitored by flow cytometry. A specific reduction in the number of ER without any constant dissociation (Kd) modification was also observed after treatment with the 5 DIAs. No modification of morphological or biochemical characteristics, including EMA expression and ER binding, were observed for RA (1 microM)-treated cells. All these results suggest that induction of a more differentiated phenotype is associated with a block in G1 cell cycle phase, resulting in total growth arrest. Apparently, RA (1 microM)-treated cells did not fulfill these criteria, since only a slight accumulation in G1 and a slowed growth rate were evaluated.

Transforming growth factor beta (TGF-beta) reverses phorbol diester resistance of a breast adenocarcinoma (MCF-7) subline

We investigated the effects of TGF-beta on a MCF-7 subline (MCF-7:RPh-4) which is resistant to phorbol diesters with respect to growth inhibition and estrogen receptor content modulation. This biological unresponsiveness of MCF-7:RPh-4 cells to phorbol esters seems to be unrelated to activation of protein kinase C. In the presence of 80 nM PMA (12-O-tetradecanoylphorbol-13-acetate), TGF-beta induced a dose-dependent inhibition of MCF-7:RPh-4 cell proliferation. MCF-7:RPh-4 cells grown in PMA-free medium for at least 28 days remained insensitive to PMA but lost sensitivity to TGF-beta. Under these conditions, addition of 80 nM PMA restored sensitivity to TGF-beta. In the presence of a fixed concentration of TGF-beta, the dose-dependent inhibition of proliferation and the decrease in estrogen receptor content induced by PMA were comparable to those observed in PMA-treated parental MCF-7 cells. These observations indicate that TGF-beta reverses PMA resistance in MCF-7:RPh-4 cells. In addition, TGF-beta does not modify the basal or PMA-stimulated phosphorylation of Mr 28,000 endogenous protein. These results suggest that TGF-beta interferes with the protein kinase C pathway independently of enzyme activation.

Transforming growth factor beta (TGF-beta) potentiates the inhibitory effect of retinoic acid on human breast carcinoma (MCF-7) cell proliferation

Anchorage-dependent and -independent MCF-7 cell growth was dose-dependently inhibited by retinoic acid (RA) but was insensitive to TGF-beta (from 1 to 100 pM). Growth of MCF-7 monolayer cultures was inhibited (50%) when exposed to 10(-6) M RA. RA was unable to completely inhibit MCF-7 cell proliferation, as concentrations above 10(-6) M were rapidly cytotoxic. However, the combination of TGF-beta and RA resulted an increase in RA inhibitory effect on MCF-7 monolayer growth and a 80% reduction in colony formation in soft agar. These results demonstrate that although TGF-beta does not inhibit the growth of MCF-7 cells, it potentiates the antiproliferative effect of RA, suggesting that it may play a part, albeit indirect, in the regulation of MCF-7 cell growth.

Modulation of estrogen receptors by phorbol diesters in human breast MCF-7 cell line

Treatment of MCF-7 cells with 12-O-tetradecanoylphorbol 13-acetate (TPA) results in an inhibition of cell proliferation and a reduction in the number of estrogen receptors (ER), shown by binding studies and immunoassay. The decrease in ER concentration induced by phorbol ester derivatives parallels their growth inhibitory effect. Moreover, the estrogen receptor of TPA-resistant RPh4 cells (which are insensitive to the antiproliferative and morphological effects of TPA) is not affected by TPA treatment. The reduction in ER concentration appear to be a specific phenomenon since it contrasted with the 2-fold increase in total cell protein content which included an increase in progesterone receptor (PgR). We also found that addition of TPA does not affect estrogen induction of PgR.

Interaction of estradiol and high density lipoproteins on proliferation of the human breast cancer cell line MCF-7 adapted to grow in serum free conditions

The responsiveness of the human mammary carcinoma cell line MCF-7 to estradiol and tamoxifen treatment has been studied in different culture conditions. Cells from exponentially growing cultures were compared with cells in their initial cycles after replating from confluent cultures ("confluent-log" cells). It has been observed that estradiol stimulation of tritiated thymidine incorporation decreases with cell density and that "confluent-log" cells are estrogen unresponsive for a period of four cell cycles in serum-free medium conditions. On the other hand, growth of cells replated from exponentially growing, as well as from confluent cultures, can be inhibited by tamoxifen or a combined treatment with tamoxifen and the progestin levonorgestrel. This growth inhibitory effect can be rescued by estradiol when cells are replated from exponentially growing cultures. The growth inhibitory effect cannot be rescued by estradiol alone (10(-10) to 10(-8) M) when cells are replated from confluent cultures. In this condition, the addition of steroid depleted serum is necessary to reverse the state of estradiol unresponsiveness. Serum can be replaced by high density lipoproteins but not by low density lipoproteins or lipoprotein deficient serum. The present data show that estradiol and HDL interact in the control of MCF-7 cell proliferation.

The chick oviduct in tissue culture. I. Initial characterization of growing primary oviduct tissue cultures

A simple three-enzyme treatment of collagenase, dispase and hyaluronidase on finely minced chick oviduct yields clumps of 50-150 cells. These cells attach to collagen-treated dishes and survive in culture for at least 2 weeks without subculturing. Oviduct cell cultures can also be induced to grow. Estradiol or epidermal growth factor (EGF) induce a 40% increase in cells in 4 days when cultures are grown in serum levels that do not support growth. Serum from estrogen-stimulated chicks promotes rapid cellular proliferation (doubling times of 1-2 days). Sera from estrogen withdrawn chicks, laying hen or horse do not support as rapid proliferation. The oviduct growth-promoting factors in serum from estrogen-stimulated chicks are not steroids or fibroblast growth factors (FGF). Removal of steroids from these sera by charcoal treatment or delipidization does not decrease the rate of growth. The addition of 1-100 nM estradiol does not increase a serum's ability to promote growth. Purified FGF or platelet-derived growth factor (PDGF) do not induce oviduct proliferation. These results were reproduced in oviduct cell cultures started from estrogen-stimulated and withdrawn chicks as well as laying hens. Thus the factors in serum from estrogen-stimulated chicks that promote rapid oviduct growth are induced by estrogen treatments in vivo, but do not seem to be only steroids.

How culture conditions modulate the morphofunctional differentiation of the human estradiol-sensitive mammary cell line (MCF-7)

The MCF-7 cell line grown on plastic surfaces is widely accepted as a model for hormone sensitivity in molecular biology. However, in vitro results concerning estrogen sensitivity remain controversial. In search of culture conditions most closely simulating the in vivo microenvironment we cultured MCF-7 cells on diverse substrates and in suspension culture. The different factors of the contact environment: (A) influence of diffusive medium, (B) influence of cell to cell contacts, and (C) influence of cell to substrate contacts were considered. Using morphological criteria:phase contrast microscopy, scanning and transmission electron microscopy we observed MCF-7 morphofunctional differentiation under the different culture conditions. Plastic, corneal endothelial cell extracellular matrix, and attached collagen gels imposed a planar medium-aggregate interface. The impermeability of the free surface and the intense basal tension antagonized epithelial polarization. Only at post-confluence did domes and clusters appear above the monolayer. On floating collagen gels and in suspension culture the cells established intimate cell-cell contacts over large surfaces and reconstituted tissular architecture. Three-dimensional growth conditions which approach the in vivo contact environment of epithelial cells should be used instead of the traditional monolayer cultures for assessing hormonal and pharmacological responses of human breast carcinomas.