The role of TGF-beta production in growth inhibition of breast-tumor cells by progestins

A molecular toolbox to study progesterone receptor signaling

Progesterone receptor (PR) signaling is required for mammary gland development and homeostasis. A major bottleneck in studying PR signaling is the lack of sensitive assays to measure and visualize PR pathway activity both quantitatively and spatially. Here, we develop new tools to study PR signaling in human breast epithelial cells. First, we generate optimized Progesterone Responsive Element (PRE)-luciferase constructs and demonstrate that these new reporters are a powerful tool to quantify PR signaling activity across a wide range of progesterone concentrations in two luminal breast cancer cell lines, MCF7 and T47D. We also describe a fluorescent lentiviral PRE-GFP reporter as a novel tool to visualize PR signaling at the single-cell level. Our reporter constructs are sensitive to physiological levels of progesterone. Second, we show that low background signaling, and high levels of PR expression are a prerequisite for robustly measuring PR signaling. Increasing PR expression by transient transfection, stable overexpression in MCF7 or clonal selection in T47D, drastically improves both the dynamic range of luciferase reporter assays, and the induction of endogenous PR target genes as measured by qRT-PCR. We find that the PR signaling response differs per cell line, target gene and hormone concentration used. Taken together, our tools allow a more rationally designed approach for measuring PR signaling in breast epithelial cells.

Modulation of HIV replication in monocyte derived macrophages (MDM) by steroid hormones

Significant sex specific differences in the progression of HIV/AIDS have been reported. Several studies have implicated steroid hormones in regulating host factor expression and modulating HIV transmission and replication. However, the exact mechanism exerted by steroid hormones estrogen and progesterone in the regulation of HIV-1 replication is still unclear. Results from the current study indicated a dose dependent down regulation of HIV-1 replication in monocyte derived macrophages pre-treated with high concentrations of estrogen or progesterone. To elucidate the molecular mechanisms associated with the down regulation of HIV-1 replication by estrogen and progesterone we used PCR arrays to analyze the expression profile of host genes involved in antiviral responses. Several chemokines, cytokines, transcription factors, interferon stimulated genes and genes involved in type-1 interferon signaling were down regulated in cells infected with HIV-1 pre-treated with high concentrations of estrogen or progesterone compared to untreated HIV-1 infected cells or HIV-1 infected cells treated with low concentrations of estrogen or progesterone. The down regulation of CXCL9, CXCL10 and CXCL11 chemokines and IL-1β, IL-6 cytokines in response to high concentrations of estrogen and progesterone pre-treatment in HIV-1 infected cells was confirmed at the protein level by quantitating chemokine and cytokine concentrations in the culture supernatant. These results demonstrate that a potent anti-inflammatory response is mediated by pre-treatment with high concentrations of estrogen and progesterone. Thus, our study suggests a strong correlation between the down-modulation of anti-viral and pro-inflammatory responses mediated by estrogen and progesterone pre-treatment and the down regulation of HIV-1 replication. These findings may be relevant to clinical observations of sex specific differences in patient populations and point to the need for further investigation.

Metformin attenuates transforming growth factor beta (TGF-β) mediated oncogenesis in mesenchymal stem-like/claudin-low triple negative breast cancer

Mesenchymal stem-like/claudin-low (MSL/CL) breast cancers are highly aggressive, express low cell-cell adhesion cluster containing claudins (CLDN3/CLDN4/CLDN7) with enrichment of epithelial-to-mesenchymal transition (EMT), immunomodulatory, and transforming growth factor-β (TGF-β) genes. We examined the biological, molecular and prognostic impact of TGF-β upregulation and/or inhibition using in vivo and in vitro methods. Using publically available breast cancer gene expression databases, we show that upregulation and enrichment of a TGF-β gene signature is most frequent in MSL/CL breast cancers and is associated with a worse outcome. Using several MSL/CL breast cancer cell lines, we show that TGF-β elicits significant increases in cellular proliferation, migration, invasion, and motility, whereas these effects can be abrogated by a specific inhibitor against TGF-β receptor I and the anti-diabetic agent metformin, alone or in combination. Prior reports from our lab show that TNBC is exquisitely sensitive to metformin treatment. Mechanistically, metformin blocks endogenous activation of Smad2 and Smad3 and dampens TGF-β-mediated activation of Smad2, Smad3, and ID1 both at the transcriptional and translational level. We report the use of ID1 and ID3 as clinical surrogate markers, where high expression of these TGF-β target genes was correlated to poor prognosis in claudin-low patients. Given TGF-β's role in tumorigenesis and immunomodulation, blockade of this pathway using direct kinase inhibitors or more broadly acting inhibitors may dampen or abolish pro-carcinogenic and metastatic signaling in patients with MCL/CL TNBC. Metformin therapy (with or without other agents) may be a heretofore unrecognized approach to reduce the oncogenic activities associated with TGF-β mediated oncogenesis.

The miR-200 and miR-221/222 microRNA families: opposing effects on epithelial identity

Carcinogenesis is a complex process during which cells undergo genetic and epigenetic alterations. These changes can lead tumor cells to acquire characteristics that enable movement from the primary site of origin when conditions become unfavorable. Such characteristics include gain of front-rear polarity, increased migration/invasion, and resistance to anoikis, which facilitate tumor survival during metastasis. An epithelial to mesenchymal transition (EMT) constitutes one way that cancer cells can gain traits that promote tumor progression and metastasis. Two microRNA (miRNA) families, the miR-200 and miR-221 families, play crucial opposing roles that affect the differentiation state of breast cancers. These two families are differentially expressed between the luminal A subtype of breast cancer as compared to the less well-differentiated triple negative breast cancers (TNBCs) that exhibit markers indicative of an EMT. The miR-200 family promotes a well-differentiated epithelial phenotype, while high miR-221/222 results in a poorly differentiated, mesenchymal-like phenotype. This review focuses on the mechanisms (specific proven targets) by which these two miRNA families exert opposing effects on cellular plasticity during breast tumorigenesis and metastasis.

Genome-wide linkage scan for breast cancer susceptibility loci in Swedish hereditary non-BRCA1/2 families: suggestive linkage to 10q23.32-q25.3

The two breast cancer genes BRCA1 and BRCA2 were identified more than 10 years ago and, depending on population, mutations in these genes are responsible for a varying percentage of familial breast cancer. In more than half the families, the increased risk of breast cancer cannot be explained by mutations in these genes, and the goal of this study was to locate novel susceptibility genes. One of the main difficulties in identifying the cause of hereditary non-BRCA1/BRCA2 breast cancer is genetic heterogeneity, possibly due to multiple, incompletely penetrant susceptibility genes, along with ethnic and geographic differences. In this study, one large family and 13 small to medium-sized families with multiple cases of breast cancer were analyzed by genome-wide linkage analysis. The genome scan was performed by genotype analysis of 10,000 SNP markers on microarrays. The strongest evidence of linkage (HLOD 2.34) was obtained on chromosome region 10q23.32-q25.3. A further two regions were identified, with LOD scores above 2.10 on 12q14-q21 and 19p13.3-q12. In a subset of families of western Swedish origin, two regions generated LOD scores exceeding 1.8: 10q23.32-q25.3 and 19q13.12-q13.32. The large family in the study exceeded LOD 1.5 in three regions: 10q23.32-q25.3, 19q13.12-q13.32, and 17p13. Our results indicate that one or more of the suggested regions may harbor genes that are involved in the development of breast cancer.

Risk of breast cancer with progestins: critical assessment of current data

Whether progestins protect against the risk of breast cancer or enhance that risk has been a major area of controversy over the past several years. Observational studies have reported conflicting results and experimental studies examining whether progestins exert mitogenic or anti-mitogenic actions on breast tissue report divergent results. Based upon a wide range of animal, epidemiologic and clinical data, most investigators agree that estrogens contribute to the development of breast neoplasms. However, the additional effect of progestins on this risk has been the subject of substantial discussion and controversy. A variety of experiments have been carried out using human breast cancer cells grown in vitro and as xenografts in nude mice. These studies demonstrated both mitogenic and anti-mitogenic effects depending upon the precise experimental conditions. Two potential reasons for these differences include differential metabolism of progestins into inhibitory pregnenes or stimulatory 5-alpha-reduced pregnanes or the presence of a protein (GPR 30) which allows the anti-mitogenic effects of progestins to be manifest. Based upon the conflicting nature of the results in experimental studies, we believe that only data in patients provide substantial insight into the actions of progestins on the intact human breast. Studies have now demonstrated that cell proliferation and breast density is higher during the luteal than during the follicular phase of the menstrual cycle. In postmenopausal women, long-term exposure to estrogen plus a progestin results in a marked enhancement of proliferation of the terminal duct lobular units as well as in breast density. These data, taken together, provide substantial evidence that progestins are mitogenic on the human breast when given long term to postmenopausal women. To critically evaluate the observational studies regarding breast cancer risk from progestins, we developed a set of stringent criteria for acceptance of individual studies. Four of the five studies meeting these criteria reported a greater risk of breast cancer with combination estrogen/progestin regimens than with estrogen alone. More importantly, the first randomized, prospective, controlled trial of the risk of breast cancer with an estrogen/progestin combination (the Women's Health Initiative Study) has now been published. This study reported a 26% increased relative risk of breast cancer with the estrogen/progestin combination. Based upon these data, we believe that progestins do add to the risk of breast cancer over and above that imparted by estrogen alone. The attributable risk during use for 5 years or less is small but increases logarithmically during long-term use. The majority of data regarding progestins are derived from regimens using MPA. However, we conclude from our analysis that the burden of proof regarding progestins has now shifted. One must now prove that an estrogen/progestin combination is safe with respect to breast cancer rather than having to prove it harmful.

Overexpression of Id-1 is associated with poor clinical outcome in node negative breast cancer

Id-1 is an important regulator of cellular growth and differentiation and controls malignant progression of breast cancer cells. The aim of our study was to assess the clinical impact of Id-1 expression in breast cancer, i.e., its potential impact on prognosis and prediction of treatment response. Id-1 protein expression was determined immunohistochemically in 191 patients with lymph-node negative breast cancer, and univariate and multivariate survival analysis was carried out. Fifteen (7.9%) specimens showed strong expression, 75 (39.3%) moderate, 55 (28.8%) weak expression and 46 (24.1%) cases no expression of Id-1. Patients with strong or moderate Id-1 expression had a significant shorter overall (p = 0.003, Cox regression) and disease-free survival (p = 0.01, Cox regression) compared to those with absent or low expression. Progesterone receptor density was significantly higher in breast cancers with absent/low Id-1 expression compared to those with moderate/strong expression (p < 0.001, t-test). Id-1 expression was significantly stronger in cases positive for p16(INK4a) expression compared to those negative for p16 (p = 0.049, Mann-Whitney test). The influence of Id-1 on clinical outcome seems much stronger in patients with negative estrogen receptor status compared to those with positive status, who received receptor antagonists as adjuvant therapy in most cases. Overexpression of Id-1 protein represents a strong independent prognostic marker in node negative breast cancer, and future therapies inhibiting Id-1 expression might be beneficial for these patients. Our results also suggest that due to the apparent interaction of Id-1 with the steroid-receptor system in breast cancer, hormonal therapies might influence Id-1 expression and its impact on clinical outcome.

Rat testicular germ cells and Sertoli cells release different types of bioactive transforming growth factor beta in vitro

Several in vivo studies have reported the presence of immunoreactive transforming growth factor-beta's (TGF-beta's) in testicular cells at defined stages of their differentiation. The most pronounced changes in TGF-beta1 and TGF-beta2 immunoreactivity occurred during spermatogenesis. In the present study we have investigated whether germ cells and Sertoli cells are able to secrete bioactive TGF-beta's in vitro, using the CCl64 mink lung epithelial cell line as bioassay for the measurement of TGF-beta. In cellular lysates, TGF-beta bioactivity was only observed following heat-treatment, indicating that within these cells TGF-beta is present in a latent form. To our surprise, active TGF-beta could be detected in the culture supernatant of germ cells and Sertoli cells without prior heat-treatment. This suggests that these cells not only produce and release TGF-beta in a latent form, but that they also release a factor which can convert latent TGF-beta into its active form. Following heat-activation of these culture supernatant's, total TGF-beta bioactivity increased 6- to 9-fold. Spermatocytes are the cell type that releases most bioactive TGF-beta during a 24 h culture period, although round and elongated spermatids and Sertoli cells also secrete significant amounts of TGF-beta. The biological activity of TGF-beta could be inhibited by neutralizing antibodies against TGF-beta1 (spermatocytes and round spermatids) and TGF-beta2 (round and elongating spermatids). TGF-beta activity in the Sertoli cell culture supernatant was inhibited slightly by either the TGF-beta1 and TGF-beta2 neutralizing antibody. These in vitro data suggest that germ cells and Sertoli cells release latent TGF-beta's. Following secretion, the TGF-beta's are converted to a biological active form that can interact with specific TGF-beta receptors. These results strengthen the hypothesis that TGF-beta's may play a physiological role in germ cell proliferation/differentiation and Sertoli cell function.

Estrogen and antiestrogen actions on transforming growth factorbeta (TGFbeta) in normal human breast epithelial (HBE) cells

We have previously shown that estradiol (E2) increases the growth of normal human breast epithelial (HBE) cells and the antiestrogen 4-hydroxytamoxifen (4-OHT) inhibits estrogen-induced proliferation. These effects of estrogens and antiestrogens on proliferation have also been well documented in breast cancer cells. One mechanism for the antiproliferative effects of antiestrogens is the stimulation of TGFbeta in hormone-dependent MCF-7 and T47D cells. The role of this inhibitory growth factor in normal human breast cells has not been well studied. Accordingly, we measured the amounts of total and active TGFbeta1 and TGFbeta2 by specific E(max) immunoassay (EIA) in culture medium from normal breast cells (epithelial and fibroblasts) and from various ER- and ER+ breast cancer cell lines. We established that HBE cells are sensitive to the antiproliferative effect of TGFbetas, and studied the effect of E2 and 4-OHT, alone or in combination, on the secretion and activation of TGFbetas by HBE cells. HBE cells secrete TGFbeta1 and even more TGFbeta2, and are sensitive to these factors. However, in contrast to MCF-7 cells, TGFbeta secretion in normal breast cells is not regulated by E2 and 4-OHT.

Biphasic effect of medroxyprogesterone-acetate (MPA) treatment on proliferation and cyclin D1 gene transcription in T47D breast cancer cells

While progesterone is a known differentiation-inducing factor in the human endometrium, for the breast epithelium both proliferation-inducing and -inhibiting effects have been described. Cyclin D1, which is required for cell cycle progression in G1 and has been shown to play an important role in the pathogenesis of breast cancer has been implicated as a possible mediator of such effects. In the present study we thus investigated the effects of the progestin agonist MPA (medroxy-progesterone acetate) on proliferation of T47D breast cancer cells. In parallel experiments, the regulation of the human cyclin D1 promoter as well as cyclin D1 protein levels under the influence of MPA were studied. Our results show an increase of proliferative activity in T47D cells after 24 and 48 h of MPA treatment followed by inhibition of proliferation after 72 h. In Western blot analysis an increased expression level of cyclin D1 protein can be observed after 24h of MPA stimulation, while at 72h the protein levels are barely detectable. Transient transfection experiments with a luciferase reporter plasmid containing the human cyclin D1 promoter showed an induction of the promoter after 24 and 36h of MPA treatment followed by a reduction in promoter activity. In conclusion, our results confirm the existence of a biphasic response of T47D cell proliferation in response to MPA treatment, consisting of stimulation of proliferation followed by inhibition, and further implicate cyclin D1 as a mediator of these effects, since the cyclin D1 promoter shows a similar biphasic response in this context.

TGF-beta and cancer

The relationships between transforming growth factor-beta (TGF-beta) and cancer are varied and complex. The paradigm that is emerging from the experimental evidence accumulated over the past decade or so is that TGF-beta can play two different and opposite roles with respect to the process of malignant progression. During early stages of carcinogenesis, TGF-beta acts predominantly as a potent tumor suppressor and may mediate the actions of chemopreventive agents such as retinoids and nonsteroidal anti-estrogens. However, at some point during the development and progression of malignant neoplasms, bioactive TGF-betas make their appearance in the tumor microenvironment and the tumor cells escape from TGF-beta-dependent growth arrest. In many cases, this resistance to TGF-beta is the consequence of loss or mutational inactivation of the genes that encode signaling intermediates. These include the types I and II TGF-beta receptors, as well as receptor-associated and common-mediator Smads. The stage of tumor development or progression at which TGF-beta-resistant clones come to dominate the tumor cell population in different types of neoplasm remains to be defined. The phenotypic switch from TGF-beta-sensitivity to TGF-beta-resistance that occurs during carcinogenesis has several important implications for cancer prevention and treatment.

Growth factors, apoptosis, and survival of mammary epithelial cells

Programmed cell death (apoptosis) occurs regularly during normal growth and development of the mammary gland. One of the most dramatic examples of apoptosis is evident during the remodeling of the breast that accompanies postlactational involution. Transgenic mouse models have demonstrated that overexpression of polypeptides such as transforming growth factor alpha (TGFalpha) and insulin like growth factor I (IGF-I) can block this remodeling, suggesting that these growth factors may be acting as survival factors for the mammary epithelium. In contrast, transgenic mice that overexpress the growth inhibitor transforming growth factor beta (TGF-beta) show increased apoptosis in the mammary epithelium throughout mammary development, suggestive of a mechanism working to counterbalance the survival factors. Experiments with mammary epithelial cell lines cultured in vitro have confirmed that these growth factors can indeed regulate apoptosis and survival in mammary epithelial cells; EGF, IGF-I, and basic fibroblast growth factor (bFGF) act as survival factors for mammary epithelial cells, while TGF-beta induces their death. In breast cancer, cytotoxic drugs and hormone ablation increase the expression of TGF-beta, which may function to induce cell death by either paracrine or autocrine mechanisms. Lastly, although it has very limited expression in the breast, TNFalpha has been shown to be effective in the rapid, direct induction of cell death in breast cancer cell lines. Together, these studies describe a complex dynamic pattern of cell death-inducing and survival factors that promote the development of the mature mammary gland and that rapidly remodel the tissue after lactation.

Mechanisms of cyclin-dependent kinase inactivation by progestins

The steroid hormone progesterone regulates proliferation and differentiation in the mammary gland and uterus by cell cycle phase-specific actions. In breast cancer cells the predominant effect of synthetic progestins is long-term growth inhibition and arrest in G1 phase. Progestin-mediated growth arrest of T-47D breast cancer cells was preceded by inhibition of cyclin D1-Cdk4, cyclin D3-Cdk4, and cyclin E-Cdk2 kinase activities in vitro and reduced phosphorylation of pRB and p107. This was accompanied by decreases in the expression of cyclins D1, D3, and E, decreased abundance of cyclin D1- and cyclin D3-Cdk4 complexes, increased association of the cyclin-dependent kinase (CDK) inhibitor p27 with the remaining Cdk4 complexes, and changes in the molecular masses and compositions of cyclin E complexes. In control cells cyclin E eluted from Superdex 200 as two peaks of approximately 120 and approximately 200 kDa, with the 120-kDa peak displaying greater cyclin E-associated kinase activity. Following progestin treatment, almost all of the cyclin E was in the 200-kDa, low-activity form, which was associated with the CDK inhibitors p21 and p27; this change preceded the inhibition of cell cycle progression. These data suggest preferential formation of this higher-molecular-weight, CDK inhibitor-bound form and a reduced number of cyclin E-Cdk2 complexes as mechanisms for the decreased cyclin E-associated kinase activity following progestin treatment. Ectopic expression of cyclin D1 in progestin-inhibited cells led to the reappearance of the 120-kDa active form of cyclin E-Cdk2 preceding the resumption of cell cycle progression. Thus, decreased cyclin expression and consequent increased CDK inhibitor association are likely to mediate the decreases in CDK activity accompanying progestin-mediated growth inhibition.

Estrogen and progestin regulation of cell cycle progression

Estrogens and progesterone, acting via their specific nuclear receptors, are essential for normal mammary gland development and differentiated function. The molecular mechanisms through which these effects are mediated are not well defined, although significant recent progress has been made in linking steroid hormone action to cell cycle progression. This review summarizes data identifying c-myc and cyclin D1 as major downstream targets of both estrogen- and progestin-stimulated cell cycle progression in human breast cancer cells. Additionally, estrogen induces the formation of high specific activity forms of the cyclin E-Cdk2 enzyme complex lacking the cyclin-dependent kinase (CDK)3 inhibitor, p21. The delayed growth inhibitory effects of progestins, which are likely to be prerequisites for manifestation of their function in differentiation, also involve decreases in cyclin D1 and E gene expression and recruitment of CDK inhibitors into cyclin D1-Cdk4 and cyclin E-Cdk2 complexes. Thus estrogens and progestins affect CDK function not only by effects on cyclin abundance but also by regulating the recruitment of CDK inhibitors and, as yet undefined, additional components which determine the activity of the CDK complexes. These effects of estrogens and progestins are likely to be major contributors to their regulation of mammary epithelial cell proliferation and differentiation.

Transforming growth factor-beta in breast cancer: a working hypothesis

Transforming Growth Factor-beta (TGF beta) is the most potent known inhibitor of the progression of normal mammary epithelial cells through the cell cycle. During the early stages of breast cancer development, the transformed epithelial cells appear to still be sensitive to TGF beta-mediated growth arrest, and TGF beta can act as an anti-tumor promoter. In contrast, advanced breast cancers are mostly refractory to TGF beta-mediated growth inhibition and produce large amounts of TGF beta, which may enhance tumor cell invasion and metastasis by its effects on extracellular matrix. We postulate that this seemingly paradoxical switch in the responsiveness of tumor cells to TGF beta during progression is the consequence of the activation of the latent TGF beta that is produced and deposited into the tumor microenvironment, thereby driving the clonal expansion of TGF beta-resistant tumor cells. While tumor cells themselves may activate TGF beta, recent observations suggest that environmental tumor promoters or carcinogens, such as ionizing radiation, can cause stromal fibroblasts to activate TGF beta by epigenetic mechanisms. As the biological effects of the anti-estrogen tamoxifen may well be mediated by TGF beta, this model has a number of important implications for the clinical uses of tamoxifen in the prevention and treatment of breast cancer. In addition, it suggests a number of novel approaches to the treatment of advanced breast cancer.

Complex role of tumor cell transforming growth factor (TGF)-beta s on breast carcinoma progression

Growth inhibition by the TGF-beta s has been extensively studied in both normal and transformed mammary epithelial cells. It has been proposed that loss of autocrine TGF-beta mediated growth regulation is a critical event in breast tumorigenesis and several lines of in vitro and in vivo data support this hypothesis. However, a positive association between the expression of TGF-beta s by tumor cells and the progression or maintenance of breast cancinoma cells has been observed in many studies in in vivo tumor models. Possible mechanisms for these growth enhancing effects of TGF-beta include immunosuppression mediated by tumor TGF-beta s, enhanced angiogenesis, increased peritumoral stroma formation, and cell adhesion. The net effect of tumor cell TGF-beta on the biology of breast carcinogenesis would depend on the balance between autocrine growth inhibition of mammary epithelial cells and these growth enhancing effects.

Effect of nomegestrol acetate on estrone-sulfatase and 17beta-hydroxysteroid dehydrogenase activities in human breast cancer cells

It is well recognized that estradiol (E2) is one of the most important hormones supporting the growth and evolution of breast cancer. Consequently, to block this hormone before it enters the cancer cell or in the cell itself, has been one of the main targets in recent years. In the present study we explored the effect of the progestin, nomegestrol acetate, on the estrone sulfatase and 17beta-hydroxysteroid dehydrogenase (17beta-HSD) activities of MCF-7 and T-47D human breast cancer cells. Using physiological doses of estrone sulfate (E1S: 5 x 10(-9)M), nomegestrol acetate blocked very significantly the conversion of E1S to E2. In the MCF-7 cells, using concentrations of 5 x 10(-6)M and 5 x 10(-5) M of nomegestrol acetate, the decrease of E1S to E2 was, respectively, -43% and -77%. The values were, respectively, -60% and -71% for the T-47D cells. Using E1S at 2 x 10(-6) M and nomegestrol acetate at 10(-5) M, a direct inhibitory effect on the enzyme of -36% and -18% was obtained with the cell homogenate of the MCF-7 and T-47D cells, respectively. In another series of studies, it was observed that after 24 h incubation of a physiological concentration of estrone (E1: 5 x 10(-9)M) this estrogen is converted in a great proportion to E2. Nomegestrol acetate inhibits this transformation by -35% and -85% at 5 x 10(-7)M and 5 x 10(-5)M, respectively in T-47D cells; whereas in the MCF-7 cells the inhibitory effect is only significant, -48%, at 5 x 10(-5)M concentration of nomegestrol acetate. It is concluded that nomegestrol acetate in the hormone-dependent MCF-7 and T-47D breast cancer cells significantly inhibits the estrone sulfatase and 17beta-HSD activities which converts E1S to the biologically active estrogen estradiol. This inhibition provoked by this progestin on the enzymes involved in the biosynthesis of E2 can open new clinical possibilities in breast cancer therapy.

Growth inhibition by anti-estrogens and progestins in TGF-beta-resistant and -sensitive breast-tumor cells

Transforming growth factor beta (TGF-beta) is a potent growth inhibitor of non-malignant breast tissue, and TGF-beta resistance could play a role in tumorigenesis. Treatment of breast-tumor cells with anti-estrogens and progestins has been shown to correlate with an increase in the levels of secreted TGF-beta, suggesting that the growth inhibition observed with these (anti)hormones is mediated by this growth factor. In the present study we have investigated the effects of anti-estrogens and progestins on breast-tumor cell lines, which are either resistant or sensitive to TGF-beta. A hormone-independent variant of the MCF7 cell line is shown to have lost its sensitivity to TGF-beta during its progression towards an autonomous phenotype, but has preserved its sensitivity to anti-estrogens. In addition, evidence is presented showing that progestins and anti-estrogens inhibit proliferation, irrespective of the sensitivity to TGF-beta in variants of the T47D cell line. Therefore, we conclude that, although TGF-beta seems an important growth inhibitor for mammary epithelial cells, both progestins and anti-estrogens can inhibit cell proliferation independent of induced TGF-beta production.