The control of progesterone receptor expression in MCF-7 breast cancer cells: effects of estradiol and sex hormone-binding globulin (SHBG)

Synthesis and estrogenic activity of BODIPY-labeled estradiol conjugates

Novel BODIPY-estradiol conjugates have been synthesized by selecting position C-3-O for labeling. The conjugation strategy was based on Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) or etherification. Estradiol derivatives used as azide partners bearing an ω-azidoalkyl function through C4-C8-long linkers have been prepared. CuAAC reactions of estradiol azides with BODIPY alkyne furnished fluorescent 3-O-labeled conjugates bearing the triazole ring as a coupling moiety. Williamson etherifications of 3-O-(ω-bromoalkyl)-17β-estradiol derivatives with BODIPY-OH resulted in labeled conjugates connected with an ether moiety. Interactions of the conjugates with estrogen receptor (ER) were investigated using molecular docking calculations in comparison with estradiol. The conjugates occupied both the classical and alternative binding sites on human ERα, with slightly lower binding affinity to references estradiol and diethystilbestrol. All compounds have displayed reasonable estrogenic activity. They increased the proliferation of ER-positive breast cancer cell line MCF7 contrary to ER-negative SKBR3 cell line. The most potent compound 13a induced the transcriptional activity of ER in dose-dependent manner in dual luciferase recombinant reporter model and increased progesterone receptor's expression, proving the retained estrogenic activity. The fluorescence of candidate compound 13a co-localised with the ERα. The newly synthesized labeled compounds might serve as good starting point for further development of fluorescent probes for modern biological applications. In addition to studying steroid uptake and transport in cells, e.g. in the processes of biodegradation of estrogen-hormones micropollutants, they could also be utilized in examination of estrogen-binding proteins.

Long-term weight loss maintenance, sex steroid hormones, and sex hormone-binding globulin

OBJECTIVE

We tested the effects of weight loss on serum estradiol, estrone, testosterone, and sex hormone-binding globulin (SHBG) in overweight/obese women 18 months after completing a year-long, 4-arm, randomized-controlled dietary weight loss and/or exercise trial.

METHODS

From 2005 to 2008, 439 overweight/obese, postmenopausal women (BMI >25 kg/m), 50 to 75 years, were randomized to a year-long intervention: diet (reduced calorie, 10% weight loss, N = 118), exercise (225 min/wk moderate-to-vigorous activity, N = 117), combined diet + exercise (N = 117), or control (N = 87). At 12 months, 399 women provided blood; of these, 156 returned at 30 months and gave a blood sample. Hormones and SHBG were measured by immunoassay. Changes were compared using generalized estimating equations, adjusting for confounders.

RESULTS

At 30 months, participants randomized to the diet + exercise intervention had statistically significant increases in SHBG levels versus controls (P = 0.001). There was no statistically significant change in SHBG in the exercise or diet intervention arms. Hormone levels did not vary by intervention arm from baseline to 30 months. Participants who maintained weight loss at 30 months had statistically significantly greater decreases in free estradiol and free testosterone (Ptrend = 0.02 and Ptrend = 0.04, respectively) and increases in SHBG (Ptrend < 0.0001) versus those who did not have sustained weight loss. Levels of other analytes did not vary by weight loss at 30 months.

CONCLUSIONS

Sustained weight loss results in reductions in free estradiol and testosterone and increases in SHBG 18-month post-intervention.

Stress hormone-mediated acceleration of breast cancer metastasis is halted by inhibition of nitric oxide synthase

Stress hormones have been shown to be important mediators in driving malignant growth and reducing treatment efficacy in breast cancer. Glucocorticoids can induce DNA damage through an inducible nitric oxide synthase (iNOS) mediated pathway to increase levels of nitric oxide (NO). Using an immune competent mouse breast cancer model and 66CL4 breast cancer cells we identified a novel role of NOS inhibition to reduce stress-induced breast cancer metastasis. On a mechanistic level we show that the glucocorticoid cortisol induces expression of keys genes associated with angiogenesis, as well as pro-tumourigenic immunomodulation. Transcriptomics analysis confirmed that in the lungs of tumour-bearing mice, stress significantly enriched pathways associated with tumourigenesis, some of which could be regulated with NOS inhibition. These results demonstrate the detrimental involvement of NOS in stress hormone signalling, and the potential future benefits of NOS inhibition in highly stressed patients.

Determination and analysis of agonist and antagonist potential of naturally occurring flavonoids for estrogen receptor (ERα) by various parameters and molecular modelling approach

Most estrogen receptor α (ERα) ligands target the ligand binding domain (LBD). Agonist 17β-estradiol (E₂) and tamoxifen (TM, known SERM), bind to the same site within the LBD. However, structures of ligand-bound complexes show that E₂ and TM induce different conformations of helix 12 (H12). During the molecular modelling studies of some naturally occurring flavonoids such as quercetin, luteolin, myricetin, kaempferol, naringin, hesperidin, galangin, baicalein and epicatechin with human ERα (3ERT and 1GWR), we observed that most of the ligands bound to the active site pocket of both 3ERT and 1GWR. The docking scores, interaction analyses, and conformation of H12 provided the data to support for the estrogenic or antiestrogenic potential of these flavonoids to a limited degree. Explicit molecular dynamics for 50 ns was performed to identify the stability and compatibility pattern of protein-ligand complex and RMSD were obtained. Baicalein, epicatechin, and kaempferol with 1GWR complex showed similar RMSD trend with minor deviations in the protein backbone RMSD against 1GWR-E₂ complex that provided clear indications that ligands were stable throughout the explicit molecular simulations in the protein and outcome of naringin-3ERT complex had an upward trend but stable throughout the simulations and all molecular dynamics showed stability with less than overall 1 Å deviation throughout the simulations. To examine their estrogenic or antiestrogenic potential, we studied the effect of the flavonoids on viability, progesterone receptor expression and 3xERE/3XERRE-driven reporter gene expression in ERα positive and estrogen responsive MCF-7 breast cancer cells. Epicatechin, myricetin, and kaempferol showed estrogenic potential at 5 µM concentration.

Nuclear tristetraprolin acts as a corepressor of multiple steroid nuclear receptors in breast cancer cells

Tristetraprolin (TTP) is a 34-kDa, zinc finger-containing factor that in mammalian cells acts as a tumor suppressor protein through two different mechanisms. In the cytoplasm TTP promotes the decay of hundreds of mRNAs encoding cell factors involved in inflammation, tissue invasion, and metastasis. In the cell nucleus TTP has been identified as a transcriptional corepressor of the estrogen receptor alpha (ERα), which has been associated to the development and progression of the majority of breast cancer tumors. In this work we report that nuclear TTP modulates the transactivation activity of progesterone receptor (PR), glucocorticoid receptor (GR) and androgen receptor (AR). In recent years these steroid nuclear receptors have been shown to be of clinical and therapeutical relevance in breast cancer. The functional association between TTP and steroid nuclear receptors is supported by the finding that TTP physically interacts with ERα, PR, GR and AR in vivo. We also show that TTP overexpression attenuates the transactivation of all the steroid nuclear receptors tested. In contrast, siRNA-mediated reduction of endogenous TTP expression in MCF-7 cells produced an increase in the transcriptional activities of ERα, PR, GR and AR. Taken together, these results suggest that the function of nuclear TTP in breast cancer cells is to act as a corepressor of ERα, PR, GR and AR. We propose that the reduction of TTP expression observed in different types of breast cancer tumors may contribute to the development of this disease by producing a dysregulation of the transactivation activity of multiple steroid nuclear receptors.

Associations of sex steroid hormones with mortality in women with breast cancer

Epidemiological studies have demonstrated associations between circulating levels of sex steroid hormones and risk of breast cancer in postmenopausal women. However, data on associations with breast cancer survival are limited. We measured levels of estradiol, estrone, testosterone, and sex hormone-binding globulin (SHBG), in serum collected on average 30 months after diagnosis from 358 postmenopausal women diagnosed with stage I-IIIA breast cancer between 1995 and 1998 who participated in a multiethnic, prospective cohort study. Women were followed through December, 2012. We evaluated associations between log-transformed analytes and breast cancer-specific and all-cause mortality fitting multivariable Cox proportional hazards models. Over a median of 14.5 years of follow-up, 102 deaths occurred; 43 of these were due to breast cancer. In models adjusted for ethnicity/study site, age, body mass index, and tumor stage, increased levels of log-transformed SHBG were associated with reduced risk of both breast cancer-specific mortality (hazard ratio, HR 0.48; 95 % confidence interval, CI 0.26-0.89) and all-cause mortality (HR 0.64, 95 % CI 0.43-0.97). There were no associations between levels of estradiol, estrone, or testosterone for either endpoint. In subgroup analyses, after correction for multiple testing, increased estrone was significantly associated with reduced risk for breast cancer-specific mortality among participants with ER-negative tumors (HR 0.16, 95 % CI 0.05-0.63) but not among participants with ER-positive tumors. Increased serum levels of SHBG were associated with decreased risk of breast cancer-specific and all-cause mortality in women with breast cancer. These results should be confirmed in larger breast cancer survivor cohorts.

Calmodulin as a potential target by which berberine induces cell cycle arrest in human hepatoma Bel7402 cells

Berberine is an isoquinoline alkaloid that has drawn extensive attention because it possesses various biological activities. Several mechanisms have been proposed to interpret the anticancer activity of berberine. However, these explanations are mostly based on its downstream-regulated genes or proteins; information on the direct target proteins that mediate the antiproliferative action of berberine remains unclear. In this study, a computational pipeline based on a ligand-protein inverse docking program and mining of the 'Connectivity MAP' data was adopted to explore the potential target proteins for berberine. The results showed that four proteins, that is calmodulin, cytochrome P450 3A4, sex hormone-binding globulin, and carbonic anhydrase II, were suggested to be the potential targets of berberine. The anticalmodulin property of berberine was demonstrated with an in vitro phosphodiesterase activity assay. Flow cytometric analysis found that G1 cell cycle arrest induced by berberine in Bel7402 cells was enhanced by cotreatment with calmodulin inhibitors. Western blotting results indicated that berberine treatment decreased phosphorylation of calmodulin kinase II and blocked subsequent MEK1 activation as well as p27 protein degradation. These results suggested that calmodulin might play crucial roles in berberine-induced cell cycle arrest in cancer cells.

Association between SHBG Asp327Asn (rs6259) polymorphism and breast cancer risk: a meta-analysis of 10,454 cases and 13,111 controls

Sex hormone-binding globulin (SHBG) is a plasma glycoprotein that plays an important role in breast cancer pathophysiology and risk definition, since it regulates the bioavailable fraction of circulating estradiol. Epidemiological studies have evaluated the association between SHBG Asp327Asn polymorphism and breast cancer risk in diverse populations. However, the results remain conflicting rather than conclusive. This meta-analysis of literatures was performed to derive a more precise estimation of the relationship. A total of 10 studies were identified for the meta-analysis, including 10,454 cases and 13,111 controls for SHBG Asp327Asn polymorphism. When all studies were pooled into the meta-analysis, there was no evidence for significant association between SHBG Asp327Asn polymorphism and breast cancer risk (for Asn/Asn vs. Asp/Asp: OR = 1.20, 95 % CI = 0.94-1.55; for Asp/Asn vs. Asp/Asp: OR = 0.94, 95 % CI = 0.87-1.01; for dominant model: OR = 0.95, 95 % CI = 0.90-1.02; for recessive model: OR = 1.22, 95 % CI = 0.95-1.57). In the subgroup analyses by ethnicity, menopausal status, and source of controls, no significant associations were found in all genetic models. Interestingly, further analyses stratified by menopausal status in different ethnicities revealed that this polymorphism might provide protective effects against breast cancer risk in postmenopausal Asian women (for dominant model: OR = 0.83, 95 % CI = 0.70-0.97). Sensitivity analyses were performed by sequential removal of individual studies and cumulative statistics have showed combined ORs were not materially altered by any individual study under all comparisons. In summary, this meta-analysis suggests that SHBG Asp327Asn polymorphism is not associated with breast cancer risk overall, while it might be an important genetic susceptibility factor in postmenopausal Asian women for developing breast cancer. Larger and well-designed studies are warranted to confirm our findings in the future.

Endocrine disrupting effects of zearalenone, alpha- and beta-zearalenol at the level of nuclear receptor binding and steroidogenesis

The mycotoxin zearalenone (ZEN) is a secondary metabolite of fungi which is produced by certain species of the genus Fusarium and can occur in cereals and other plant products. Reporter gene assays incorporating natural steroid receptors and the H295R steroidogenesis assay have been implemented to assess the endocrine disrupting activity of ZEN and its metabolites α-zearalenol (α-ZOL) and β-zearalenol (β-ZOL). α-ZOL exhibited the strongest estrogenic potency (EC(50) 0.022±0.001 nM), slightly less potent than 17-β estradiol (EC(50) 0.015±0.002 nM). ZEN was ~70 times less potent than α-ZOL and twice as potent as β-ZOL. Binding of progesterone to the progestagen receptor was shown to be synergistically increased in the presence of ZEN, α-ZOL or β-ZOL. ZEN, α-ZOL or β-ZOL increased production of progesterone, estradiol, testosterone and cortisol hormones in the H295R steroidogenesis assay, with peak productions at 10 μM. At 100 μM, cell viability decreased and levels of hormones were significantly reduced except for progesterone. β-ZOL increased estradiol concentrations more than α-ZOL or ZEN, with a maximum effect at 10 μM, with β-ZOL (562±59 pg/ml)>α-ZOL (494±60 pg/ml)>ZEN (375±43 pg/ml). The results indicate that ZEN and its metabolites can act as potential endocrine disruptors at the level of nuclear receptor signalling and by altering hormone production.

Sex Hormone-Binding Globulin (SHBG), estradiol and breast cancer

The human serum Sex Hormone-Binding Globulin (SHBG) plays an important role in breast cancer pathophysiology and risk definition, since it regulates the bioavailable fraction of circulating estradiol. We here summarize data reported over the years concerning the involvement of SHBG and SHBG polymorphisms in the definition of breast cancer risk. We also report what is known about the direct action of SHBG in breast cancer cells, illustrating its interaction with these cells and the subsequent initiation of a specific intracellular pathway leading to cross-talk with the estradiol-activated pathway and, finally, to the inhibition of several effects of estradiol in breast cancer cells. In conclusion, as a result of its unique property of regulating the estrogen free fraction and cross-talking with the estradiol pathways, by inhibiting estradiol-induced breast cancer cell growth and proliferation, SHBG is associated with a reduced risk of developing the neoplasm after estrogen exposure.

Human sex hormone-binding globulin gene expression- multiple promoters and complex alternative splicing

BACKGROUND

Human sex hormone-binding globulin (SHBG) regulates free sex steroid concentrations in plasma and modulates rapid, membrane based steroid signaling. SHBG is encoded by an eight exon-long transcript whose expression is regulated by a downstream promoter (P(L)). The SHBG gene was previously shown to express a second major transcript of unknown function, derived from an upstream promoter (P(T)), and two minor transcripts.

RESULTS

We report that transcriptional expression of the human SHBG gene is far more complex than previously described. P(L) and P(T) direct the expression of at least six independent transcripts each, resulting from alternative splicing of exons 4, 5, 6, and/or 7. We mapped two transcriptional start sites downstream of P(L) and P(T), and present evidence for a third SHBG gene promoter (P(N)) within the neighboring FXR2 gene; PN regulates the expression of at least seven independent SHBG gene transcripts, each possessing a novel, 164-nt first exon (1N). Transcriptional expression patterns were generated for human prostate, breast, testis, liver, and brain, and the LNCaP, MCF-7, and HepG2 cell lines. Each expresses the SHBG transcript, albeit in varying abundance. Alternative splicing was more pronounced in the cancer cell lines. P(L)- P(T)- and P(N)-derived transcripts were most abundant in liver, testis, and prostate, respectively. Initial findings reveal the existence of a smaller immunoreactive SHBG species in LNCaP, MCF-7, and HepG2 cells.

CONCLUSION

These results extend our understanding of human SHBG gene transcription, and raise new and important questions regarding the role of novel alternatively spliced transcripts, their function in hormonally responsive tissues including the breast and prostate, and the role that aberrant SHBG gene expression may play in cancer.

Physical activity and postmenopausal breast cancer: effect modification by breast cancer subtypes and effective periods in life

Physical activity (PA) has been inversely associated with postmenopausal breast cancer risk. However, it is unclear how and in which life periods PA may be effective to reduce breast cancer risk. Moreover, the evidence is still not judged as 'convincing' as there is some heterogeneity among study results. Most studies regarded breast cancer as a single disease, at best separated by menopausal status. Yet, breast cancers are heterogeneous and likely have different etiologies. Therefore, we analyzed the association of PA with different breast cancer subtypes in 3,414 postmenopausal cases and 6,569 controls from a case-control study on breast cancer conducted 2002-2005 in Germany (MARIE study). PA in the age periods 30-49 and 50+ years was assessed, including leisure-time PA (sports, cycling, walking) and non-recreational PA (occupational and household activities). There was a significant protective effect of leisure-time PA for ER+/PR+ carcinomas (adjusted odds ratio = 0.71, 95% confidence interval: 0.60, 0.85; trend P = 0.0001), but no effect for ER-/PR- carcinomas. Moreover, looking at physical activity pattern over time, the effect of PA after menopause on reducing breast cancer risk was more pronounced than the effect of PA before menopause. Overall, effects of PA were independent from adult weight gain, body mass index, and energy intake. These findings suggest that leisure-time PA after menopause may reduce postmenopausal breast cancer risk at least in part via hormonal pathways and not solely by changing body composition. Inactive postmenopausal women should be encouraged to become physically active even later in life.

Disruption of ERalpha signalling pathway by PPARgamma agonists: evidences of PPARgamma-independent events in two hormone-dependent breast cancer cell lines

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor that can be activated by natural ligands such as 15-deoxy-delta(12,14)-prostaglandin J2 (15d-PGJ(2)) as well as synthetic drugs such as thiazolidinediones. The treatment of human breast cancer cell lines with PPARgamma agonists is known to have antiproliferative effects but the role of PPARgamma activation in the process remains unclear. In the present study, we investigated the effects of four PPARgamma agonists, Rosiglitazone (RGZ), Ciglitazone (CGZ), Troglitazone (TGZ) and the natural agonist 15d-PGJ(2), on estrogen receptor alpha (ERalpha) signalling pathway in two hormone-dependent breast cancer cell lines, MCF-7 and ZR-75-1. In both of them, TGZ, CGZ and 15d-PGJ(2) induced an inhibition of ERalpha signalling associated with the proteasomal degradation of ERalpha. ZR-75-1 cells were more sensitive than MCF-7 cells to these compounds. Treatments that induced ERalpha degradation inhibited cell proliferation after 24 h. In contrast, 24 h exposure to RGZ, the most potent activator of PPARgamma disrupted neither ERalpha signalling nor cell proliferation. 9-cis retinoic acid never potentiated the proteasomal degradation of ERalpha. PPARgamma antagonists (T0070907, BADGE and GW 9662) did not block the proteolysis of ERalpha in MCF-7 and ZR-75-1 cells treated with TGZ. ERalpha proteolysis still occurred in case of PPARgamma silencing as well as in case of treatment with the PPARgamma-inactive compound Delta2-TGZ, demonstrating a PPARgamma-independent mechanism. The use of thiazolidinedione derivatives able to trigger ERalpha degradation by a PPARgamma-independent pathway could be an interesting tool for breast cancer therapy.

Progesterone, glucocorticoid, but not estrogen receptor mRNA is altered in breast cancer stroma

Our laboratory has previously found that anti-mitogenic nuclear receptor mRNA is elevated in late stage tumours and this study was performed to scrutinize the possibility of cancer-stroma crosstalk using hormone signaling in these tissues. RNA levels in stromal tissue were examined for the estrogen alpha, estrogen beta, androgen, progesterone and glucocorticoid nuclear receptors by a semi-quantitative PCR. Significant differences in expression between the cancer stroma and control tissue were seen, analyzing for both cancer grade and estrogen receptor status. Stroma and control tissue were significantly different for the progesterone and glucocorticoid nuclear receptors (p=5.908 x 10(-7) and 2.761 x 10(-5), respectively). Glucocorticoid receptor also showed a significant increase to mRNA levels in the stroma of estrogen receptor negative tumours (p=5.85 x 10(-5)). By contrast, the estrogen receptors alpha and beta, those most closely associated with breast tissue growth, showed no significant change in mRNA (p=0.372 and 0.655, respectively). Androgen receptor mRNA also remained unaffected (p=0.174).

Association of endometrial cancer risk with a functional polymorphism (Asp327Asn) in the sex hormone-binding globulin gene

BACKGROUND

Sex steroid hormones play a central role in the development of endometrial cancer. Sex hormone-binding globulin (SHBG) modulates the bioavailability of circulating sex hormones and regulates their signaling systems in target cells. Epidemiologic studies have demonstrated that blood SHBG levels are associated inversely with the risk of endometrial cancer. A functional polymorphism, an amino acid substitution of asparagine (Asp) for aspartic acid (Asn) at residue 327 (Asp(327)Asn) (reference sequence 6259), in the SHBG gene recently was identified and has been associated with an increased half-life and elevated blood levels of SHBG. The authors tested the hypothesis that this genetic variance is associated with a reduced risk of endometrial cancer in the Shanghai Endometrial Cancer Study, a population-based, case-control study that was conducted in urban Shanghai, China between 1997 and 2003.

METHODS

This study included 1037 women with newly diagnosed endometrial cancer ages 30 years and 69 years and 1031 age-matched controls from the community who had completed an in-person interview and donated a blood and/or buccal cell sample to the study. Genotyping for the Asp(327)Asn polymorphism was performed by using the TaqMan method. Odds ratio (ORs) and 95% confidence intervals (95% CIs) derived from logistic regression models were used to evaluate the association between the genetic variation and endometrial cancer risk.

RESULTS

The allele frequencies of Asn were 15.0% in cases and 17.1% in controls (P = .06). The variant Asn(327) allele was associated with a reduced risk of endometrial cancer in postmenopausal women (OR, 0.72; 95% CI, 0.55-0.93) but not in premenopausal women (OR, 1.02; 95% CI, 0.74-1.42). The inverse association was more pronounced among postmenopausal women who had a low body mass index (OR, 0.48; 95% CI, 0.31-0.76) or longer years of menstruation (OR, 0.64; 95% CI, 0.46-0.89), although the results from tests for multiplicative interaction were not statistically significant.

CONCLUSIONS

The current results suggested that the codon 327 Asn allele in the SHBG gene may be related to a reduced risk of endometrial cancer among postmenopausal women.

Additive growth inhibitory effects of ibandronate and antiestrogens in estrogen receptor-positive breast cancer cell lines

INTRODUCTION

Bisphosphonates are inhibitors of osteoclast-mediated tumor-stimulated osteolysis, and they have become standard therapy for the management of bone metastases from breast cancer. These drugs can also directly induce growth inhibition and apoptosis of osteotropic cancer cells, including estrogen receptor-positive (ER+) breast cancer cells.

METHODS

We examined the anti-proliferative properties of ibandronate on two ER+ breast cancer cell lines (MCF-7 and IBEP-2), and on one ER negative (ER-) cell line (MDA-MB-231). Experiments were performed in steroid-free medium to assess ER regulation and the effect of ibandronate in combination with estrogen or antiestrogens.

RESULTS

Ibandronate inhibited cancer cell growth in a dose- and time-dependent manner (approximate IC50: 10(-4) M for MCF-7 and IBEP-2 cells; 3 x 10(-4) M for MDA-MB-231 cells), partly through apoptosis induction. It completely abolished the mitogenic effect induced by 17beta-estradiol in ER+ breast cancer cells, but affected neither ER regulation nor estrogen-induced progesterone receptor expression, as documented in MCF-7 cells. Moreover, ibandronate enhanced the growth inhibitory action of partial (4-hydroxytamoxifen) and pure (ICI 182,780, now called fluvestrant or Faslodex) antiestrogens in estrogen-sensitive breast cancer cells. Combination analysis identified additive interactions between ibandronate and ER antagonists.

CONCLUSION

These data constitute the first in vitro evidence for additive effects between ibandronate and antiestrogens, supporting their combined use for the treatment of bone metastases from breast cancer.

Association of breast cancer risk with a common functional polymorphism (Asp327Asn) in the sex hormone-binding globulin gene

Sex hormones play a central role in the development of breast cancer. Sex hormone-binding globulin (SHBG) modulates the bioavailability of circulating sex hormones and regulates their signaling system in the breast tissue. We evaluated the association of a common functional polymorphism (Asp327Asn) in the SHBG gene with breast cancer risk in a population-based case-control study (1,106 cases and 1,180 controls) conducted in Shanghai, China. The variant Asn allele was associated with a reduced breast cancer risk in postmenopausal women [odds ratio (OR), 0.73; 95% confidence interval (95% CI), 0.53-0.99], but not in premenopausal women (OR, 1.03; 95% CI, 0.82-1.27). The protective association was much stronger in postmenopausal women with a low body mass index (BMI; OR, 0.46; 95% CI, 0.29-0.75) or waist-to-hip ratio (OR, 0.51; 95% CI, 0.32-0.83) than those with a high BMI or waist-to-hip ratio (P for interaction < 0.05). Furthermore, the association was stronger for estrogen receptor-positive (OR, 0.64; 95% CI, 0.42-0.98) than for estrogen receptor-negative breast cancer (OR, 0.85; 95% CI, 0.50-1.45). Among postmenopausal controls, blood SHBG levels were 10% higher in carriers of the variant Asn allele than noncarriers (P = 0.06). Postmenopausal control women with the Asn allele and low BMI or waist-to-hip ratio had 20% higher SHBG levels (P < 0.05). This study suggests that the Asn allele in the SHBG gene may be related to a reduced risk of breast cancer among postmenopausal women by increasing their blood SHBG levels.

Pyrethroid insecticides, fenvalerate and permethrin, inhibit progesterone-induced alkaline phosphatase activity in T47D human breast cancer cells

Pyrethroid insecticides exhibited a weak estrogenic activity by stimulation of MCF-7 cell proliferation and induction of alkaline phosphatase (AlkP) enzyme activity in cultured Ishikawa cells. Previously it was reported that fenvalerate and permethrin significantly inhibited the 17beta-estradiol-induced MCF-7 BUS cell proliferation. Although certain pyrethroid insecticides exert estrogenic or antiestrogenic activities, it is not clear whether pyrethroid insecticides act as progesterone agonists or antagonists. Therefore, the aim of this study was to evaluate the effects of fenvalerate and permethrin on AlkP activity as a progesterone-specific response in T47D cells. In the present study, the stimulation of AlkP activity was concentration dependent with addition of progesterone, and maximum activity was observed at concentration of 1 x 10(-8) M. Both fenvalerate (1 x 10(-6) M) and permethrin (1 x 10(-6) M) did not stimulate the AlkP activity, but progesterone (1 x 10(-8) M)-induced AlkP activity was significantly inhibited at 1 x 10(-6) M concentration of fenvalerate and permethrin, respectively. Progesterone receptor (PR) levels in cytosolic protein of T47D cells were studied to determine the relationship between cellular PR expression and AlkP activity. Similar to AlkP activity, progesterone (1 x 10(-8) M) significantly increased PR protein levels compared to control. However, PR protein levels were not affected in T47D cells cultured with fenvalerate and permethrin alone, whereas fenvalerate and permethrin significantly decreased progesterone-induced PR protein levels. Our data indicate that fenvalerate and permethrin exhibit antiprogestagenic activity in T47D human breast cancer cells.

Membrane 5alpha-pregnane-3,20-dione (5alphaP) receptors in MCF-7 and MCF-10A breast cancer cells are up-regulated by estradiol and 5alphaP and down-regulated by the progesterone metabolites, 3alpha-dihydroprogesterone and 20alpha-dihydroprogesterone, with associated changes in cell proliferation and detachment

Previous studies have shown that the progesterone metabolite, 5alpha-pregnane-3,20-dione (5alphaP), exhibits mitogenic and metastatic activity in breast cell lines and that specific, high affinity receptors for 5alphaP are located in the plasma membrane fractions of tumorigenic (ER/PR-positive) MCF-7 cells. The aim of this study was to determine the effects of the mitogenic (estradiol; 5alphaP) and anti-mitogenic (3alpha-hydroxy-4-pregnen-20-one, 3alphaHP; 20alpha-hydroxy-4-pregnen-3-one, 20alphaHP) endogenous steroid hormones on 5alphaP receptor (5alphaP-R) numbers and on cell proliferation and adhesion of MCF-7 and MCF-10A cells. Exposure of MCF-7 cells for 24h to estradiol or 5alphaP resulted in significant (p < 0.05-0.001) dose-dependent increases in 5alphaP-R levels. Conversely, treatment with 3alphaHP or 20alphaHP resulted in significant (p < 0.05-0.01) dose-dependent decreases in 5alphaP-R levels. Treatment with one mitogenic and one anti-mitogenic hormone resulted in inhibition of the mitogen-induced increases, whereas treatment with two mitogenic or two anti-mitogenic hormones resulted in additive effects on 5alphaP-R numbers. Treatments with cycloheximide and actinomycin D indicate that changes in 5alphaP-R levels depend upon transcription and translation. The non-tumorigenic breast cell line, MCF-10A, was also shown to posses specific, high affinity plasma membrane receptors for 5alphaP that were up-regulated by estradiol and 5alphaP and down-regulated by 3alphaHP. Estradiol binding was demonstrated in MCF-10A cell membrane fractions and may explain the estradiol action in these cells that lack intracellular ER. In both MCF-7 and MCF-10A cells, the increases in 5alphaP-R due to estradiol or 5alphaP, and decreases due to 3alphaHP or 20alphaHP correlate with respective increases and decreases in cell proliferation as well as detachment. These results show distribution of 5alphaP-R in several cell types and they provide further evidence of the significance of progesterone metabolites and their novel membrane-associated receptors in breast cancer stimulation and control. The findings that 3alphaHP and 20alphaHP down-regulate 5alphaP-R and suppress mitogenic and metastatic activity suggest that these endogenous anti-mitogenic progesterone metabolites deserve considerations in designing new breast cancer therapeutic agents.

Role of progestins with partial antiandrogenic effects

An experts' meeting on the 'Role of progestins with partial antiandrogenic effects' was held in Berlin from January 19 to 22, 2001. The meeting was chaired by Dr R. Sitruk-Ware (New York, USA) and participants included Ms F. Fruzzetti (Pisa, Italy), J. Hanker (Trier, Germany), J. Huber (Vienna, Austria), F. Husmann (Bad Sassendorf, Germany), S. O. Skouby (Copenhagen, Denmark), J. H. H. Thijssen (Utrecht, The Netherlands), and R. Druckmann (Nice, France). The present paper reports the conclusions of the meeting. However, the publication of the Women's Health Initiative study, which appeared after the meeting, led to additional comments and revisions.

Extracellular calcium downregulates estrogen receptor alpha and increases its transcriptional activity through calcium-sensing receptor in breast cancer cells

Skeleton is the most common organ targeted by breast cancer cells, especially from estrogen receptor alpha (ER)-positive neoplasms. Metastatic cells can stimulate directly or indirectly osteoclast-mediated bone resorption. Tumor-induced osteolysis is often extensive and leads to the release of large quantities of calcium. Metastatic cancer cells can be thus exposed to high calcium concentrations (40 mM has been reported at the resorption site). However, the effects of Ca2+ on breast cancer cells have been minimally examined. We showed that 20-mM extracellular Ca2+ induced a downregulation of ER protein in MCF-7 cells and caused ER-mediated transactivation of a reporter gene by 55 +/- 10% (mean +/- SD) in MVLN cells (MCF-7 cells stably transfected with ERE and luciferase reporter gene). Moreover, 3 mM Ca2+ increased progesterone receptor (PgR) expression by 45 +/- 8%. Mg2+ tested at up to 20 mM did not exert any effects, while 17beta-estradiol downregulated ER, transactivated the reporter gene, and enhanced PgR expression. The pure antiestrogen ICI 182,780 was able to abrogate the transactivation of the reporter gene and the increase in PgR levels induced by Ca2+, indicating that Ca2+ may exert a weak and specific estrogenic effect in MCF-7 cells. Ca2+ effects on ER probably start at the cell membrane level since a large Ca2+ influx caused by the ionophore A23187 failed to activate ER. We have thus studied the involvement of the membrane calcium-sensing receptor (CaR) that is known to be expressed notably in MCF-7 cells. We first tested the effects of a specific activator of CaR. Exposure to 10(-4) M calcimimetic NPS R-467 mirrored the changes observed with extracellular Ca2+ by inducing a marked decrease in ER protein levels, increasing the transcriptional activity of ER (67 +/- 12%) and stimulating PgR expression (41 +/- 4%). As expected, the NPS S-467 isomer was less effective. Furthermore, a highly selective CaR antagonist partly suppressed the downregulation of ER as well as transactivation of the reporter gene induced by Ca(2+). Our results suggest that the effects of extracellular Ca2+ on ER expression and activity are mediated, at least in part, by the CaR. In summary, calcium released during the process of metastatic bone destruction could modulate the functions of the estrogen receptor, a key receptor involved in breast cancer cells growth and function, and thus participate in the pathogenesis of tumor-induced osteolysis.

Estrogen Responsiveness of IBEP-2, A New Human Cell Line Derived from Breast Carcinoma

IBEP-2, an established cell line recently derived from breast carcinoma, was characterized with regard to estrogen receptor (ER) expression, cell mitogenic response to estrogenic stimulation and sensitivity to antiestrogens. In addition, we examined ER modulation following binding of agonist and antagonists, and the ER-mediated induction of progesterone receptor (PgR). ER level in IBEP-2 cells, determined by enzyme-linked immunoassay (EIA), was slightly higher than that measured in MCF-7 cells (662 v.s. 595 fmol/mg protein). When tested on IBEP-2 and MCF-7, various agonists stimulated cell growth with EC50's reflecting different estrogenic potencies (E(2) approximately diethylstilbestrol > E(1) > genistein). IBEP-2 appeared slightly more sensitive than MCF-7, especially to E(2) (at least 4-fold difference between EC50 values). By contrast, IBEP-2 and MCF-7 were equally sensitive to the growth inhibitory effect of antiestrogens 4-hydroxy-tamoxifen (OH-Tam) and ICI 182,780. As revealed by immunoblotting and immunofluorescence using anti-ER alpha antibodies, ER expression in IBEP-2 cells was modulated by E(2) and estrogen antagonists like it has been shown in other ER-positive cell lines, that is, E(2) and ICI 182,780 caused ER downregulation, whereas OH-Tam induced ER accumulation. Ligand-induced downregulation of ER involved degradation in proteasomes, since it was suppressed by the proteasome inhibitor MG-132. Exposure of IBEP-2 cells to E(2) resulted in a marked (at least 25-fold) induction of PgR, documented by EIA, immunoblotting and immunofluorescence. PgR induction due to E(2) was not modified by MG-132. Interestingly, MG-132 alone produced an ER-independent increase of PgR expression. IBEP-2 might prove to be valuable to study ER-mediated induction of PgR.

Expression of glucocorticoid and progesterone nuclear receptor genes in archival breast cancer tissue

BACKGROUND

Previous studies in our laboratory have shown associations of specific nuclear receptor gene variants with sporadic breast cancer. In order to investigate these findings further, we conducted the present study to determine whether expression levels of the progesterone and glucocorticoid nuclear receptor genes vary in different breast cancer grades.

METHODS

RNA was extracted from paraffin-embedded archival breast tumour tissue and converted into cDNA. Sample cDNA underwent PCR using labelled primers to enable quantitation of mRNA expression. Expression data were normalized against the 18S ribosomal gene multiplex and analyzed using analysis of variance.

RESULTS

Analysis of variance indicated a variable level of expression of both genes with regard to breast cancer grade (P = 0.00033 for glucocorticoid receptor and P = 0.023 for progesterone receptor).

CONCLUSION

Statistical analysis indicated that expression of the progesterone nuclear receptor is elevated in late grade breast cancer tissue.