Compared effects of GnRH analogs and 4-hydroxytamoxifen on growth and steroid receptors in antiestrogen sensitive and resistant MCF-7 breast cancer cell sublines

Summary Antiestrogens, such as tamoxifen, have a direct antitumor action and are widely used in cancer therapy. The direct antitumor action of GnRH analogs has been documented in bothin vitro and clinical studies. GnRH analog direct action could therefore provide an alternative approach in postmenopausal patients developing antiestrogen resistance, a frequent cause of relapse during hormonal treatment of breast cancer. This study was carried out to compare the effects of two GnRH analogs (the agonist Decapeptyl and the antagonist BIM 21009C) and the antiestrogen 4-hydroxy-tamoxifen (OH-TAM) on proliferation in antiestrogen-responsive or antiestrogen-resistant human breast cancer cell lines (MCF-7, MCF-7 LY2). Ineffective when used without estrogen stimulation, both of the GnRH analogs and OH-TAM inhibit the 17-estradiol-stimulated growth of the estrogen-responsive cell line MCF-7. Compared with parental MCF-7 cell line responsiveness, the antiestrogen-resistant variant MCF-7 LY2 appears to be resistant to GnRH analogs. These findings indicate similarities between the two types of compounds with regard to their antiestrogenic effects on growth observedin vitro. However, since unlike OH-TAM, Decapeptyl displays no effect on steroid receptor levels of sensitive MCF-7 cells, the intracellular inhibitory mechanisms of these drugs are probably in part different. This study suggests that the direct effect of the studied GnRH analogs would not be a potent tool for treating antiestrogen-resistant breast tumors.     

Luteolin inhibits proliferation induced by IGF-1 pathway dependent ERα in human breast cancer MCF-7 cells

The growth of many breast tumors is stimulated by IGF-1, which activates signal transduction pathways inducing cell proliferation. ERα is important in this process. The aim of the study was to investigate relationships in vitro among inhibitory effects of luteolin on the growth of MCF-7 cells, IGF-1 pathway and ERα. Our results showed that luteolin could effectively block IGF-1-stimulated MCF-7 cell proliferation in a dose- and time- dependent manner and block cell cycle progression and induce apoptosis evidenced by the flow cytometric detection of sub-G1DNA content. Luteolin markedly decreased IGF-1-dependent IGF-1R and Akt phosphorylation without affecting Erk1/2 phosphorylation. Further experiments pointed out that ERα was directly involved in IGF-1 induced cell growth inhibitory effects of luteolin, which significantly decreased ERα expression. Knockdown of ERα in MCF-7 cells by an ERα-specific siRNA decreased the IGF-1 induced cell growth inhibitory effects of luteolin. ERα is thus a possible target of luteolin. These findings indicate that the inhibitory effect of luteolin on the growth of MCF-7 cells is via inhibiting IGF-1 mediated PI3K-Akt pathway dependent on ERα expression.     

In vitro regulation of vascular endothelial growth factor by estrogens and antiestrogens in estrogen-receptor positive breast cancer

BACKGROUND: The effects of antiestrogens on angiogenesis in breast cancer are not fully defined. In this study we investigated the in vitro effects of antiestrogens at different concentrations on vascular endothelial growth factor (VEGF) production in estrogen receptor (ER)-positive breast cancer cells. METHODS: The dose-dependent effects of 17beta-estradiol (E2), 4-hydroxytamoxifen (4OHT), and ICI182,780 were analyzed both with reference to growth rates and VEGF protein production using enzyme-linked immunosorbent assay (ELISA) in MCF-7 cells. RESULTS: E2 stimulated both the growth rates and VEGF production of MCF-7 cells in the same manner. Although 4OHT stimulated the growth rates as an agonistic effect in an estrogen-free media at levels ranging from 1 nM to 1 micro M, it did not stimulate VEGF expression at the same levels except for at 1 micro M. Although 4OHT had a weak agonistic effect on VEGF production at 1 micro M in an estrogen-free media, it significantly inhibited E2-stimulated VEGF production at the same level. A cytotoxic effect was observed with 10 micro M 4OHT that paradoxically caused a prominent increase in VEGF production. ICI182,780 had no significant effects on the growth rates or VEGF production in this cell line. CONCLUSIONS: These results support the hypothesis that tamoxifen could inhibit angiogenesis induced by estrogens in ER-positive breast cancer cells.     

siRNA沉默DNMT1对人乳腺癌细胞MCF-7生长的影响

目的 靶向人DNMT1（DNA methyltransferase 1, DNMT1）构建RNA干扰载体,研究其对乳腺癌细胞周期、增殖及凋亡的影响。方法 靶向DNMT1基因设计三条短发夹状RNA(short hairpin RNA, shRNA) 的寡核苷酸片段,构建重组体pGCsi-DNMT1,转染至乳腺癌细胞株MCF-7,定量PCR 法检测DNMT1 mRNA表达水平;流式细胞技术分析细胞周期的变化;MTT 法检测细胞生长情况;Annexin V/PI双染法观察细胞凋亡情况;定量PCR 法分析沉默DNMT1基因后对RASSF1A、p16、p21、p27及ERβ基因表达的影响。结果 在构建的靶向DNMT1的shRNA重组质粒pGCsi-DNMT1中,成功筛选到pGCsi-T3能显著下调DNMT1的表达。实时定量PCR检测结果证实重组质粒pGCsi-DNMT1对乳腺癌MCF-7细胞中DNMT1基因的转录有明显的抑制作用。MCF-7细胞转染后,pGCsi-DNMT1可明显抑制乳腺癌MCF-7细胞的增殖;大量细胞发生凋亡;细胞周期分析可见S期明显减少,而G₁/G₀期细胞显著增加;定量PCR检测到乳腺癌细胞中RASSF1A、p16、p21及ERβ基因mRNA表达水平明显升高,而p27基因表达水平未见明显变化。结论 重组质粒pGCsi DNMT1能特异有效地抑制MCF-7细胞内DNMT1的表达、 抑制细胞增殖、促进细胞凋亡,并可通过抑制DNMT1的活性来解除相关基因启动子区的高度甲基化状态,从而促进肿瘤相关基因的表达,提示DNMT1可作为乳腺癌基因治疗的新靶标。     

Melatonin does not inhibit estradiol-stimulated proliferation in MCF-7 and BG-1 cells

Melatonin, an indolic pineal hormone, is produced primarily at night in mammals and is important in controlling biological rhythms. Previous research suggested that melatonin can attenuate proliferation in the estrogen-responsive MCF-7 breast cancer cell line. We tested whether these anti-proliferative effects may have physiological consequences upon two estrogen-responsive cell lines, MCF-7 (a breast cancer cell line) and BG-1 (an ovarian adenocarcinoma cell line). Melatonin (10(-9)- 10(-5) M) attenuated proliferation of MCF-7 and BG-1 cells by >20% in the absence of estrogen. However, 17beta-estradiol exposure negated the ability of melatonin to inhibit proliferation. To substantiate this finding, cells were estrogen starved followed by multiple treatments with estradiol and melatonin. Melatonin did not inhibit estradiol- stimulated proliferation under this protocol. Estradiol increased MCF-7 and BG-1 cell cycle transition from G1 to S phase, however, melatonin did not inhibit this transition nor did it down-regulate estradiol- induced pS2 mRNA levels measured by northern blotting, further indicating that melatonin was unable to attenuate estradiol-induced proliferation and gene expression. We also examined the effects of melatonin on estradiol-induced proliferation in MCF-7 cell xenografts in athymic nude mice. Melatonin at a dose 28 times greater than 17beta- estradiol did not inhibit estradiol-induced proliferation in vivo. Furthermore, pinealectomy did not increase proliferation. Therefore, we conclude that melatonin does not directly inhibit estradiol-induced proliferation.      

Estrogen up-regulates neuropeptide Y Y1 receptor expression in a human breast cancer cell line

Normal breast tissue mainly expresses the neuropeptide Y (NPY) Y2 receptor whereas primary human breast carcinomas express the Y1 receptor (Y1R) subtype. We hypothesized that activation of estrogen signaling systems plays a role in the induction of Y1R. To investigate this possibility, we used estrogen receptor-positive (ER+) human breast carcinoma cell line, MCF-7, and examined the effect of estrogen on Y1R gene expression and its signaling pathways. Saturation binding studies revealed that MCF-7 cells express high-affinity NPY receptor. NPY inhibited forskolin-stimulated adenosine 3'5'-cyclic monophosphate (cAMP) accumulation and mobilized intracellular Ca(2+) in MCF-7 cells. Chronic estrogen treatment enhanced NPY-mediated inhibition of cAMP accumulation by 4-fold and caused a significant increase in Y1R mRNA expression through ERalpha. Similarly, estrogen increased Y1R mRNA expression in T-47D (ER+) but not in MDA-MB231 or MDA-MB468 (ER-) cell lines. Cycloheximide decreased basal Y1R mRNA expression; however, it did not affect its increase by estrogen. Moreover, estrogen treatment of MCF-7 cells did not increase Y1R mRNA stability. The up-regulation of Y1R expression by estrogen is prevented by hydroxyurea but not by nocodazole or IB-MECA (cell cycle inhibitors). Lastly, NPY inhibited estrogen-induced cell proliferation through Y1R. In conclusion, MCF-7 cells express a functional Y1R coupled to both Ca(2+) and cAMP pathways. Estrogen up-regulates Y1R expression through ERalpha. This effect is independent of increased Y1R mRNA stability or new protein synthesis, and likely occurs during S phase completion of the cell cycle. Estrogen plays an important role in the up-regulation of Y1R, which in turn regulates estrogen-induced cell proliferation in breast cancer cells.     

Differential effects of dietary phyto-oestrogens daidzein and equol on human breast cancer MCF-7 cells

The in vitro effects of two closely related phyto-oestrogens daidzein and equol on the oestrogen receptor positive human breast cancer cells MCF-7 were examined. There is differential metabolism of daidzein in humans, and the conversion of daidzein to equol by intestinal microbes occurs only in 30% of the population. The differential potency of these two compounds is thus of considerable importance since it may be likely that the relative risk of hormone-dependent cancers may be higher in ‘non-responders’. In the present study, we compared the ability of both these compounds to induce mRNA expression of the oestrogen-responsive pS2 gene, to compete with oestradiol for binding to the oestrogen receptor (ER) and to affect cellular proliferation. Our studies demonstrate that equol is a 100-fold more potent than daidzein in stimulating an oestrogenic response. Equol was also more effective than daidzein in competing with ³H-oestradiol for binding to the ER. These results suggest that equol has a higher affinity for the ER. Both compounds stimulated the growth of MCF-7 cells in a concentration-dependent manner (10⁻⁸–10⁻⁵ M). Although equol exhibits oestrogenic activity, exposure of MCF-7 cells to equol simultaneously with oestradiol was effective in reducing pS2 mRNA expression. This was not observed with daidzein. However, long-term exposure of MCF-7 cells to both daidzein and equol resulted in the downregulation of ER mRNA expression.     

THE EFFECTS OF ESTRADIOL ON BREAST CANCER CELL LINES

The estradiol effects on breast cancer cell lines including estrogen receptors (ER) positive and negative were studied with flow cytometry analysis, scanning and transmission electron microscopy (SEM and TEM), immunogold and immunofluorescence staining techniques. The results showed that estradiol markedly stimulated the division and proliferation of the ER( ) MCF-7 cells at 10 nM, but had no marked effect on the cell cycle of the ER(-) H466B cells at the same concentration, and that tamo-xifen inhibited the stimulation of estradiol on MCF-7 cells. Estradiol obviously influenced the ultrastruc-ture of MCF-7 cells. Immunocytochemical localization of epidermal growth factor receptor (EGFR) on the MCF-7 cell membrane surface indicated that one of the mechanisms involving the growth of MCF-7 breast cancer cell and the stimulating effect on MCF-7 cells growth by estradiol is autocrine secretion.     

Retinoid antagonism of estrogen-responsive transforming growth factor alpha and pS2 gene expression in breast carcinoma cells.

Exposure of MCF-7 breast carcinoma cells to estradiol results in an increase in transforming growth factor alpha (TGF-alpha) synthesis and secretion. Since TGF-alpha is a potent inducer of proliferation in MCF-7 cells, the increase in TGF-alpha production by estradiol is thought to play an important role in the estrogen stimulation of growth of these cells. Retinoic acid inhibits the proliferation of MCF-7 cells and antagonizes the estrogen stimulation of growth. Addition of retinoic acid resulted in a greater than 70% inhibition of estradiol-induced TGF-alpha synthesis and secretion in MCF-7 cells. The increase in TGF-alpha mRNA expression by estradiol was also inhibited by exposure of the cells to retinoic acid. Pretreatment of the cells with retinoic acid for 24 or 72 h caused more than 50 and 90% inhibition, respectively, of the estradiol-enhanced expression of TGF-alpha mRNA. Expression of pS2 mRNA in MCF-7 cells was stimulated approximately 8-fold by estradiol. Retinoic acid treatment suppressed by greater than 80% both the basal and estradiol-induced pS2 mRNA expression. Retinoic acid modulation of the estrogen receptor gene mRNA was not responsible for the retinoic acid inhibition of the stimulation of pS2 and TGF-alpha gene expression by estradiol, since estrogen receptor gene expression was increased rather than decreased in the presence of retinoic acid. The nuclear retinoic acid receptors alpha and gamma mRNA were expressed in MCF-7 cells and its retinoic acid-resistant derivative RROI. Addition of estradiol to MCF-7 cells resulted in a decreased expression of retinoic acid receptor gamma mRNA; this reduction is prevented by the presence of retinoic acid. These results indicate that retinoic acid can inhibit estradiol-induced TGF-alpha and pS2 mRNA expression in MCF-7 cells. The suppression of TGF-alpha expression may represent one possible mechanism by which retinoic acid antagonizes the stimulation of MCF-7 proliferation by estradiol.     

ERα/LKB1 complex upregulates E-cadherin expression and stimulates breast cancer growth and progression upon adiponectin exposure

Adiponectin is the major adipocytes-secreted protein involved in obesity-related breast cancer growth and progression. We proved that adiponectin promotes proliferation in ERα-positive breast cancer cells, through ERα transactivation and the recruitment of LKB1 as ERα-coactivator. Here, we showed that adiponectin-mediated ERα transactivation enhances E-cadherin expression. Thus, we investigated the molecular mechanism through which ERα/LKB1 complex may modulate the expression of E-cadherin, influencing tumor growth, progression and distant metastasis. We demonstrated that adiponectin increases E-cadherin expression in ERα-positive 2D and higher extent in 3D cultures. This occurs through a direct activation of E-cadherin gene promoter by ERα/LKB1-complex. The impact of E-cadherin on ERα-positive breast cancer cell proliferation comes from the evidence that in the presence of E-cadherin siRNA the proliferative effects of adiponectin is no longer noticeable. Since E-cadherin connects cell polarity and growth, we investigated if the adiponectin-enhanced E-cadherin expression could influence the localization of proteins cooperating in cell polarity, such as LKB1 and Cdc42. Surprisingly, immunofluorescence showed that, in adiponectin-treated MCF-7 cells, LKB1 and Cdc42 mostly colocalize in the nucleus, impairing their cytosolic cooperation in maintaining cell polarity. The orthotopic implantation of MCF-7 cells revealed an enhanced E-cadherin-mediated breast cancer growth induced by adiponectin. Moreover, tail vein injection of MCF-7 cells showed a higher metastatic burden in the lungs of mice receiving adiponectin-treated cells compared to control. From these findings it emerges that adiponectin treatment enhances E-cadherin expression, alters cell polarity and stimulates ERα-positive breast cancer cell growth in vitro and in vivo, sustaining higher distant metastatic burden.     

15-hydroxyprostaglandin dehydrogenase is a tumor suppressor of human breast cancer

Prostaglandin E(2) plays a growth-stimulatory role in breast cancer, and the rate-limiting enzyme in its synthesis, cyclooxygenase-2, is often overexpressed in these cancers. Little is known about the role of the key prostaglandin catabolic enzyme 15-hydroxyprostaglandin dehydrogenase (15-PGDH) in breast cancer pathogenesis. Using a pharmacologically based screen for epigenetically silenced genes, we found low levels of 15-PGDH in MDA-MB-231 cells [estrogen receptor (ER) negative] but high levels in MCF-7 cells (ER positive) and observed its up-regulation following demethylation treatment. Further analysis revealed methylation of the 15-PGDH promoter in one breast cancer cell line and 30% of primary tumors. Analysis of 15-PGDH expression revealed low levels in 40% of primary breast tumors and identified a correlation between 15-PGDH and ER expression. Transfection assays showed that transient up-regulation of 15-PGDH levels in MDA-MB-231 cells resulted in a decreased clonal growth, and stable up-regulation significantly decreased the ability of these cells to form tumors in athymic mice. In contrast, transient silencing of 15-PGDH in MCF-7 cells resulted in their enhanced proliferation, and a stable silencing in these cells enhanced cell cycle entry in vitro and tumorigenicity in vivo. Forced expression of 15-PGDH inhibited the ER pathway and silencing of 15-PGDH up-regulated expression of aromatase. In addition, 15-PGDH levels were down-regulated by estrogen but up-regulated by the tumor suppressor gene CAAT/enhancer binding protein alpha. Our results indicate for the first time that 15-PGDH may be a novel tumor suppressor gene in breast cancer, and suggest that this enzyme can modulate the ER pathway.     

稳定转染ERβ基因对MCF-7乳腺癌细胞系生长特性的影响

目的研究在不同处理因子作用下,外源基因ERβ的表达对MCF-7乳腺癌细胞系生长特性的影响。方法利用lipofectamine 2000将ERβ真核表达载体pCDNA3,ERβ导入MCF-7乳腺癌细胞系。采用含雌激素应答元件（ERE）的荧光素酶报告基因及Western blot方法,检测转染细胞中ERβ的转录活性和蛋白表达水平,筛选阳性克隆。以亲本细胞MCF-7及转染空载体质粒pCDNA3的MCF-7细胞为对照,在雌激素E2和雌激素受体拮抗剂4-OHT作用下观察细胞的生长特点。结果在转染ERβ基因的MCF3细胞系中,ERβ的转录激活活性明显升高;Western blot检测证实,ERβ的蛋白表达水平显著增高。在无处理因子情况下,外源基因ERβ在MCF-7细胞系中的表达对细胞的形态及生长速度无明显影响。与亲本细胞MCF-7及转染空载体质粒的MCF-7细胞相比,稳定转染ERβ的MCF-7细胞对雌激素的敏感性下降,但对4-OHT处理的敏感性无明显减少。结论外源性ERβ基因在MCF-7乳腺癌细胞中的稳定表达不增加对4-OHT的耐药性,但使之对雌激素的敏感性下降。     

Targeting c-Src kinase enhances tamoxifen’s inhibitory effect on cell growth by modulating expression of cell cycle and survival proteins

Purpose Many studies have implicated the non-receptor tyrosine kinase c-Src in the development and metastatic progression of many types of cancer. In breast cancer, c-Src has been proposed to mediate the actions of estrogen in cell cycle progression. Methods In this study we investigated the interaction between c-Src inhibition and estrogen receptor (ER) function using the ER-positive and tamoxifen-sensitive MCF-7 breast cancer cells. Results Pharmacological inhibition of c-Src blocked estrogen-dependent proliferation in MCF-7 cells and enhanced the inhibitory effects of tamoxifen or estrogen-deprivation on cell growth. Maximum inhibition (95%) of cell growth was obtained when tamoxifen and c-Src blockade were combined. Inhibition of c-Src kinase decreased levels of the ER targets c-Myc and cyclin D1 expression but not of Bcl-2. Nevertheless, blocking c-Src kinase in tamoxifen-treated MCF-7 cells led to apoptosis. Inhibition of c-Src kinase altered the ratio of Mcl-1 isoforms in favor of cell death whereas expression of the proapoptotic molecules Bad, Bak, and Bax was not altered. Surprisingly, blocking ER function increased the levels of Bad phosphorylation at serine 112 (BadpS112), an inactive (nonapoptotic) form of Bad. This inactivation of Bad upon ER blockade seemed to depend on c-Src function as chemical inhibition of c-Src kinase reduced BadpS112 levels in cells with impaired ER function but not in estrogen-treated cells. Conclusion These results indicate a crucial role for c-Src kinase in the survival of ER-positive breast cancer cells only when ER function is blocked. Therefore, this study suggests that targeting simultaneously c-Src and ER may effectively inhibit growth of ER-positive breast cancer.     

Ganoderma lucidum inhibits proliferation of human breast cancer cells by down-regulation of estrogen receptor and NF-kappaB signaling

Ganoderma lucidum, an oriental medical mushroom, has been used in Asia for the prevention and treatment of a variety of diseases, including cancer. We have previously demonstrated that G. lucidum inhibits growth and induces cell cycle arrest at G0/G1 phase through the inhibition of Akt/NF-kappaB signaling in estrogen-independent human breast cancer cells. However, the molecular mechanism(s) responsible for the inhibitory effects of G. lucidum on the proliferation of estrogen-dependent (MCF-7) and estrogen-independent (MDA-MB-231) breast cancer cells remain to be elucidated. Here, we show that G. lucidum inhibited the proliferation of breast cancer MCF-7 and MDA-MB-231 cells by the modulation of the estrogen receptor (ER) and NF-kappaB signaling. Thus, G. lucidum down-regulated the expression of ERalpha in MCF-7 cells but did not effect the expression of ERbeta in MCF-7 and MDA-MB-231 cells. In addition, G. lucidum inhibited estrogen-dependent as well as constitutive transactivation activity of ER through estrogen response element (ERE) in a reporter gene assay. G. lucidum decreased TNF-alpha-induced (MCF-7) as well as constitutive (MDA-MB-231) activity of NF-kappaB. The inhibition of ER and NF-kappaB pathways resulted in the down-regulation of expression of c-myc, finally suppressing proliferation of estrogen-dependent as well as estrogen-independent cancer cells. Collectively, these results suggest that G. lucidum inhibits proliferation of human breast cancer cells and contain biologically active compounds with specificity against estrogen receptor and NF-kappaB signaling, and implicate G. lucidum as a suitable herb for chemoprevention and chemotherapy of breast cancer.     

瘦素对乳腺癌MCF-7细胞增殖的影响及调控机制的研究

目的:研究瘦素对人乳腺癌MCF-7细胞增殖的影响及对雌、孕激素受体和VEGF的mRNA表达水平的影响,进而揭示瘦素对乳腺癌MCF-7细胞系作用的分子生物学机制。方法:体外培养人乳腺癌MCF-7细胞系,分为对照组、瘦素组和雌激素组。给药后用MTT法测570nm分光光度值。实时荧光定量PCR法观察各组雌、孕激素受体及VEGF的mRNA表达水平。结果:与对照组相比,瘦素可以呈时间和剂量依赖的方式促进MCF-7细胞增殖,并上调细胞中雌、孕激素受体及VEGF的mRNA表达水平,P<0.05。结论:瘦素有促进乳腺癌细胞增殖的作用,该作用的发挥可能与其上调雌、孕激素受体与VEGF的表达有关。为乳腺癌的内分泌治疗提供了新的理论依据。