TGFβ-dependent induction of interleukin-11 and interleukin-8 involves SMAD and p38 MAPK pathways in breast tumor models with varied bone metastases potential

We have delineated TGFβ signaling pathways in the production of osteolytic factors interleukin-8 and interleukin-11 in breast cancer cells with different bone metastases potential. Bone seeking MDA-MB-231(hm) cells expressed higher levels of IL-11, but lower levels of IL-8 compared to MDA-MB-231 cells. MCF-7 cells (mainly osteoblastic) did not express IL-8 or IL-11; MDA-MB-468 cells (weakly metastatic) expressed IL-8, but not IL-11. The up-regulation of IL-11 and IL-8 was associated with the rapid activation of SMAD2/3 and p38 MAPK through the TGFβ/TGFβR system. Analysis of TGFβ receptors indicated that MCF-7 cells do not express TGFβRII, and MDA-MB-468 cells do not express SMAD4. Inactivation of SMAD4 or p38PMAPK gene via RNAi resulted in the inhibition of IL-11 and IL-8 production in MDA-MB-231(hm) cells; and over-expression of SMAD4 gene resulted in IL-11 production in MDA-MB-468 cells. TGFβ-1 induced SMAD3 translocation to the nuclei in MDA-MB-231, MDA-MB-231(hm) as well as in SMAD4 deficient MDA-MB-468, indicating that an alternate non-canonical pathway could be responsible for TGFβ-1 induced cytokine production in MDA-MB-468 cells. Thus, four breast cancer cell lines used in this study show differential expression and up-regulation of the osteolytic factors in response to TGFβ-1 that involves both SMAD pathway, a non-canonical SMAD pathway, as well as p38 MAPK pathways.     

Changes in Radiation Sensitivity and Steroid Receptor Content Induced by Hormonal Agents and Ionizing Radiation in Breast Cancer Cells in Vitro

Possible influences of tamoxifen and estradiol on in vitro radiation sensitivity and cellular receptor content after irradiation and/or tamoxifen treatment were studied in breast cancer cell lines; estrogen receptor (ER) and progesterone receptor (PgR) positive cell lines MCF-7 and MCF-7/TAM^R-1 and the ER and PgR negative cell line MDA-MB-231. The tamoxifen resistant MCF-7/TAM^R-1 cells were more resistant to ionizing radiation than the MCF-7 and MDA-MB-231 cells. Exposure to tamoxifen made the MCF-7 cells more radiation resistant, while estradiol made the MDA-MB-231 cells more radiation sensitive. A radiation dose of 6 Gy reduced the ER content in cytosol in both MCF-7 and MCF-7/TAM^R-1 cells, but brought no alterations to the PgR content. In MCF-7/TAM^R-1 cells tamoxifen exposure significantly increased the ER and reduced the PgR content, an effect not observed in the MCF-7 cells. To conclude, the present study indicates that irradiation and tamoxifen may modify the ER and PgR content in cytosol in breast cancer cells. Hormonal treatment may alter the radiation sensitivity, even in ER negative cells, suggesting that hormonal agents may act both via receptor and non-receptor binding mechanisms.     

Cytokines facilitate chemotactic motility of breast carcinoma cells

BACKGROUND: Both growth and motility of various tumor cells have been shown to be influenced by surrounding cells such as lymphocytes, histiocytes and fibroblasts through various cytokines, growth factors and extracellular matrices. The role of cytokines and extracellular matrices produced by lymphocytes, histiocytes and fibroblasts on migration and invasion of breast carcinoma cells has not been fully investigated METHODS: We investigated the effect of hepatocyte growth factor (HGF), interleukin (IL)-6, IL-8, IL-11, soluble type IV collagen and soluble laminin on the migration of 3 human breast carcinoma cell lines, MDA-MB-231, MCF-7 and T-47D, using a cell culture insert and a biocoat matrigel invasion chamber to assess migration across a matrigel-coated polyethylene telephtalate membrane. RESULTS: HGF, IL-6, IL-11 and IL-8 induced significant migration of MDA-MB-231 cells depending on the dose of each cytokine. However, type IV collagen and laminin inhibited migration of MDA-MB-231 cells. In contrast, IL-8 inhibited migration of MCF-7 cells and IL-6 induced significant migration of T-47D cells, while no other cytokine or extracellular matrix induced significant migration of MCF-7 and T-47D cells. Only HGF induced significant invasion of MDA-MB-231 cells depending on the dose. MCF-7 and T-47D cells did not invade in response to any of the cytokines and extracellular matrices tested. CONCLUSIONS: These results suggest the possibility that the potency of chemotaxis or chemoinvasion differs according to the breast carcinoma cell line and that various cytokines and extracellular matrices secreted by lymphocytes, histiocytes and fibroblasts in the stroma of breast carcinoma can affect the invasion of breast carcinoma cells.     

Upregulated hsa_circ_0000129 expression promotes proliferation and migration of breast cancer cells

Circular RNAs (circRNAs) are considered potential biomarkers in the pathogenesis and detection of several types of cancer. The present study aimed to investigate the role of hsa_circ_0000129 in the pathogenesis and molecular mechanism underlying breast cancer. A total of 68 pairs of breast cancer and corresponding paracancerous tissue samples, three different breast cancer cell lines (MCF-7, MDA-MB-231 and MDA-MB-468) and a normal human breast cell line (MCF-10A) were used to investigate the expression of hsa_circ_0000129. The effect of hsa_circ_0000129 on cell proliferation, migration and colony formation was assessed in MCF-7 and MDA-MB-468 cells, along with the expression of enhancer of zeste homolog 2 (EZH2). The results demonstrated that hsa_circ_0000129 expression was significantly higher in breast cancer tissues compared with normal tissues. In addition, high hsa_circ_0000129 expression was significantly associated with lymph node metastasis and a higher tumor-node-metastasis stage. Comparisons between the breast cancer cell lines (MCF-7, MDA-MB-231 and MDA-MB-468) and MCF-10A cells indicated similar results. MCF-7 cells overexpressed with hsa_circ_0000129 significantly increased cell proliferation, migration and colony formation compared with the negative control group, the effects of which were reversed following hsa_circ_0000129 knockdown in MDA-MB-468 cells. Furthermore, EZH2 expression was positively associated with hsa_circ_0000129 expression. Taken together, the results of the present study suggest that hsa_circ_0000129 may represent a promising prognostic biomarker for breast cancer. In addition, the role of hsa_circ_0000129 in breast cancer cell lines indicates a mechanism for tumorigenesis, as well as a potent target for the treatment of malignant progression.     

Characterization of epidermal growth factor receptor and action on human breast cancer cells in culture

Epidermal growth factor (EGF) may play a role in regulating growth of breast cancer cells in vivo. We have examined the action of EGF on breast cancer cells in vitro and characterized the EGF receptor as a model system for its action in vivo. All of the fourteen breast cancer cell lines which grow attached to culture dishes specifically bound EGF, including one purportedly normal breast line (HBL-100). The one cell line examined which grows as a suspension, DU-4475, did not express measurable levels of EGF binding. The number of EGF binding sites per cell for the different cell lines varied from 200 EGF binding sites/cell (for MDA-MB-436) to 700,000 EGF binding sites/cell (for MDA-MB-231), with most cell lines having approximately 10,000 EGF binding sites/cell. Scatchard analysis of EGF binding to four of the breast cell lines indicated a single class of high-affinity binding sites for MDA-MB-231 cells (Kd = 200 pM; n = 220 fmol of EGF bound/mg of cell protein); and for T-47D cells (Kd = 4 nM, n = 85 fmol of EGF bound/mg of cell protein) and curvilinear plots for MCF-7 cells and HBL-100 cells. The EGF binding to MDA-MB-231 cells was specific for EGF and was maximum after 2 hr at 37 degrees, followed by a progressive loss of cell-associated radio-activity, which was prevented by the action of the lysosomal inhibitory agent chloroquine. Specific covalent binding of 125I-EGF to MDA-MB-231 cells indicated that the EGF receptor had molecular weights of 165,000 and 140,000. MCF-7 cells and T-47D cells grown in serum-free medium supplemented with 10 nM EGF for 3 days had significantly increased protein, DNA, and cell number, whereas MDA-MB-231 and ZR-75-1 cells did not respond significantly to EGF. These results indicate that EGF receptors are consistently expressed by breast cells grown attached to a surface but that some cell lines expressing EGF receptors do not respond mitogenically to EGF. The biochemical characteristics of EGF receptors in MDA-MD-231 breast cells are similar to those observed for EGF receptors in other human tissues.     

Oestrogen sulphatase activity in hormone-dependent and hormone-independent breast-cancer cells: modulation by steroidal and non-steroidal therapeutic agents.

Oestrogen sulphatase may play an important role in providing intracellular oestrogens from E1S for the growth and maintenance of breast tumours. In this study, we characterized oestrogen sulphatase in the hormone-dependent (ER/PR+) MCF-7 and in the hormone-independent (ER/PR-) MDA-MB-231 breast-cancer cells and, furthermore, examined its modulation by MPA, 4-OH-A4, tamoxifen, danazol, ethinyloestradiol and DHAS in both these cell types. Our detailed study of oestrogen sulphatase activity as a function of incubation time, E1S concentration and numbers of MCF-7 and MDA-MB-231 cells showed that more E1S was hydrolysed by MDA-MB-231 cells than by MCF-7 cells at all time points and all substrate concentrations. Additionally, although the Km values of E1S for oestrogen sulphatase in both MCF-7 and MDA-MB-231 cells were similar, the Vmax values, and therefore the activity, differed greatly. The effect of various steroidal and non-steroidal compounds also suggested differences in these 2 cell lines with respect to oestrogen sulphatase inhibition or stimulation. MPA significantly increased the hydrolysis of [3H]E1S in both cell lines, possibly through its effect on membrane fluidity. Tamoxifen increased E1S hydrolysis in MDA-MB-231 cells but not in MCF-7 cells, whereas 4-OH-A4 inhibited E1S in MCF-7 cells but not in MDA-MB-231 cells. Danazol (an isoxazol derivative of 17 alpha-ethinyltestosterone), 17 alpha-ethinyloestradiol and DHAS all significantly inhibited oestrogen sulphatase activity in both cell lines. Furthermore, danazol had a growth-inhibitory effect on both MCF-7 and MDA-MB-231 cells, although MCF-7 cells appeared to be more sensitive to growth inhibition by danazol.     

Effect of transforming growth factor-beta1 on oestrogen metabolism in MCF-7 and MDA-MB-231 breast cancer cell lines.

Transforming growth factor-beta (TGF-beta) has been shown to inhibit the growth of mammary epithelial cells and may play a protective role in mammary carcinogenesis. In contrast, oestrogens promote the development of breast cancer. Oestrone sulphate (E1S) is a huge reservoir of active oestrogens in the breast being converted to the weak oestrogen, oestrone (E1), by oestrone sulphatase. E1 is reversibly converted by oestradiol-17beta hydroxysteroid dehydrogenase to the potent oestrogen, oestradiol (E2). The aim of this study was to assess the effect of the TGF-beta1 isoform on growth and oestrogen metabolism in the hormone-dependent MCF-7 and hormone-independent MDA-MB-231 human breast cancer cell lines. The results showed that TGF-beta1 significantly inhibited cell growth and stimulated the conversion of E1S to E1 and E1 to E2 in the MCF-7 cell line. In the MDA-MB-231 cell line TGF-beta1 significantly stimulated cell growth and inhibited the interconversions between E1 and E2. In conclusion, the growth inhibitory effect of TGF-beta1 on the MCF-7 cell line would appear to confer a protective effect in breast cancer. However, its ability to increase the amount of E2 would increase the risk of breast cancer. Which of these effects predominates in vivo remains to be explored. The growth stimulatory effect of TGF-beta1 on the MDA-MB-231 cell line probably acts through a mechanism independent of the effect of TGF-beta1 on oestrogen concentrations since this cell line is hormone unresponsive.     

miR-125a增强多西他赛对乳腺癌生长的抑制作用

背景与目的:研究表明miR-125a通过下调Her-2或者Her-3的表达抑制乳腺癌细胞生长,可能是指导乳腺癌治疗的靶点.本研究旨在观察miR-125a是否具有增强多西他赛对乳腺癌细胞株和裸鼠荷瘤模型的生长抑制作用.方法:转染miR-125a联合不同浓度多西他赛处理MCF-7和MDA-MB-231乳腺癌细胞株和MDA-MB-231乳腺癌裸鼠模型,观察细胞株和裸鼠接种肿瘤的生长情况.结果:miR-125a与多西他赛可协同抑制MDA-MB-231及MCF-7乳腺癌细胞株、MDA-MB-231乳腺癌裸鼠模型肿瘤的增殖,单纯转染miR-125a也可抑制MDA-MB-231及MCF-7乳腺癌细胞株的增殖.结论:miR-125a与多西他赛有协同抗乳腺癌作用,可成为乳腺癌靶向治疗的潜在靶点.     

Antiestrogenic effects of Z-1, 1-dichloro-2,3 diphenyl-2-(4-methoxyphenyl)cyclopropane(5a) on human breast cancer cells in culture.

Compound 5a ([Z]-1, 1-Dichloro-2,3 diphenyl-2-(4-methoxyphenyl)cyclopropane) is a novel cyclopropyl compound which was shown to be a pure antiestrogen. In the present study, the antiproliferative activity of 5a was examined on estrogen receptor (ER)-positive MCF-7 and ER-negative MDA-MB-231 human breast cancer cells and A-549 human lung cancer cells using the hemocytometric trypan blue exclusion method. Compound 5a inhibited the growth of MCF-7 cells in a dose-related manner over a concentration range of 10(-9) to 10(-5) M, but did not alter the growth of MDA-MB-231 or A-549 cells. Co-administration of estradiol (10(-8) M) reversed the antiproliferative activity of 5a (10(-7) M) on MCF-7 cells. Further, an ER-dependent mechanism of action is supported by the specific ER binding of 5a in MCF-7 cells observed in this study. The influence of 5a on the cell surface morphology of MCF-7 and MDA-MB-231 cells was studied using scanning electron microscopy (SEM). Compound 5a at 10(-6) M reduced the length and density of microvilli (MV) on MCF-7 cells, which was reversed by co-administration of estradiol (10(-8) M). This compound did not alter the cell surface morphology of ER-negative MDA-MB-231 cells. In conclusion, 5a and tamoxifen inhibited the growth of ER-prositive MCF-7 cells in an estradiol-reversible manner, and had no effect on ER-negative MDA-MB-231 cells. The results of this study with human breast cancer cells suggest that 5a may be highly effective in the treatment of estrogen-dependent breast cancer and/or in the prophylactic treatment of women with a high risk of breast cancer development.     

Expression of pRB, cyclin/cyclin-dependent kinases and E2F1/DP-1 in human tumor lines in cell culture and in xenograft tissues and response to cell cycle agents

Purpose: Cell cycle regulatory components are interesting targets for cancer therapy. Expression of pRb, cyclin D1, cdk4, cyclin E, cdk2, E2F1 and DP-1 was determined in MCF-7 and MDA-MB-468 breast carcinoma cells, H460 and Calu-6 non-small cell lung carcinoma cells, H82 and SW2 small cell lung carcinoma cells, HCT116 and HT29 colon carcinoma cells and LNCaP and DU-145 prostate carcinoma cells. Methods: For Western blotting, the ratio with actin expression was used to normalize the data; all lines were run on the same gels. Results: In cell culture, pRb was not detected in MB-468 and H82 was low in SW2 and DU-145 and highest in HCT116; in tumors, pRb was not detected in MB-468, H82, SW2, and DU-145 and was highest in LNCaP and Calu-6. Cyclin D1 was not detected in SW2 cells in culture, was low in MB-468 and H82, and was highest in LNCaP and H460; in tumors, cyclin D1 was low in MB-468, H460, SW2 and DU145, and was highest in LNCaP. In cell culture, cdk4 was lowest in Calu-6, HCT116, HT29 and DU-145 and highest in H82 and SW2; in tumors, cdk4 was low in MCF-7, MB-468, H460, Calu-6 and HCT116 and was very high in the SW2. Expression of cyclin E was very low in MCF-7 and HT29 and high in H460 in culture and was very low in MCF-7, H460, Calu-6, H82, HT29 and DU-145 in tumors and high in HCT116 and LNCaP. In cell culture, E2F1 was lowest in MB-468, Calu-6, HT29 and DU-145 cells and highest in LNCaP cells; in tumors, E2F1 was lowest in MCF-7, MB-468 and Calu-6 and highest in LNCaP. In cell culture, DP-1 was lowest in MB-468, HCT116 and HT29 and highest in SW2. The MCF-7 and MB-468 lines were most resistant to flavopiridol and olmoucine and the H460 and Calu-6 lines were most resistant to genistein. The SW2 tumor was most responsive to flavopiridol and olomoucine. Conclusions: There is a high degree of variability in the expression of cell cycle components in human tumor cell lines, resulting in complexity in predicting response to cell cycle directed agents. Received: 27 October 1999 / Accepted: 16 March 2000     

尿多酸肽对乳腺癌细胞bcl-2表达的影响

目的:探讨肿瘤细胞分化诱导剂尿多酸肽(CDA-Ⅱ)对乳腺癌bcl-2表达的影响.方法:将CDA-Ⅱ与不同生物学特性的乳腺癌细胞株MCF-7和MDA-MB-231进行体外培养,同时以维甲酸为阳性对照,观察CDA-Ⅱ对乳腺癌细胞生长曲线、bcl-2表达及形态学等方面的影响.结果:CDA-Ⅱ可减缓两株乳腺癌细胞的生长和增殖能力,减少乳腺癌细胞bcl-2的表达.结论:CDA-Ⅱ可抑制不同生物学特性的两株乳腺癌细胞的生长和增殖能力,减少乳腺癌细胞bcl-2表达,为CDA-Ⅱ治疗乳腺癌提供实验依据.     

Temporal and quantitative regulation of mitogen-activated protein kinase (MAPK) modulates cell motility and invasion.

We have shown that ER-negative and invasive human breast cancer cell lines MDA-MB-468 and MDA-MB-231 have constitutively higher mitogen activated protein kinase (ERK1&2/MAPK) when compared to the ER-positive and non-invasive MCF-7 human breast cancer cells. In MCF-7 cells, TGFalpha stimulation induced only transient MAPK activation, leading to a transient increase in cell migration. However, MDA 231 and MDA 468 cells, TGFalpha stimulation induced sustained MAPK activation, which correlated with enhanced cell motility and in vitro invasion. Serum stimulation activates ERK/MAPK activity persistently in both ER-positive and ER-negative breast cancer cells, leading to enhanced and sustained cell migration. Inhibition of MAPK activation by anti-sense MEK expression in MDA-MB-468 cells significantly inhibits cell migration and in vitro invasion. In contrast, MCF-7 cells expressing constitutively activated MEK show a significant increase in MAPK activity and cell migration, but this failed to enhance in vitro invasion. The kinetic profiles of MAPK activation and inhibition show a relationship between the duration and magnitude of MAPK activation and cell migration in both ER-positive and ER-negative human breast cancer cells. These studies show that cell motility is modulated by the magnitude and the duration of MAPK activation; but increased activation of MAPK may not be sufficient to allow in vitro invasion in non-invasive MCF-7 breast cancer cells.     

PPAPDC1A在体内外对乳腺癌细胞增殖、侵袭和转移能力的影响

目的:通过构建稳定过表达和干扰PPAPDC1A的乳腺癌细胞株,探讨PPAPDC1A对乳腺癌细胞增殖、侵袭和转移能力的影响。方法:利用CCK-8和Transwell实验检测PPAPDC1A稳定过表达和干扰后对乳腺癌细胞体外增殖和侵袭能力的影响。采用裸鼠皮下成瘤实验检测PPAPDC1A对乳腺癌细胞体内增殖和裸鼠致瘤性的作用。利用免疫组织化学染色法检测各组肿瘤组织中Ki-67的表达。通过裸鼠尾静脉注射实验检测PPAPDC1A对乳腺癌MCF-7细胞和MDA-MB-231细胞体内转移能力的影响。结果:成功建立稳定过表达PPAPDC1A的乳腺癌MCF-7细胞株和稳定干扰PPAPDC1A的乳腺癌MDA-MB-231细胞株;CCK-8和Transwell实验结果显示,与MCF-7和MCF-7-Vector细胞株相比,MCF-7-PPAPDC1A细胞株的生长速度显著增快,穿膜细胞数量多（P＜0.05）;与此相反,MDA-MB-231-shPPAPDC1A组细胞的生长速度和穿膜细胞数明显少于MDA-MB-231-shNC和MDA-MB-231 细胞株（P＜0.05）。动物实验结果显示,与MCF-7-Vector组相比,MCF-7-PPAPDC1A组的肿瘤生长速度较快,肿瘤的体积较大,Ki-67的阳性率高,肺转移灶的数目增多（P＜0.05）;与此相反,与MDA-MB-231-shNC组相比MDA-MB-231-shPPAPDC1A组的肿瘤生长速度较慢,肿瘤的体积较小,Ki-67的阳性率低,肺转移灶的数目减少（P＜0.05）。结论:PPAPDC1A对乳腺癌细胞的增殖、侵袭和转移有促进作用。     

Differential regulation of expression of three transforming growth factor beta species in human breast cancer cell lines by estradiol

Transforming growth factor (TGF)-beta is a potent regulator of many cell functions and a growth inhibitor for mammary epithelial cells. We now know of three highly homologous members of the human TGF-beta gene family. We have studied the expression of TGF-beta 1, -beta 2, and -beta 3 mRNA in four human breast cancer cell lines. Using the RNase protection assay, we have detected mRNA expression of TGF-beta 1, -beta 2, and -beta 3 by T-47D cells, TGF-beta 1 and -beta 3 by ZR-75-1 cells, and TGF-beta 1 by MCF-7 cells. Treatment of these estrogen receptor-positive cells with 10 nM estradiol for 48 h resulted in decreased mRNA levels of TGF-beta 2 and -beta 3 but did not affect mRNA levels of TGF-beta 1. Expression of TGF-beta 1 and -beta 2 mRNA by an estrogen receptor-negative cell line, MDA-MB-231, was not changed by estradiol treatment. Treatment of cells with the antiestrogen tamoxifen (1 microM) did not significantly alter mRNA levels for any of the three TGF-beta species. We have further determined that estradiol treatment of T-47D was associated with diminished secretion of TGF-beta into the medium. Both TGF-beta 1 and -beta 2 inhibited the proliferation of MCF-7 cells, and neither protein affected the growth of T-47D cells. TGF-beta 1 was at least 10-fold more potent than TGF-beta 2 at inhibiting the growth of MCF-7 cells.     

Targeting of nuclear factor kappaB Pathways by dehydroxymethylepoxyquinomicin, a novel inhibitor of breast carcinomas: antitumor and antiangiogenic potential in vivo.

We previously designed and synthesized the new nuclear factor kappaB (NF-kappaB) inhibitor dehydroxymethylepoxyquinomicin (DHMEQ) derived from the structure of the antibiotic epoxyquinomicin C. We looked into the effect of DHMEQ on cellular phenotypes and tumor growth in mice injected with human breast carcinoma cell line MDA-MB-231 or MCF-7. In estrogen-independent breast adenocarcinoma cell line MDA-MB-231, NF-kappaB is constitutively activated. The addition of DHMEQ (10 microg/mL) completely inhibited the activated NF-kappaB for at least 8 hours. On the other hand, NF-kappaB is not activated in estrogen-dependent MCF-7 cells. In this cell line, DHMEQ completely inhibited the tumor necrosis factor-alpha-induced activation of NF-kappaB. DHMEQ did not inhibit the degradation of IkappaB but inhibited the nuclear translocation of NF-kappaB by both p65/p50 and RelB/p52 pathways. MDA-MB-231 cells secrete interleukin (IL)-6 and IL-8 without stimulation, and DHMEQ decreased the secretion levels of both cytokines. When MDA-MB-231 or MCF-7 cells were stimulated by tumor necrosis factor-alpha, the inhibitory effects of DHMEQ were still maintained. I.p. administration of DHMEQ (thrice a week) significantly inhibited the tumor growth of MDA-MB-231 (12 mg/kg) or MCF-7 (4 mg/kg) in severe combined immunodeficiency mice. No toxicity was observed during the experiment, including the loss of body weight. An immunohistological study on resected MCF-7 tumors showed that DHMEQ inhibited angiogenesis and promoted apoptosis. Furthermore, in Adriamycin-resistant MCF-7 cells highly expressing multidrug resistance gene-1, DHMEQ also exhibited the above capability, including down-regulation of IL-8. Thus, DHMEQ might be a potent drug for the treatment of various breast carcinomas by inhibiting the NF-kappaB activity.     

Antiestrogens modulate MT1 melatonin receptor expression in breast and ovarian cancer cell lines

An interaction between cellular estrogen response and melatonin signaling mediated by G-protein coupled receptors is present in breast cancer cells. In this study, the effect of antiestrogens on basal and melatonin-modulated expression of MT1 melatonin receptor in breast and ovarian cancer cells was examined. For this purpose, the effects of the selective estrogen receptor modulator tamoxifen and pure antiestrogen ICI 182,780 on MT1 expression in estrogen receptor (ER) alpha-positive and -negative breast and ovarian cancer cell lines cultured in medium supplemented with 1 nM 17-beta estradiol were assessed by Western blot analysis. We were able to detect expression of the MT1 receptor in SK-OV-3 and OVCAR-3 cells and report its up-regulation by melatonin in both ovarian cancer cell lines. MT1 expression was observed to be significantly weaker in ERalpha-positive MCF-7 and OVCAR-3 cells than in ERalpha-negative MDA-MB-231 and SK-OV-3 cells. Treatment with the pure antiestrogen ICI 182,780 increased MT1 receptor expression in OVCAR-3 ovarian cancer cells, but decreased MT1 expression in MCF-7 breast cancer cells. No effect of ICI 182,780 on MT1 expression was observed in the ERalpha-negative cell lines SK-OV-3 and MDA-MB-231. After treatment with 4-OH tamoxifen, down-regulation of basal MT1 receptor expression in ERalpha-positive MCF-7 cells and inhibition of melatonin-induced up-regulation of MT1 in OVCAR-3 ovarian cancer cells were observed. In contrast, treatment with 4-OH tamoxifen increased the MT1 receptor level in ERalpha-negative SK-OV-3 ovarian cancer cells. Our findings support the existence of close interaction between estrogen and melatonin signaling. Moreover, our data suggest that melatonin signaling is modulated by antiestrogens in breast and ovarian cancer cells.