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

Cytosolic Levels of An Estrogen-Induced Breast Cancer-Associated Peptide (TFF1/pS2) in Colorectal Cancer: Clinical Significance and Relationship with Steroid Receptors

Background

The Trefoil Factor 1 (TFF1/pS2), a peptide consisting of 60 amino acids, is the most abundant estrogen-induced messenger RNA in MCF-7 breast cancer cells and is also expressed by colorectal carcinomas. The objective of this work was to evaluate the cytosolic TFF1 content in colorectal carcinomas, its possible relationship with estrogen and progesterone receptors as well as with clinicopathological tumor parameters, and its potential prognostic significance.

Methods

Cytosolic TFF1 levels were examined by immunoradiometric assay in 178 patients with resectable colorectal cancer. The mean follow-up period was 32 months.

Results

There was a wide variability of cytosolic TFF1 levels in tumor-surrounding mucosa samples (0.09-42.5 ng/mg protein) as well as in tumors (0.01-270 ng/mg protein). Comparison of paired mucosa and carcinoma samples showed significantly higher TFF1 levels in tumors (mean: 17.1 ng/mg protein) than in mucosa samples (10 ng/mg protein) (p=0.027). TFF1 levels were significantly higher in mucosa samples surrounding distal colon and rectal tumors (p=0.0001) and in tumor samples obtained from older patients (p=0.007). However, there were no significant differences in tumor TFF1 levels with respect to clinicopathological parameters such as the patient's sex, tumor location, stage, histological grade, ploidy, S-phase, or tumor estrogen and progesterone receptors. In addition, there was no significant relationship between tumor TFF1 levels and disease outcome.

Conclusions

TFF1 may play an as yet undetermined role in the tumorigenesis of colorectal carcinomas. However, cytosolic levels of TFF1 do not seem to have any prognostic significance in colorectal carcinomas.

Melatonin Suppresses the Growth of Ovarian Cancer Cell Lines (OVCAR-429 and PA-1) and Potentiates the Effect of G1 Arrest by Targeting CDKs

Melatonin is found in animals as well as plants. In animals, it is a hormone that anticipates the daily onset of darkness and regulates physiological functions, such as sleep timing, blood pressure, and reproduction. Melatonin has also been found to have anti-tumor properties. Malignant cancers are the most common cause of death, and the mortality rate of ovarian tumor is the highest among gynecological diseases. This study investigated the anti-tumor effects of melatonin on the ovarian cancer lines, OVCAR-429 and PA-1. We observed the accumulation of melatonin-treated cells in the G₁ phase due to the down-regulation of CDK 2 and 4. Our results suggest that in addition to the known effects on prevention, melatonin may also provide anti-tumor activity in established ovarian cancer.

Breast cancer cells: Modulation by melatonin and the ubiquitin-proteasome system--a review

Melatonin inhibits human breast cancer cells stimulated with estrogen. This antiproliferative action depends on the presence of the estrogen receptor alpha (ERα) in the human MCF-7 cell line and is strictly dose-dependent. Since researchers concerned with melatonin and breast cancer have not considered the relevance of the ubiquitin-proteasome system to this research in this review we do so. The fact that the first breast cancer susceptibility gene to be identified, Brca1, functions as a ubiquitin ligase indicates that the ubiquitin-proteasome system has a role in regulating susceptibility to breast cancer. While mutations of this gene increase the incidence of breast cancer, the wild type gene suppresses estrogen-dependent transcriptional events relying on the estrogen receptor ERα. Three other ubiquitin ligases, SCF(Skp2), E6AP and APC, interact directly with ERα at the ERE and AP-1 promoters of ERα target genes. Melatonin, like proteasome inhibitors, decreases estrogen-induced gene transcription. Indeed, it has been reported that melatonin specifically inhibits estrogen-induced transcription mediated by ERα at the ERE and AP1 gene promoters. Herein, we present a model in which the inhibitory action of melatonin on MCF-7 cells is mediated, directly or indirectly, by the ubiquitin-proteasome system. In this model ERα, apoptotic proteins, and cell cycle proteins, all influenced by melatonin, are substrates of key ubiquitin ligases including SCF(Skp2), E6AP, and SCF(B-TrCP). Since dysfunction of the ubiquitin-proteasome system is a risk factor for breast cancer, this model provides a context in which to test the clinical potential, and limitations, of melatonin and proteasome inhibitors.

Research Resource: STR DNA profile and gene expression comparisons of human BG-1 cells and a BG-1/MCF-7 clonal variant

Human ovarian cancer BG-1 cells are a valuable in vitro model that has enabled several laboratories to study the estrogenic responses of ovarian cancers. We recently discovered that there are two different BG-1 cell lines being used for experiments, denoted here as BG-1 FR and BG-1 NIEHS, which exhibit striking morphological differences. The objective of this study was to methodically analyze these two BG-1 variants and compare their characteristics. Short tandem repeat analysis revealed that the DNA profile of BG-1 FR cells was unique, yet the Short tandem repeat pattern of BG-1 NIEHS was identical with that of MCF-7 cells. From a cytogenetic analysis, it became apparent that the BG-1 FR line had the same profile as previously reported, whereas the BG-1 NIEHS and MCF-7 cells share a similar genetic display. A significant number of unique chromosomal translocations were observed between the BG-1 NIEHS and MCF-7 cells, suggesting that acquired genotypic differences resulted in the formation of two lines from a common origin. Although all cell types demonstrated a similar estrogen responsiveness in reporter gene assays, a microarray analysis revealed distinct estrogen-responsive gene expression patterns with surprisingly moderate to low overlap. We conclude that BG-1 FR is the original ovarian cancer cell line, whereas the BG-1 NIEHS is a variant from the MCF-7 cells. These findings provide much needed clarification of the identities and characteristics of key cell line models that are widely used to study estrogen action in female reproductive cancers.

Molecular mechanisms of melatonin's inhibitory actions on breast cancers

Melatonin is involved in many physiological functions and it plays an important role in many pathological processes as well. Melatonin has been shown to reduce the incidence of experimentally induced cancers and can significantly inhibit the growth of some human tumors, namely hormone-dependent cancers. The anticancer effects of melatonin have been observed in breast cancer, both in in vivo with models of chemically induced rat mammary tumors, and in vitro studies on human breast cancer cell lines. Melatonin acts at different physiological levels and its antitumoral properties are supported by a set of complex, different mechanisms of action, involving apoptosis activation, inhibition of proliferation, and cell differentiation.

Melatonin and estrogen in breast cyst fluids

Increased breast cancer risks have been reported among women with gross cystic breast disease (GCBD), although the mechanism for this increase remains unexplained. Relationships between GCBD characteristics, breast cancer risk factors, and the biochemical composition and growth properties of 142 breast cyst fluid (BCF) samples were studied among 93 women with GCBD. Concentrations of melatonin, estrogen (17-beta-estradiol), dehydroepiandrosterone-sulfate (DHEA-S), epidermal growth factor (EGF), transforming growth factor beta (TGF-B1 and TGF-B2), sodium (Na), and potassium (K) were quantified in BCF samples, and human breast cancer cells (MCF-7) were treated with BCF in vitro. Patients were grouped according to BCF Na:K ratios previously linked with increased breast cancer risks (Na:K </= 3, Type 1), and mean concentrations of BCF constituents were compared with low risk (Na:K > 3, Type 2) and mixed cyst groups. Women with larger and more frequently occurring cysts had higher BCF estrogen and DHEA-S, and lower TGF-B1 levels. Women with Type 1 cysts had elevated BCF melatonin, estrogen, DHEA-S, and EGF, and lower concentrations of TGF-B2 compared to women with Type 2 cysts. BCF generally inhibited cell growth relative to serum-treated controls, consistent with previous studies. Melatonin and estrogen in BCF independently predicted growth inhibition and stimulation, respectively. Biological monitoring of BCF may help identify women with GCBD at greatest risk for breast cancer development.

Melatonin cytotoxicity in human leukemia cells: relation with its pro-oxidant effect

Melatonin has a variety of functions in human physiology and is involved in a number of pathological events including neoplastic processes. The tissue protective actions of melatonin are attributed to its antioxidant activity though, under certain conditions, melatonin might also exert oxidant effects, particularly in cancer cells. This study evaluated the effects of 10(-5) and 10(-3) m concentrations of melatonin on human leukemia cells. Moderate cytotoxic effects of melatonin at 10(-3) m concentrations were observed in CMK, Jurkat and MOLT-4 cells which was associated with significant reactive oxygen species (ROS) generation. Melatonin treatment was not associated with significant cytotoxicity in HL-60 cells, although the generation of ROS was significantly increased. K562 and Daudi cells did not appear to be effected by melatonin treatment. Cellular membrane lipid peroxidation was not influenced by melatonin with the exception of CMK cells. Cell cycle kinetics were not affected in melatonin-treated samples, again with the exception of CMK cells which showed increased apoptosis. Melatonin, therefore, induces the production of ROS that may be associated with cytotoxicity depending on the concentration of melatonin in some leukemia cells and does not appear to stimulate leukemia cell growth. These pro-oxidant actions of melatonin may assist in limiting leukemic cell growth.

Differential regulation of estrogen receptor alpha, glucocorticoid receptor and retinoic acid receptor alpha transcriptional activity by melatonin is mediated via different G proteins

Melatonin has been shown to bind to the MT1 G protein-coupled receptor (GPCR) in MCF-7 breast cancer cells to modulate the estrogen response pathway suppressing estrogen-induced estrogen receptor alpha (ERalpha) transcriptional activity, blunting ER/DNA binding activity and suppressing cell proliferation. In these studies we have examined the effect of melatonin on the transcriptional activity of the ERalpha and other members of the steroid/thyroid hormone receptor superfamily, namely, the glucocorticoid receptor (GR) and the retinoic acid receptor alpha (RARalpha). As with the ERalpha, melatonin represses ligand (dexamethasone)-induced activation of the GR. This effect of melatonin on ERalpha and GR is blocked by pertussis toxin (PTX) suggesting that melatonin's actions may be mediated via a PTX-sensitive G(alphai) protein. In contrast, melatonin potentiates the action of all-trans-retinoic acid on RARalpha transcriptional activation and enhances RARalpha/DNA binding activity, an action which is not PTX-sensitive. Expression of a dominant-positive G(alphai2) protein, with which the MT1 receptor has been shown to couple, is able to mimic the effect of melatonin on ERalpha but not RARalpha transcriptional activation in breast cancer cells. This demonstrates that GPCRs can modulate the transcriptional activity of various steroid receptors in response to their ligand through activation of different G protein signaling pathways.

Melatonin inhibits telomerase activity in the MCF-7 tumor cell line both in vivo and in vitro

In this study for the first time the relationship between melatonin and telomerase activity was investigated. Melatonin exhibits oncostatic properties, but the actual mechanism of action by which the indole reduces tumor cell activity is not clear. Telomerase is an enzyme responsible of telomere elongation and is activated in most human cancers. In the current in vivo study, eight nude mice received a MCF-7 xenograft and thereafter they were treated for 5 weeks with 0.1 mg/mL of melatonin in the drinking water. Melatonin treatment caused a significant reduction in the weight of tumors and reduced metastases when compared with the control group. As indicated by the Telomerase Repeats Amplification Protocol (TRAP) assay, a significant decrease in telomerase activity was observed in the group treated with melatonin. In related in vitro studies, cultured MCF-7 cells were treated with three different concentrations of melatonin and a control without indole treatment. A significant dose-dependent decrease in Telomerase reverse transcriptase (TERT), the catalytic subunit of telomerase, mRNA expression was observed in the melatonin-treated cells. We also observed a significant reduction in TR, the RNA telomerase subunit, mRNA expression at physiological concentrations of melatonin (1 nm). Significant differences in TEP1, an associated telomerase protein, mRNA expression were also observed. In conclusion, melatonin influences telomerase both in vivo and in vitro, decreasing its activity in the tumors of nude mice and the mRNA expression of the TERT and TR subunits, essential factors for the proper function of the telomerase enzyme.

Melatonin inhibits estrogen receptor transactivation and cAMP levels in breast cancer cells

We have previously demonstrated that the pineal hormone, melatonin, can inhibit the growth of estrogen receptor-alpha (ERalpha)-positive breast cancer cells and suppress ERalpha gene transcription. To investigate the relationship between the estrogen response pathway and melatonin's growth inhibition, ERalpha-positive MCF-7 human breast cancer cells were transiently transfected with an estrogen response element (ERE) luciferase reporter construct and then treated with melatonin (10(-9)-10(-6) M) for 30 min followed by 10(-9) M 17-beta-estradiol (E2) or treated with each compound alone. Melatonin pre-treatment significantly reduced E2-induced ERalpha transactivation and ERalpha-ERE binding activity. We also conducted experiments to determine if melatonin modulates cAMP levels in MCF-7 cells. Melatonin inhibited the forskolin-induced and E2-induced elevation of cAMP levels by 57 and 45%, respectively. These data indicate that melatonin can act as a biological modifier to affect ERalpha transcriptional activity by regulating signal transduction pathways which impinge on the ERalpha and by altering E2-mediated ERalpha transactivation and ERalpha DNA binding activity.

Circadian concepts in normal and neoplastic breast

Normal breast exhibits rhythmic properties linked to the hormonal environment of the gland in animals and humans. Breast tumors also display rhythmic properties; however, they differ from those found normally in animals and humans. Breast cancer in humans is characterized by disruption or modification of normal circadian patterns, which may be of prognostic value. The relationships between melatonin biology and breast cancer require exploration. The present work summarizes the data concerning circadian concepts in breast cancer and explores future directions in the breast cancer treatment by chronomodulation of medications during the 24h, taking advantage of the circadian time structure of breast tissue to improve the treatment outcome.

Rotating night shifts and risk of breast cancer in women participating in the nurses' health study

BACKGROUND

Melatonin shows potential oncostatic action, and light exposure during night suppresses melatonin production. There is little information, however, about the direct effect of night work on the risk of cancer. We investigated the effect of night work in breast cancer.

METHODS

We examined the relationship between breast cancer and working on rotating night shifts during 10 years of follow-up in 78 562 women from the Nurses' Health Study. Information was ascertained in 1988 about the total number of years during which the nurses had worked rotating night shifts with at least three nights per month. From June 1988 through May 1998, we documented 2441 incident breast cancer cases. Logistic regression models were used to calculate relative risks (RRs) and 95% confidence intervals (CIs), adjusted for confounding variables and breast cancer risk factors. All statistical tests were two-sided.

RESULTS

We observed a moderate increase in breast cancer risk among the women who worked 1-14 years or 15-29 years on rotating night shifts (multivariate adjusted RR = 1.08 [95% CI = 0.99 to 1.18] and RR = 1.08 [95% CI = 0.90 to 1.30], respectively). The risk was further increased among women who worked 30 or more years on the night shift (RR = 1.36; 95% CI = 1.04 to 1.78). The test for trend was statistically significant (P =.02).

CONCLUSIONS

Women who work on rotating night shifts with at least three nights per month, in addition to days and evenings in that month, appear to have a moderately increased risk of breast cancer after extended periods of working rotating night shifts.

Effects of melatonin on the proliferation and cis-diamminedichloroplatinum (CDDP) sensitivity of cultured human ovarian cancer cells

OBJECTIVES

In this study, we investigated the antiproliferative effect and telomerase activity of melatonin with or without cis-diamminedichloroplatinum (CDDP) on CDDP-sensitive HTOA cells and CDDP-resistant OVCAR-3 cells of cultured human ovarian cancer.

METHODS

HTOA cells and OVCAR-3 cells were cultured in RPMI-1640 at 37 degrees C with 5% CO(2) for 132 h. To examine the antiproliferative effect of melatonin, cells were cultured with or without melatonin (10(-12)-10(-6) M) and thereafter counted in a 96-well microplate using the alamarBlue assay. To examine the effect of melatonin and CDDP, cells were divided into group A (intermittent CDDP, 0.5 microg/ml), group B (intermittent CDDP + melatonin), and group C (sequential (12-h interval) CDDP/melatonin) and thereafter counted in a 96-well microplate using the alamarBlue assay. In different series, cells were cultured and treated with either ethanol, melatonin, CDDP, or CDDP + melatonin. After harvest, telomerase activity was semiquantified with a fluorescence-based telomeric repeat amplification protocol (F-TRAP).

RESULTS

(1) Melatonin produced no antiproliferative effect on both types of ovarian cancer cells. (2) Melatonin 10(-6) M induced the antiproliferative effect in groups B and C compared with group A in the HTOA cell line. (3) Melatonin 10(-9) M produced the antiproliferative effect in groups B and C compared with group A in the OVCAR-3 cell line. (4) Telomerase activity in the HTOA cell line did not change but, in the OVCAR-3 cell line, was significantly lower in the CDDP + melatonin group compared with the ethanol and CDDP groups.

CONCLUSIONS

Melatonin enhanced CDDP sensitivity in two ovarian cancer cell lines. Thus, melatonin may improve ovarian cancer chemotherapy.

Chemoprevention of NMU-induced rat mammary carcinoma with the combination of melatonin and 9-cis-retinoic acid

In experimental trials using the N-nitroso-N-methylurea (NMU)-induced rat mammary tumor model, a significant decrease in tumor incidence (to 5%) was observed in rats treated with melatonin and 9-cis-retinoic acid (9 cRA) compared to controls (55%). Although 9cRA alone decreased tumor incidence to 26%, this response did not reach statistical significance. Tumor incidence was significantly inhibited to 20% in the animals that received melatonin and 9cRA on alternating days. Latency to tumor onset was prolonged in animals receiving either of the combination treatments compared with controls, and tumor multiplicity was also significantly decreased.

Magnetic fields (MF) of 50 Hz at 1.2 microT as well as 100 microT cause uncoupling of inhibitory pathways of adenylyl cyclase mediated by melatonin 1a receptor in MF-sensitive MCF-7 cells

Magnetic fields (MF) of 60 Hz at 1.2 microT were previously shown to inhibit the antiproliferative effect of melatonin on MCF-7 cells (Liburdy,R.P., 1993, J. Pimeal Res. 14, 89-97). In addition, three laboratories (Blackman,C.F. and Benane,S.G., 1998; Luben,R.A. and Morgan,A.P., 1998; Morris,J.E., Chrisler,W.B., Miller,D.L., Sasser,L.B. and Anderson,L.E., 1998; 20th Annual Meeting of the Bioelectromagnetics Society, At. Pete Beach, FL) independently reported results consistent with this finding. In this study, we investigated the molecular basis of the biological effects of MF using MCF-7 cells. Only 1a melatonin receptors were identified by the [125I]melatonin binding assay and RT-PCR analysis. Moreover, preceding exposures to MF of 100 microT for 3, 5 and 7 days blocked the melatonin-induced inhibition of cAMP accumulation in a time-dependent manner, while none of the melatonin receptor functions or GTPase and adenylyl cyclase activities were affected. Estrogen-evoked cell proliferation was not altered by MF either. Exposure to 1.2 microT MF exerted the same effects on the melatonin-signaling pathway as that to 100 microT. Thus, this is the first study to provide evidence that MF may cause uncoupling of signal transduction from melatonin receptors to adenylyl cyclase.

Melatonin and mammary pathological growth

In this article we review the state of the art on the role of the pineal gland and melatonin in mammary cancer tumorigenesis in vivo as well as in vitro. The former hypothesis of a possible role of the pineal gland in mammary cancer development was based on the evidence that the pineal, via its main secretory product, melatonin, downregulates some of the pituitary and gonadal hormones which control mammary gland development and are also responsible for the growth of hormone-dependent mammary tumors. Furthermore, melatonin could act directly on tumoral cells, thereby influencing their proliferative rate. Other possible origins of melatonin's antitumoral actions could be found in its antioxidant or immunoenhancing properties. The working hypotheses of most experiments were that the activation of the pineal gland, or the administration of melatonin, should give rise to antitumoral behavior; conversely, suppression of the pineal gland or melatonin deficits should stimulate mammary tumorigenesis. From in vivo studies on animal models of tumorigenesis, the general conclusion is that experimental manipulations activating the pineal gland, or the administration of melatonin, enlarge the latency and reduce the incidence and growth rate of chemically induced mammary tumors, while pinealectomy usually has the opposite effects. The direct actions of melatonin on mammary tumors have been suggested because of its ability to inhibit, at physiological doses (1 nM), the in vitro proliferation and invasiveness of MCF-7 human breast cancer cells. The fact that most studies have been performed on two models, chemically induced mammary adenocarcinoma in rats (in vivo studies) and the cell tumor line MCF-7 (in vitro studies), makes the generalization of the results somewhat difficult. However, the characteristics of these actions, comprising different aspects of tumor biology such as initiation, proliferation, and metastasis, as well as the doses (physiological range) at which the effect is accomplished, give special value to these findings. On the strength of these data, the small number of clinical studies focusing on the possible therapeutic value of melatonin on breast cancer is surprising.