Exposure to cadmium chloride influences astrocyte-elevated gene-1 (AEG-1) expression in MDA-MB231 human breast cancer cells

Transcriptome analysis discloses antioxidant detoxification mechanism of Gracilaria bailinae under different cadmium concentrations and stress durations

To remedy Cd pollution in the ocean, macroalgae are used as a bioremediation tool because of their ability to absorb and accumulate Cd. Gracilaria bailinae has high economic and ecological value and can survive in Cd contaminated waters; however, the underlying molecular mechanisms remain unclear. In this study, physiological and biochemical indexes were analyzed after 1, 3, 5, or 7 days of Cd2+ exposure; further, the transcriptome of G. bailinae was examined after a 7-day exposure to a Cd2+ culture environment with Cd levels of 0 mg L-1 (cd1, control), 1 mg L-1 (cd2, low concentration), and 2.5 mg L-1 (cd3, high concentration). The results showed that in the cd2 group, G. bailinae maintained a stable RGR that did not differ significantly (P > 0.05) from that of the cd1 group. However, the soluble protein and MDA contents, as well as the activities of SOD, CAT and POD, were significantly increased (P< 0.05) compared to the cd1 group. No significant differences (P > 0.05) were found among the different Cd2+ stress durations. In contrast, compared with the cd1 group, the RGR, soluble protein content, SOD, CAT, and POD activities were significantly decreased (P< 0.05), while the MDA content was significantly increased (P< 0.05) in the cd3 group. Furthermore, significant differences (P< 0.05) were observed among the various tested Cd2+ stress durations within the cd3 group. Compared to the cd1 group, a total of 30,072 DEGs and 21,680 were identified in the cd2 and cd3 treatments, respectively. More up-regulated genes were found in cd2 group than in cd3 group. GO enrichment analysis showed that these genes were related to peptidase activity, endopeptidase activity, ion transport, peptide biosynthetic and metabolism. In addition, DEGs related to histidine metabolism and the stilbene, diarylheptane, and gingerol pathways were significantly up-regulated in the cd2 group compared to the cd3 group, which resulted in enhanced activities of antioxidant enzymes and promoted cell wall regeneration. The results of this study reveal the response mechanism of G. bailinae to Cd2+ stress, providing valuable insights for assessing the bioremediation potential of G. bailinae for Cd-contaminated waters.

In Vitro Cytotoxic Effect of Aqueous Extracts from Leaves and Rhizomes of the Seagrass Posidonia oceanica (L.) Delile on HepG2 Liver Cancer Cells: Focus on Autophagy and Apoptosis

Aqueous extracts from Posidonia oceanica's green and brown (beached) leaves and rhizomes were prepared, submitted to phenolic compound and proteomic analysis, and examined for their potential cytotoxic effect on HepG2 liver cancer cells in culture. The chosen endpoints related to survival and death were cell viability and locomotory behavior, cell-cycle analysis, apoptosis and autophagy, mitochondrial membrane polarization, and cell redox state. Here, we show that 24 h exposure to both green-leaf- and rhizome-derived extracts decreased tumor cell number in a dose-response manner, with a mean half maximal inhibitory concentration (IC₅₀) estimated at 83 and 11.5 μg of dry extract/mL, respectively. Exposure to the IC₅₀ of the extracts appeared to inhibit cell motility and long-term cell replicating capacity, with a more pronounced effect exerted by the rhizome-derived preparation. The underlying death-promoting mechanisms identified involved the down-regulation of autophagy, the onset of apoptosis, the decrease in the generation of reactive oxygen species, and the dissipation of mitochondrial transmembrane potential, although, at the molecular level, the two extracts appeared to elicit partially differentiating effects, conceivably due to their diverse composition. In conclusion, P. oceanica extracts merit further investigation to develop novel promising prevention and/or treatment agents, as well as beneficial supplements for the formulation of functional foods and food-packaging material with antioxidant and anticancer properties.

Metadherin (AEG-1/MTDH/LYRIC) expression: Significance in malignancy and crucial role in colorectal cancer

Metadherin (AEG-1/MTDH/LYRIC) is a 582-amino acid transmembrane protein, encoded by a gene located at chromosome 8q22, and distributed throughout the cytoplasm, peri-nuclear region, nucleus, and nucleolus as well as the endoplasmic reticulum (ER). It contains several structural and interacting domains through which it interacts with transcription factors such as nuclear factor-κB (NF-κB), promyelocytic leukemia zinc finger (PLZF), staphylococcal nuclease domain containing 1 (SND1) and lung homing domain (LHD). It is regulated by miRNAs and mediates its oncogenic function via activation of cell proliferation, survival, migration and metastasis, as well as, angiogenesis and chemoresistance via phosphatidylinositol-3-kinase/AKT (PI3K/AKT), NF-κB, mitogen-activated protein kinase (MAPK) and Wnt signaling pathways. In this chapter, metadherin is reviewed highlighting its role in mediating growth, metastasis and chemoresistance in colorectal cancer (CRC). Metadherin, as well as its variants, and antibodies are associated with CRC progression, poorer prognosis, decreased survival and advanced clinico-pathology. The potential of AEG-1/MTDH/LYRIC as a diagnostic and prognostic marker as well as a therapeutic target in CRC is explored.

Cadmium-Associated Molecular Signatures in Cancer Cell Models

The exposure of cancer cells to cadmium and its compounds is often associated with the development of more malignant phenotypes, thereby contributing to the acceleration of tumor progression. It is known that cadmium is a transcriptional regulator that induces molecular reprogramming, and therefore the study of differentially expressed genes has enabled the identification and classification of molecular signatures inherent in human neoplastic cells upon cadmium exposure as useful biomarkers that are potentially transferable to clinical research. This review recapitulates selected studies that report the detection of cadmium-associated signatures in breast, gastric, colon, liver, lung, and nasopharyngeal tumor cell models, as specifically demonstrated by individual gene or whole genome expression profiling. Where available, the molecular, biochemical, and/or physiological aspects associated with the targeted gene activation or silencing in the discussed cell models are also outlined.

Biological and molecular modifications induced by cadmium and arsenic during breast and prostate cancer development

Breast and prostate cancer are two of the most common malignancies worldwide. Both cancers can develop into hormone -dependent or -independent subtypes and are associated to environmental exposure in the context of an inherited predisposition. As and Cd have been linked to the onset of both cancers, with the exception of As, which lacks a definitive association with breast carcinogenesis. The two elements exert an opposite effect dependent on acute versus chronic exposure. High doses of As or Cd were shown to induce cell death in acute experimental exposure, while chronic exposure triggers cell proliferation and viability, which is no longer limited by telomere shortening and apoptosis. The chronically exposed cells also increase their invasion capacity and tumorigenic potential. At molecular level, malignant transformation is evidenced mainly by up-regulation of BCL-2, MMP-2, MMP-9, VIM, Snail, Twist, MT, MLH and down-regulation of Casp-3, PTEN, E-CAD, and BAX. The signaling pathways most commonly activated are KRAS, p53, TGF-β, TNF-α, WNT, NRF2 and AKT. This knowledge could potentially raise public awareness over the health risks faced by the human population living or working in a polluted environment and smokers. Human exposure to As and Cd should be minimize as much as possible. Healthcare policies targeting people belonging to these risk categories should include analysis of: DNA damage, oxidative stress, molecular alterations, and systemic level of heavy metals and of essential minerals. In this review, we present the literature regarding cellular and molecular alterations caused by exposure to As or Cd, focusing on the malignant transformation of normal epithelial cells after long-term intoxication with these two carcinogens.

Effect of Manganese Chloride and of Cotreatment with Cadmium Chloride on the In Vitro Proliferative, Motile and Invasive Behavior of MDA-MB231 Breast Cancer Cells

We examined the dose⁻response effect of MnCl₂ on the proliferative behavior of triple-negative breast cancer MDA-M231 cells vs. immortalized HB2 cells from breast epithelium taken as nontumoral counterparts. We also tested the effect of MnCl₂ on tumor cell invasiveness in vitro by evaluating the relative invasion indexes through Boyden chamber assays. Moreover, we checked whether cotreatment with both MnCl₂ and CdCl₂ could modify the observed biological response by MDA-MB231 cells. Our results show a promotional impact of MnCl₂ on cell proliferation, with 5 µM concentration inducing the more pronounced increase after 96-h exposure, which is not shared by HB2 cells. Exposure to 5 µM MnCl₂ induced also an elevation of the relative invasion index of cancer cells. The Mn-mediated stimulatory effects were counteracted by cotreatment with CdCl₂. These data support the concept that human exposure to high environmental concentrations of Mn may increase the risk of carcinogenesis and metastasis by prompting the expansion and dissemination of triple-negative breast cancer cells. On the other hand, the Mn-counteracting anticancer property of Cd looks promising and deserves a more detailed characterization of the involved intracellular targets aimed to the molecular modeling of specific antineoplastic agents against malignant breast cancer spreading.

Molecular Signatures Associated with Treatment of Triple-Negative MDA-MB231 Breast Cancer Cells with Histone Deacetylase Inhibitors JAHA and SAHA

Jay Amin hydroxamic acid (JAHA; N8-ferrocenylN¹-hydroxy-octanediamide) is a ferrocene-containing analogue of the histone deacetylase inhibitor (HDACi) suberoylanilide hydroxamic acid (SAHA). JAHA's cytotoxic activity on MDA-MB231 triple negative breast cancer (TNBC) cells at 72 h has been previously demonstrated with an IC₅₀ of 8.45 μM. JAHA's lethal effect was found linked to perturbations of cell cycle, mitochondrial activity, signal transduction, and autophagy mechanisms. To glean novel insights on how MDA-MB231 breast cancer cells respond to the cytotoxic effect induced by JAHA, and to compare the biological effect with the related compound SAHA, we have employed a combination of differential display-PCR, proteome analysis, and COMET assay techniques and shown some differences in the molecular signature profiles induced by exposure to either HDACis. In particular, in contrast to the more numerous and diversified changes induced by SAHA, JAHA has shown a more selective impact on expression of molecular signatures involved in antioxidant activity and DNA repair. Besides expanding the biological knowledge of the effect exerted by the modifications in compound structures on cell phenotype, the molecular elements put in evidence in our study may provide promising targets for therapeutic interventions on TNBCs.

Cytotoxic effects of seven Tunisian hospital wastewaters on the proliferation of human breast cancer cell line MDA-231: correlation with their chemical characterization

Hospital wastewaters contain large amounts of pharmaceutical residues, which may eventually be discharged into the aquatic environment through wastewater treatment plants, raising the question of their impact on human and environmental health. This has prompted the launch of several monitoring studies into the most commonly administered compounds in urban wastewater. The aim of this study was, therefore, to explore the cytotoxic potential of wastewaters samples collected from seven hospitals in Tunisia. The physicochemical analyses showed a large fluctuation of certain parameters in the collected samples, such as chemical oxygen demand (ranged from 860 to 1720 mg L^-1), biochemical oxygen demand (ranged from 385 to 747 mg L^-1), total organic carbon (ranged from 256 to 562 g L^-1), total suspended solids (ranged from 905 to 1450 mg L^-1), conductivity (ranged from 3.31 to 7.14 μsm/cm), and turbidity (ranged from 100 to 480 NTU). The analysis using inductively coupled plasma mass spectrometry (ICP-MS) also showed that hospital wastewater contains high concentrations of Hg (ranged from 0.0024 to 0.019 mg L^-1). This could be explained by the variation of the activity and the services in certain hospitals compared to others. All hospital wastewater samples induced the proliferation of human breast cancer cell line MDA-231, even at low concentrations (20 μL/assay). Moreover, the maximum induction reached at the concentration of 60 μL/assay in wastewater samples from hospitals located in Monastir, Sidi Bouzid, Mahdia, and Sfax with percentages of induction up to 42.33, 14, 7.61, and 5.42%, respectively. These observations could be due to the presence of endocrine disrupting compounds (EDCs) in these wastewaters. Given this, our results evidenced the potential risk of these hospital effluents to environmental and public health.

AEG-1/MTDH/LYRIC: A Promiscuous Protein Partner Critical in Cancer, Obesity, and CNS Diseases

Since its original discovery in 2002, AEG-1/MTDH/LYRIC has emerged as a primary regulator of several diseases including cancer, inflammatory diseases, and neurodegenerative diseases. AEG-1/MTDH/LYRIC has emerged as a key contributory molecule in almost every aspect of cancer progression, including uncontrolled cell growth, evasion of apoptosis, increased cell migration and invasion, angiogenesis, chemoresistance, and metastasis. Additionally, recent studies highlight a seminal role of AEG-1/MTDH/LYRIC in neurodegenerative diseases and obesity. By interacting with multiple protein partners, AEG-1/MTDH/LYRIC plays multifaceted roles in the pathogenesis of a wide variety of diseases. This review discusses the current state of understanding of AEG-1/MTDH/LYRIC regulation and function in cancer and other diseases with a focus on its association/interaction with several pivotal protein partners.

Overexpression of astrocyte elevated gene-1 (AEG-1) in cervical cancer and its correlation with angiogenesis

OBJECTIVES

To explore the expression of astrocyte elevated gene-1 (AEG-1) in cervical cancer and analyze its correlation with microvascular density (MVD), nuclear factor kappaB (NF-kB p65) and vascular endothelial growth factor (VEGF).

MATERIALS AND METHODS

Immunohistochemical MaxVision method was adopted to detect the expression level of AEG-1, NF-kB p65 and VEGF in 45 samples of invading cervical cancer and 12 samples of cervicitis from The First Affiliated Hospital of Wenzhou Medical University. Tumor microvascular endothelial marker CD34 combined with Weidner was used to determine the MVD in cervical cancer tissue. The positive expression and staining conditions of AEG-1, NF-kB p65 and VEGF in cervical cancer tissues were observed under a light microscope. Correlations between expression of AEG-1 protein and those of NF-Kb p65 and VEGF, as well as MVD, were analyzed using Pearson correlation.

RESULTS

The expression levels of AEG-1 were 0.186±0.043 in cervical cancer and 0.051±0.002 in chronic cervicitis (p<0.01). Moreover, expression of AEG-1 was related to vascular invasion and lymphatic metastasis of cervical cancer (p<0.01), but not with age of the patients, differentiation degree, tumour size, pathological type and parametrial infiltration (p>0.05). Pearson correlation analysis showed that the expression of AEG-1 was linked with NF-kB p65 (r=0.501, p=0.000), VEGF (r=0.718, p=0.000) as well as MVD in cervical cancer tissue (r=0.815, p=0.000).

CONCLUSIONS

AEG-1 is highly expressed in cervical cancer and promotes angiogenesis, which might be related to the fact that AEG-1 activating the signal pathway of NF-kB could up-regulate the level of VEGF expression.

Expression of astrocyte elevated gene-1 (AEG-1) as a biomarker for aggressive pancreatic ductal adenocarcinoma

Background

Altered expression of astrocyte elevated gene-1 (AEG-1) is associated with tumorigenesis and progression. The present study aimed to investigate the clinical and prognostic significance of AEG-1 expression in pancreatic ductal adenocarcinoma (PDAC).

Methods

Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and Western blot analyses were employed to assess AEG-1 expression in three pancreatic cancer cell lines and normal pancreatic duct epithelial cells. qRT-PCR and immunohistochemical analyses were performed to detect AEG-1 expression in ten pairs of PDAC and normal pancreas tissues. Immunohistochemistry was then used to examine AEG-1 expression in paraffin-embedded tissues obtained from 105 patients, and its association with clinicopathological parameters including cancer classification was examined. Kaplan-Meier analysis was performed to study the survival rates of patients.

Results

Expression of AEG-1 mRNA and protein was markedly higher in pancreatic cancer cell lines than that in the normal pancreatic duct epithelial cells. AEG-1 expression was evidently upregulated in PDAC tissues compared to that of the matched distant normal pancreas tissues. qRT-PCR data revealed that the tumor/non-tumor ratio of AEG-1 expression was >1.5-fold (up to 6.5-fold). Immunohistochemical data showed that AEG-1 protein was detected in 98.09% (103/105) of PDAC tissues; and they were found to be associated with tumor size (P = 0.025), advanced clinical stage (P = 0.004), T classification (P = 0.006), N classification (P = 0.003), and M classification (P = 0.007). Furthermore, Kaplan-Meier analysis showed that patients with high AEG-1-expressed PDAC had shorter overall survival. A multivariate Cox regression analysis revealed that clinical stage, T classification, and AEG-1 expression were the independent prognostic predictors for PDAC.

Conclusions

This study suggests that AEG-1 protein was highly expressed in PDAC and associated with poor prognosis of the patients.

Progress of cancer research on astrocyte elevated gene-1/Metadherin (Review)

Tumor development is initiated by an accumulation of numerous genetic and epigenetic alterations that promote tumor initiation, invasion and metastasis. Astrocyte elevated gene-1 [AEG-1; also known as Metadherin (MTDH) and Lysine-rich CEACAM1 co-isolated (LYRIC)] has emerged in recent years as a potentially crucial mediator of tumor malignancy, and a key converging point of a complex network of oncogenic signaling pathways. AEG-1/MTDH has a multifunctional role in tumor development that has been found to be involved in the following signaling cascades: i) The Ha-Ras and PI3K/Akt pathways; ii) the nuclear factor-κB signaling pathway; iii) the ERK/mitogen-activated protein kinase and Wnt/β-catenin pathways; and iv) the Aurora-A kinase signaling pathway. Studies have established that AEG-1/MTDH is crucial in tumor progression, including transformation, the evasion of apoptosis, invasion, angiogenesis and metastasis. In addition, recent clinical studies have convincingly associated AEG-1/MTDH with tumor progression and poor prognosis in a number of cancer types, including hepatocellular, esophageal squamous cell, gallbladder and renal cell carcinomas, breast, non-small cell lung, prostate, gastric and colorectal cancers, and glioma, melanoma, neuroblastoma and osteosarcoma. AEG-1/MTDH may be used as a biomarker to identify subgroups of patients who require more intensive treatments and who are likely to benefit from AEG-1/MTDH-targeted therapies. The therapeutic targeting of AEG-1/MTDH may simultaneously block metastasis, suppress tumor growth and enhance the efficacy of chemotherapeutic treatments.

Astrocyte elevated gene-1 activates MMP9 to increase invasiveness of colorectal cancer

The molecular mechanism underlying the invasiveness of colorectal cancer (CRC) cells remains largely unknown. Here, we found that astrocyte elevated gene-1 (AEG-1) was significantly upregulated in CRC tissues, compared with the adjacent normal tissues from human patients. Ectopic expression of AEG-1 enhanced the invasive ability of CRC cells, while small interfering RNA (siRNA)-induced knockdown of AEG-1 inhibited the invasive ability of CRC cells. Transcription, protein levels, and secretion of matrix metalloproteinase 9 (MMP9), all increased by AEG-1 overexpression in CRC cells, and all decreased by AEG-1 inhibition. Suppression of endogenous MMP9 abrogated the effects of AEG-1 on invasiveness, without affecting AEG-1 levels. Taken together, these findings suggest that AEG-1 contributes to CRC invasiveness and metastasis by enhancing MMP9 activity. Thus, AEG-1 appears to be a novel therapeutic target for preventing the metastasis of CRC.

AEG-1/MTDH/LYRIC, the beginning: initial cloning, structure, expression profile, and regulation of expression

Since its initial identification as a HIV-1-inducible gene in 2002, astrocyte elevated gene-1 (AEG-1), subsequently cloned as metadherin (MTDH) and lysine-rich CEACAM1 coisolated (LYRIC), has emerged over the past 10 years as an important oncogene providing a valuable prognostic marker in patients with various cancers. Recent studies demonstrate that AEG-1/MTDH/LYRIC is a pleiotropic protein that can localize in the cell membrane, cytoplasm, endoplasmic reticulum (ER), nucleus, and nucleolus, and contributes to diverse signaling pathways such as PI3K-AKT, NF-κB, MAPK, and Wnt. In addition to tumorigenesis, this multifunctional protein is implicated in various physiological and pathological processes including development, neurodegeneration, and inflammation. The present review focuses on the discovery of AEG-1/MTDH/LYRIC and conceptualizes areas of future direction for this intriguing gene. We begin by describing how AEG-1, MTDH, and LYRIC were initially identified by different research groups and then discuss AEG-1 structure, functions, localization, and evolution. We conclude with a discussion of the expression profile of AEG-1/MTDH/LYRIC in the context of cancer, neurological disorders, inflammation, and embryogenesis, and discuss how AEG-1/MTDH/LYRIC is regulated. This introductory discussion of AEG-1/MTDH/LYRIC will serve as the basis for the detailed discussions in other chapters of the unique properties of this intriguing molecule.

Differential gene expression in rainbow trout (Oncorhynchus mykiss) liver and ovary after exposure to zearalenone

Zearalenone (ZEA) is a mycotoxin of worldwide occurrence, and it has been shown to produce numerous adverse effects in both laboratory and domestic animals. However, regardless of recent achievements, the molecular mechanisms underlying ZEA toxicity remain elusive, and little is known about transcriptome changes of fish cells in response to ZEA occurrence. In the present study, differential display PCR was used to generate a unique cDNA fingerprint of differentially expressed transcripts in the liver and ovary of juvenile rainbow trout after either 24, 72, or 168 h of intraperitoneal exposure to ZEA (10 mg/kg of body mass). From a total of 59 isolated cDNA bands (ESTs), 5 could be confirmed with Real-Time qPCR and their nucleotide sequences were identified as mRNAs of: acty (β-centractin), the cytoskeleton structural element; bccip, responsible for DNA repair and cell cycle control; enoa (α-enolase), encoding enzyme of the glycolysis process; proc (protein C), that takes part in the blood coagulation process; and frih, encoding the heavy chain of ferritin, the protein complex important for iron storage. Further qPCR analysis of the confirmed ESTs expression profiles revealed significant mRNA level alterations in both tissues of exposed fish during the 168 h study. The results revealed a complex network of genes associated with different biological processes that may be engaged in the cellular response to ZEA exposure, i.e. blood coagulation or iron-storage processes.

Effect of transfection with PLP2 antisense oligonucleotides on gene expression of cadmium-treated MDA-MB231 breast cancer cells

Emerging evidence indicates that cadmium (Cd) is able to regulate gene expression, drastically affecting the pattern of transcriptional activity in human normal and pathological cells. We have already shown that exposure of MDA-MB231 breast cancer cells to 5 μM CdCl(2) for 96 h, apart from significantly affecting mitochondrial metabolism, induces modifications of the expression level of genes coding for members of stress response-, mitochondrial respiration-, MAP kinase-, NF-κB-, and apoptosis-related pathways. In the present study, we have expanded the knowledge on the biological effects of Cd-breast cancer cell interactions, indicating PLP2 (proteolipid protein-2) as a novel member of the list of Cd-upregulated genes by MDA-MB231 cancer cells and, through the application of transfection techniques with specific antisense oligonucleotides, we have demonstrated that such over-expression may be an upstream event to some of the changes of gene expression levels already observed in Cd-treated cells, thus unveiling new possible molecular relationship between PLP2 and genes linked to the stress and apoptotic responses.

Clinical implications of AEG-1 in liver metastasis of colorectal cancer

The aim of the study was to investigate the role of AEG-1 in colorectal cancer and the relationship between AEG-1 protein expression and pathological characteristics and prognosis in colorectal cancer. The AEG-1 mRNA and protein expression level between the tumor cells from the cases with liver metastasis and those from the ones without live metastasis were detected by RT-PCR and immunohistochemistry staining. The relationship between AEG-1 and clinicopathological parameters of colorectal cancer was determined. AEG-1 expressed positively in 218 (41.92%) of the 520 cases examined. It showed that both mRNA and protein level AEG-1 were over-expressed in the cases with liver metastasis compared with those without liver metastasis (P=0.01). After immunohistochemistry analysis, the expression of AEG-1 protein was related to age, Duke's stage and distant metastasis (P=0.001, 0.001 and 0.016, respectively). After survival analysis, the cases with highly expressed AEG-1 protein attained a significantly poorer postoperative disease-specific survival than those with none/low-expressed AEG-1 protein (P=0.001). In the Cox regression test, histological grade, Duke's stage and AEG-1 were detected as the independent prognostic factors (P=0.035, 0.001 and 0.010, respectively). AEG-1 protein may be a potential new early liver metastasis biomarker of colorectal cancer.

The role of cadmium and nickel in estrogen receptor signaling and breast cancer: metalloestrogens or not?

During the past half-century, incidences of breast cancer have increased globally. Various factors--genetic and environmental--have been implicated in the initiation and progression of this disease. One potential environmental risk factor that has not received a lot of attention is the exposure to heavy metals. While several mechanisms have been put forth describing how high concentrations of heavy metals play a role in carcinogenesis, it is unclear whether chronic, low-level exposure to certain heavy metals (i.e., cadmium and nickel) can directly result in the development and progression of cancer. Cadmium and nickel have been hypothesized to play a role in breast cancer development by acting as metalloestrogens--metals that bind to estrogen receptors and mimic the actions of estrogen. Since the lifetime exposure to estrogen is a well-established risk factor for breast cancer, anything that mimics its activity will likely contribute to the etiology of the disease. However, heavy metals, depending on their concentration, are capable of binding to a variety of proteins and may exert their toxicities by disrupting multiple cellular functions, complicating the analysis of whether heavy metal-induced carcinogenesis is mediated by the estrogen receptor. The purpose of this review is to discuss the various epidemiological, in vivo, and in vitro studies that show a link between the heavy metals, cadmium and nickel, and breast cancer development. We will particularly focus on the studies that test whether these two metals act as metalloestrogens in order to assess the strength of the data supporting this hypothesis.