Estrogen-induced G1/S transition of G0-arrested estrogen-dependent breast cancer cells is regulated by mitochondrial oxidant signaling

Role of uncoupling proteins in cancer

Uncoupling proteins (UCPs) are a family of inner mitochondrial membrane proteins whose function is to allow the re-entry of protons to the mitochondrial matrix, by dissipating the proton gradient and, subsequently, decreasing membrane potential and production of reactive oxygen species (ROS). Due to their pivotal role in the intersection between energy efficiency and oxidative stress, UCPs are being investigated for a potential role in cancer. In this review we compile the latest evidence showing a link between uncoupling and the carcinogenic process, paying special attention to their involvement in cancer initiation, progression and drug chemoresistance.

Alcoholic liver injury: Influence of gender and hormones

This article discusses several subjects pertinent to a consideration of the role of gender and hormones in alcoholic liver injury (ALI). Beginning with an overview of factors involved in the pathogenesis of ALI, we review changes in sex hormone metabolism resulting from alcohol ingestion, summarize research that points to estrogen as a cofactor in ALI, consider evidence that gut injury is linked to liver injury in the setting of alcohol, and briefly review the limited evidence regarding sex hormones and gut barrier function. In both women and female animals, most studies reveal a propensity toward greater alcohol-induced liver injury due to female gender, although exact hormonal influences are not yet understood. Thus, women and their physicians should be alert to the dangers of excess alcohol consumption and the increased potential for liver injury in females.

Antioxidant butylated hydroxyanisole inhibits estrogen-induced breast carcinogenesis in female ACI rats

Exposure to estrogens is suggested to be a risk factor in human breast cancer development. The mechanisms underlying estrogen-induced cancer have not been fully elucidated. Both estrogen receptor (ER)-mediated proliferative processes and ER-independent generation of oxidative stress are suggested to play important roles in estrogen-induced breast carcinogenesis. In the current study, we investigated the role of oxidative stress in breast carcinogenesis using the ACI rat model of mammary tumorigenesis. Female ACI rats were treated with 17beta-estradiol (E(2)), butylated hydroxyanisole (BHA), or a combination of E(2) + BHA for up to 240 days. Cotreatment of rats with E(2) + BHA reduced estrogen-induced breast tumor development with tumor incidence of 24%, a significant decrease relative to E(2) where tumor incidence was 82%. Proliferative changes in the breast tissue of E(2) + BHA-treated animals were similar to those observed in E(2)-treated animals. Tissue levels of 8-isoprostane, a marker of oxidant stress, as well as the activities of antioxidant enzymes including glutathione peroxidase, superoxide dismutase, and catalase were quantified in the breast tissues of rats treated with E(2) + BHA and compared to activity levels found in E(2)-treated animals and respective age-matched controls. Cotreatment with BHA inhibited E(2)-mediated increases in 8-isoprostane levels as well as activities of antioxidant enzymes. In summary, these data suggest that estrogen-mediated oxidant stress plays a critical role in the development of estrogen-dependent breast cancers and BHA inhibits E(2)-dependent breast carcinogenesis by decreasing oxidant stress.

Regulation of mitochondrial respiratory chain biogenesis by estrogens/estrogen receptors and physiological, pathological and pharmacological implications

There has been increasing evidence pointing to the mitochondrial respiratory chain (MRC) as a novel and important target for the actions of 17beta-estradiol (E(2)) and estrogen receptors (ER) in a number of cell types and tissues that have high demands for mitochondrial energy metabolism. This novel E(2)-mediated mitochondrial pathway involves the cooperation of both nuclear and mitochondrial ERalpha and ERbeta and their co-activators on the coordinate regulation of both nuclear DNA- and mitochondrial DNA-encoded genes for MRC proteins. In this paper, we have: 1) comprehensively reviewed studies that reveal a novel role of estrogens and ERs in the regulation of MRC biogenesis; 2) discussed their physiological, pathological and pharmacological implications in the control of cell proliferation and apoptosis in relation to estrogen-mediated carcinogenesis, anti-cancer drug resistance in human breast cancer cells, neuroprotection for Alzheimer's disease and Parkinson's disease in brain, cardiovascular protection in human heart and their beneficial effects in lens physiology related to cataract in the eye; and 3) pointed out new research directions to address the key questions in this important and newly emerging area. We also suggest a novel conceptual approach that will contribute to innovative regimens for the prevention or treatment of a wide variety of medical complications based on E(2)/ER-mediated MRC biogenesis pathway.

Overexpression of catalase delays G0/G1- to S-phase transition during cell cycle progression in mouse aortic endothelial cells

Although it is understood that hydrogen peroxide (H(2)O(2)) promotes cellular proliferation, little is known about its role in endothelial cell cycle progression. To assess the regulatory role of endogenously produced H(2)O(2) in cell cycle progression, we studied the cell cycle progression in mouse aortic endothelial cells (MAECs) obtained from mice overexpressing a human catalase transgene (hCatTg), which destroys H(2)O(2). The hCatTg MAECs displayed a prolonged doubling time compared to wild-type controls (44.0 +/- 4.7 h versus 28.6 +/- 0.8 h, p<0.05), consistent with a diminished growth rate and H(2)O(2) release. Incubation with aminotriazole, a catalase inhibitor, prevented the observed diminished growth rate in hCatTg MAECs. Inhibition of catalase activity with aminotriazole abrogated catalase overexpression-induced antiproliferative action. Flow cytometry analysis indicated that the prolonged doubling time was principally due to an extended G(0)/G(1) phase in hCatTg MAECs compared to the wild-type cells (25.0 +/- 0.9 h versus 15.9 +/- 1.4 h, p< 0.05). The hCatTg MAECs also exhibited decreased activities of the cyclin-dependent kinase (Cdk) complexes responsible for G(0)/G(1)- to S-phase transition in the cell cycle, including the cyclin D-Cdk4 and cyclin E-Cdk2 complexes. Moreover, the reduction in cyclin-Cdk activities in hCatTg MAECs was accompanied by increased protein levels of two Cdk inhibitors, p21 and p27, which inhibit the Cdk activity required for the G(0)/G(1)- to S-phase transition. Knockdown of p21 and/or p27 attenuated the antiproliferative effect of catalase overexpression in MAECs. These results, together with the fact that catalase is an H(2)O(2) scavenger, suggest that endogenously produced H(2)O(2) mediates MAEC proliferation by fostering the transition from G(0)/G(1) to S phase.

Expression of a family of noncoding mitochondrial RNAs distinguishes normal from cancer cells

We reported the presence in human cells of a noncoding mitochondrial RNA that contains an inverted repeat (IR) of 815 nucleotides (nt) covalently linked to the 5' end of the mitochondrial 16S RNA (16S mtrRNA). The transcript contains a stem-loop structure and is expressed in human proliferating cells but not in resting cells. Here, we demonstrate that, in addition to this transcript, normal human proliferating cells in culture express 2 antisense mitochondrial transcripts. These transcripts also contain stem-loop structures but strikingly they are down-regulated in tumor cell lines and tumor cells present in 17 different tumor types. The differential expression of these transcripts distinguishes normal from tumor cells and might contribute a unique vision on cancer biology and diagnostics.

Ageing, oxidative stress and cancer: paradigms in parallax

Two paradigms central to geroscience research are that aging is associated with increased oxidative stress and increased cancer risk. Therefore, it could be deduced that cancers arising with ageing will show evidence of increased oxidative stress. Recent studies of gene expression in age-controlled breast cancer cases indicate that this deduction is false, posing parallax views of these two paradigms, and highlighting the unanswered question: does ageing cause or simply permit cancer development?

Genes responsive to both oxidant stress and loss of estrogen receptor function identify a poor prognosis group of estrogen receptor positive primary breast cancers

Introduction

Oxidative stress can modify estrogen receptor (ER) structure and function, including induction of progesterone receptor (PR), altering the biology and clinical behavior of endocrine responsive (ER-positive) breast cancer.

Methods

To investigate the impact of oxidative stress on estrogen/ER-regulated gene expression, RNA was extracted from ER-positive/PR-positive MCF7 breast cancer cells after 72 hours of estrogen deprivation, small-interfering RNA knockdown of ER-α, short-term (8 hours) exposure to various oxidant stresses (diamide, hydrogen peroxide, and menadione), or simultaneous ER-α knockdown and oxidant stress. RNA samples were analyzed by high-throughput expression microarray (Affymetrix), and significance analysis of microarrays was used to define gene signatures responsive to estrogen/ER regulation and oxidative stress. To explore the association of these signatures with breast cancer biology, microarray data were analyzed from 394 ER-positive primary human breast cancers pooled from three independent studies. In particular, an oxidant-sensitive estrogen/ER-responsive gene signature (Ox-E/ER) was correlated with breast cancer clinical parameters and disease-specific patient survival (DSS).

Results

From 891 estrogen/ER-regulated probes, a core set of 75 probes (62 unique genes) responsive to all three oxidants were selected (Ox-E/ER signature). Ingenuity pathway analysis of this signature highlighted networks involved in development, cancer, and cell motility, with intersecting nodes at growth factors (platelet-derived growth factor-BB, transforming growth factor-β), a proinflammatory cytokine (tumor necrosis factor), and matrix metalloproteinase-2. Evaluation of the 394 ER-positive primary breast cancers demonstrated that Ox-E/ER index values correlated negatively with PR mRNA levels (r_p = -0.2; P = 0.00011) and positively with tumor grade (r_p = 0.2; P = 9.741 × e^-5), and were significantly higher in ER-positive/PR-negative versus ER-positive/PR-positive breast cancers (t-test, P = 0.0008). Regardless of PR status, the Ox-E/ER index associated with reduced DSS (n = 201; univariate Cox, P = 0.078) and, using the optimized cut-point, separated ER-positive cases into two significantly different DSS groups (log rank, P = 0.0009).

Conclusion

An oxidant-sensitive subset of estrogen/ER-responsive breast cancer genes linked to cell growth and invasion pathways was identified and associated with loss of PR and earlier disease-specific mortality, suggesting that oxidative stress contributes to the development of an aggressive subset of primary ER-positive breast cancers.

Estrogen-induced breast cancer: alterations in breast morphology and oxidative stress as a function of estrogen exposure

Epidemiological evidence indicates that prolonged lifetime exposure to estrogen is associated with elevated breast cancer risk in women. Oxidative stress and estrogen receptor-associated proliferative changes are suggested to play important roles in estrogen-induced breast carcinogenesis. In the present study, we investigated changes in breast morphology and oxidative stress following estrogen exposure. Female ACI rats were treated with 17beta-estradiol (E(2), 3 mg, s.c.) for either 7, 15, 120 or 240 days. Animals were euthanized, tissues were excised, and portions of the tissues were either fixed in 10% buffered formalin or snap-frozen in liquid nitrogen. Paraffin-embedded tissues were examined for histopathologic changes. Proliferative changes appeared in the breast after 7 days of E(2) exposure. Atypical ductal proliferation and significant reduction in stromal fat were observed following 120 days of E(2) exposure. Both in situ and invasive carcinomas were observed in the majority of the mammary glands from rats treated with E(2) for 240 days. Palpable breast tumors were observed in 82% of E(2)-treated rats after 228 days, with the first palpable tumor appearing after 128 days. No morphological changes were observed in the livers, kidneys, lungs or brains of rats treated with E(2) for 240 days compared to controls. Furthermore, 8-isoprostane (8-isoPGF(2alpha)) levels as well as the activities of antioxidant enzymes, such as glutathione peroxidase, superoxide dismutase and catalase, were quantified in the breast tissues of rats treated with E(2) for 7, 15, 120 and 240 days and compared to activity levels in age-matched controls. 8-isoPGF(2alpha) levels displayed time-dependent increases upon E(2) treatment and were significantly higher than control levels at the 15, 120 and 240 day time-points. 8-isoPGF(2alpha) observed in E(2)-induced mammary tumors were significantly higher than levels found in control mammary tissue from age-matched animals. Similarly, alterations in glutathione peroxidase and superoxide dismutase activities were detected in both mammary and tumor tissue from E(2)-treated rats. Taken together, our data reveal that proliferative changes in the breast tissue of ACI rats are associated with increases in 8-isoPGF(2alpha) formation as well as changes in the activities of antioxidant enzymes. These oxidative changes appear to be a function of E(2) exposure and occur prior to tumor development.

Lipotoxic effects of triacylglycerols in J774.2 macrophages

OBJECTIVE

Triacylglycerols (TGs) are being considered as an independent risk factor in atherosclerosis and metabolic syndrome, acting by dysregulation of the TG/high-density lipoprotein axis. Accumulation of lipids in subendothelial space attracts macrophages, leading to atherosclerotic plaque formation and increased plaque instability due to formation of foam cells and macrophage death. The aim of this study was to evaluate lipotoxic effects in macrophages caused by TG uptake.

METHODS

J774.2 macrophages were exposed to soybean or olive oil-based lipid emulsions as a source of TGs (1 mg/mL) in a presence or absence of lipase inhibitor paraoxon (20 microM) or to bovine serum albumin-complexed palmitic (150 microM), linoleic (600 microM), and oleic (600 microM) fatty acids.

RESULTS

The results demonstrated accumulation of TGs, G1/S arrest, and cell death with necrotic morphologic features after exposure to TG emulsions. These effects were prevented by treatment with an antioxidant N-acetyl-cysteine (0.5 mM). Paraoxon inhibited intracellular TG degradation but did not prevent lipotoxicity and cell death. Olive oil TG triggered macrophage death in a manner similar to soybean oil. Treatment of the macrophages with free fatty acid, mainly with palmitic acid, showed a reactive oxygen species-independent cell death pathway, which was different from that of TG and was not prevented by N-acetyl-cysteine.

CONCLUSION

This study shows a direct lipotoxic pathway for TG molecules in macrophages, which is not associated with degradation of TG molecule to free fatty acids. This study for the first time can explain at a cellular level how TGs as an independent risk factor aggravate atherosclerotic outcomes.

Estrogen-induced redox sensitive Id3 signaling controls the growth of vascular cells

In this study, we investigated a mechanism by which estrogen-induced oxidants control endothelial cell differentiation into tubelike structures via redox sensitive signaling molecule Id3. Using a matrigel cell culture, we determined whether superoxide or hydrogen peroxide signaled estrogen-induced tube formation. Overexpression of the superoxide scavenger MnSOD and the hydrogen peroxide scavenger catalase inhibited tube formation in estrogen treated endothelial cells. Since tube formation on matrigel is not specific for endothelial cells, we verified our results in a co-culture model that better represents tube formation in vivo. Antioxidants ebselen and N-acetylcysteine as well as overexpression of MnSOD and catalase inhibited tube formation in estrogen exposed endothelial cells co-cultured with fibroblasts. We previously showed that estrogen-induced mitochondrial oxidants depended on the cytoskeleton so we tested tube formation dependence on the cytoskeleton. Estrogen-induced tube formation was inhibited by the actin cytoskeleton disruptor cytochalasin D and the microtubule destabilizer colchicine. Estrogen increased Id3 phosphorylation which was reduced by catalase and N-acetylcysteine treatments. We determined the functional role of Id3 in tube formation by RNA intereference and showed Id3 siRNA to inhibit tube formation in estrogen exposed cells. The major novel findings presented here are that: (i) estrogen-induced tube formation requires the presence of Id3, a member of the helix-loop-helix family of transcriptional factors and (ii) estrogen increases Id3 phosphorylation via a redox-dependent process. Furthermore, these studies demonstrate Id3 to be an important signaling molecule in estrogen stimulated vascularization and may serve as a therapeutic target in the prevention and treatment of vasculoproliferative disorders.

Mechanisms of hormone carcinogenesis: evolution of views, role of mitochondria

CumuIative and excessive exposure to estrogens is associated with increased breast cancer risk. The traditional mechanism explaining this association is that estrogens affect the rate of cell division and apoptosis and thus manifest their effect on the risk of breast cancer by affecting the growth of breast epithelial tissues. Highly proliferative cells are susceptible to genetic errors during DNA replication. The action of estrogen metabolites offers a complementary genotoxic pathway mediated by the generation of reactive estrogen quinone metabolites that can form adducts with DNA and generate reactive oxygen species through redox cycling. In this chapter, we discussed a novel mitochondrial pathway mediated by estrogens and their cognate estrogen receptors (ERs) and its potential implications in estrogen-dependent carcinogenesis. Several lines of evidence are presented to show: (1) mitochondrial localization of ERs in human breast cancer cells and other cell types; (2) a functional role for the mitochondrial ERs in regulation of the mitochondrial respiratory chain (MRC) proteins and (3) potential implications of the mitochondrial ER-mediated pathway in stimulation of cell proliferation, inhibition of apoptosis and oxidative damage to mitochondrial DNA. The possible involvement of estrogens and ERs in deregulation of mitochondrial bioenergetics, an important hallmark of cancer cells, is also described. An evolutionary view is presented to suggest that persistent stimulation by estrogens through ER signaling pathways of MRC proteins and energy metabolic pathways leads to the alterations in mitochondrial bioenergetics and contributes to the development of estrogen-related cancers.

Tumors caused by overexpression and forced activation of Stat5 in mammary epithelial cells of transgenic mice are parity-dependent and developed in aged, postestropausal females

In transgenic mice overexpressing Stat5 or a constitutively activated Stat5 variant (STAT5ca), we show for the first time that parity is required for the development of tumors in postestropausal females. Tumors were detected in glands of multiparous transgenic female mice after latency period of 14 months, but rarely in their age-matched virgin (AMV) counterparts. This period was not affected by distinguishable tumor pathologies and was not dependent upon transgenic Stat5 variant. To associate Stat5 deregulation, parity and the postestropausal tumor occurrence with mammary cancer formation, the activities of endogenous and transgenic Stat5 were measured in the glands of aged multiparous and AMV females. No differences in phosphorylated Stat5 (pStat5) levels were found between the 2 cohorts. However, promoter sequences comprising the Stat5 binding sites from the cyclin D1 or the bcl-x genes associate differentially with acetylated histone H4 in aged multiparous and AMV STAT5ca transgenic females. Individual epithelial cells varied greatly with respect to the presence of nuclear pStat5. A small subset of epithelial cells, in which pStat5 and cyclin D1 were co-expressed, was exclusively present in the multiparous glands. Changes in chromatin structure might persist past the reproductive life time of the multiparous mice and contribute to the transcription of the cyclin D1 gene by activated Stat5. This may cause the detectable expression of cyclin D1 and add to the process of tumorigenesis.

Gossypol reduction of tumor growth through ROS-dependent mitochondria pathway in human colorectal carcinoma cells

Among 13 different cell lines, gossypol (GOS) showed the most potent cytotoxic effect against human colorectal carcinoma cells including HT29, COLO205, COLO320HSR and COLO320DM cells according to an MTT assay. The cytotoxic effect of GOS was mediated by its induction of apoptosis as characterized by the occurrence of DNA ladders, apoptotic bodies and chromosome condensation in both COLO205 and HT29 cells. Activation of caspase 3, 6, 8 and 9, but not caspase 1, accompanied by the appearance of cleaved fragments of PARP (85 kDa), and caspase 3 (p17/p15), was identified in GOS-treated cells. Decreases in Bcl-xL and phosphorylated Bad proteins were found in GOS-treated cells. GOS induction of ROS production was detected by in vitro plasmid digestion, and an increase in the intracellular peroxide level was observed in GOS-treated COLO205 cells by the DCHF-DA assay. Antioxidants including N-acetyl-L-cysteine (NAC), catalase (CAT), tempol (TEM) and melatonin (MEL), but not allopurinol (ALL), pyrrolidine dithiocarbamate (PDTC) or diphenylene iodonium (DPI), significantly inhibited GOS-induced Reactive oxygen species (ROS) production through blocking the occurrence of apoptosis. GOS induced mitochondrial dysfunction characterized by a loss of the mitochondria membrane potential via DiOC6 staining, and the release of cytochrome c (Cyt c) and apoptosis-inducing factor (AIF) from mitochondria to the cytoplasm was observed. Removing mitochondria by ethidium bromide (EtBr) treatment significantly reduced the apoptotic effect of GOS in COLO205 cells. Furthermore, an intraperitoneal injection of GOS or gossypol acetic acid (GAA) significantly reduced the growth of colorectal carcinoma induced by a subcutaneous injection of COLO205 cells in nude mice. Results of the present study provide the first evidences demonstrating the in vitro and in vivo antitumor effects of GOS via an ROS-dependent mitochondrial apoptosis in colorectal carcinoma.

Alteration of expression levels of the oxidative phosphorylation system (OXPHOS) in breast cancer cell mitochondria

Mitochondria are dynamic intracellular organelles playing a central role in cell metabolism by generating ATP, through the oxidative phosphorylation system (OXPHOS). Altered mitochondrial functions have been identified as causative or contributing factors in some degenerative diseases and are becoming crucial to understanding cancer mechanisms. We report on distinct expression differences between mitochondria of normal and breast-infiltrating ductal carcinoma (IDC) cells. Mitochondria isolated from HMC (human mammary carcinoma) and HMEC (human mammary epithelial cell) cultures were assayed for expression levels of the multi-protein OXPHOS complexes using Western blot and densitometric analyses. Depressed expression levels were detected for all HMC OXPHOS complexes. Drastic signal reduction was observed for the succinate-dehydrogenase complex II iron-sulphur protein SDH-B (3.38%), while decreasing was reported for the NADH-ubiquinone oxidoreductase complex I Fe-S protein 3 NDUFS3 (32.78%) and the ubiquinol-cytochrome c reductase complex III protein 2 UQCRC2 (50.34%). A significant signal dropping was detected for the ATP-synthase complex V F(1)beta subunit (18.07%). For the cytochrome-oxidase complex IV (CO), near-depletion of the mitochondrial-encoded COI (4.37%) and no apparent variation of the COIV (97.26%) subunits were observed. CO and ATP-synthase were also assayed by cryo-immunoelectron microscopy (CIEM) on unfractionated HMC and HEMC cell mitochondria. COI and F(1)beta differential expression, invariance of COIV levels were corroborated, while HMC mitochondria morphology deterioration was highlighted. MitoTracker Red and fluorescence immunolabelling merging confirmed CIEM data. MitoTracker Red and Green co-staining showed mitochondria membrane property modulation. These data describe bioenergetic and phenotypic alterations of IDC cell mitochondria, possibly providing new cancer hallmarks.

Estrogen-induced generation of reactive oxygen and nitrogen species, gene damage, and estrogen-dependent cancers

In addition to the direct effect of estrogen on mitochondria and the redox cycling of catechol estrogen, estrogen-induced proinflammatory cytokines, such as interleukin-1 beta (IL-1beta) and tumor necrosis factor alpha (TNF-alpha), also generate reactive oxygen and nitrogen species (RO/NS). Different cellular signaling pathways may operate in response to varying levels of estrogen-induced RO/NS, leading to genotoxic damage, cell apoptosis, or cell growth. At high levels of RO/NS, cells receiving genotoxic insults, if not repaired, may engage the apoptotic pathways. There is increasing evidence supporting that estrogen-induced alterations in the genome of cells is produced by oxidative attack. Furthermore, ROS generated by estrogen exposure and/or active metabolites of estrogen in combination with receptor-mediated proliferation of genetically damaged cells may be involved in tumor development. This view is supported by the findings of DNA modifications produced in vitro or in vivo by natural and synthetic estrogens in the target organs of cancer both in experimental models and in humans. Interaction of estrogen-induced oxidants and estrogen metabolites with DNA was shown to generate mutations in genes. Cotreatment with an inhibitor of IL-1beta and TNF-alpha synthesis, pentoxifylline, decreased stilbene estrogen-induced levels of myeloperoxidase (MPO), 8-hydroxydeoxyguanosine formation, and gene mutations, and prevented stilbene estrogen-induced lesions. Stable MCF-7 clones overexpressing IL-1beta resulted in a high level of IL-1beta peptide secretion undergoing cell apoptosis, and an elevated level of p53 protein in response to high oxidative stress when compared to nontransfected cells, whereas MCF-7 clones overexpressing IL-1beta that resulted in a moderate level of IL-1beta secretion stimulated the clonal expansion of MCF-7 and TM3 cells. Estrogen-induced MCF-7 cell growth and cyclin D1 expression were suppressed by antioxidants and mitochondrial blockers. These studies support that in addition to ovarian estrogen-mediated ER signaling, mitogenic signals may also come from estrogen-induced RO/NS. Further validation of this concept that the concentration of the RO/NS within the cellular microenvironment determines its stimulatory or inhibitory growth signals as well as its genotoxic effects regulating the growth of estrogen-dependent tumors may result in novel preventive strategies.

Cyclin D1 and breast cancer

Cyclin D1 is one of the frequently overexpressed proteins and one of the commonly amplified genes in breast cancer. This article reviews the roles of cyclin D1 in cell-cycle regulation (normal and abnormal), mammary gland development and carcinogenesis and the relationship to oestrogen in breast tissues. It concludes by presenting the clinical, prognostic and therapeutic implications of our current knowledge of cyclin D1 in breast cancer.

Functional estrogen receptors in the mitochondria of breast cancer cells

Steroid hormones have been reported to indirectly impact mitochondrial functions, attributed to nuclear receptor-induced production of proteins that localize in this cytoplasmic organelle. Here we show high-affinity estrogen receptors in the mitochondria of MCF-7 breast cancer cells and endothelial cells, compatible with classical estrogen receptors ERalpha and ERbeta. We report that in MCF-7, estrogen inhibits UV radiation-induced cytochrome C release, the decrease of the mitochondrial membrane potential, and apoptotic cell death. UV stimulated the formation of mitochondrial reactive oxygen species (mROS), and mROS were essential to inducing mitochondrial events of cell death. mROS mediated the UV activation of c-jun N-terminal kinase (JNK), and protein kinase C (PKC) delta, underlying the subsequent translocation of Bax to the mitochondria where oligomerization was promoted. E2 (estradiol) inhibited all these events, directly acting in mitochondria to inhibit mROS by rapidly up-regulating manganese superoxide dismutase activity. We implicate novel functions of ER in the mitochondria of breast cancer that lead to the survival of the tumor cells.

Estrogen-induced DNA synthesis in vascular endothelial cells is mediated by ROS signaling

Background

Since estrogen is known to increase vascular endothelial cell growth, elevated estrogen exposure from hormone replacement therapy or oral contraceptives has the potential to contribute in the development of abnormal proliferative vascular lesions and subsequent thickening of the vasculature. How estrogen may support or promote vascular lesions is not clear. We have examined in this study whether estrogen exposure to vascular endothelial cells increase the formation of reactive oxygen species (ROS), and estrogen-induced ROS is involved in the growth of endothelial cells.

Methods

The effect of estrogen on the production of intracellular oxidants and the role of estrogen-induced ROS on cell growth was studied in human umbilical vein endothelial cells. ROS were measured by monitoring the oxidation of 2'7'-dichlorofluorescin by spectrofluorometry. Endothelial cell growth was measured by a colorimetric immunoassay based on BrdU incorporation into DNA.

Results

Physiological concentrations of estrogen (367 fmol and 3.67 pmol) triggered a rapid 2-fold increase in intracellular oxidants in endothelial cells. E2-induced ROS formation was inhibited to basal levels by cotreatment with the mitochondrial inhibitor rotenone (2 μM) and xanthine oxidase inhibitor allopurinol (50 μM). Inhibitors of NAD(P)H oxidase, apocynin and DPI, did not block E2-induced ROS formation. Furthermore, the NOS inhibitor, L-NAME, did not prevent the increase in E2-induced ROS. These findings indicate both mitochondria and xanthine oxidase are the source of ROS in estrogen treated vascular endothelial cells. E2 treated cells showed a 2-fold induction of BrdU incorporation at 18 h which was not observed in cells exposed to vehicle alone. Cotreatment with ebselen (20 μM) and NAC (1 mM) inhibited E2-induced BrdU incorporation without affecting the basal levels of DNA synthesis. The observed inhibitory effect of NAC and ebselen on E2-induced DNA synthesis was also shown to be dose dependent.

Conclusion

We have shown that estrogen exposure stimulates the rapid production of intracellular ROS and they are involved in growth signaling of endothelial cells. It appears that the early estrogen signaling does not require estrogen receptor genomic signaling because we can inhibit estrogen-induced DNA synthesis by antioxidants. Findings of this study may further expand research defining the underlying mechanism of how estrogen may promote vascular lesions. It also provides important information for the design of new antioxidant-based drugs or new antioxidant gene therapy to protect the cardiovascular health of individuals sensitive to estrogen.

Regulation of mitochondrial respiratory chain structure and function by estrogens/estrogen receptors and potential physiological/pathophysiological implications

It is well known that the biological and carcinogenic effects of 17beta-estradiol (E2) are mediated via nuclear estrogen receptors (ERs) by regulating nuclear gene expression. Several rapid, non-nuclear genomic effects of E2 are mediated via plasma membrane-bound ERs. In addition, there is accumulating evidence suggesting that mitochondria are also important targets for the action of estrogens and ERs. This review summarized the studies on the effects of estrogens via ERs on mitochondrial structure and function. The potential physiological and pathophysiological implications of deficiency and/or overabundance of these E2/ER-mediated mitochondrial effects in stimulation of cell proliferation, inhibition of apoptosis, E2-mediated cardiovascular and neuroprotective effects in target cells are also discussed.