Electromagnetic fields alter the expression of estrogen receptor cofactors in breast cancer cells

Breast cancer is the most common malignancy of women in Western societies. The increasing exposure to electromagnetic fields has been suspected to contribute to the rising incidence of breast cancer in industrialized countries. The majority of breast tumors is treated with the partial antiestrogen tamoxifen. Most tumors become resistant to tamoxifen in the course of treatment resulting in treatment failure. Electromagnetic fields reduce the efficacy of tamoxifen similar to tamoxifen resistance. In this study we investigated the mechanism by which electromagnetic fields influence the sensitivity to tamoxifen. In cells exposed to 1.2 microT of a 50 Hz electromagnetic field gene expression of cofactors of the estrogen receptors was compared to sham exposed cells. Using a gene array technology several cofactors were found to be differentially expressed. The expression of the coactivators, SRC-1 and AIB1, and of two corepressors, N-Cor and SMRT, was quantified by RT-PCR. Both coactivators were expressed more strongly in the exposed cells while the expression of two corepressors decreased. The RNA analysis was confirmed by Western blots. The contradirectional changes in gene expression of coactivators and corepressors by electromagnetic fields results in a lower sensitivity to tamoxifen. Electromagnetic fields may contribute to the induction of tamoxifen resistance in vivo.     

Identification of eight genes that are potentially involved in tamoxifen sensitivity in breast cancer cells

Although the antiestrogen agent tamoxifen has long been used to treat women with hormone receptor positive invasive breast carcinoma, the mechanisms of its action and acquired resistance to tamoxifen during treatment are largely unknown. A number of studies have revealed that over-activation of some signaling pathways can cause tamoxifen resistance; however, very little information is available regarding the genes whose loss-of-function alternation contribute to tamoxifen resistance. Here we used a forward genetic approach in vitro to generate tamoxifen resistant cells from the tamoxifen sensitive breast cancer cell line ZR-75-1, and further identified the disrupted gene in different tamoxifen resistant clones. Retinol binding protein 7, DNA polymerase-transactivated protein 3, γ-glutamyltransferase-like activity 1,slit-robo RhoGTPase-activating protein, tetraspan NET-4, HSPC194, amiloride-sensitive epithelial sodium channel gene,and Notch2, were the eight mutated genes identified in different tamoxifen resistant clones, suggesting their requirement for tamoxifen sensitivity in ZR-75-1 cells. Since the functions of these genes are not related to each other, it suggests that multiple pathways can influence tamoxifen sensitivity in breast cancer ceils.     

Novel markers of gene methylation and expression in breast cancer

An optimized methylation-sensitive restriction fingerprinting technique was used to search for differentially methylated CpG islands in the tumor genome and detected seven genes subject to abnormal epigenetic regulation in breast cancer: SEMA6B, BIN1, VCPIP1, LAMC3, KCNH2, CACNG4, and PSMF1. For each gene, the rate of promoter methylation and changes in expression were estimated in tumor and morphologically intact paired specimens of breast tissue (N = 100). Significant methylation rates of 38, 18, and 8% were found for SEMA6B, BIN1, and LAMC3, respectively. The genes were not methylated in morphologically intact breast tissue. The expression of SEMA6B, BIN1, VCPIP1, LAMC3, KCNH2, CACNG4, and PSMF1 was decreased in 44–94% of tumor specimens by the real-time RT-PCR assay. The most profound changes in SEMA6B and LAMC3 suggest that these genes can be included in biomarker panels for breast cancer diagnosis. Fine methylation mapping of the most frequently methylated CpG islands (SEMA6B, BIN1, and LAMC3) provides a fundamental basis for developing efficient methylation tests for these genes.     

Twist对小鼠乳腺癌细胞基因表达谱的调控研究

摘要 Twist是一个bHLH（basic Helix-loop-Helix）类型的转录因子,近年来研究发现,Twist在乳腺癌中的表达显著升高,并能促进乳腺癌的转移。为了探索Twist促进乳腺癌转移的分子机制,本文采用RNA干扰技术在小鼠乳腺癌细胞株4T1中沉默Twist的表达,通过全基因组基因芯片技术检测了Twist沉默前后4T1细胞基因表达谱的差异性。体内实验结果证明Twist表达被沉默后4T1细胞的肺转移能力明显被抑制。芯片结果表明：表达差异显著的基因有167条,其中与肿瘤相关的基因有26条,包括15条上调基因和11条下调基因。这些基因中可能存在能被Twist调控并与肿瘤转移相关的基因,为以后研究Twist影响乳腺癌转移的分子机制提供了帮助。     

Regulatory mechanisms for abnormal expression of the human breast cancer specific gene 1 in breast cancer cells

Breast cancer specific gene 1, also referred as synu-clein γ, was originally isolated from a human breasttumor cDNA library[1]. It reveals extensive sequencehomology to a family of neuronal cytosolic proteins,synuclein α and synuclein β[2,3]. Synuclein…     

Systemic identification of estrogen-regulated genes in breast cancer cells through cap analysis of gene expression mapping

To explore the estrogen-regulated genes genome-widely in breast cancer, cap analysis of gene expression (CAGE) sequencing was performed in MCF-7 cells under estrogen treatment. Estrogen-regulated expressional changes were found in 1537 CAGE tag clusters (TCs) (?1.5 or ?0.66-folds). Among them, 15 TCs were situated in the vicinity of (?10 kb) reported estrogen receptor-binding sites. Knockdown experiments of the 15 TC-associated genes demonstrated that the genes such as RAMP3, ISOC1 and GPRC5C potentially regulate the growth or migration of MCF-7 cells. These results suggest that CAGE sequencing will reveal novel estrogen target genes in breast cancer.     

An epigenomic approach to therapy for tamoxifen-resistant breast cancer

Tamoxifen has been a frontline treatment for estrogen receptor alpha (ERα)-positive breast tumors in premenopausal women. However, resistance to tamoxifen occurs in many patients. ER still plays a critical role in the growth of breast cancer cells with acquired tamoxifen resistance, suggesting that ERα remains a valid target for treatment of tamoxifen-resistant (Tam-R) breast cancer. In an effort to identify novel regulators of ERα signaling, through a small-scale siRNA screen against histone methyl modifiers, we found WHSC1, a histone H3K36 methyltransferase, as a positive regulator of ERα signaling in breast cancer cells. We demonstrated that WHSC1 is recruited to the ERα gene by the BET protein BRD3/4, and facilitates ERα gene expression. The small-molecule BET protein inhibitor JQ1 potently suppressed the classic ERα signaling pathway and the growth of Tam-R breast cancer cells in culture. Using a Tam-R breast cancer xenograft mouse model, we demonstrated in vivo anti-breast cancer activity by JQ1 and a strong long-lasting effect of combination therapy with JQ1 and the ER degrader fulvestrant. Taken together, we provide evidence that the epigenomic proteins BRD3/4 and WHSC1 are essential regulators of estrogen receptor signaling and are novel therapeutic targets for treatment of Tam-R breast cancer.     

Tamoxifen induces TGF-β1 activity and apoptosis of human MCF-7 breast cancer cells in vitro

We report here that the antiestrogen tamoxifen (TAM) induces cell death in human breast cancer cell line MCF-7. We assessed the type of cell death induced by TAM in this breast cancer cell line on the basis of morphological and biochemical characteristics. Dying cells showed morphological characteristics of apoptosis, such as chromatin condensation and nuclear disintegration. DNA isolated from these cells revealed a pattern of distinctive DNA bands on agarose gel. The DNA fragmentation in MCF-7 cells induced by TAM could also be detected by terminal deoxynucleotidyl transferase-mediated dUTP-biotin end labeling. Northern blot hybridization revealed a substantial increase in the amounts of TRPM-2 and TGF-β1 mRNAs in MCF-7 cells after treatment with TAM. In contrast, the mRNA level of the estrogen-induced pS2 gene was strongly suppressed. The biological activity of TGF-β was increased at least fourfold in the media from MCF-7 cells treated with TAM. The results presented in this study suggest that TAM induces apoptosis of MCF-7 cells and it may be mediated by the secretion of active TGF-β. © 1996 Wiley-Liss, Inc.     

Tamoxifen therapy benefit predictive signature combining with prognostic signature in surgical-only ER-positive breast cancer

Tamoxifen treatment is important assistant for estrogen-receptor-positive breast cancer (BRCA) after resection. This study aimed to identify signatures for predicting the prognosis of patients with BRCA after tamoxifen treatment. Data of gene-specific DNA methylation (DM), as well as the corresponding clinical data for the patients with BRCA, were obtained from The Cancer Genome Atlas and followed by systematic bioinformatics analyses. After mapping these DM CPG sites onto genes, we finally obtained 352 relapse-free survival (RFS) associated DM genes, with which 61,776 gene pairs were combined, including 1,614 gene pairs related to RFS. An 11 gene-pair signature was identified to cluster the 189 patients with BRCA into the surgical low-risk group (136 patients) and high-risk group (53 patients). Then, we further identified a tamoxifen-predictive signature that could classify surgical high-risk patients with significant differences on RFS. Combining surgical-only prognostic signature and tamoxifen-predictive signature, patients were clustered into surgical-only low-risk group, tamoxifen nonbenefit group, and tamoxifen benefit group. In conclusion, we identified that the gene pair PDHA2–APRT could serve as a potential prognostic biomarker for patients with BRCA after tamoxifen treatment.     

Signal transduction of the melatonin receptor MT1 is disrupted in breast cancer cells by electromagnetic fields

The growth of estrogen‐receptor positive breast cancer cells is inhibited by the pineal gland hormone, melatonin. Concern has been raised that power‐line frequency and microwave electromagnetic fields (EMFs) could reduce the efficiency of melatonin on breast cancer cells. In this study we investigated the impact of EMFs on the signal transduction of the high‐affinity receptor MT1 in parental MCF‐7 cells and MCF‐7 cells transfected with the MT1 gene. The binding of the cAMP‐responsive element binding (CREB) protein to a promoter sequence of BRCA‐1 after stimulation with melatonin was analyzed by a gel‐shift assay and the expression of four estrogen‐responsive genes was measured in sham‐exposed breast cancer cells and cells exposed to a sinusoidal 50 Hz EMF of 1.2 µT for 48 h. In sham‐exposed cells, binding of CREB to the promoter of BRCA‐1 was increased by estradiol and subsequently diminished by treatment with melatonin. In cells exposed to 1.2 µT, 50 Hz EMF, binding of CREB was almost completely omitted. Expression of BRCA‐1, p53, p21^WAF, and c‐myc was increased by estradiol stimulation and subsequently decreased by melatonin treatment in both cell lines, except for p53 expression in the transfected cell line, thereby proving the antiestrogenic effect of melatonin at molecular level. In contrast, in breast cancer cells transfected with MT1 exposed to 1.2 µT of the 50 Hz EMF, the expression of p53 and c‐myc increased significantly after melatonin treatment but for p21^WAF the increase was not significant. These results convincingly prove the negative effect of EMF on the antiestrogenic effect of melatonin in breast cancer cells. Bioelectromagnetics 31:237–245, 2010. © 2009 Wiley‐Liss, Inc.     

共济失调毛细血管扩张症致病基因与乳腺癌易感性

乳腺癌是与环境因素密切相关的肿瘤之一,致癌因素诱发的DNA损伤信号被传送到多个效应因子,最终导致细胞坏死和癌变。其中,共济失调性毛细血管扩张症致病基因(Ataxia-telangiectasia mutated,ATM)编码的ATM蛋白激酶是DNA损伤应答的主要调控因子,其通过磷酸化一系列下游底物来应对DNA损伤,这在抑制乳腺癌的发生发展中起到了重要的作用。ATM基因突变后,导致损伤DNA不能得到正确修复,最终加速了乳腺癌的转化和增殖。随着对ATM基因结构、功能及乳腺癌易感性机制研究的深入,ATM基因与乳腺癌易感性关系已引起广泛的重视。以下就ATM基因突变、多态性和甲基化等几个方面与乳腺癌易感性的关系进行了简要概述。     

Induction of GPR40 positively regulates cell motile and growth activities in breast cancer MCF-7 cells

Abstract

Free fatty acid (FFA) receptors belong to a member of G-protein-coupled receptors. GPCR 120 (GPR120) and GPR40 are identified as FFA receptors and activated via the binding of long- and medium-chain FFAs. The aim of this study was to assess the effects of GPR120 and GPR40 on cell motility and growth in breast cancer cells treated with tamoxifen (TAM). MCF-7 cells were continuously treated with TAM for approximately 6?months. The expression level of GPR40 gene was markedly higher in the long-term TAM treated (MCF-TAM) cells than in MCF-7 cells. In cell motility assay, MCF-TAM cells indicated the high cell motile activity, compared with MCF-7 cells. The cell motile activity of MCF-TAM cells was suppressed by a selective GPR40 antagonist, GW1100. To evaluate the effects of GPR40 on cell growth activity under estrogen-free conditions, cells were maintained in serum-free DMEM without phenol red for 2?days. In estrogen-free conditioned medium, the cell growth rate of MCF-TAM cells was significantly higher than that of MCF-7 cells. In addition, treatment of GW1100 reduced the cell growth rate of MCF-TAM cells. These results suggest that the cell motile and growth activities may be positively regulated through the induction of GPR40 by the long-term TAM treatment in MCF-7 cells.     

Network-based approach to identify prognosis-related genes in tamoxifen-treated patients with estrogen receptor-positive breast cancer

Tamoxifen is an estrogen receptor (ER) antagonist that is most commonly used for the treatment of ER-positive breast cancer. However, tamoxifen resistance remains a major cause of cancer recurrence and progression. Here, we aimed to identify hub genes implicated in the progression and prognosis of ER-positive breast cancer following tamoxifen treatment. Microarray data ({"type":"entrez-geo","attrs":{"text":"GSE9893","term_id":"9893"}}GSE9893) for 155 tamoxifen-treated primary ER-positive breast cancer samples were obtained from the Gene Expression Omnibus database. In total, 1706 differentially expressed genes (DEGs), including 859 up-regulated and 847 down-regulated genes, were identified between relapse and relapse-free samples. Weighted correlation network analysis clustered genes into 13 modules, among which the tan and blue modules were the most significantly related to prognosis. From these two modules, we further identified and validated two prognosis-related hub genes (G-rich RNA sequence binding factor 1 (GRSF1) and microtubule-associated protein τ (MAPT)) via survival analysis based on several publicly available datasets. High expression of GRSF1 predicted poor prognosis, whereas MAPT indicated favorable outcomes in ER-positive breast cancer. Using breast cancer cell lines and tissue samples, we confirmed that GRSF1 was significantly up-regulated and MAPT was down-regulated in the tamoxifen-resistant group compared with the tamoxifen-sensitive group. The prognostic value of GRSF1 and MAPT was also verified in 48 tamoxifen-treated ER-positive breast cancer patients in our hospital. Gene set enrichment analysis (GSEA) suggested that GRSF1 was potentially involved in RNA degradation and cell cycle pathways, while MAPT was strongly linked to immune-related signaling pathways. Taken together, our findings established novel prognostic biomarkers to predict tamoxifen sensitivity, which may facilitate individualized management of breast cancer.