Non-tumorigenic Human Breast Epithelial Cells Research Articles

ERβ shifts from mitochondria to nucleus during estrogen-induced neoplastic transformation of human breast epithelial cells and is involved in estrogen-induced synthesis of mitochondrial respiratory chain proteins

Both estrogen receptors (ER) alpha (ERα) and beta (ERβ) are localized in the nucleus, plasma membrane, and mitochondria, where they mediate the different physiological effects of estrogens. It has been observed that the relative subcellular localization of ERs is altered in several cancer cells. We have demonstrated that MCF-10F cells, the immortal and non-tumorigenic human breast epithelial cells (HBEC) that are ERα-negative and ERβ-positive, are transformed in vitro by 17β-estradiol (E 2), generating highly invasive cells that are tumorigenic in severe combined immunodeficient mice. E 2-transformed MCF-10F (trMCF) cells exhibit progressive loss of ductulogenesis, invasive (bsMCF) and tumorigenic (caMCF) phenotypes. Immunolocalization of ERβ by confocal fluorescent microscopy and electron microscopy revealed that ERβ is predominantly localized in mitochondria of MCF-10F and trMCF cells. Silencing ERβ expression with ERβ-specific small interference RNA (siRNA-ERβ) markedly diminishes both nuclear and mitochondrial ERβ in MCF-10F cells. The ERβ shifts from its predominant localization in the mitochondria of MCF-10F and trMCF cells to the nucleus of bsMCF cells, becoming predominantly nuclear in caMCF cells. Furthermore, we demonstrated that the mitochondrial ERβ in MCF-10F cells is involved in E 2-induced expression of mitochondrial DNA (mtDNA)-encoded respiratory chain (MRC) proteins. This is the first report of an association of changes in the subcellular localization of ERβ with various stages of E 2-induced transformation of HBEC and a functional role of mitochondrial ERβ in mediating E 2-induced MRC protein synthesis. Our findings provide a new insight into one of the potential roles of ERβ in human breast cancer.

Physiologic estrogen receptor alpha signaling in non-tumorigenic human mammary epithelial cells

Currently, a number of breast cancer cell lines exist that serve as models for both estrogen receptor alpha (ERalpha) positive and ERalpha negative disease. Models are also available for pre-neoplastic breast epithelial cells that do not express ERalpha; however, there are no ideal systems for studying pre-neoplastic cells that are ERalpha positive. This has been largely due to the inability to establish an estrogen growth stimulated, non-tumorigenic breast epithelial cell line, as most human breast epithelial cells engineered to overexpress ERalpha have been found to be growth inhibited by estrogens. We have developed independently derived clones from the non-cancerous MCF-10A human breast cell line that express ERalpha and are growth stimulated by 17-beta-estradiol (E2) in the absence of epidermal growth factor (EGF), a cytokine normally required for MCF-10A cell proliferation. This effect is blocked by the selective estrogen receptor modulator (SERM), Tamoxifen and the selective estrogen receptor downregulator, ICI 182,780 (Faslodex, Fulvestrant). Exposure of these cells to EGF and E2 results in a growth inhibitory phenotype similar to previous reports. These data present a reconciling explanation for the previously described paradoxical effects of ERalpha overexpression, and provide a model for examining the carcinogenic effects of estrogens in non-tumorigenic human breast epithelial cells.

Camptothecin Induces Nuclear Export of Prohibitin Preferentially in Transformed Cells through a CRM-1-dependent Mechanism

Prohibitin is a growth-suppressive protein that has multiple functions in the nucleus and the mitochondria. Our earlier studies had shown that prohibitin represses the activity of E2F transcription factors while enhancing p53-mediated transcription. At the same time, prohibitin has been implicated in mediating the proper folding of mitochondrial proteins. We had found that treatment of cells with camptothecin, a topoisomerase 1 inhibitor, led to the export of prohibitin and p53 from the nucleus to the mitochondria. Here we show that the camptothecin-induced export of prohibitin occurs preferentially in transformed cell lines, but not in untransformed or primary cells. Cells that did not display the translocation of prohibitin were refractive to the apoptotic effects of camptothecin. The translocation was mediated by a putative nuclear export signal at the C-terminal region of prohibitin; fusion of the nuclear export signal (NES) of prohibitin to green fluorescence protein led to its export from the nucleus. Leptomycin B could inhibit the nuclear export of prohibitin showing that it was a CRM-1-dependent event driven by Ran GTPase. Confirming this, prohibitin was found to physically interact with CRM-1, and this interaction was significantly higher in transformed cells. Delivery of a peptide corresponding to the NES of prohibitin prevented the export of prohibitin to cytoplasm and protected cells from apoptosis. These results suggest that the regulated translocation of prohibitin from the nucleus to the mitochondria facilitates its pleiotropic functions and might contribute to its anti-proliferative and tumor suppressive properties.

Plasma membrane calcium-ATPase 2 and 4 in human breast cancer cell lines

There is evidence to suggest that plasma membrane Ca 2+-ATPase (PMCA) isoforms are important mediators sssof mammary gland physiology. PMCA2 in particular is upregulated extensively during lactation. Expression of other isoforms such as PMCA4 may influence mammary gland epithelial cell proliferation and aberrant regulation of PMCA isoform expression may lead or contribute to mammary gland pathophysiology in the form of breast cancers. To explore whether PMCA2 and PMCA4 expression may be deregulated in breast cancer, we compared mRNA expression of these PMCA isoforms in tumorigenic and non-tumorigenic human breast epithelial cell lines using real time RT-PCR. PMCA2 mRNA has a higher level of expression in some breast cancer cell lines and is overexpressed more than 100-fold in ZR-75-1 cells, compared to non-tumorigenic 184B5 cells. Although differences in PMCA4 mRNA levels were observed between breast cell lines, they were not of the magnitude observed for PMCA2. We conclude that PMCA2 mRNA can be highly overexpressed in some breast cancer cells. The significance of PMCA2 overexpression on tumorigenicity and its possible correlation with other properties such as invasiveness requires further study.

Chemoprevention of mammary carcinogenesis by 1α-hydroxyvitamin D 5, a synthetic analog of Vitamin D

Numerous analogs of Vitamin D have been synthesized in recent years with the hope of generating a compound that retains the anticarcinogenic activity of Vitamin D without causing any toxicity. We synthesized such an analog, 1α-hydroxy-24-ethylcholecalciferol [1α-hydroxyvitamin D 5 or 1α(OH)D 5], and showed that it was tolerated by rats and mice at a much higher dose than 1α,25 dihydroxy cholecalciferol [1α,25(OH) 2D 3]. This property makes it a prime candidate for chemoprevention studies. In the mouse mammary gland organ culture (MMOC), 1α(OH)D 5 inhibited carcinogen-induced development of both mammary alveolar and ductal lesions. In vivo carcinogenesis study showed statistically significant reduction of tumor incidence and multiplicity in N-methyl- N-nitrosourea (MNU)-treated rats that were fed 25–50 μg 1α(OH)D 5/kg diet. There were no adverse effects on plasma calcium concentrations. In order to determine if the effect of 1α(OH)D 5 would be selective in suppressing proliferation of transformed cells, its effects on cell growth and proliferation were compared between BT474 (cancer) and MCF12F (non-tumorigenic) human breast epithelial cells. Results showed that 1α(OH)D 5 induced apoptosis and cell cycle G1 phase arrest in BT474 breast cancer cells without having any effects on proliferation of the MCF12F cells. In addition, in MMOC it had no growth inhibitory effects on normal epithelial cell proliferation in the absence of carcinogen. Similarly, non-tumorigenic human breast epithelial cells in explant culture did not respond to 1α(OH)D 5, whereas treatment with 1α(OH)D 5 induced cell death in the explants of cancer tissue. These results collectively indicate that 1α(OH)D 5 selectively induced apoptosis only in transformed cells but not in normal breast epithelial cells. Interestingly, the growth inhibitory effects of 1α(OH)D 5 were observed in Vitamin D receptor positive (VDR +) breast cancer cells, but not in highly metastatic VDR − breast cancer cells, such as MDA-MB-435 and MDA-MB-231, suggesting that 1α(OH)D 5 action may be mediated, in part, by VDR.

Correlation between cell cycle regulators and the immortalization and transformation of human breast epithelial cell lines.

Cellular proliferation, essential for normal development, may result in neoplastic growth when the cell cycle clock is disrupted. In order to determine whether the protein expression of cell cycle regulators differs among normal, immortalized non-tumorigenic and malignant human breast epithelial cells (HBECs), we analyzed the protein expression of cyclins D1, D3, A and E, cyclin-dependent kinase (cdk) 4 and c-fos in exponentially growing MCF-10M, MCF-10F, and MCF-7 cells. The tumorigenicity of HBECs in vivo correlated with both cell cycle regulators and early-gene protein expression in vitro. The differential expression of cyclin E- and cyclin A-related proteins and their putative relevance in the tumorigenic properties of HBECs are also discussed.

Molecular cytogenetic analysis of a nontumorigenic human breast epithelial cell line that eventually turns tumorigenic: Validation of an analytical approach combining karyotyping, comparative genomic hybridization, chromosome painting, and single-locus fluorescence in situ hybridization

The immortalized, nontumorigenic human breast epithelial cell line HMT-3522 has been used as a model for premalignant and, eventually, malignant development. During cultivation, the karyotype evolution was followed. At an early stage, a very long constant phase showed a near-diploid karyotype, with only five marker chromosomes. DNA from this phase was used for comparative genomic hybridization (CGH) analysis, confirming a previously known MYC amplification, and the integration sites were subsequently determined by single-locus fluorescence in situ hybridization (FISH). Furthermore, gains of 5q22-qter and 20q11-qter and deletion of most of chromosome 6 (6p23-qter) were detected by CGH. Because of uncertainty about some of the indicated changes, including a deletion of Ip35-pter, the CGH findings were investigated more closely by chromosome painting, leading to a revision of the karyotype: 45,XX,del(I)(p35),-6,dup(8)(pter-->qter::qter-->q24),der(12) t(6;12)(p23; p13),der(14)t(5;14)(q22;q32.3),der(17)t(8;17;20)(17pter-->17q25 ::8qter--> 8q23::8q24-->8qter::8q24-->8qter:: 8q23-->8q24.1::20q11-->20qter). Some karyotypic changes were confirmed by CGH; others had to be revised; and, in the Ip35 region, classical cytogenetics seems superior to CGH. However, CGH revealed a karyotypically unsuspected dup(20q) that might be of special relevance to breast tumor initiation or progression. Our study confirms that CGH is supplementary to current technologies, e.g., karyotyping and Southern analysis, but cannot replace them. In addition, our cell line turned out to be an excellent model for comparison among the different methods. The results imply that future cytogenetic analyses of complex karyotypes should be based on a combination of karyotyping, CGH, and FISH.

Molecular cytogenetic analysis of a nontumorigenic human breast epithelial cell line that eventually turns tumorigenic: Validation of an analytical approach combining karyotyping, comparative genomic hybridization, chromosome painting, and single‐locus fluorescence in situ hybridization

Molecular cytogenetic analysis of a nontumorigenic human breast epithelial cell line that eventually turns tumorigenic: Validation of an analytical approach combining karyotyping, comparative genomic hybridization, chromosome painting, and single‐locus fluorescence in situ hybridization

Coexpression of CD44 variant (v10/ex14) and CD44S in human mammary epithelial cells promotes tumorigenesis.

CD44 is the major hyaluronan cell surface receptor and functions as an adhesion molecule in many different cell types, including human breast epithelial cells. The coexpression of certain CD44 variants (CD44v), such as CD44v (v10/ex14), with CD44s (standard form) appears to be closely associated with human breast tumor metastasis. In this study we have established a stable transfection of CD44v (v10/ex14) cDNA into nontumorigenic human breast epithelial cells (HBL100) which contain endogenous CD44s. Our results indicate that coexpression of both CD44v (v10/ex14) and CD44s alters the following important biological properties of these cells: 1) there is a significant reduction in hyaluronic acid (HA)-mediated cell adhesion; 2) there is an increased migration capability in collagen-matrix gel; and 3) these cells constitutively produce certain angiogenic factors and effectively promote tumorigenesis in athymic nude mice. These findings suggest that coexpression of CD44v (v10/ex14) and CD44s may trigger the onset of cell transformation required for breast cancer development.

Characterization of a nontumorigenic human breast epithelial cell line stably transfected with the human estrogen receptor (ER) cDNA

Estrogens play an important role in breast cancer and the effect of estrogen on growth of breast cancer cells has been extensively studied. However, only little information is available about the response of normal breast epithelial cells to estrogen, mainly due to the difficulties in establishing estrogen receptor (ER)-positive human breast epithelial cells in culture. We have stably transfected the human estrogen receptor (hER) wt cDNA into the ER-negative, spontaneously immortalized human breast epithelial cell line, HMT-3522S1, in order to develop a model for studying the effect of estrogen on nonmalignant human breast epithelial cells. Characterization of the transfected clone F9 confirmed incorporation of the estrogen receptor gene in the genome, expression of hER mRNA and hER protein. However, proliferation of F9 cells was inhibited by both estradiol (E 2) and tamoxifen, whereas the pure antiestrogen ICI 182,780 had no effect on cell proliferation. This seems paradoxical since E 2 stimulated the expression of the endogenous genes, TGF-α, cathepsin D, and α 1-antitrypsin. In breast cancer cell lines, high expression of these genes is correlated to estrogen-stimulated cell proliferation. The spontaneously immortalized HMT-3522S1 cells transfected with wt ER cDNA behave similarly to cell lines from nonmalignant breast tissue immortalized by carcinogens and transfected with mutated ER cDNA as described by others. The discrepancy between growth inhibition and induction of positive growth factors by E 2 indicates that either ER-positive nonmalignant breast epithelial cells are growth-inhibited by E 2 in contrast to malignant cells or that introduction of the ER into ER-negative cells is not sufficient for restoring ‘normal’ estrogen responsiveness.

In vitro karyotype evolution and cytogenetic instability in the non-tumorigenic human breast epithelial cell line HMT-3522

The “spontaneously” immortalized cell line HMT-3522, derived from a fibrocystic breast lesion, is used as a model for premalignant breast epithelium. During 205 passages the cytogenetic evolution was followed. The results were compared with our earlier results on oncogene expression and growth factor requirements. During in vitro growth, gain and loss of markers, loss of normal chromosomes, and duplication of the chromosome complement could be demonstrated. The variability increased during in vitro growth, This variability, probably created randomly, leads to cells with different growth capacities, from which sidelines may be selected and become stemlines. The karyotypic evolution (including polyploidization) demonstrated here may be a result of genetic instability and heterogeneity. Although tumorigenicity was not achieved, either due to lack of cancer-specific gene alterations or to lack of proper selection pressure, the results suggest an ongoing process towards malignancy.

A new diploid nontumorigenic human breast epithelial cell line isolated and propagated in chemically defined medium.

A new, nontumorigenic human breast epithelial cell line, HMT-3522, has been established from fibrocystic breast tissue. Cells were explanted and propagated in chemically defined medium including insulin, transferrin, epidermal growth factor, hydrocortisone, estradiol, prolactin, and Na-selenite. The epithelial nature of the cell line was established by immunocytochemical detection of cytokeratins. Moreover, electronmicroscopy revealed monolayers of polarized cells connected by desmosomes and provided with apical microvilli. Milk fat globule membrane antigen, specific for the apical membrane domain of normal, luminal breast epithelial cells, was expressed only in confluent cultures where some cells overlaid others, indicating "stem cell"-like properties. After 25 to 30 passages, the cells are diploid with a few marker chromosomes and loss of chromosomes in the D-group. The cells are nontumorigenic in athymic mice; they lack estrogen receptors, and estradiol does not stimulate growth. The HMT-3522 cell line may represent a useful model for the study of breast cell differentiation and carcinogenesis in vitro.