High susceptibility of a human breast epithelial cell type with stem cell characteristics to telomerase activation and immortalization

We have recently characterized two types of normal human breast epithelial cells (HBECs) from reduction mammoplasty. Type I cells express estrogen receptor, luminal epithelial cell markers, and stem cell characteristics (i.e., the ability to differentiate into other cell types and to form budding/ductal structures on Matrigel), whereas Type II cells show basal epithelial cell phenotypes. In this study, we have examined whether Type I HBECs are more susceptible to telomerase activation and immortalization after transfection with SV40 large T-antigen. The results show that both types of cells acquire extended life span [(EL); i.e., bypassing senescence] at a comparable frequency. However, they differ significantly in the ability to become immortal in continuous culture, ie., 11 of 11 Type I EL clones became immortal compared with 1 of 10 Type II EL clones. Both parental Type I and Type II cells as well as their transformed EL clones at early passages [approximately 30 cumulative population doubling level (cpdl)] showed a low level of telomerase activity as measured by the telomeric repeat amplification protocol assay. For all 11 of the Type I EL clones and the single Type II EL clone that became immortal, telomerase activities were invariably activated at middle passages (approximately 60 cpdl) or late passages (approximately 100 cpdl). For the four Type II EL clones randomly selected from the nine Type II clones that did not become immortal, the telomerase activities were found to be further diminished at mid-passage, before the end of the life span. Thus, normal HBECs do have a low level of telomerase activity, and Type I HBECs with stem cell characteristics are more susceptible to telomerase activation and immortalization, a basis on which they may be major target cells for breast carcinogenesis.     

端粒酶永生化原始乳腺癌组织来源细胞及其意义

背景与目的：乳腺癌细胞系大部分来源于乳腺癌转移所致的胸水或非原始乳腺癌组织来源，与真正的乳腺癌的生物学性状有很大差异。而仅部分细胞系直接由乳腺癌原代细胞在体外培养条件下成为永生化的细胞系，过表达人端粒酶逆转录酶（hTERT）可使正常人上皮细胞永生化。本研究将通过hTERT转染人原始乳腺癌组织来源的细胞建立永生化乳腺癌细胞系，并研究过表达hTERT对其他基因表达的影响。方法：通过重组逆转录病毒pBABE-hTERT-puro将hTERT基因导人原始乳腺癌组织来源的细胞，建立稳定表达hTERT的永生乳腺癌细胞。再利用微阵列技术检测乳腺癌细胞中hTERT诱导的基因表达改变。结果：Real-TimeRT-PCR证实hTERT转染后的乳腺癌细胞中hTERT过度并稳定表达，为转染前表达量的1400倍以上，并使得被转染的细胞永生化，可以传40～50代以上。微阵列结果进一步证实hTERT在转染后的细胞中过表达，另外，有22个基因在转染后的乳腺癌细胞中上调，未观察到所有细胞株中均下调的基因。结论：过表达hTERT可导致乳腺癌原代细胞的永生化，并对部分基因有上调作用。     

Expression of estrogen receptors in a normal human breast epithelial cell type with luminal and stem cell characteristics and its neoplastically transformed cell lines

Although approximately two-thirds of breast cancers are estrogen receptor (ER)-positive, only a small proportion of epithelial cells in the mammary gland express the ER. The origin of the ER-positive breast cancers is unknown. Recently, we have developed a culture method to grow two morphologically and antigenically distinguishable types of normal human breast epithelial cells (HBEC) derived from reduction mammoplasty. In this report, we studied the expression of ER in these two types of cells and their transformed cell lines. The results indicate that Type I HBEC with luminal and stem cell characteristics expressed a variant ER (approximately 48 kd) by Western blot analysis. This variant ER contains a deletion in the DNA binding domain (exon 2) as revealed by RT-PCR analysis. The lack of the DNA-binding domain of the variant ER was also confirmed by the ER-estrogen responsive element binding assay, as well as by the immunofluorescence staining of the ER using anti-ER antibodies which recognize either the C-terminal or N- terminal region. In contrast, Type II HBEC with basal epithelial phenotype are ER-negative. Simian virus 40 (SV40) transformed Type I and Type II HBEC lines also expressed the variant ER. Tumors formed in athymic nude mice by in vitro transformed tumorigenic Type I cell lines, however, expressed a high level of wild type ER which was undetectable in these cells grown in vitro before and after tumor formation. Thus, there appears to be a differential ER mRNA splicing between the in vitro and in vivo mileu.      

Expression profiling of purified normal human luminal and myoepithelial breast cells: identification of novel prognostic markers for breast cancer

The normal duct-lobular system of the breast is lined by two epithelial cell types, inner luminal secretory cells and outer contractile myoepithelial cells. We have generated comprehensive expression profiles of the two normal cell types, using immunomagnetic cell separation and gene expression microarray analysis. The cell-type specificity was confirmed at the protein level by immunohistochemistry in normal breast tissue. New prognostic markers for survival were identified when the luminal- and myoepithelial-specific molecules were evaluated on breast tumor tissue microarrays. Nuclear expression of luminal epithelial marker galectin 3 correlated with a shorter overall survival in these patients, and the expression of SPARC (osteonectin), a myoepithelial marker, was an independent marker of poor prognosis in breast cancers as a whole. These data provide a framework for the interpretation of breast cancer molecular profiling experiments, the identification of potential new diagnostic markers, and development of novel indicators of prognosis.     

Oxidative stress pathways highlighted in tumor cell immortalization: association with breast cancer outcome

An improved understanding of cell immortalization and its manifestation in clinical tumors could facilitate novel therapeutic approaches. However, only rare tumor cells, which maintain telomerase expression in vitro, immortalize spontaneously. By expression-profiling analyses of limited-life primary breast tumor cultures pre- and post-hTERT transduction, and spontaneously immortalized breast cancer cell lines, we identified a common signature characteristic of tumor cell immortalization. A predominant feature of this immortalization signature (ImmSig) was the significant overexpression of oxidoreductase genes. In contrast to epithelial cells derived from low histologic grade primary tumors, which required hTERT transduction for the acquisition of ImmSig, spontaneously immortalizing high-grade tumor cultures displayed similar molecular changes independent of exogenous hTERT. Silencing the hTERT gene reversed ImmSig expression, increased cellular reactive oxygen species levels, altered mitochondrial membrane potential and induced apoptotic and proliferation changes in immortalized cells. In clinical breast cancer samples, cell-proliferation-pathway genes were significantly associated with ImmSig. In these cases, ImmSig expression itself was inversely correlated with patient survival (P=0), and was particularly relevant to the outcome of estrogen receptor-positive tumors. Our data support the notion that ImmSig assists in surmounting normal barriers related to oxidative and replicative stress response. Targeting a subset of aggressive breast cancers by reversing ImmSig components could be a practical therapeutic strategy.     

维生素D调控Wnt/β-catenin信号通路抑制乳腺癌干细胞活性

目的 探讨维生素D对乳腺癌干细胞活性的影响及其可能的作用机制。方法 采用MTT法检测不同浓度（1 μmol/L、5 μmol/L、10 μmol/L和20 μmol/L）维生素D对乳腺癌SUM159细胞活力的影响,用无血清培养基悬浮培养富集乳腺癌干细胞CSCSUM159,分析维生素D对乳腺癌干细胞活性的影响。Western blot和Real-time qPCR 分别检测乳腺癌干细胞标志物CD133、CD44、Oct-4、Nanog以及Wnt/β-catenin信号通路相关分子p-GSK-3β、β-catenin、c-Myc和cyclin-D1的表达。结果 MTT法检测结果显示,1 μmol/L、5 μmol/L、10 μmol/L和20 μmol/L维生素D均可显著抑制乳腺癌SUM159细胞的活力（P＜0.01）。无血清悬浮培养可有效富集乳腺癌干细胞CSCSUM159。维生素D可使乳腺癌干细胞CSCSUM159的成球数量减少,且细胞成球大小较对照组小。Western blot和Real-time qPCR检测结果显示,维生素D干预后,乳腺癌干细胞CSCSUM159中CD133、CD44和Nanog的蛋白表达下调,Wnt/β-catenin信号通路相关分子p-GSK-3β、β-catenin和c-Myc蛋白表达及β-catenin、c-Myc和cyclin-D1 mRNA表达亦下调（P＜0.05）。结论 维生素D可抑制乳腺癌干细胞活性,可能与其调控Wnt/β-catenin信号通路活性有关。     

Gene expression profiling of breast cell lines identifies potential new basal markers

A better molecular characterization of breast cell lines (BCL) may help discover new markers to apply to tumour samples. We performed gene and protein expression profiling of 31 BCL using whole-genome DNA microarrays and immunohistochemistry (IHC) on 'cell microarrays' (CMA), respectively. Global hierarchical clustering discriminated two groups of BCL: group I corresponded to luminal cell lines, group II to basal and mesenchymal cell lines. Correlations with centroids calculated from a published 'intrinsic 500-gene set' assigned 15 cell lines as luminal, eight as basal and four as mesenchymal. A set of 1.233 genes was differentially expressed between basal and luminal samples. Mesenchymal and basal subtypes were rather similar and discriminated by only 227 genes. The expression of 10 proteins (CAV1, CD44, EGFR, MET, ETS1, GATA3, luminal cytokeratin CK19, basal cytokeratin CK5/6, CD10, and ERM protein moesin) encoded by luminal vs basal discriminator genes confirmed the subtype classification and the validity of the identified markers. Our BCL basal/luminal signature correctly re-classified the published series of tumour samples that originally served to identify the molecular subtypes, suggesting that the identified markers should be useful for tumour classification and might represent promising targets for disease management.     

THY1基因在上皮性卵巢癌组织中的表达及其意义

目的 探讨THY1基因在上皮性卵巢癌组织中的表达及其临床意义.方法 应用免疫组织化学和末端脱氧核苷酸转移酶介导缺口末端标记法(TUNEL),检测76例上皮性卵巢癌组织芯片中THY1和Ki67的蛋白表达及细胞凋亡情况,收集患者的临床病理学和生存资料.结果 在组织芯片中,64例上皮性卵巢癌组织的THY1表达得以成功检测,其中42例(65.6%)THY1蛋白表达下调.THY1蛋白表达与临床分期、远处转移有关.在THY1蛋白表达下调标本中,Ki67的抗原标记指数为33.7%±3.5%,显著高于THY1蛋白正常表达标本(17.3%±6.1%,P=0.003),而THY1蛋白表达与细胞凋亡无关(P=0.530).22例THY1正常表达患者的平均生存时间为53.9个月,42例THY1表达下调患者的平均生存时间为41.6个月,两组生存率差异无统计学意义(P=0.907).结论 上皮性卵巢癌中THY1蛋白的表达下调与肿瘤细胞的增殖和转移密切相关,可以作为临床评估上皮性卵巢癌恶性进展的分子标志物.     

Recent translational research: stem cells as the roots of breast cancer

Common phenotypes of cancer and stem cells suggest that breast cancers arise from stem cells. Breast epithelial cells with stem cell phenotypes have been shown to be more susceptible to immortalization and neoplastic transformation. Breast tumor stem cells with CD44⁺/CD24^-/lowLineage^- markers have been isolated. The role of these cells in tumor progression and clinical outcome is not clear. The relationship between breast stem cell and tumor stem cell may be elucidated by further studies of carcinogenesis of nonadherent mammosphere cells with stem cell features and by derivation of CD44⁺/CD24^-/low cells from an adherent breast epithelial stem cell type.     

Isolation and characterization of normal adult human epithelial pluripotent stem cells

Both reproductive and therapeutic cloning of human stem cells have been made possible with recent technological advances in the isolation of embryonic stem cells and of pluripotent stem cells from adult tissues. We have isolated normal human kidney and human breast epithelial stem cells, as well as having characterized "immortalized" cells from human neuronal and human pancreatic tissue (Trosko et al., Methods 20:245-264, 2000). The isolation was motivated by the stem cell theory of carcinogenesis. Based on the assumption that stem cells would not express connexin genes, nor have functional gap junctional intercellular communication (GJIC), we have demonstrated that the human kidney, breast, neuronal, and pancreatic stem cells can divide either symmetrically or asymmetrically, depending on whether they are grown in microenvironmental conditions that suppress GJIC (the undifferentiated, proliferative state) or induce GJIC (the differentiated state). Normal breast epithelial stem cells appear to be intrinsically "immortal" until induced to express GJIC, at which time, with appropriate substrate and microenvironmental nutrients, they can form three-dimensional "organoids." expressing markers associated with the mature mammary tissue and forming a physical structure very similar to the in vivo budding, ductal structures. The breast stem cells can be prevented from "mortalizing" and can be converted to neoplastic cells, which maintain many phenotypes of the stem cells.     

Luminal B型局部晚期乳腺癌新辅助化疗疗效预测基因的研究

目的 筛选Luminal B型局部晚期乳腺癌新辅助化疗疗效预测基因。方法 收集10例Luminal B型乳腺癌患者,均行DA方案新辅助化疗（多西他赛 75mg／m2静滴,d1;表阿霉素80mg／m2 静滴d1,21天为1周期,共4个周期）,根据化疗疗效分为完全病理缓解（pCR）组（n=3）和非完全病理缓解（npCR）组（n=7）。采用人基因表达谱cDNA芯片从10例乳腺癌患者中筛选新辅助化疗疗效相关基因,荧光定量PCR验证差异表达基因。结果 pCR组与npCR组癌组织相比,上调基因231个,下调基因195个;pCR组癌组织与癌旁组织相比,上调的基因357个,下调的基因544个;npCR组癌组织与癌旁组织相比,上调基因143个,下调基因101个;pCR组与npCR组癌旁组织比较,上调基因98个,下调基因67个。pCR组与npCR组癌组织比较,筛选出6个与肿瘤有关的基因,其中上调基因为CYP4Z1、FGFL6、BCAR4,下调基因为FABP4、S100B、ALPH1L1。荧光定量PCR进一步验证显示,两组mRNA表达差异的基因为CYP4Z1和BCAR4,pCR组两种基因表达均显著低于npCR组（P＜0.05）。结论 对局部晚期Luminal B型乳腺癌低表达BCAR4和CYP4Z1的患者新辅助治疗选择采用DA方案化疗更有可能获得pCR。     

Aberrant methylation and silencing of ARHI,an imprinted tumor suppressor gene in which the function is lost in breast cancers

ARHI is a maternally imprinted tumor suppressor gene that maps to a site on chromosome 1p31 where loss of heterozygosity has been observed in 40% of human breast and ovarian cancers. ARHI is expressed in normal ovarian and breast epithelial cells, but ARHI expression is lost in a majority of ovarian and breast cancers. Expression of ARHI from the paternal allele can be down-regulated by multiple mechanisms in addition to loss of heterozygosity. This article explores the role of DNA methylation in silencing ARHI expression. There are three CpG islands in the ARHI gene. CpG islands I and II are located in the promoter region, whereas CpG island III is located in the coding region. Consistent with imprinting, we have found that all three CpG islands were partially methylated in normal human breast epithelial cells. Additional confirmation of imprinting has been obtained by studying DNA methylation and ARHI expression in murine A9 cells that carry either the maternal or the paternal copy of human chromosome 1. All three CpG islands were methylated, and ARHI was not expressed in A9 cells that contained the maternal allele. Conversely, CpG islands were not methylated and ARHI was expressed in A9 cells that contained the paternal allele of human chromosome 1. Aberrant methylation was found in several breast cancer cell lines that exhibited decreased ARHI expression. Hypermethylation was detected in 67% (6 of 9) of breast cancer cell lines at CpG island I, 33% (3 of 9) at CpG island II, and 56% (5 of 9) at CpG island III. Hypomethylation was observed in 44% (4 of 9) of breast cancer cell lines at CpG island II. When methylation of CpG islands was studied in 20 surgical specimens, hypermethylation was not observed in CpG island I, but 3 of 20 cases exhibited hypermethylation in CpG island II (15%), and 4 of 20 cases had hypermethylation in CpG island III (20%). Treatment with 5-aza-2'-deoxycytidine, a methyltransferase inhibitor, could reverse aberrant hypermethylation of CpG island I, II and III and partially restore ARHI expression in some, but not all of the cell lines. Treatment with 5-aza-2'-deoxycytidine partially reactivated ARHI expression in cell lines with hypermethylation of CpG islands I and II but not in cell lines with partial methylation or hypomethylation of these CpG islands. To test the impact of CpG island methylation on ARHI promoter activity more directly, constructs were prepared with the ARHI promoter linked to a luciferase reporter and transfected into SKBr3 and human embryo kidney 293 cells. Methylation of the entire construct destroyed promoter activity. Selective methylation of CpG island II alone or in combination with CpG island I also abolished ARHI promoter activity. Methylation of CpG I alone partially inhibited promoter activity of ARHI. Thus, hypermethylation of CpG island II in the promoter region of ARHI is associated with the complete loss of ARHI expression in breast cancer cells. Other epigenetic modifications such as hypermethylation in CpG island III may also contribute to the loss of ARHI expression.     

基底样乳腺癌和管腔A 乳腺癌干祖细胞的生物学行为比较*

目的:从人基底样和管腔A 乳腺癌分离肿瘤干/祖细胞,并比较其增殖、自我更新和分化能力等生物学特点。方法:应用乳腺微球无血清悬浮培养法富集乳腺癌干/祖细胞,并通过细胞生长曲线测定和连续克隆形成实验检测了干/祖细胞在体外的增殖能力和自我更新能力,建立裸鼠移植瘤检测在体内的成瘤情况,流式细胞术检测CD44和CD24的表达水平。结果:基底样和管腔A 乳腺癌均能在无血清培养基中形成乳腺微球,基底样癌的肿瘤干细胞含量较高,并形成细胞数量多、直径大的微球,球内细胞在体内、外有更强的扩增能力。基底样癌传代过程中,细胞容易贴壁分化,传代多不超过15代;而管腔A 癌,虽然丧失克隆形成能力的悬浮单细胞明显增多,但均可传代20次以上;两者CD44和CD24的表达也有明显差异。结论:基底样乳腺癌和管腔A 乳腺癌的干/祖细胞表现出差别明显的生物学行为,乳腺癌的肿瘤干细胞可能是异质性的。      

S100P calcium-binding protein overexpression is associated with immortalization of human breast epithelial cells in vitro and early stages of breast cancer development in vivo

The mechanism of cell immortalization of human breast epithelial cells leading to neoplastic transformation is not clear. The isolation and characterization of a spontaneously immortalized human breast epithelial cell line, MCF-10F, have provided a valuable tool to identify genes involved in this process. Using the technique of differential display, we have identified seven cDNA bands differentially displayed in the MCF-10F cells when compared with the mortal S130 cells from which MCF-10F was originated. One of these bands was isolated and cloned. Sequence analysis revealed 99% homology to the EF-hand calcium-binding protein S100P (Placental). The clone was overexpressed in the immortal cell line MCF-10F when compared to the mortal counterpart S130 or other primary cultures of human breast epithelial cells. In addition, it was highly expressed in chemically transformed breast epithelial cell lines (BP1E and D3. 1), breast cancer cell line T47D, as well as in three invasive ductal carcinomas when compared to their normal adjacent tissue. The S100P protein was localized by immunohistochemistry, using a monoclonal antibody against the same amino acid sequence of the gene cloned, in ductal hyperplasias, in situ and invasive ductal carcinoma, but not in the normal tissues. We concluded that S100P overexpression is an early event that might play an important role in the immortalization of human breast epithelial cells in vitro and tumor progression in vivo.