Department of Medicine, University of Virginia Health System, Charlottesville, VA, USA.
Oncogene. 2013 Oct 31;32(44):5233-40. doi: 10.1038/onc.2012.558. Epub 2012 Nov 26.
Estrogen is a risk factor of breast cancer. Elevated expression of aromatase (estrogen synthase) in breast tissues increases local estradiol concentrations and is associated with breast cancer development, but the causal relationship between aromatase and breast cancer has not been identified. Accumulating data suggest that both estrogen receptor (ER)-dependent and -independent effects are involved in estrogen carcinogenesis. We established a model by expressing aromatase in ERα- MCF-10A human breast epithelial cells to investigate ERα-independent effects of estrogen in the process of malignant transformation. Overexpression of aromatase significantly increased anchorage-independent growth. Parental- or vector-expressing MCF-10A cells did not form colonies under the same conditions. The anchorage-independent growth of MCF-10A(arom) cells can be completely abolished by pre-treatment with the aromatase inhibitor, letrozole. Neither MCF-10A(arom) nor MCF-10A(vector) cells grown in monolayer were affected by short-term exposure to estradiol. Enhanced motility is another characteristic of cellular transformation. Motility of MCF-10A(arom) cells was increased, which could be inhibited by letrozole. Increases in stem cell population in breast cancer tissues are associated with tumor recurrence and metastasis. CD44(high)/CD24(low) is a stem cell marker. We found that CD24 mRNA levels were reduced in MCF-10A(arom) cells compared with those in parental- and vector-transfected cells. By examining individual clones of MCF-10A(arom) with various aromatase activities, we found that the CD24 mRNA levels were inversely correlated with aromatase activity. The ability of MCF-10A(arom) cells to form mammospheres in the absence of serum was increased. Our results suggest that overexpression of aromatase in MCF-10A cells causes malignant transformation. Estrogen metabolite-mediated genotoxicity and induction of a stem cell/progenitor cell population are possible mechanisms. These studies provide additional evidence for ERα-independent mechanism(s) in estrogen carcinogenesis and implicate superiority of aromatase inhibitors to antiestrogens for breast cancer prevention.
雌激素是乳腺癌的一个风险因素。在乳腺组织中芳香酶（雌激素合成酶）的表达升高会增加局部雌二醇浓度，并与乳腺癌的发展相关，但芳香酶与乳腺癌之间的因果关系尚未确定。越来越多的证据表明，雌激素致癌作用涉及雌激素受体（ER）依赖性和非依赖性效应。我们通过在 ERα-MCF-10A 人乳腺上皮细胞中表达芳香酶建立了一个模型，以研究在恶性转化过程中雌激素的 ERα 非依赖性效应。芳香酶的过表达显著增加了非锚定依赖性生长。在相同条件下，亲本或载体表达的 MCF-10A 细胞未形成集落。用芳香酶抑制剂来曲唑预处理可完全消除 MCF-10A(arom)细胞的非锚定依赖性生长。单层培养的 MCF-10A(arom)或 MCF-10A(vector)细胞均不受短期暴露于雌二醇的影响。增强的迁移能力是细胞转化的另一个特征。MCF-10A(arom)细胞的迁移能力增加，来曲唑可抑制其迁移能力。乳腺癌组织中干细胞群体的增加与肿瘤复发和转移有关。CD44(high)/CD24(low)是干细胞标志物。我们发现，与亲本和载体转染细胞相比，MCF-10A(arom)细胞中的 CD24 mRNA 水平降低。通过检查具有不同芳香酶活性的 MCF-10A(arom)的单个克隆，我们发现 CD24 mRNA 水平与芳香酶活性呈负相关。MCF-10A(arom)细胞在无血清条件下形成乳腺球体的能力增加。我们的结果表明，MCF-10A 细胞中芳香酶的过表达导致恶性转化。雌激素代谢物介导的遗传毒性和诱导干细胞/祖细胞群体可能是其机制。这些研究为雌激素致癌作用中的 ERα 非依赖性机制提供了更多证据，并表明芳香酶抑制剂优于抗雌激素用于乳腺癌预防。
