Schneider S M, Offterdinger M, Huber H, Grunt T W
Laboratory for Cell Growth and Differentiation, University of Vienna, Austria.
Cancer Res. 2000 Oct 1;60(19):5479-87.
Retinoid signaling via retinoic acid (RA) and retinoid X receptors (RARs and RXRs) regulates mammary epithelial cell growth and differentiation. Loss of RAR-beta might represent an early event during breast carcinogenesis. Higher differentiated, estrogen-dependent, estrogen receptor (ER)-positive (ER+) mammary carcinoma cells have been found to contain relatively high levels of RAR-alpha and to be responsive to retinoids, whereas most undifferentiated, estrogen-independent, ER-negative (ER-) cells are characterized by low RAR-alpha expression and by retinoid resistance. In contrast, RAR-gamma is detectable at equal levels in both ER+ and ER- cells. In the present investigation, we directly examined the relative contribution of the distinct retinoid receptors to the retinoid response of breast cancer cells by comparing the effects of low concentrations of specific retinoids, which selectively activate individual receptor subtypes, on growth, cell cycle distribution, apoptosis, and on the autoregulation of RAR-alpha and RAR-gamma in ER- SK-BR-3 and ER+ T47D breast cancer cells. In vitro growth activity was determined by using a colorimetric cell viability assay and analysis of cell cycle distribution, and apoptosis was performed by flow cytometry of propidium iodide-stained or fluorescent Annexin V-labeled cells, respectively, whereas expression of RAR-alpha and RAR-gamma was determined by Northern blotting. Both cell lines are retinoid sensitive and express high amounts of RAR-alpha, RAR-gamma, and RXR-alpha. RAR-alpha-selective compounds (AM80 and AM580) inhibit cell growth, induce G1 arrest, stimulate apoptosis, and up-regulate RAR-alpha and RAR-gamma mRNA as efficiently as RAR/RXR-pan-reactive (9-cis RA) and RAR-pan-reactive retinoids (all-trans RA, TTNPB). Remarkably, an RAR-alpha antagonist (Ro 41-5253) not only blocks the RAR-alpha-selective agonists but also the pan-reactive compounds. In contrast, RAR-13-selective (CD417), RAR-gamma-selective (CD437/AHPN), and RXR-alpha-selective (Ro 25-7386) retinoids exert no effects on the examined parameters. Thus, our results support the idea that RAR-alpha is the crucial receptor mediating the biological effects during retinoid signaling in both ER- SK-BR-3 and ER+ T47D human breast cancer cells.
经由视黄酸（RA）和类视黄醇X受体（RAR和RXR）的类视黄醇信号传导调节乳腺上皮细胞的生长和分化。RAR-β的缺失可能是乳腺癌发生过程中的早期事件。已发现分化程度较高、雌激素依赖性、雌激素受体（ER）阳性（ER+）的乳腺癌细胞含有相对较高水平的RAR-α，并且对类视黄醇有反应，而大多数未分化、雌激素非依赖性、ER阴性（ER-）细胞的特征是RAR-α表达低且对类视黄醇耐药。相比之下，在ER+和ER-细胞中均可检测到同等水平的RAR-γ。在本研究中，我们通过比较低浓度的特异性类视黄醇（其选择性激活各个受体亚型）对ER-SK-BR-3和ER+ T47D乳腺癌细胞的生长、细胞周期分布、凋亡以及RAR-α和RAR-γ的自调节作用，直接研究了不同类视黄醇受体对乳腺癌细胞类视黄醇反应的相对贡献。使用比色细胞活力测定法和细胞周期分布分析来确定体外生长活性，分别通过碘化丙啶染色或荧光膜联蛋白V标记细胞的流式细胞术进行凋亡检测，而RAR-α和RAR-γ的表达则通过Northern印迹法测定。两种细胞系对类视黄醇敏感，并且表达大量的RAR-α、RAR-γ和RXR-α。RAR-α选择性化合物（AM80和AM580）抑制细胞生长、诱导G1期停滞、刺激凋亡，并上调RAR-α和RAR-γ mRNA，其效率与RAR/RXR泛反应性（9-顺式视黄酸）和RAR泛反应性类视黄醇（全反式视黄酸、TTNPB）相同。值得注意的是，一种RAR-α拮抗剂（Ro 41-5253）不仅阻断RAR-α选择性激动剂，还阻断泛反应性化合物。相比之下，RAR-β选择性（CD417）、RAR-γ选择性（CD437/AHPN）和RXR-α选择性（Ro 25-7386）类视黄醇对所检测的参数没有影响。因此，我们的结果支持这样一种观点，即RAR-α是在ER-SK-BR-3和ER+ T47D人乳腺癌细胞的类视黄醇信号传导过程中介导生物学效应的关键受体。
