Roman S D, Ormandy C J, Manning D L, Blamey R W, Nicholson R I, Sutherland R L, Clarke C L
Department of Medical Oncology, University of Sydney, Westmead, New South Wales, Australia.
Cancer Res. 1993 Dec 15;53(24):5940-5.
Retinoic acid inhibits proliferation and steroid receptor gene expression in human breast cancer cell lines. Retinoic acid receptors (RAR)alpha, -beta, and -gamma are expressed in these cells and the expression of RAR alpha is significantly greater in estrogen receptor (ER)-positive cells. This study was undertaken to determine whether the same relationship between RAR alpha and ER gene expression was present in human breast cancers and to explore the possibility that the higher level of RAR alpha in ER-positive cells was due to estrogen regulation of RAR alpha gene expression. RAR alpha and ER mRNA expression were determined by Northern blot analysis in 116 primary breast tumors; 94 (81%) tumors were ER-positive and of these 87 (93%) were also RAR alpha-positive. The coexpression of ER and RAR alpha was statistically significant (P = 0.0052 by chi 2 contingency analysis). There was also a positive correlation (by linear regression analysis) between the levels of expression of ER and RAR alpha mRNA (r2 = 0.251, P = 0.0001), which confirmed the relationship previously documented in breast cancer cell lines and suggested that RAR alpha expression may be modulated in breast cancer in vivo by estrogens acting via the ER. The ability of estradiol to regulate RAR alpha gene expression was examined in vitro using T-47D cells which had been rendered sensitive to estrogen by repeated passage in steroid-depleted medium. Estradiol increased RAR alpha gene expression, but not that of RAR beta or RAR gamma, in a concentration-dependent manner, with the effect being maximal at 10(-10) M and less marked at higher concentrations. The effect was rapid, being detectable 1 h after and maximal 6 h after treatment with 10(-10) M estradiol. Co-treatment of cells with estradiol and antiestrogens (tamoxifen or ICI 164384, 4 x 10(-7) M for 6 h) inhibited the estradiol induction of RAR alpha gene expression, demonstrating that the effect was ER mediated. The estradiol sensitivity of the effect was underscored by the demonstration that addition of untreated serum to cells growing under steroid-depleted conditions was sufficient to induce maximal RAR alpha gene expression. This effect was totally abolished by addition of ICI 164384. In summary, the demonstration that estradiol increased RAR alpha mRNA levels in breast cancer cells supports the hypothesis that the correlation between RAR alpha and ER gene expression in breast tumors and breast cancer cell lines is due to estradiol augmentation of RAR alpha gene expression.
维甲酸可抑制人乳腺癌细胞系的增殖及类固醇受体基因表达。维甲酸受体（RAR）α、β和γ在这些细胞中均有表达，且RARα在雌激素受体（ER）阳性细胞中的表达显著更高。本研究旨在确定在人乳腺癌中RARα与ER基因表达之间是否存在相同的关系，并探讨ER阳性细胞中RARα水平较高是否归因于雌激素对RARα基因表达的调控。通过Northern印迹分析测定了116例原发性乳腺肿瘤中RARα和ER mRNA的表达；94例（81%）肿瘤为ER阳性，其中87例（93%）也为RARα阳性。ER与RARα的共表达具有统计学意义（经卡方列联分析，P = 0.0052）。ER和RARα mRNA表达水平之间也存在正相关（经线性回归分析，r2 = 0.251，P = 0.0001），这证实了先前在乳腺癌细胞系中记录的关系，并表明在体内乳腺癌中RARα表达可能受雌激素通过ER发挥作用的调节。使用通过在无类固醇培养基中反复传代而对雌激素敏感的T-47D细胞，在体外研究了雌二醇调节RARα基因表达的能力。雌二醇以浓度依赖的方式增加RARα基因表达，但不增加RARβ或RARγ的表达，在10^(-10) M时作用最大，更高浓度时作用减弱。该作用迅速，在用10^(-10) M雌二醇处理1小时后即可检测到，6小时后达到最大。用雌二醇和抗雌激素（他莫昔芬或ICI 164384，4×10^(-7) M处理6小时）共同处理细胞可抑制雌二醇对RARα基因表达的诱导，表明该作用是由ER介导的。在无类固醇条件下生长的细胞中添加未处理的血清足以诱导最大的RARα基因表达，这突出了该作用对雌二醇的敏感性。添加ICI 164384可完全消除该作用。总之，雌二醇增加乳腺癌细胞中RARα mRNA水平的证明支持了以下假设：乳腺肿瘤和乳腺癌细胞系中RARα与ER基因表达之间的相关性是由于雌二醇增强了RARα基因表达。
