Riegel A T, Aitken S C, Martin M B, Schoenberg D R
Endocrinology. 1987 Apr;120(4):1283-90. doi: 10.1210/endo-120-4-1283.
Low levels of estrogen receptor (200-500 per cell) are present in the liver of hormonally naive male Xenopus. However, administration of estradiol results in a rapid 2- to 5-fold increase in cellular estrogen receptor content concurrent with the de novo transcriptional activation of the genes for the yolk protein precursor vitellogenin. Studies on Xenopus embryogenesis suggest that estrogen receptor induction is required for the activation of vitellogenin transcription. The purpose of the present study was to examine the mechanism of estrogen receptor induction in male Xenopus liver. The experimental protocol used 4-hydroxytamoxifen, an antiestrogen with a high affinity for the estrogen receptor, to inhibit the effects of estradiol. Changes in estrogen receptor content were then determined through the use of an exchange assay. 4-Hydroxytamoxifen alone suppressed the level of estrogen receptor from 800 sites per cell in hormonally naive animals to 250 sites per cell. Administration of estradiol 24 h after the antiestrogen resulted in the induction of estrogen receptor to a level equivalent to that found in control animals (800 sites per cell). However, under the same conditions, estradiol was unable to overcome the antiestrogen inhibition of vitellogenin gene transcription. Although 4-hydroxytamoxifen displayed a high affinity for the hepatic estrogen receptor, it did not inhibit the binding of estradiol to a middle affinity cytoplasmic estrogen-binding protein. These results suggest that different mechanisms are involved in the induction of estrogen receptor and vitellogenin gene transcription.
在未接触激素的雄性非洲爪蟾肝脏中存在低水平的雌激素受体（每细胞200 - 500个）。然而，给予雌二醇会导致细胞雌激素受体含量迅速增加2至5倍，同时卵黄蛋白前体卵黄生成素的基因从头转录激活。对非洲爪蟾胚胎发育的研究表明，雌激素受体的诱导是卵黄生成素转录激活所必需的。本研究的目的是探讨雄性非洲爪蟾肝脏中雌激素受体诱导的机制。实验方案使用了4 - 羟基他莫昔芬，一种对雌激素受体具有高亲和力的抗雌激素，以抑制雌二醇的作用。然后通过交换测定法确定雌激素受体含量的变化。单独使用4 - 羟基他莫昔芬可将未接触激素动物的雌激素受体水平从每细胞800个位点抑制至每细胞250个位点。在给予抗雌激素24小时后给予雌二醇，导致雌激素受体诱导至与对照动物相同的水平（每细胞800个位点）。然而，在相同条件下，雌二醇无法克服抗雌激素对卵黄生成素基因转录的抑制作用。尽管4 - 羟基他莫昔芬对肝脏雌激素受体显示出高亲和力，但它并不抑制雌二醇与中等亲和力的细胞质雌激素结合蛋白的结合。这些结果表明，雌激素受体诱导和卵黄生成素基因转录涉及不同的机制。
