Montano M M, Ekena K, Krueger K D, Keller A L, Katzenellenbogen B S
Department of Molecular and Integrative Physiology, University of Illinois, Urbana 61801, USA.
Mol Endocrinol. 1996 Mar;10(3):230-42. doi: 10.1210/mend.10.3.8833652.
The estrogen receptor (ER) is a transcription factor whose activity is normally activated by the hormone estradiol and inhibited by antiestrogen. It has been found that certain mutational changes in the activation function-2 region in the hormone-binding domain of the human ER result in ligand activity inversion mutants, i.e. receptors that are now activated by antiestrogen and inhibited by estrogen. The ER point mutant L540Q is activated by several antiestrogens (the more pure antiestrogens ICI 164,384 and RU 54,876 or the partial antiestrogen trans-hydroxytamoxifen) but not by estradiol. The presence of the F domain and an intact activation function-i in the A/B domain are required for this activity, as is the DNA-binding ability of the receptor. This inverted ligand activity is observed with several estrogen-responsive promoters, both simple and complex; however, the activating ability of antiestrogens is observed only in some cells, highlighting the important role of cell-specific factors in ligand interpretation. The introduction of two additional amino acid changes close to 540 results in receptors that are still not activated by estradiol but are now able to distinguish between partial antiestrogens (which remain agonistic) and pure antiestrogens (which show a greatly reduced stimulatory activity). These ligand activity inversion mutants remain stable in cells in the presence of the antiestrogen ICI 164,384, as does a related ER mutant receptor that shows the normal, wild type ER ligand activity profile in which ICI 164,384 is transcriptionally inactive. Thus, the presence of adequate levels of mutant ER may be necessary but not sufficient for ICI 164,384 to elicit transcriptional activity. These findings highlight the means by which the carboxyl-terminal region in domain E functions to interpret the activity of a ligand, and they demonstrate that rather minimal changes in the ER can result in receptors with inverted response to antiestrogen and estrogen. Such point mutations, if present in estrogen target cells, would result in antiestrogens being seen as growth stimulators, rather than suppressors, with potentially detrimental consequences in terms of breast cancer treatment with antiestrogens.
雌激素受体（ER）是一种转录因子，其活性通常由激素雌二醇激活，并被抗雌激素抑制。已发现人ER激素结合域中激活功能-2区域的某些突变会导致配体活性反转突变体，即现在被抗雌激素激活并被雌激素抑制的受体。ER点突变体L540Q可被几种抗雌激素激活（更纯的抗雌激素ICI 164,384和RU 54,876或部分抗雌激素反式羟基他莫昔芬），但不能被雌二醇激活。这种活性需要F结构域的存在以及A/B结构域中完整的激活功能-1，受体的DNA结合能力也是如此。在几个简单和复杂的雌激素反应性启动子中都观察到了这种反转的配体活性；然而，抗雌激素的激活能力仅在某些细胞中观察到，这突出了细胞特异性因子在配体解读中的重要作用。在靠近540处引入另外两个氨基酸变化会产生仍然不能被雌二醇激活但现在能够区分部分抗雌激素（仍然具有激动作用）和纯抗雌激素（显示出大大降低的刺激活性）的受体。这些配体活性反转突变体在存在抗雌激素ICI 164,384的细胞中保持稳定，一种相关的ER突变体受体也是如此，该受体显示出正常的野生型ER配体活性谱，其中ICI 164,384在转录上无活性。因此，存在足够水平的突变体ER可能是ICI 164,384引发转录活性所必需的，但不是充分的。这些发现突出了E结构域中的羧基末端区域解释配体活性的方式，并且它们证明ER中相当微小的变化可以导致对抗雌激素和雌激素反应反转的受体。这种点突变如果存在于雌激素靶细胞中，将导致抗雌激素被视为生长刺激剂而非抑制剂，这在抗雌激素治疗乳腺癌方面可能产生有害后果。
