Ince B A, Montano M M, Katzenellenbogen B S
Department of Physiology and Biophysics, University of Illinois, Urbana 61801.
Mol Endocrinol. 1994 Oct;8(10):1397-406. doi: 10.1210/mend.8.10.7531820.
We show that some transcriptionally inactive human estrogen receptor (ER) mutants can be activated by 17 beta-estradiol (E2), and sometimes by antiestrogens, in the presence of elevated levels of intracellular cAMP. ER-deficient Chinese hamster ovary or 3T3 mouse fibroblast cells were transfected with mutant ERs (the point mutant L540Q, the frameshift mutant S554fs, or the carboxy-terminal truncated receptor ER1-530) and various estrogen response element-containing reporter genes. Individual treatments with E2, the antiestrogens trans-hydroxytamoxifen and ICI 164,384, or with 3-isobutyl-1-methyl-xanthine plus cholera toxin (IBMX plus CT) which raise intracellular cAMP, generally do not activate the mutant receptors. However, cotreatment with IBMX/CT and one of the three ligands (E2, trans-hydroxytamoxifen, or ICI164,384) results in the unexpected recovery of strong activation of the L540Q or S554fs receptors, the magnitude of which is dependent upon promoter- and cell-contexts. Unlike L540Q and S554fs, the transcriptionally inactive ER1-530 is not activated by any combination of ligands and IBMX/CT. These data demonstrate that some ER mutants that form transcriptionally nonproductive ER-E2 complexes can be successfully activated by the combination of an agonist or antagonist ligand and an agent thought to act via phosphorylation pathways. Also highlighted is the promoter- and cell-specific nature of the transcriptional response to different ligand-ER complexes. Lastly, the enhanced transcriptional activity of wild type ER and some ER mutants in the presence of antiestrogens and elevated intracellular cAMP may provide a partial explanation of the ability of some estrogen-dependent human breast tumors to resist antiestrogen therapies currently employed.
我们发现,在细胞内cAMP水平升高的情况下,一些转录无活性的人雌激素受体(ER)突变体可被17β-雌二醇(E2)激活,有时也可被抗雌激素激活。用突变型ER(点突变L540Q、移码突变S554fs或羧基末端截短受体ER1-530)和各种含雌激素反应元件的报告基因转染ER缺陷的中国仓鼠卵巢细胞或3T3小鼠成纤维细胞。单独用E2、抗雌激素反式羟基他莫昔芬和ICI 164,384,或用升高细胞内cAMP的3-异丁基-1-甲基黄嘌呤加霍乱毒素(IBMX加CT)处理,通常不会激活突变受体。然而,将IBMX/CT与三种配体之一(E2、反式羟基他莫昔芬或ICI164,384)共同处理,会意外地使L540Q或S554fs受体强烈激活,其激活程度取决于启动子和细胞环境。与L540Q和S554fs不同,转录无活性的ER1-530不会被任何配体与IBMX/CT的组合激活。这些数据表明,一些形成转录无活性ER-E2复合物的ER突变体可通过激动剂或拮抗剂配体与一种被认为通过磷酸化途径起作用的试剂的组合成功激活。还强调了对不同配体-ER复合物转录反应的启动子和细胞特异性性质。最后,野生型ER和一些ER突变体在抗雌激素和细胞内cAMP升高时增强的转录活性,可能部分解释了一些雌激素依赖性人类乳腺肿瘤抵抗目前所用抗雌激素疗法的能力。