Medical Sciences, Indiana University School of Medicine, Bloomington, IN, USA.
Cancer Biol Ther. 2010 Mar 1;9(5):389-96. doi: 10.4161/cbt.9.5.10926. Epub 2010 Mar 11.
Fulvestrant (ICI 182, 780) is a selective estrogen receptor downregulator (SERD) and potent antiestrogen. In estrogen receptor-alpha-positive ERalpha(+) breast cancer, the drug immobilizes ERalpha in the nuclear matrix, inducing receptor polyubiquitination and subsequent degradation via the 26S proteasome. We previously reported that fulvestrant-induced ERalpha degradation depends on the interaction of ERalpha with cytokeratins 8 and 18 (CK8/CK18). Here we further investigate the role of these two cytokeratins in the antagonistic activity of the SERD. Using ER-responsive reporter assays, we demonstrate greater antiestrogenic activity of fulvestrant in CK8/CK18(+) vs. CK8/CK18(-) cancer cells and loss of CK8/CK18 expression was observed in a breast cancer cell model for acquired fulvestrant resistance. In contrast, the presence of CK8/CK18 had no effect on the antiestrogenic activity of 4-hydroxytamoxifen, which was unable to induce an interaction between these CKs and ERalpha. By utilizing the ligand activity inversion ERalpha mutant L540Q to further examine the mechanism of fulvestrant action, we demonstrate that the ERalpha mutant does not interact with CK8/CK18 in the presence of fulvestrant and L540Q is not immobilized to the nuclear matrix after antiestrogen treatment. In transcription assays, fulvestrant displayed agonist activity, stimulating L540Q-mediated gene expression. In addition, fulvestrant did not induce an ERbeta interaction with CK8/CK18 and subsequent ERbeta degradation. Collectively, these results suggest that CK8/18 play an important role in the antiestrogenic action of fulvestrant in breast cancer cells and that these two cytokeratins could serve as prognostic markers for SERD therapy response in breast cancer patients.
氟维司群（ICI 182,780）是一种选择性雌激素受体降解剂（SERD）和有效的抗雌激素。在雌激素受体-α阳性（ERα+）乳腺癌中，该药物将 ERα固定在核基质中，通过 26S 蛋白酶体诱导受体多泛素化和随后的降解。我们之前报道过，氟维司群诱导的 ERα降解依赖于 ERα与细胞角蛋白 8 和 18（CK8/CK18）的相互作用。在这里，我们进一步研究了这两种细胞角蛋白在 SERD 拮抗活性中的作用。使用 ER 反应性报告基因检测，我们证明氟维司群在 CK8/CK18+ vs. CK8/CK18- 癌细胞中的抗雌激素活性更强，并且在获得性氟维司群耐药的乳腺癌细胞模型中观察到 CK8/CK18 表达缺失。相比之下，CK8/CK18 的存在对 4-羟基他莫昔芬的抗雌激素活性没有影响，4-羟基他莫昔芬不能诱导这两种 CK 与 ERα 相互作用。通过利用配体活性反转 ERα 突变体 L540Q 进一步研究氟维司群作用的机制，我们证明在氟维司群存在的情况下，ERα 突变体不会与 CK8/CK18 相互作用，并且 L540Q 在抗雌激素处理后不会固定在核基质上。在转录检测中，氟维司群显示激动剂活性，刺激 L540Q 介导的基因表达。此外，氟维司群不会诱导 ERβ 与 CK8/CK18 相互作用和随后的 ERβ 降解。综上所述，这些结果表明 CK8/18 在氟维司群在乳腺癌细胞中的抗雌激素作用中发挥重要作用，并且这两种细胞角蛋白可以作为乳腺癌患者 SERD 治疗反应的预后标志物。
