Saji Shigehira, Omoto Yoko, Shimizu Chikako, Horiguchi Shin-ichiro, Watanabe Toru, Funata Nobuaki, Hayash Shin-ichi, Gustafsson Jan-Ake, Toi Masakazu
Department of Surgery, Breast Oncology Unit, Tokyo Metropolitan Komagome Hospital, 3-18-22 Honkomagome, Bunkyo-ku, Tokyo 113-8677, Japan.
Breast Cancer. 2002;9(4):303-7. doi: 10.1007/BF02967608.
Since 1996 when estrogen receptor beta(ER beta) was discovered, much effort has been devoted to the question of the value of ER beta as a prognostic and/or predictive factor in breast cancer and its potential as a novel target for pharmacological intervention. When estrogen receptors are applied on sucrose gradients and quantified by ligand binding, we found that in contrast to ER alpha, which has a narrow tissue distribution, ER beta is expressed in many tissues including both normal and malignant breast tissue. Receptor protein levels in tissues can also be measured from the intensities of bands after Western blotting and can be quantified when purified and quantified receptor is used as a standard. With this technique, we found that there were some tumors which had over 600 fmol/mg of ER beta protein but no detectable estradiol binding. In such tumors, RT-PCR analysis revealed that ER beta cx is the only ER beta isoform present. ER beta cx is a splice variant which utilizes an alternative exon 8. This change in the C-terminus results in very poor binding to estradiol (E2) and has a dominant negative effect on ER alpha function. Immunohistochemical analysis with an ER beta cx specific antibody in 115 ER alpha-positive breast cancers revealed that about half of the samples expressed ER beta cx protein. Initial analysis of samples from patients with preoperative tamoxifen treatment revealed that ER alpha-positive tumors expressing ER beta cx and lacking PR seemed to be resistant to the anti-estrogen. We conclude that, in order to better characterize breast cancers and design appropriate therapy for individual patients, assays for ER beta cx must be made available to clinicians.
自1996年雌激素受体β（ERβ）被发现以来，人们一直致力于研究ERβ作为乳腺癌预后和/或预测因子的价值及其作为药物干预新靶点的潜力。当将雌激素受体应用于蔗糖梯度并通过配体结合进行定量时，我们发现，与组织分布狭窄的ERα不同，ERβ在包括正常和恶性乳腺组织在内的许多组织中均有表达。组织中的受体蛋白水平也可以通过蛋白质印迹后条带的强度来测量，并且当使用纯化和定量的受体作为标准时可以进行定量。通过这项技术，我们发现有些肿瘤的ERβ蛋白含量超过600 fmol/mg，但未检测到雌二醇结合。在这类肿瘤中，逆转录-聚合酶链反应（RT-PCR）分析显示，ERβcx是唯一存在的ERβ异构体。ERβcx是一种剪接变体，它利用了一个替代的外显子8。这种C末端的变化导致其与雌二醇（E2）的结合非常差，并对ERα功能产生显性负效应。用ERβcx特异性抗体对115例ERα阳性乳腺癌进行免疫组织化学分析，结果显示约一半的样本表达ERβcx蛋白。对术前接受他莫昔芬治疗患者的样本进行的初步分析显示，表达ERβcx且缺乏孕激素受体（PR）的ERα阳性肿瘤似乎对抗雌激素耐药。我们得出结论，为了更好地对乳腺癌进行特征描述并为个体患者设计合适的治疗方案，临床医生必须能够进行ERβcx检测。
