Eng F C, Barsalou A, Akutsu N, Mercier I, Zechel C, Mader S, White J H
Departments of Physiology and Medicine, McGill University, Montréal H3G 1Y6, Canada.
J Biol Chem. 1998 Oct 23;273(43):28371-7. doi: 10.1074/jbc.273.43.28371.
We have analyzed interaction of coactivators with the wild-type estrogen receptor alpha (ER), HEG0, and a mutant, L536P-HEG0, which is constitutively active in several transiently transfected cells and a HeLa line that stably propagates an estrogen-sensitive reporter gene. Different classes of coactivators do not recognize the ER ligand binding domain (LBD) in the same manner. Steroid receptor coactivator-1 (SRC-1), amplified in breast cancer-1 (AIB-1), transcriptional intermediary factor-1 (TIF-1), transcriptional intermediary factor-2 (TIF-2), and receptor interacting protein 140 (RIP140) interacted with HEG0 and L536P-HEG0 in the presence of estradiol, but generally not in the presence of anti-estrogens. However, ICI164,384 stimulated some interaction of RIP140 with LBDs. SRC-1, AIB-1, and RIP140 interacted constitutively with the L536P ER, whereas TIF-1 and TIF-2 interacted only weakly in the absence of hormone. Reciprocal competition for binding to the ER LBD was observed between different classes of coactivators. Moreover, coexpression of RIP140 blocked enhanced transactivation by HEG0 observed in the presence of TIF-2, suggesting that RIP140 may play a negative role in ER signaling. We conclude that constitutive activity of L536P-HEG0 is manifested to similar degrees in different cell types and likely arises from constitutive coactivator binding; different classes of coactivators recognize distinct but overlapping binding sites on the ER LBD. Finally, the observation that L536P-HEG0 interacted constitutively with AIB-1, a coactivator that has been implicated in ER signaling in breast and ovarian cancer, suggests that similar mutations in the ER may contribute to hormone-independent proliferation of breast and ovarian cells.
我们分析了共激活因子与野生型雌激素受体α（ER）、HEG0以及突变体L536P - HEG0之间的相互作用，L536P - HEG0在几种瞬时转染细胞和稳定传播雌激素敏感性报告基因的HeLa细胞系中具有组成性活性。不同类别的共激活因子以不同方式识别ER配体结合域（LBD）。在雌二醇存在下，类固醇受体共激活因子-1（SRC - 1）、乳腺癌-1中扩增的蛋白（AIB - 1）、转录中介因子-1（TIF - 1）、转录中介因子-2（TIF - 2）以及受体相互作用蛋白140（RIP140）与HEG0和L536P - HEG0相互作用，但在抗雌激素存在时通常不相互作用。然而，ICI164,384刺激了RIP140与LBDs的一些相互作用。SRC - 1、AIB - 1和RIP140与L536P ER组成性相互作用，而TIF - 1和TIF - 2在无激素时仅微弱相互作用。在不同类别的共激活因子之间观察到对ER LBD结合的相互竞争。此外，RIP140的共表达阻断了在TIF - 2存在下观察到的HEG0增强的反式激活，表明RIP140可能在ER信号传导中起负作用。我们得出结论，L536P - HEG0的组成性活性在不同细胞类型中以相似程度表现，可能源于组成性共激活因子结合；不同类别的共激活因子识别ER LBD上不同但重叠的结合位点。最后，L536P - HEG0与AIB - 1组成性相互作用的观察结果，AIB - 1是一种与乳腺癌和卵巢癌中的ER信号传导有关的共激活因子，表明ER中的类似突变可能导致乳腺和卵巢细胞的激素非依赖性增殖。
