Klinge C M, Bodenner D L, Desai D, Niles R M, Traish A M
Department of Biochemistry, the University of Louisville School of Medicine, Louisville, KY 40292, USA.
Nucleic Acids Res. 1997 May 15;25(10):1903-12. doi: 10.1093/nar/25.10.1903.
The mechanism by which retinoids, thyroid hormone (T3) and estrogens modulate the growth of breast cancer cells is unclear. Since nuclear type II nuclear receptors, including retinoic acid receptor (RAR), retinoid X receptor (RXR) and thyroid hormone receptor (TR), bind direct repeats (DR) of the estrogen response elements (ERE) half-site (5'-AGGTCA-3'), we examined the ability of estrogen receptor (ER) versus type II nuclear receptors, i.e. RARalpha, beta and gamma, RXRbeta, TRalpha and TRbeta, to bind various EREs in vitro . ER bound a consensus ERE, containing a perfectly palindromic 17 bp inverted repeat (IR), as a homodimer. In contrast, ER did not bind to a single ERE half-site. Likewise, ER did not bind two tandem (38 bp apart) half-sites, but low ER binding was detected to three tandem copies of the same half-site. RARalpha,beta or gamma bound both ERE and half-site constructs as a homodimer. RXRbeta did not bind full or half-site EREs, nor did RXRbeta enhance RARalpha binding to a full ERE. However, RARalpha and RXRbeta bound a half-site ERE cooperatively forming a dimeric complex. The RARalpha-RXRbeta heterodimer bound the Xenopus vitellogenin B1 estrogen responsive unit, with two non-consensus EREs, with higher affinity than one or two copies of the full or half-site ERE. Both TRalpha and TRbeta bound the full and the half-site ERE as monomers and homodimers and cooperatively as heterodimers with RXRbeta. We suggest that the cellular concentrations of nuclear receptors and their ligands, and the nature of the ERE or half-site sequence and those of its flanking sequences determine the occupation of EREs in estrogen-regulated genes in vivo .
类视黄醇、甲状腺激素（T3）和雌激素调节乳腺癌细胞生长的机制尚不清楚。由于包括视黄酸受体（RAR）、类视黄醇X受体（RXR）和甲状腺激素受体（TR）在内的II型核受体可结合雌激素反应元件（ERE）半位点（5'-AGGTCA-3'）的直接重复序列（DR），我们检测了雌激素受体（ER）与II型核受体（即RARα、β和γ、RXRβ、TRα和TRβ）在体外结合各种ERE的能力。ER作为同二聚体结合一个包含完美回文17 bp反向重复序列（IR）的共有ERE。相比之下，ER不与单个ERE半位点结合。同样，ER也不与两个串联（相隔38 bp）的半位点结合，但检测到其与同一半位点的三个串联拷贝有低亲和力结合。RARα、β或γ作为同二聚体结合ERE和半位点构建体。RXRβ不结合完整或半位点ERE，也不增强RARα与完整ERE的结合。然而，RARα和RXRβ协同结合一个半位点ERE，形成二聚体复合物。RARα-RXRβ异二聚体以更高的亲和力结合非洲爪蟾卵黄蛋白原B1雌激素反应单元，该单元有两个非共有ERE，其亲和力高于一个或两个拷贝的完整或半位点ERE。TRα和TRβ均作为单体、同二聚体结合完整和半位点ERE，并与RXRβ作为异二聚体协同结合。我们认为，核受体及其配体的细胞浓度，以及ERE或半位点序列及其侧翼序列的性质决定了体内雌激素调节基因中ERE的占据情况。
