Estrogen Receptor Ligands Modulate Its Interaction with DNA

Abstract

The estrogen receptor (ER) belongs to a superfamily of ligand-inducible transcription factors. Functions of these proteins (dimerization, DNA binding, and interaction with other transcription factors) are modulated by binding of their corresponding ligands. It is, however, controversial whether various ER ligands affect the receptor's ability to bind its specific DNA element (ERE).By using real time interaction analysis we have investigated the kinetics of human (h)ER binding to DNA in the absence and presence of 17␤-estradiol, 17␣-ethynyl estradiol, analogs of tamoxifen, raloxifene, and ICI-182,780. We show that ligand binding dramatically influences the kinetics of hER interaction with specific DNA. We have found that binding of estradiol induces the rapid formation of a relatively unstable ER⅐ERE complex, and binding of ICI-182,780 leads to slow formation (k a is approximately 10 times lower) of a stable receptor-DNA complex (k d is almost 2 orders of magnitude lower). Therefore, binding of estradiol accelerates the frequency of receptor-DNA complex formation more than 50-fold, compared with unliganded ER, and more than 1000-fold compared with ER liganded with ICI-182,780. We hypothesize that a correlation exists between the rate of gene transcription and the frequency of receptor-DNA complex formation. We further show that a good correlation exists between the kinetics of hER-ERE interaction induced by a ligand and its biological effect.Steroid hormones are widely distributed small, lipophilic molecules that participate in intracellular communication and control a wide spectrum of developmental and physiological processes. Their effects are mediated by specific intracellular receptors, a family of proteins that are characterized by a high affinity for the corresponding hormones and an ability to discriminate between structurally closely related ligands. These ligand-inducible receptors can modulate transcription of target genes by virtue of their binding to a specific sequence on DNA in target promoters known as hormone response elements. Although distinct proteins, these receptors are members of a large superfamily of steroid hormone receptors and share many common structural and functional features (1-4).Binding of 17␤-estradiol (E 2 ) 1 to estrogen receptor (ER) is followed by a conformational change, leading to dissociation of the receptor from the complex with the heat shock proteins hsp90 and p59 (5, 6), dimerization (7,8), and activation of DNA binding. After DNA binding the activated receptor can interact with basal transcription factors (9). These interactions are thought to stabilize the preinitiation complex at the promoter, allowing RNA polymerase to initiate transcription (10). Recently a number of transcriptional intermediary factors have been identified that can modify estrogen responsiveness, and several of these proteins interact with the ligand binding domain of the ER in a ligand-dependent manner (11-13). It is obvious that the ligand plays a key role in initiating this cascade of events. ...

p300 and estrogen receptor cooperatively activate transcription via differential enhancement of initiation and reinitiation

“…4). These findings are generally consistent with the results of previous experiments on the binding of ER (in the absence of associated heat shock proteins) to naked DNA in vitro (see, e.g., Murdoch et al 1990;Furlow et al 1993;Metzger et al 1995;Cheskis et al 1997). We do not, however, extrapolate these data to the behavior of ER in vivo, as these experiments with free polypeptide ER do not involve issues such as the association of heat shock proteins with ER and nuclear localization.…”

Pure oestrogen antagonists for the treatment of advanced breast cancer

“…However, binding of oestradiol to the ER initiates a cascade of events leading to strong ER dimerisation, increased nuclear localisation and binding to ERE in the regulatory regions of target genes, and gene transcription (mediated by AF1 and AF2 of the ER) (Beato 1989, Tsai & O'Malley 1994, Cheskis et al 1997. AF1 (located in domains A and B of the amino terminal of the ER) is activated by growth factors acting through the mitogen-activated protein kinase (MAPK) pathway, while AF2 (located in domain E of the carboxy terminal of the ER ligandbinding domain) is activated by oestradiol.…”

In vivo activation of gene transcription via oestrogen response elements by a raloxifene analogue

“…Raloxifene binds both ERa and ERb (Glasebrook et al 1993, Gize et al 1997, and the importance of ERs for the physiological effects of raloxifene has been demonstrated in various cell types using the selective ER antagonist ICI182.780 (Ashby et al 1997, Viereck et al 2003. The interaction between raloxifene and ER causes structural differences in the complex compared with the oestrogen-ER complex (Bryant et al 1999), and these structural differences result in assembly of other coregulators (Cheskis et al 1997), which causes the tissue-specific agonistic/antagonistic effects of raloxifene.…”