Binding of xenoestrogen ligands to estrogen receptors and effect of xenoestrogens on the binding of estrogen receptors to DNA sequences

The binding of 17β-estradiol (E2) to its receptors ERα and ERβ, leads to many of the observed biological responses to the hormone. Experimental investigations of the interaction of estrogenic ligand with the estrogen receptors (ERs) and ligand-ER complex with DNA, may give insight as to how these ligands exert their biological effects. The binding of several compounds to ERs has been investigated. Results suggest that all the ligands tested show various degrees of affinity towards both ERs. We also have investigated the interactions of xenoestrogen—or phytoestrogen—bound ERs with the xenopus vit A2, and human pS2 estrogen responsive elements (EREs), and putative EREs from human mitochondrial DNA. Relative association and dissociation rate for the interaction of ER-ligand complexes with the EREs were determined using BIACORE 2000 surface plasmon resonance instrument. The relative association and dissociation rates of binding of the ER-ligand complexes to the EREs are all distinctly different. In the absence of ligand, both the ERs show significant affinity for both the vit A2 and human pS2 EREs. In contrast no interaction of ERs or ER-E2 complexes with the random sequence oligonucleotide was observed. It was also observed that the affinity of ERα for the D-loop I, and D-loop II sequences was eliminated in the presence of the estrogen antagonist ICI-182, 780. We conclude that with respect to mitochondria DNA the D-loop I and D-loop II oligonucleotides may function as EREs, whereas the random sequence may not.