Cooperative binding of estrogen receptor to imperfect estrogen-responsive DNA elements correlates with their synergistic hormone-dependent enhancer activity.
The Xenopus vitellogenin (vit) gene B1 estrogen-inducible enhancer is formed by two closely adjacent 13 bp imperfect palindromic estrogen-responsive elements (EREs), i.e. ERE-2 and ERE-1, having one and two base substitutions respectively, when compared to the perfect palindromic consensus ERE (GGTCANNNTGACC). Gene transfer experiments indicate that these degenerated elements, on their own, have a low or no regulatory capacity at all, but in vivo act together synergistically to confer high receptor- and hormone-dependent transcription activation to the heterologous HSV thymidine kinase promoter. Thus, the DNA region upstream of the vitB1 gene comprising these two imperfect EREs separated by 7 bp, was called the vitB1 estrogen-responsive unit (vitB1 ERU). Using in vitro protein-DNA interaction techniques, we demonstrate that estrogen receptor dimers bind cooperatively to the imperfect EREs of the vitB1 ERU. Binding of a first receptor dimer to the more conserved ERE-2 increases approximately 4- to 8-fold the binding affinity of the receptor to the adjacent less conserved ERE-1. Thus, we suggest that the observed synergistic estrogen-dependent transcription activation conferred by the pair of hormone-responsive DNA elements of the vit B1 ERU is the result of cooperative binding of two estrogen receptor dimers to these two adjacent imperfect EREs.
Martinez
E
E
Institut de Biologie Animale, Université de Lausanne, Switzerland.
Wahli
W
W
D000818:Animals; D001483:Base Sequence; D001667:Binding, Competitive; D004268:DNA-Binding Proteins / Q000378:metabolism*; D003850:Deoxyribonuclease I / Q000378:metabolism; D004357:Drug Synergism; D004742:Enhancer Elements, Genetic; D004967:Estrogens / Q000235:genetics* / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D011960:Receptors, Estrogen / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D014819:Vitellogenins / Q000235:genetics; D014981:Xenopus / Q000235:genetics*
D004268:DNA-Binding Proteins; D004967:Estrogens; D011960:Receptors, Estrogen; D014819:Vitellogenins; D003850:Deoxyribonuclease I