RELATIONSHIP BETWEEN ESTROGEN STRUCTURE AND CONFORMATIONAL-CHANGES IN ESTROGEN RECEPTOR/DNA COMPLEXES

The effect of estrogen structure on the conformation of the complex formed with estrogen receptor (ER) and the consensus estrogen response element (ERE(c)) has been examined with gel mobility shift assay. Proteins in MCF-7 cell extracts formed three distinct complexes with ERE. Only the slowest moving complex contained ER as indicated by binding with anti-ER antibodies H222 and D547. This ER-ERE complex displayed increased electrophoretic mobility when formed in the presence of estradiol (E(2)) and bound radiolabeled 16 alpha-iodoestradiol. The antiestrogen ICI 164,384 decreased the mobility of the ER-ERE complex and blocked the effect of E(2). The results reported here indicate that the position and location of hydroxyl groups on the estratriene nucleus is an important factor in determining the mobility of ER-ERE(c) (or a variant ERE) in gel shift assays. The ability of E(2) analogs to cause conformational changes detectable as altered mobility was not directly related either to their binding affinity for ER or to their ability to activate E(2) responsive genes. Although several dihydroxyestrogens (estradiol-16 alpha, 1- and 2-hydroxyestratrien-17 beta-ol) caused an increase in the mobility of the ER-ERE(c), other ligands (estradiol-17 alpha, 4-hydroxyestratriene-17 beta-ol, 3-hydroxy estratriene, estratrien-17 beta-ol and 5-androsten-3 beta, 17 beta-diol) with a capacity for activating at least some E, responsive genes in MCF-7 cells had little or no effect. On the basis of these and previously published results, it can be concluded that specific structure features of estrogens are responsible for conformational changes of ER-ERE complexes detectable in gel-shift assays. Furthermore, the identified structural characteristics of the ligand which are required for gel-shift are not the same as those previously reported to be essential for stimulation of transcriptional activity of ER.