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

The effect of estrogen structure on the conformation of the complex fo rmed with estrogen receptor (ER) and the consensus estrogen response e lement (ERE(c)) has been examined with gel mobility shift assay. Prote ins in MCF-7 cell extracts formed three distinct complexes with ERE. O nly the slowest moving complex contained ER as indicated by binding wi th anti-ER antibodies H222 and D547. This ER-ERE complex displayed inc reased electrophoretic mobility when formed in the presence of estradi ol (E(2)) and bound radiolabeled 16 alpha-iodoestradiol. The antiestro gen ICI 164,384 decreased the mobility of the ER-ERE complex and block ed the effect of E(2). The results reported here indicate that the pos ition and location of hydroxyl groups on the estratriene nucleus is an important factor in determining the mobility of ER-ERE(c) (or a varia nt ERE) in gel shift assays. The ability of E(2) analogs to cause conf ormational changes detectable as altered mobility was not directly rel ated either to their binding affinity for ER or to their ability to ac tivate E(2) responsive genes. Although several dihydroxyestrogens (est radiol-16 alpha, 1- and 2-hydroxyestratrien-17 beta-ol) caused an incr ease in the mobility of the ER-ERE(c), other ligands (estradiol-17 alp ha, 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 character istics of the ligand which are required for gel-shift are not the same as those previously reported to be essential for stimulation of trans criptional activity of ER.