Effects of 17.beta.-estradiol analogs on activation of estrogen response element regulated chloramphenicol acetyltransferase expression

Abstract

These experiments were designed to examine the effect of structural modifications to the estradiol-17 beta (E2) molecule on the estrogen response element (ERE) dependent activation of the thymidine kinase (tk) promoter. Estrogen receptor (ER) positive MCF-7 cells were transfected with plasmids containing one or two vitellogenin EREs inserted upstream of the tk promoter in p(-37)tk. Transient expression of the CAT gene in these constructs was measured after cells had been maintained for 36-42 h in the presence of E2 or an E2 analogue. E2 induced CAT expression at levels as low as 10(-13) M, with maximum induction at 10(-11) M. CAT activity decreased at higher concentrations of E2. Estratriene, which has low affinity for ER, was active only at micromolar concentrations. 3-Hydroxyestratriene displayed maximal activity at 10(-9) M, with higher levels being less active. Still higher concentrations (10(-7) M) of estratrien-17 beta-ol were required to induce maximum CAT activity. All positional and conformational alterations in the D-ring hydroxyl group of E2 yielded active ligands. Movement of the phenolic hydroxyl group of E2 to other positions on the A-ring produced dihydroxyestrogens with varied capacities to activate CAT (2-hydroxyestratrien-17 beta-ol produced maximum CAT activation at 10(-11) M; 1-hydroxyestratrien-17 beta-ol required a 10(-8) M concentration for maximum activity; 4-hydroxyestratrien-17 beta-ol gave maximum CAT activation at 10(-6) M). Only those androstanediols or 5-androstenediols with a 3 beta-hydroxyl group were capable of activating CAT expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracellular Levels and Secretion of Insulin‐Like‐Growth‐Factor‐Binding Proteins in MCF‐7/6, MCF‐7/AZ and MDA‐MB‐231 Breast Cancer Cells

“…These observations might be an indication that the action of estrogens on the regulation of IGFBPs is also dependent on other non-estrogenic factors which would not be influenced by ICI 182,780 or tamoxifen [39]. This is plausible since activation of estrogen-receptor transcription interacts with that of other transcription factors [41,421. Another explanation would be that the action of estrogens is indirect [43], and that the cellular and secreted IGFBPs are down-regulated by the action of an estrogen-inducible protein.…”

Toxicity of Endogenous and Environmental Estrogens: What Is the Role of Elemental Interactions?

“…They examined the ability of a series of estradiol analogs to bind to the estrogen receptor and elicit biological responses including induction of the progesterone receptor, pS2 mRNA, cathepsin D mRNA, and CAT activity from reporter constructs containing the c-ERE. They found clearly different patterns of activation of these responses by the different estrogen analogs (45)(46)(47) and emphasized the possible biological significance of these observations.…”

“…Perhaps the clearest example of this possiblity to date comes from a recent series of experiments from Brooks and his colleagues (45)(46)(47). They examined the ability of a series of estradiol analogs to bind to the estrogen receptor and elicit biological responses including induction of the progesterone receptor, pS2 mRNA, cathepsin D mRNA, and CAT activity from reporter constructs containing the c-ERE.…”

Quantitative structure‐activity relationships for polychlorinated hydroxybiphenyl estrogen receptor binding affinity: An Assessment of conformer flexibility

“…However, the influence of an aqueous environment on ligand and ER geometry and the conformational flexibility of ER ligands [7] create significant challenges to mapping the estrogen binding domain. Ligands can also induce alterations in the tertiary structure of the ER binding complex, which in turn may alter binding to estrogen hormone responsive elements and subsequent transactivational events [8][9][10][11].…”