RESUMO
The catechol estrogens (CE), 2-hydroxyestradiol (2-OH-E2) and 4-hydroxyestradiol (4-OH-E2) were analyzed for their binding affinity to the estrogen receptor of MCF-7 cells. Applying a competitive binding assay to cytosols prepared from MCF-7 breast cancer cells, we measured a relative binding affinity of 23% (2-OH-E2) and 26% (4-OH-E2) compared to E2. Nuclear binding assays with the same cell line demonstrated a high specific binding with Kd's of 0.31 nM (2-OH-E2) and 0.21 nM (4-OH-E2). The relative binding affinity measured was 25% and 42% for 2-OH-E2 and 4-OH-E2, respectively. Based on this nuclear binding it can be concluded that the estrogen receptor occupied by CE is bound within the nucleus and might therefore be transcriptionally active.
Assuntos
Neoplasias da Mama/metabolismo , Neoplasias da Mama/patologia , Estradiol/análogos & derivados , Receptores de Estrogênio/metabolismo , Ligação Competitiva , Neoplasias da Mama/ultraestrutura , Núcleo Celular/química , Núcleo Celular/metabolismo , Núcleo Celular/ultraestrutura , Citosol/química , Citosol/metabolismo , Citosol/ultraestrutura , Estradiol/análise , Estradiol/isolamento & purificação , Estradiol/metabolismo , Estrogênios de Catecol/análise , Estrogênios de Catecol/isolamento & purificação , Estrogênios de Catecol/metabolismo , Humanos , Prolactina/metabolismo , Receptores de Estrogênio/análise , Receptores de Progesterona/análise , Receptores de Progesterona/metabolismo , Células Tumorais CultivadasRESUMO
The binding affinity and relative estrogenic potency of 2-bromo-, 4-bromo-, 2-methyl- and 4-methylestradiol was evaluated in MCF-7 breast cancer cells. The relative binding affinities compared to estradiol were 47% for 2-methyl-, 25% for 4-methyl-, 37% for 4-bromo- and 17% for 2-bromoestradiol. However, both 2- and 4-methyl- as well as 2- and 4-bromoestradiol were able (a) to translocate the cytosolic estrogen receptor into the nucleus and (b) to induce the progesterone receptor in a concentration dependent manner. Finally, all ring-A substituted estrogens used in this study induced the pS2 mRNA as demonstrated by Northern-blotting. From these findings we conclude that 2-bromo-, 4-bromo-, 2-methyl- and 4-methylestradiol are agonistic ligands for the estrogen receptor in MCF-7 breast cancer cells.