Breast Cancer Associated Estrogen Receptors: Catechol Estrogen Receptors in ER-Minus Mice

摘要

Previous studies suggest the presence of a distinct non-ER-alpha/ER- beta estrogen-signaling pathway in the ER-alpha-KO mouse. To further characterize the receptor mechanism regulating these novel 4OHE2-induced responses, we have synthesized (3H)4OHE2 (4-hydroxy-estradiol) and (3H)4OHEl (4- hydroxyestrone) using a cytochrome P450-mediated enzymatic procedure. Using ER- alpha-KO cellular cytosolic extracts, (3H)4OHE2 specific binding was competed with various unlabeled catechol estrogen compounds but not unlabeled 17-beta-E2 and ICI 182,780. (3H)4OHE2 binding studies indicated significant binding differences among various tissues in WT (wild-type), ER-alpha-KO and ArKO (aromatase knockout) female mice which may indicate regulation by either E2 or ER-square. In WT & ER-alpha-KO mice, the highest concentrations of specific (3H) 4OHE2 binding were found in the bladder, lung & skeletal muscle. Interestingly, the highest concentrations of specific (3H)4OHE2 binding among ArKO tissues were found in the mammary, uterus and ovary. Scatchard analysis of (3H)4OHE1 binding in ER-alpha-KO mice identified a single class of high-affinity (Kd (caret)/= 1.7 nM), saturable binding sites in several tissues not competed by E2. Collectively, our results suggest the interaction of these radiolabeled catechol estrogen compounds with a putative mouse 'ER-gamma' protein. Efforts to clone this 'ER- gamma' are ongoing.