Inhibition of estradiol binding to its receptor by the cupric ion

Abstract

Treatment of human recombinant estrogen receptor (hER) expressed in yeast with very low concentrations of the cupric ion decreased its ability to bind [3H]estradiol ([3H]E2) and [125I]tamoxifen aziridine (minimal Cu2+ concentration: 1 nM). This decrease was reflected in a loss of immunoreactivity for monoclonal antibodies raised against the hormone binding domain (HBD). An ER recombinant expressing solely the HBD confirmed that the ion operated at this level. Cysteines located within this domain contributed to the inhibitory action of the Cu2+ in view of a partial restoration of the [3H]E2 binding activity with β-mercaptoethanol. Histidines were also implicated since the influence of Cu2+ on the [3H]E2 binding parameters (Scatchard plot analysis) was maintained after oxidation of thiol groups by methyl methanethiosulfonate, and partly reversed by imidazole.