Decrease of hormone binding capacity of estrogen receptor by calcium.
We have addressed the question as to whether calcium may modify the [3H]estradiol ([3H]E2) binding properties of the estrogen receptor (ER). A human recombinant full length ER (yER) expressed in yeast was used to limit the potential interference of ER-associated proteins and proteases present in the target tissues. Ca++ (0.1-10 mM) always produced an important loss of [3H]E2 binding capacity without any effect on the hormone binding affinity of residual receptors. This loss was reflected in a decrease of immunoreactivity for monoclonal antibodies raised against the hormone binding domain. An ER recombinant expressing solely this domain confirmed that the ion operated at this level. Binding of [125I]Z-17 alpha-(2-iodovinyl)-11 beta-chloromethyl estradiol-17 beta (an compound with very high selectivity for ER) as well as [125I]tamoxifen aziridine were similarly affected. Size-exclusion chromatography failed to reveal the emergence of any ER isoforms of low molecular weight rejecting the hypothesis of a Ca(++)-induced proteolysis. In agreement with this conclusion, EDTA reversed the loss of [3H]E2 binding capacity. Phosphoamino acids (PY, PT and PS) partly antagonized the effect of Ca++ suggesting its interaction with phosphoamino acid residues. Worthy of note, the effect of Ca++ appeared more marked when assessed by DCC than HAP assay. The phosphocalcic nature of the HAP matrix may explain this phenomenon which was observed with cytosolic ER from various origins.
Maaroufi
Y
Y
Laboratoire J.-C. Heuson de Cancérologie Mammaire, Service de Médecine Interne, Institut Jules Bordet, Brussels, Belgium.
Ben Hardouze
A
A
Leclercq
G
G
D000818:Animals; D001672:Biocompatible Materials / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002417:Cattle; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D002850:Chromatography, Gel; D017886:Durapatite / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D004958:Estradiol / Q000378:metabolism*; D006801:Humans; D019606:Phosphoamino Acids / Q000494:pharmacology; D051381:Rats; D011960:Receptors, Estrogen / Q000187:drug effects / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism
D001672:Biocompatible Materials; D002614:Chelating Agents; D019606:Phosphoamino Acids; D011960:Receptors, Estrogen; D011994:Recombinant Proteins; D004958:Estradiol; D017886:Durapatite; D004492:Edetic Acid; D002118:Calcium