Reversible inhibition of estrogen receptor activation by molybdate.

Contradictory findings on the effects of sodium molybdate on estrogen receptor activation have been recently reported. In a preliminary report (Mauck, L. A., and Notides, A. C. (1980) Proceedings of the 62nd Annual Meeting of the Endocrine Society, Abstr. 209) it was suggested that sodium molybdate prevents heat activation of the calf uterine estrogen receptor. This effect was reversible upon dialysis and reheating. In contrast, in a detailed study of the molybdate effects on the uterine estrogen receptor of BALB/c mouse, (Shyamala, G., and Leonhard, L. (1980) J. Biol. Chem. 255, 6028-6031) it was shown that molybdate blocks activation irreversibly. To clarify this issue, we have examined the effects of this reagent on the estrogen receptor of calf uterus, rat, and BALB/c mouse. Activation was evaluated by an increase in sedimentation rate on sucrose gradients and by increased affinity for nuclei. We report hat he temperature-promoted transformation of the inactive receptor-estradiol complexes formed at 0 “C into the activated state is completely inhibited when heating is performed in the presence of 10 mM sodium or ammonium molybdate. Postincubation of activated hormone-receptor complexes at 0 “C with molybdate did not alter the receptor state. When molybdate-inhibited receptor-estradiol complexes were dialyzed for 3 h at 0 “C the receptor remained in the inactive state. However, reheating after dialysis promoted receptor transformation into the activated state. Similarly, incubation of molybdate-inhibited receptor-estradiol complexes with 0.4 M NaCl, KC1, or NH4C1 at 0 “C for 2 or 15 h followed by reheating resulted in receptor activation. The molybdate inhibition of receptor activation could also be reversed by 200 mM arginine or lysine. Thus, it appears that the inhibitory effect of molybdate on the activation of the calf uterine estrogen receptor is fully reversible. Similar data were obtained with uterine estrogen receptor of the rat and BALB/c mouse. While the mechanism of action of molybdate remains unclear, our data suggest that receptor activation is inhibited through nonspecific ionic interactions with the receptor or a cytosolic component required for activation. Such interactions can be disrupted by dialysis, salts, and amino acids, thereby releasing the cytosol from the inhibiting action of molybdate.