3H]-Estradiol binding by chick liver nuclear extracts: mechanism of increase in binding following estradiol injection

Abstract

Specific high affinity binding of [ 3H]-estradiol by 0.5 M KCl extracts of chick liver nuclei is substantially increased by estradiol injection of the immature chick. The effect is observed shortly after estradiol injection, while the estradiol-induced production of serum phosphoproteins (vitellogenic response) is not detectable until about 24 hr.Cycloheximide given 90 min before estradiol inhibits the increase in nuclear binding for 12–15 hr. At 24–48 hr the levels of nuclear binding are similar to those in the estradiol-treated animals not given cycloheximide, but serum phosphoprotein levels are depressed by about 80% at 48 hr. By 75 hr however the serum of the cycloheximide-treated estrogenized chicks contains about twice as much phosphoprotein as does serum of chicks given estradiol alone.It is suggested that the inhibition of protein synthesis for 12–15 hr delays the vitellogenic response until sufficient levels of nuclear [ 3H]-estradiol binding protein can be synthesized. A correlation between the levels of nuclear [ 3H]-estradiol binding at 24 hr and phosphoprotein at 48 hr is shown in a dose-response experiment. In vitro , nafoxidine-HCl (Upjohn 11,100 A) inhibits binding of [ 3H]-estradiol by the chick liver nuclear extracts. In vivo , a single injection of nafoxidine with estradiol inhibits phosphoprotein production.Injection of nafoxidine alone results in a small but significant increase in [ 3H]-estradiol binding by nuclear extracts, but it is not estrogenic. A possible interpretation is that nafoxidine transfers low levels of a putative cytosol receptor to the nucleus, but is unable to induce the amplification mechanism required to give the levels of nuclear estradiol-binding protein needed for the vitellogenic response.