Unusual estrogen-binding protein of the rat liver: effects on nuclear accumulation of estradiol-receptor complexes in vitro

The accumulation of [3H]estradiol-receptor complexes by liver nuclei after preliminary incubation of the hormone with rat liver cytosol was investigated. It was shown that the addition of a purified preparation of the unusual estrogen-binding protein (UEBP) isolated from the liver of males to the cytosol of females induces a dose-dependent inhibition of the subsequent accumulation of specifically bound [3H]estradiol in the nuclei. The addition of 1.5 μM 2α-hydroxytestosterone, testosterone, 1-dehydrotestosterone, 5α-androstane-3α,17β-diol, and 5α-dihydrotestosterone - a compound possessing pronounced affinity for the UEBP - to the liver cytosol of males leads to a 2-5-fold increase in subsequent nuclear accumulation of the estrogen-receptor complexes. Androsterone, which does not interact with the UEBP, does not exhibit such an effect. When liver cytosol of females, lacking the UEBP, is used, the indicated steroids are ineffective with respect to estrogen reception. It was concluded that the UEBP of the liver of male rats is capable of modulating estrogen reception