Specific binding of 4-hydroxyestradiol to mouse uterine protein: evidence of a physiological role for 4-hydroxyestradiol

Abstract

There are several indications of a possible physiological role for 4-hydroxyestradiol (4-OHE 2 ) in hormone-responsive tissues. To examine a hormonal activity of 4-OHE 2 , we have studied the binding of 3 H-labeled 4-OHE 2 to mouse uterine cytosolic protein. In uteri of 3-week-old mice, total binding was 319·4 13·9 fmol/mg protein. Binding in the presence of excess unlabeled 4-OHE 2 dropped to 82·1 1·7 fmol/mg protein, whereas 214·6 9·4 fmol/mg protein bound while incubating in an excess of unlabeled 17 -estradiol (E 2 ). The difference between the two binding values in the presence of excess steroid (132·5 11·1 fmol/mg protein) is taken as selective binding of 4-OHE 2 to a specific protein. In mice older than 4 weeks, the specific 4-OHE 2 binding declined: 32·0 4·0 fmol/mg protein at 8 weeks, 54·8 6·3 fmol/mg protein at 12 weeks and 54·6 5·2 fmol/mg protein at 9 months. Of other organs tested (liver, kidney, lung and whole brain) only lung showed significant selective binding of 4-OHE 2 . When E 2 -binding sites are blocked, 4-OHE 2 binding follows first-order kinetics, yielding a dissociation constant (K d ) value of 11·8 2·1 nM. The specific binding of 4-OHE 2 was not inhibited by any other steroids or estrogen metabolites that were tested, except for 2-hydroxyestradiol (2-OHE 2 ), which displayed competitive inhibition of 4-OHE 2 binding with an inhibition constant (K i ) value of 98·2 12·6 nM. These results lead us to conclude that 4-OHE 2 binds to a specific binding protein, distinct and different from binding to estrogen receptors (ER and ER ). The physiological role of this binding remains to be elucidated.

Protein disulfide isomerase is a multifunctional regulator of estrogenic status in target cells

“…gen metabolites, such as the well-known anticancer activity of 2-methoxy-E 2 [37,38], the unique actions of 4-hydroxy-E 2 [28,29], and the immunosuppressive effect of estriol [39].…”

“…Notably, 4-hydroxy-E 2 is a biologically active estrogen derivative [28,29], and PDI has a comparable binding affinity for E 2 and 4-hydroxy-E 2 (Fig. 1C).…”

Effects of 17β-estradiol, and its metabolite, 4-hydroxyestradiol on fertilization, embryo development and oxidative DNA damage in sand dollar (Dendraster excentricus) sperm

“…In addition, 4OHE2 has been shown to bind to estrogen receptors with relative binding affinities of 26 to 42%, relative to E2 (Schutze et al, 1994). 4-OHE2-specific binding proteins, separate from the classical nuclear estrogen receptors, have also been characterized and may provide unique estrogenic activity (Das et al, 1998; Markides and Liehr, 2005). …”

In Vivo Suppression of Bisphenol A on Estradiol 2- and 4-Hydroxylase Activities in Hepatic Microsomal Fractions of Male and Female Sprague-Dawley Rats

“…Hepatic hydroxylation of E2 to catechols 2-OHE and 4-OHE in rats is catalyzed by CYP1A1/2, 1B1, 2B1/2, 2C11 and 3A (Yager and Liehr, 1996;Zhu and Conney, 1998;Dawling et al, 2003) and the subfamily CYP1B1 has been identified as a major enzyme catalyzing 4-hydroxylation of E2 (Markides and Liehr, 2005). Furthermore, 2-OHE can be metabolized to 2-methoxyestradiol that has an inhibitory effect on cell proliferation (Seegers et al, 1989;Fotsis et al, 1994;Klauber et al, 1997).…”