Molecular cloning and characterization of mouse estradiol 17β-dehydrogenase (A-specific), a member of the aldoketoreductase family

Abstract

Several mammalian livers contain monomeric 17β-hydroxysteroid dehydrogenase (17β-HSD) with A-stereospecificity in hydrogen transfer, which differs from the B-specific dimeric enzyme of human placenta in its ability to catalyze the oxidoreduction of xenobiotic trans-dihydrodiols of aromatic hydrocarbons and carbonyl compounds. Here, we report the isolation and characterization of a mouse cDNA clone encoding monomeric 17β-HSD of the liver. This clone had an entire coding region for a protein of 323 amino acid residues with a molecular weight of 37,055. The deduced se-quence of the protein aligned with a high degree of identity with rat and rabbit 20α-HSDs, rat and human 3α-HSD/dihydrodiol dehydrogenases, and bovine prostaglandin F synthase, which are members of the aldoketoreductase family, but was distinct from human 17β-HSD and carbonyl reductase, members of the short chain dehydrogenases. The expression of the cDNA in Escherichia coli resulted in synthesis of a protein that was active toward androgens, estrogens, and xenobiotic substrates. The recombinant and mouse liver 17β-HSDs also exhibited low 20α-HSD activity toward progestins, which is similar to bifunctional activity of human placental 17β-HSD. Therefore, the mouse enzyme was given the designation of estradiol 17β-dehydrogenase (A-specific). Northern analysis of mouse tissues revealed the existence of a single 1.7-kilobase 17β-HSD mRNA species in the liver, kidney, testis, and stomach. The liver mRNA content was considerably more abundant than those found in the other tissues, as 17β-HSD protein was mainly detected in the liver by Western analysis.