Several mammalian livers contain monomeric 17 beta-hydroxysteroid dehydrogenase (17 beta-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 17 beta-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 sequence of the protein aligned with a high degree of identity with rat and rabbit 20 alpha-HSDs, rat and human 3 alpha-HSD/dihydrodiol dehydrogenases, and bovine prostaglandin F synthase, which are members of the aldoketoreductase family, but was distinct from human 17 beta-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 17 beta-HSDs also exhibited low 20 alpha-HSD activity toward progestins, which is similar to bifunctional activity of human placental 17 beta-HSD. Therefore, the mouse enzyme was given the designation of estradiol 17 beta-dehydrogenase (A-specific). Northern analysis of mouse tissues revealed the existence of a single 1.7-kilobase 17 beta-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 17 beta-HSD protein was mainly detected in the liver by Western analysis.

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We previously cloned a cDNA for pig lung tetrameric carbonyl reductase which shows significant similarity to a putative 27‐kDa protein predicted from the cDNA for murine adipocyte RNA which had been increased in its differentiation [Nakanishi, M., Deyashiki, Y., Nakayama, T., Sato, K. & Hara, A. (1993) Biochem. Biophys. Res. Commun. 194, 1311–1316]. In this investigation, we isolated and sequenced a full‐length cDNA for the tetrameric enzyme from a mouse lung cDNA library. It consisted of 984 bp and coded for a protein of 244 amino acid residues, of which 202 residues were identified by protein sequencing. The expression of the cDNA in Escherichia coli resulted in synthesis of a protein structurally and functionally similar to the enzyme purified from mouse lung. The nucleotide sequence of the cDNA was virtually identical to that of the cDNA for the adipocyte 27‐kDa protein. Although Northern‐blot analysis of mouse tissues showed the enzyme mRNA to be 1.1 kb only in lung, low expression of the mRNA in all the extrapulmonary tissues, including adipose tissue, was demonstrated by a reverse‐transcription PCR method. Western‐blot analysis also indicated the presence of the enzyme in the adipose tissue. This is the first report on an identification of the putative gene product of adipocytes as tetrameric carbonyl reductase, the expression of which is tissue‐specifically regulated.

We previously cloned a cDNA for pig lung tetrameric carbonyl reductase which shows significant similarity to a putative 27-kDa protein predicted from the cDNA for murine adipocyte RNA which had been increased in its differentiation [Nakanishi, M., Deyashiki, Y., Nakayama, T., Sato, K. & Hara, A. (1993) Biochem. Biophys. Res. Commun. 194, 1311-1316]. In this investigation, we isolated and sequenced a full-length cDNA for the tetrameric enzyme from a mouse lung cDNA library. It consisted of 984 bp and coded for a protein of 244 amino acid residues, of which 202 residues were identified by protein sequencing. The expression of the cDNA in Escherichia coli resulted in synthesis of a protein structurally and functionally similar to the enzyme purified from mouse lung. The nucleotide sequence of the cDNA was virtually identical to that of the cDNA for the adipocyte 27-kDa protein. Although Northern-blot analysis of mouse tissues showed that enzyme mRNA to be 1.1 kb only in lung, low expression of the mRNA in all the extrapulmonary tissues, including adipose tissue, was demonstrated by a reverse-transcription PCR method. Western-blot analysis also indicated the presence of the enzyme in the adipose tissue. This is the first report on an identification of the putative gene product of adipocytes as tetrameric carbonyl reductase, the expression of which is tissue-specifically regulated.