Identification of a principal mRNA species for human 3α-hydroxysteroid dehydrogenase isoform (AKR1C3) that exhibits high prostaglandin D2 11-ketoreductase activity

Human 3 alpha-hydroxysteroid dehydrogenase exists in four isoforms, which belong to the aldo-keto reductase (AKR) superfamily and are named AKR1C1-AKR1C4. The properties of AKR1C3 have not been fully characterized compared to the other isoforms. In addition, a cDNA that shows more than 99% homology with AKR1C3 cDNA has been cloned from human myeloblasts. We have here expressed and purified a recombinant enzyme (designated as DBDH) from this cDNA, DBDH oxidized xenobiotic alicyclic alcohols and 3 alpha- or 17 beta-hydroxy-5 beta-androstanes, and catalyzed the reversible conversion between prostaglandin D-2 and 9 alpha,11 beta-prostaglandin F-2 more efficiently than that of 3 alpha- or 17 beta-hydroxysteroids: the respective K-m values were 0.6 and 6.8 mu M, and k(cat)/K-m values were about 1,000 min(-1) . mM(-1). Anti-inflammatory drugs highly inhibited the enzyme. The recombinant AKR1C3 prepared by site-directed mutagenesis of DBDH also showed the same properties as the wild-type DBDH. Analyses of expression of mRNAs for DBDH and AKR1C3 by reverse transcription-PCR indicated that only one mRNA species for DBDH is expressed in 33 human specimens of liver, kidney, lung, brain, heart, spleen, adrenal gland, small intestine, placenta, prostate, and testis. These results suggest that AKR1C3 acts as prostaglandin D-2 11-ketoreductase, and that its principal gene in the human has a coding region represented by DBDH cDNA.