Close kinship of human 20 alpha-hydroxysteroid dehydrogenase gene with three aldo-keto reductase genes

Background: 20 alpha-Hydroxysteroid dehydrogenase (HSD) is a member of the aldo-keto reductase (AKR) superfamily and catalyses the reaction of progest erone to the inactive form 20 alpha-hydroxyprogesterone. Progesterone plays an important role in the maintenance of pregnancy, and, in rodents, plasma progesterone levels decrease abruptly just before parturition. The inducti on of 20 alpha-HSD is thought to be responsible for the decrease in plasma progesterone at term. High homology between human 20 alpha-HSD [AKR 1C1] cD NA with other AKRs had caused difficulty in gene isolation and expression a nalysis. Thus, the metabolism of progesterone in the human reproductive sys tem remained unclear. Results: By hybridization with rat 20 alpha-HSD [AKR 1C8] cDNA and high-str ingency polymerase chain reaction (PCR) with gene-specific primers, we were able to isolate the human 20 alpha-HSD, bile acid-binding protein (BABP) [ AKR 1C2], prostaglandin F synthase (PGFS) [AKR 1C3], and dihydrodiol dehydr ogenase (DD) 4 [AKR 1C4] genes. These genes had similar exon-intron organiz ations and shared a high homology. The four recombinant enzymes encoded by these genes showed distinct substrate specificity. By reverse transcription -PCR analysis, human 20 alpha-HSD, BABP and PGFS mRNAs were expressed ubiqu itously, while DD4 mRNA was restricted to the liver. Promoter activities of the 20 alpha-HSD, BABP and PGFS genes were high, both in ovarian granulosa cells and hepatocytes. Radiation hybridization analysis revealed that all these genes were located close together in chromosome 10. Conclusion: The human gene encoding for the progesterone-metabolizing enzym e 20 alpha-HSD in the female reproductive system was cloned, and its expres sion and gene localization were elucidated. BABP, PGFS and DD4 genes, which were highly homologous to the 20 alpha-HSD gene, were also cloned, and the ir structure and function were characterized.