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J Bryndová, P Klusoová, M Kuka, K Mazancová-Vagnerová, I Mikík

Institute of Physiology, Czech Academy of Sciences, Vídeská 1083, CZ-142 20 Prague 4-Kr, Czech Republic

(Requests for offprints should be addressed to J Pácha; Email: pacha{at}biomed.cas.cz)

The ligand specificity and activation of steroid receptors depend considerably on the enzymatic activities involved in local pre-receptor synthesis and the metabolism of the steroids. Several enzymes in particular, steroid dehydrogenases have been shown to participate in this process. Here we report the isolation of 20-hydroxysteroid dehydrogenase (ch20HSD) cDNA from chicken intestine and the distribution of ch20HSD mRNA and 20-reductase activity in various avian tissues. Using a reverse transcription PCR and comparison with the known sequences of mammalian 20ßHSDs, we have isolated a new ch20HSD cDNA. This cDNA predicted 276 amino acid residues that shared about 75% homology with mammalian 20ßHSD. Sequences specific to the short-chain dehydrogenase/reductase superfamily (SDR) were found, the Gly-X-X-X-Gly-X-Gly cofactor-binding motif (residues 11–17) and the catalytic activity motif Tyr-X-X-X-Lys (residues 193–197). The cDNA coding for ch20HSD was expressed in Escherichia coli by placing it under isopropylthiogalactoside (IPTG) inducible control. Both the IPTG cells of E. coli and the isolated recombinant protein reduced progesterone to 20-dihydroprogesterone, corticosterone to 20-dihydrocorticosterone and 5-dihydrotestosterone to its 3-ol derivative. The 20-reductase and 3-reductase activities of ch20HSD catalyzed both 3/ß- and 20/20ß-epimers. The mRNA transcripts of ch20HSD were found in the kidney, colon, and testes; weaker expression was also found in the heart, ovaries, oviduct, brain, liver, and ileum. 20-Reductase activity has been proven in tissue slices of kidney, colon, ileum, liver, oviduct, testis, and ovary; whereas the activity was nearly absent in the heart and brain. A similar distribution of 20-reductase activity was found in tissue homogenates measured under V_max conditions. These results suggest that chicken 20HSD is the latest member of the SDR superfamily to be found, is expressed in many avian tissues and whose precise role remains to be determined.