CHARACTERIZATION OF 17-BETA-HYDROXYSTEROID DEHYDROGENASE-IV

17 beta-Hydroxysteroid dehydrogenase (17 beta-HSD) IV is coded by 2.9 kb mRNA translated to an 80 kDa protein which is N-terminally cleaved to a 32 kDa enzyme. The 17 beta-HSD IV is dedicated to steroid inactiv ation and reveals only 25% amino acid similarity with 17 beta-HSD I-II I enzymes. Despite five Asn-Xaa-Ser/Thr (Xaa = unspecified amino acid) sites in the 80 kDa protein the enzyme is not glycosylated. The porci ne 32 kDa 17 beta-HSD IV forms dimers of 75 kDa. The highest 17 beta-H SD IV mRNA expression and specific activities are found in liver and k idney followed by ovary and testes. In porcine gonads the immunofluore scence assigned the 17 beta-HSD IV to granulosa cells and to Leydig an d Sertoli cells. As shown by the treatment with phorbol-myristate-acet ate in vitamin D-differentiated monocytic leukemia THP1 cells, steroid synthesis and inactivation are regulated differentially by the protei n kinase C pathway: an increase in aromatase is accompanied by a decre ase in 17 beta-HSD IV mRNA levels.