3β-Hydroxysteroid Dehydrogenase Activity in Human Osteoblast-Like Cells

Abstract

This paper describes for the first time the presence of 3β-hydroxysteroid dehydrogenase (3β-HSD) activity in osteoblast-like cells and investigates its characteristics. 3β-HSD activity was detected by the formation of androstenedione from [³H]dehydroepiandrosterone (DHEA) in whole cell assays of human osteoblast-like cells, HOS and MG-63. The radiolabeled product, androstenedione, was purified by thin-layer chromatography and identified by recrystallization on admixture with authentic androstenedione to show constant specific activities. The apparent Michaelis constant (Km) for DHEA in HOS was found to be 9.9μM and that in MG-63 was 80.4μM. The expression of the 3μ-HSD messenger ribonucleic acid in HOS and MG-63 was demonstrated through a reverse transcription-polymerase chain reaction. The PCR products were confirmed by Southern blot analysis. The existence of 3β-HSD in osteoblast-like cells indicates that these cells convertΔ5 androgens into more biologically active Δ4 3-keto steroids. These results, together with the demonstration of other steroid converting enzyme systems, suggest that the osteoblast cells play an important role in facilitating hormonal action in bone tissue.