17Beta-hydroxysteroid dehydrogenases in human bone cells

Interconversion of estrogens by osteoblasts may play a role in regulating bone mass. As a first step toward exploring this possibility, we investigated the expression and activity of 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) in cultured human osteoblasts (HOB) and osteoblast-like osteosarco...

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Bibliographic Details
Published in:Journal of bone and mineral research 1998-10, Vol.13 (10), p.1539-1546
Main Authors: Dong, Y, Qiu, Q Q, Debear, J, Lathrop, W F, Bertolini, D R, Tamburini, P P
Format: Article
Language:English
Subjects:
17-Hydroxysteroid Dehydrogenases - genetics
17-Hydroxysteroid Dehydrogenases - metabolism
Animals
Bone and Bones - enzymology
Bone Neoplasms - enzymology
Catalysis
Cells, Cultured
Enoyl-CoA Hydratase
Humans
Hydro-Lyases
Isoenzymes - metabolism
Kinetics
Multienzyme Complexes
Osteosarcoma - enzymology
Oxidation-Reduction
Peroxisomal Multifunctional Protein-2
Polymerase Chain Reaction
Recombinant Proteins - metabolism
Spodoptera
Tumor Cells, Cultured
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Summary:Interconversion of estrogens by osteoblasts may play a role in regulating bone mass. As a first step toward exploring this possibility, we investigated the expression and activity of 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) in cultured human osteoblasts (HOB) and osteoblast-like osteosarcoma cells (MG63, TE85, and SaOS-2). Significant 17beta-HSD activity was detected in cell-free extracts of all bone cells with oxidation of estradiol to estrone predominating over reduction. Reverse transcription-polymerase chain reaction (RT-PCR) experiments showed that the mRNA for 17beta-HSD I was detectable only in MG63 cells, albeit at low levels, while 17beta-HSD II was present in MG63, TE85, and HOB, but not SaOS-2, and 17beta-HSD III was absent from each bone cell type. 17Beta-HSD IV was the only isoform present in all bone cells analyzed. Further analysis of the expression of 17beta-HSD IV in these bone cells by immunoblotting revealed both the full-length 83 kDa protein and the proteolytic 38 kDa form. The kinetic parameters for estradiol oxidation by purified recombinant 17beta-HSD IV (Km = 49.7 microM, Vmax = 79.4 nmol/minute/mg of protein) and its HSD-domain (Km = 79.4 microM, Vmax = 476 nmol/minute/mg of protein) were significantly higher than previously reported, but consistent with the values obtained with crude cell-free extracts of SaOS-2 cells (Km = 98.8 microM, Vmax = 0.07 nmol/minute/mg of protein) which contain only 17beta-HSD IV based on RT-PCR. These studies show that bone cells have the capacity to interconvert circulating estrogens and suggest that bone cell 17beta-HSDs serve primarily to attenuate the continuing actions of estradiol through conversion to its less potent form, estrone, under certain conditions.
ISSN:0884-0431