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 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.
Dong
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Institute of Bone and Joint Disorders and Cancer, Bayer Corporation, West Haven, Connecticut 06516, USA.
Qiu
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QQ
Debear
J
J
Lathrop
W F
WF
Bertolini
D R
DR
Tamburini
P P
PP
D015067:17-Hydroxysteroid Dehydrogenases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001859:Bone Neoplasms / Q000201:enzymology; D001842:Bone and Bones / Q000201:enzymology*; D002384:Catalysis; D002478:Cells, Cultured; D004746:Enoyl-CoA Hydratase; D006801:Humans; D006836:Hydro-Lyases; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D009097:Multienzyme Complexes; D012516:Osteosarcoma / Q000201:enzymology; D010084:Oxidation-Reduction; D064029:Peroxisomal Multifunctional Protein-2; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000378:metabolism; D018411:Spodoptera; D014407:Tumor Cells, Cultured
D007527:Isoenzymes; D009097:Multienzyme Complexes; D011994:Recombinant Proteins; D015067:17-Hydroxysteroid Dehydrogenases; C044256:3 (or 17)-beta-hydroxysteroid dehydrogenase; D006836:Hydro-Lyases; D064029:Peroxisomal Multifunctional Protein-2; C104587:HSD17B4 protein, human; D004746:Enoyl-CoA Hydratase