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.
Institute of Bone and Joint Disorders and Cancer, Bayer Corporation, West Haven, Connecticut 06516, USA.
Y
Y
Dong
Q Q
QQ
Qiu
J
J
Debear
W F
WF
Lathrop
D R
DR
Bertolini
P P
PP
Tamburini
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