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17β‐Hydroxysteroid Dehydrogenases in Human Bone Cells
Author(s) -
Dong Yu,
Qiu Qing Qing,
Debear Joanna,
Lathrop William F.,
Bertolini Donald R.,
Tamburini Paul P.
Publication year - 1998
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1359/jbmr.1998.13.10.1539
Subject(s) - osteoblast , cell culture , hydroxysteroid dehydrogenases , recombinant dna , gene isoform , microbiology and biotechnology , estrone , bone cell , messenger rna , chemistry , cell , reverse transcription polymerase chain reaction , hydroxysteroid , enzyme , alkaline phosphatase , biochemistry , in vitro , biology , dehydrogenase , endocrinology , gene , hormone , genetics
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 17β‐hydroxysteroid dehydrogenases (17β‐HSDs) in cultured human osteoblasts (HOB) and osteoblast‐like osteosarcoma cells (MG63, TE85, and SaOS‐2). Significant 17β‐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 17β‐HSD I was detectable only in MG63 cells, albeit at low levels, while 17β‐HSD II was present in MG63, TE85, and HOB, but not SaOS‐2, and 17β‐HSD III was absent from each bone cell type. 17β‐HSD IV was the only isoform present in all bone cells analyzed. Further analysis of the expression of 17β‐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 17β‐HSD IV ( K m = 49.7 μM, V max = 79.4 nmol/minute/mg of protein) and its HSD‐domain ( K m = 79.4 μM, V max = 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 ( K m = 98.8 μM, V max = 0.07 nmol/minute/mg of protein) which contain only 17β‐HSD IV based on RT‐PCR. These studies show that bone cells have the capacity to interconvert circulating estrogens and suggest that bone cell 17β‐HSDs serve primarily to attenuate the continuing actions of estradiol through conversion to its less potent form, estrone, under certain conditions.