Details

Autor(en) / Beteiligte

• Steckelbroeck, Stephan
• Jin, Yi
• Gopishetty, Sridhar
• Oyesanmi, Busola
• Penning, Trevor M.

Titel

Human Cytosolic 3α-Hydroxysteroid Dehydrogenases of the Aldo-keto Reductase Superfamily Display Significant 3β-Hydroxysteroid Dehydrogenase Activity

Ist Teil von

• The Journal of biological chemistry, 2004-03, Vol.279 (11), p.10784-10795

Ort / Verlag

Elsevier Inc

Erscheinungsjahr

2004

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The source of NADPH-dependent cytosolic 3β-hydroxysteroid dehydrogenase (3β-HSD) activity is unknown to date. This important reaction leads e.g. to the reduction of the potent androgen 5α-dihydrotestosterone (DHT) into inactive 3β-androstanediol (3β-Diol). Four human cytosolic aldo-keto reductases (AKR1C1–AKR1C4) are known to act as non-positional-specific 3α-/17β-/20α-HSDs. We now demonstrate that AKR1Cs catalyze the reduction of DHT into both 3α- and 3β-Diol (established by 1H NMR spectroscopy). The rates of 3α- versus 3β-Diol formation varied significantly among the isoforms, but with each enzyme both activities were equally inhibited by the nonsteroidal anti-inflammatory drug flufenamic acid. In vitro, AKR1Cs also expressed substantial 3α[17β]-hydroxysteroid oxidase activity with 3α-Diol as the substrate. However, in contrast to the 3-ketosteroid reductase activity of the enzymes, their hydroxysteroid oxidase activity was potently inhibited by low micromolar concentrations of the opposing cofactor (NADPH). This indicates that in vivo all AKR1Cs will preferentially work as reductases. Human hepatoma (HepG2) cells (which lack 3β-HSD/Δ5–4 ketosteroid isomerase mRNA expression, but express AKR1C1–AKR1C3) were able to convert DHT into 3α- and 3β-Diol. This conversion was inhibited by flufenamic acid establishing the in vivo significance of the 3α/3β-HSD activities of the AKR1C enzymes. Molecular docking simulations using available crystal structures of AKR1C1 and AKR1C2 demonstrated how 3α/3β-HSD activities are achieved. The observation that AKR1Cs are a source of 3β-tetrahydrosteroids is of physiological significance because: (i) the formation of 3β-Diol (in contrast to 3α-Diol) is virtually irreversible, (ii) 3β-Diol is a pro-apoptotic ligand for estrogen receptor β, and (iii) 3β-tetrahydrosteroids act as γ-aminobutyric acid type A receptor antagonists.