Abstract
Four human aldo–keto reductases (AKRs) that belong to the AKR1C subfamily function in vitro as 3-keto-, 17-keto- and 20-ketosteroid reductases or as 3α-, 17β- and 20α- hydroxysteroid oxidases to varying degrees. By acting as ketosteroid reductases or hydroxysteroid oxidases these AKRs can either convert potent sex hormones (androgens, estrogens and progestins) into their inactive metabolites or they can form potent hormones by catalyzing the reverse reaction. In this manner they may regulate occupancy and trans-activation of steroid hormone receptors. Tissue distribution studies previously indicated that AKR1C2 (type 3 3α-hydroxysteroid dehydrogenase (3α-HSD)) and AKR1C3 (type 2 3α-HSD) are highly expressed in human prostate. An assessment of the directionality of these AKR1C isozymes in a cellular environment would help identify which isozymes are responsible for 5α-dihydrotestosterone (5α-DHT) formation or its elimination in the prostate. An imbalance in 5α-DHT levels has been implicated in development of prostate carcinoma and benign prostatic hyperplasia. We focused our attention on AKR1C2 since this is the isoform that will oxidize 3α-androstanediol (3α-diol) to 5α-DHT in vitro, suggesting it could elevate 5α-DHT levels. To determine whether AKR1C2 preferentially functions as a reductase or an oxidase in a cellular context, we transiently transfected AKR1C2 (pcDNA3-AKR1C2) into COS-1 cells and stably transfected pcDNA3-AKR1C2 and pLNCX-AKR1C2 constructs into PC-3 and LNCaP cells, respectively. COS-1 is a monkey kidney cell line, while PC-3 and LNCaP cells are androgen receptor (−) and (+) prostate adenocarcinoma cell lines, respectively. In transient COS-1-AKR1C2 and in stable PC3-AKR1C2 transfectants, AKR1C2 functioned as a 3-ketosteroid reductase inactivating 5α-DHT. In androgen dependent human prostate cancer cells LNCaP, it was not possible to ascertain the preferred direction of AKR1C2 by stable transfection due to the high rate of 5α-DHT and 3α-diol glucuronidation. Based on these findings AKR1C2 may diminish 5α-DHT and prevent this ligand from activating the androgen receptor in situ.
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