Expression profiling of genes in androgen metabolism in androgen-independent prostate cancer cells under an androgen-deprived environment: mechanisms of castration resistance

Objective: In an earlier study, we obtained androgen-independent prostate cancer cells (LNCaP-AI) and flutamide tolerantLNCaP-AI (LNCaP-AI+F cells) that could survive in an androgen-free environment without or with flutamide, respectively. In the present study, we investigated the molecular mechanism of the castration resistance. Material and Methods: qRT-PCR was applied to measure the expression levels of genes coding for enzymes in the lysophosphatidylcholine (LPC) metabolic pathway and responsible for cholesterol and androgen metabolism in these cell lines. An ExProfileTM Human PI3K-AKT Signaling Related Gene qPCR Array was also used to investigate the expression levels of genes in the intracellular metabolic pathways in an emasculated hormone environment. Results: Compared with androgen-responsive prostate cancer (LNCaP) cells, phospholipase D1 (PLD1) expression was increased 259and 410-folds in LNCaP-AI and LNCaP-AI+F cells, respectively, and the PI3K/AKT signaling pathway was enhanced. Additionally, the expression of cholesterol metabolic enzymes and rate-limiting enzymes, such as organic anion-transporting polypeptide 1B3 (OATP1B3) (LNCaP-AI cells: 19.08-fold; LNCaP-AI+F cells: 14.34-fold), low density lipoprotein receptor (LDL-r ) (LNCaP-AI cells: 23.34-fold; LNCaP-AI+F cells: 8.78-fold), squalene epoxidase (SQLE) (LNCaP-AI cells: 22.03-fold; LNCaP-AI+F cells: 10.27-fold), and scavenger receptor B1 (SCARB1) (LNCaP-AI cells: 10.27-fold; LNCaP-AI+F cells: 5.75-fold), was significantly increased. Furthermore, the expression of androgen synthetases, such as steroid 17-alpha-monooxygenase (CYP17A1) (LNCaP-AI cells: 28.59-fold; LNCaP-AI+F cells: 4.32-fold), steroid 5 alpha-reductase 2 (SRD5A2) (LNCaP-AI cells: 51.50-fold; LNCaP-AI+F cells: 12.91-fold), aldo-keto reductases (AKR1C1, AKR1C2, AKR1C3) (LNCaP-AI: 8.63-fold; LNCaP-AI+F cells: 7.10-fold), and androgen receptor (AR) (LNCaP-AI: 39.18-fold; LNCaP-AI+F cells: 36.56-fold), was increased significantly (P < 0.05). Conclusions: Our results revealed that the survival of LNCaP AI cells in androgen-free medium is due to selfsynthesis of androgen, increased cholesterol intake and increased AR expression. These evidences suggest that the castration-resistant LNCaP cells are not androgen-independent but have developed or activated a set of AR-related signaling pathways to increase endogenous androgen biosynthesis and AR expression.