Decreased expression of glucocorticoid receptor in prostate carcinomas and its anti-tumorigenic activity in PC cells in vitro.

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Glucocorticoids are extensively used for combinational chemotherapy of patients with advanced prostate cancer (PC). Despite the wide use of these hormones, there has not been a systematic analysis of the expression and function of glucocorticoid receptor (GR) in PC cells. GR is a well-known transcription factor that belongs to a superfamily of nuclear hormone receptors. We performed immunostaining of 20 benign prostate hyperplasia (BPH), 35 high grade PIN (HGPIN) and 71 PC samples (Gleason score 6-10), and observed that GR expression and nuclear localization of GR was strongly decreased/absent in ∼ 90% of PCs compared to apparently normal prostate glands and BPH. The decreased GR expression appeared to be an early event in PC tumorigenesis as GR immunostaining was also decreased in high grade PIN cells even though to a lesser extent than in epithelial cells in PCs. Interestingly, some PC cell lines including LNCaP cells, lack GR expression similar to PC tumors. To better understand the role of GR in PC cells, we generated LNCaP cell line stably expressing GR using CMV.GR lentivirus. Treatment of LNCaP-GR cells with the glucocorticoid, fluocinolone acetonide (FA), resulted in strong inhibition of both proliferation of cells in monolayer and anchorage independent growth in soft agar. The effects correlated with up-regulation of p21 and p27, decreased expression of cyclin D1 and proliferation marker Ki67, and down-regulated phosphorylation of c-Myc. Furthermore, the activated GR signaling resulted in the overall normalization of the LNCaP cell phenotype. The expression of PC markers hepsin and AMACR, that are usually overexpressed in PCs, was down-regulated in LNCaP-GR cells. In contrast, maspin which is usually lost in PCs, was up-regulated in LNCaP-GR cells. The evaluation of GR effect on cell signaling revealed an inhibition of activity of MAP-kinases (MAPKs) involved in the regulation of survival and proliferation such as p38, JNK/SAPK, Mek1/2 and its down-stream target Erk1/2. We also found that GR overexpression resulted in the inhibition of numerous transcription factors including known GR interactors AP-1 and NF-kappaB, and others such as Ets-1, C/EBP, ATF, SRF, CREB and PAX6. Taken together these data suggest that GR may act as a tumor suppressor in prostate through inhibition of different signaling pathways involved in PC cell proliferation, survival and differentiation. Work was supported by DOD prostate grant DAMD17-03-1-0522 and Northwestern University Prostate SPORE Developmental Project.