Abstract 4536: Expression and cellular activation of peroxisome proliferator-activated receptor γ in granulosa cell tumors

Abstract

Abstract Granulosa cell tumors (GCT) of the ovary are rare, hormonally-active neoplasms characterized by endocrine manifestations, an indolent course and late relapse. Chemotherapy and hormonal therapy have proved to be of limited efficacy. Nuclear receptors (NR) have a central pathogenic role in endocrine malignancy and present as potential targets for therapeutic intervention. NR have established roles in granulosa cell biology but their roles in GCT remain largely unexplored. In order to systematically examine the NR family in GCT, we used ABI Taqman® Low Density Array microfluidic cards to analyse 14 GCT and two GCT-derived cell lines for expression of the 48 NR. The levels of expression were remarkably consistent across the GCT. We found that peroxisome proliferator-activated receptor gamma (PPARγ) had greater than ten-fold absolute expression when compared with either the NCBI tumour or brain reference RNA pools. PPARγ agonists are regarded as potential therapeutic agents in the treatment of inflammatory diseases and certain cancers. Given the high expression levels of PPARγ in GCT, we investigated whether the use of PPARγ and/or retinoid × receptor (RXR) agonists or antagonists have an effect on the GCT-derived cell lines, KGN and COV434. We used real-time cell analysis (RTCA) to investigate the cytotoxicity of the PPARγ agonist, troglitazone, and the RXR agonist, 9-cis-retinoic acid, by continuous monitoring of cell growth, proliferation and viability in the GCT-derived cell lines in real-time. We observed that a combination of troglitazone and 9-cis-retinoic acid significantly inhibited cell proliferation in the cell lines (56% compared to control). Because we have previously reported that steroid receptors are transrepressed in these GCT cells due to constitutive activation of the NF-κB signalling pathway, we tested the effect of troglitazone and 9-cis-retinoic acid in conjunction with a NF-κB inhibitor, BAY-117082. We observed a further decrease in cell proliferation (85% compared to control). This was a PPARγ-mediated effect as it was reversed by co-administration with the PPARγ antagonist, GW9662. The decrease in proliferation was due to cellular apoptosis. We also investigated whether PPARγ is transcriptionally active in these cells using a reporter construct, specific for PPARγ, and observed that GCT cells were not responsive to either PPARγ agonists or antagonists in vitro. This was found to be due to NF-κB transrepression; when NF-κB was inactivated, PPARγ signaling was restored. We conclude that, while the use of PPARγ agonists may have potential as therapeutic agents for treating GCT, a combination of therapies involving the abrogation of NF-κB signaling may be of greater efficacy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4536. doi:10.1158/1538-7445.AM2011-4536