Down-regulation of peroxisome proliferator-activated receptor gamma in human cervical carcinoma

Objective. Peroxisome proliferator-activated receptor gamma (PPAR gamma) is a member of the nuclear hormone receptor superfamily. Treatment of PPAR gamma ligands has been shown to inhibit the growth of various human cancer cells. However, it has not been reported whether human cervical carcinoma cells express PPAR gamma. In this study, we investigated the expression of PPAR gamma in human normal cervix and cervical carcinoma tissues, and as well as the effect of PPAR gamma ligands on cervical cancer cells survival. Methods. Fresh cervical tissues from a study group of 10 study patients diagnosed with cervical carcinoma were analyzed for the expression of PPAR gamma using real-time RT-PCR and Western blot analysis. Immunohistochemical staining for PPAR gamma was also performed on the serial sections of 40 cervical carcinomas. In addition, we evaluated the feasibility of PPAR gamma ligands, as a potential therapeutic drug against cervical cancer cells using MTT assay and FACS analysis. Results. We found that there were lower expression levels of PPAR gamma mRNA and protein in cervical carcinoma tissues than in normal cervical tissues. The extent and intensity of immunoreactivre PPAR gamma in normal cervix tissues were statistically much greater than those of carcinoma tissues. In order to study effects of PPAR ligand on cell proliferation, we chose ciglitizone that showed very potent growth inhibitory effects on the proliferation of two human cervical cancer cell lines (C-33-A and C-4II). C-4II cells express high expression of PPAR gamma, while C-33A cells express low level of PPAR gamma. Treatment with ciglitizone inhibited the growth of C-4II cells in a dose-dependent manner, while the growth inhibitory effect of ciglitizone was much less in C-33A cells. In order to test whether ciglitizone-induced growth suppressive effects on cervical cancer cell lines is PPAR-dependent, we treated cervical cancer cells with ciglitizone and/or GW9662 (a PPAR gamma antagonist). No significant difference in cell survival was found in cells treated with ciglitizone alone vs. co-treated with ciglitizone and GW9662. GW9662 alone did not induce any cell growth arrest in the cells that we used (data not shown). Thus, we concluded that growth suppressive effects by ciglitizone may not be dependent upon status of PPAR expression. To clarify the mechanism by which ciglitizone inhibits the growth of cervical carcinoma cells, flow cytometry and Western blotting assay were performed. As results, we demonstrated that a large portion of C-4II cells (but not in C-33A) after ciglitizone treatment were arrest at G1 phase with the induction of p21(Cip1/Waf1) and p27(kip1) protein. Conclusions. These results suggest that PPAR gamma is down-regulated in Multiple human cervical Cancer tissues and cell lines, Ciglitizone may suppress human cervical cancer cells in PPAR-independent manner. (c) 2005 Elsevier Inc. All rights reserved.