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

Abstract

Objective. Peroxisome proliferator-activated receptor gamma (PPARg) is a member of the nuclear hormone receptor superfamily. Treatment of PPARg 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 PPARg. In this study, we investigated the expression of PPARg in human normal cervix and cervical carcinoma tissues, and as well as the effect of PPARg 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 PPARg using real-time RT-PCR and Western blot analysis. Immunohistochemical staining for PPARg was also performed on the serial sections of 40 cervical carcinomas. In addition, we evaluated the feasibility of PPARg 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 PPARg mRNA and protein in cervical carcinoma tissues than in normal cervical tissues. The extent and intensity of immunoreactive PPARg 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 PPARg, while C-33A cells express low level of PPARg. Treatment with ciglitizone inhibited the growth of C-4II cells in a dosedependent manner, while the growth inhibitory effect of ciglitizone was much less in C-33A cells. In order to test whether ciglitizoneinduced growth suppressive effects on cervical cancer cell lines is PPAR-dependent, we treated cervical cancer cells with ciglitizone and/ or GW9662 (a PPARg 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 p21Cip1/Waf1 and p27kip1 protein.