Peroxisome proliferator-activated receptor γ ligands induce cell cycle arrest and apoptosis in human renal carcinoma cell lines

Aim: To study the effect of peroxisome proliferator-actived receptor γ (PPARγ) ligands on cell proliferation and apoptosis in human renal carcinoma cell lines. Methods: The expression of PPARγ was investigated by reverse transcriptase polymerase chain reaction (RT-PCR), Western blot and immunohistochemistry. The effect of thiazolidinedione (TZD) PPARγ ligands on growth of renal cell carcinoma (RCC) cells was measured by MTT assay and flow cytometric analysis. Cell death ELISA, Hoechst 33342 fluorescent staining and DNA ladder assay were used to observe the effects of PPARγ ligands on apoptosis. Regulatory proteins of cell cycle and apoptosis were detected by Western blot analysis. Results: PPARγ was expressed at much higher levels in renal tumors than in the normal kidney (2.16±0.85 vs 0.90±0.73; P<0.01). TZD PPARγ ligands inhibited RCC cell growth in a dose-dependent manner with IC ₅₀ values of 7.08 μmol/L and 11.32 μmol/L for pioglitazone, and 5.71 μmol/L and 8.38 μmol/L for troglitazone in 786-O and A498 cells, respectively. Cell cycle analysis showed a G ₀/G ₁ arrest in human RCC cells following 24-h exposure to TZD. Analysis of cell cycle regulatory proteins revealed that TZD decreased the protein levels of proliferating cell nuclear antigen, pRb, cyclin D ₁, and Cdk4 but increased the levels of p21 and p27 in a time-dependent manner. Furthermore, high doses of TZD induced massive apoptosis in renal cancer cells, with increased Bax expression and decreased Bcl-2 expression. Conclusion: TZD PPARγ ligands showed potent inhibitory effect on proliferation, and could induce apoptosis in RCC cells. These results suggest that ligands for PPARγ have potential antitumor effects on renal carcinoma cells.