Activation of peroxisome proliferator-activated receptor gamma by troglitazone inhibits cell growth through the increase of p27KiP1 in human. Pancreatic carcinoma cells.

ABSTRACT

In the present study, we examine whether human pancreatic carcinoma cells express peroxisome proliferator-activated receptor gamma (PPARgamma) and the effect of PPARgamma activation by its selective ligand on cellular growth in pancreatic cancer cells. Immunohistochemical study of resected human pancreata using a polyclonal PPARgamma antibody revealed that PPARgamma protein expression in the nuclei of carcinoma cells was observed in 9 of 10 pancreatic adenocarcinomas. In contrast, normal pancreatic duct epithelial cells in the samples expressed no PPARgamma. Reverse transcription-PCR and Northern blot analysis demonstrated that all four tested human pancreatic cancer cell lines, PK-1, PK-8, PK-9, and MIA Paca-2, expressed PPARgamma mRNA. Luciferase assay in PK-1 cells showed that troglitazone, a selective ligand for PPARgamma, transactivated the transcription of a peroxisome proliferator response element-driven promoter in a dose-dependent fashion. Troglitazone inhibited the growth of all four pancreatic carcinoma cell lines in a dose-dependent manner. Cell cycle analysis by flow cytometry demonstrated that troglitazone induced G1 arrest in PK-1 cells. To examine the role of cyclin-dependent kinase inhibitors in the G1 arrest by troglitazone, we determined p27KiP1, p21CiP1/Waf1, or p18Ink4c protein expression by Western blot analysis in troglitazone-treated PK-1 cells. Troglitazone increased p27Kip1 but not p21Cip1/Waf1 or p18Inkc protein levels in time- and dose-dependent manners. To clarify the functional importance of p27Kip1 in the cell growth inhibition by troglitazone. All these results suggest that PPARgamma could be considered as a possible target molecule for treatment in human pancreatic carcinomas.