Activation of peroxisome proliferator-activated receptor gamma by troglitazone inhibits cell growth through the increase of p27(Kip1) in human pancreatic carcinoma cells

In the present study, we examine whether human pancreatic carcinoma cells e xpress peroxisome proliferator-activated receptor gamma (PPAR gamma) and th e effect of PPAR gamma activation by its selective ligand on cellular growt h in pancreatic cancer cells. Immunohistochemical study of resected human p ancreata using a polyclonal PPAR gamma antibody revealed that PPAR gamma pr otein expression in the nuclei of carcinoma cells was observed in 9 of 10 p ancreatic adenocarcinomas. In contrast, normal pancreatic duct epithelial c ells in the samples expressed no PPAR gamma. Reverse transcription-PCR and Northern blot analysis demonstrated that all four tested human pancreatic c ancer cell lines, PK-1, PK-8, PK-9, and MIA Paca-2, expressed PPAR gamma mR NA. Luciferase assay in PK-1 cells showed that troglitazone, a selective li gand for PPAR gamma, transactivated the transcription of a peroxisome proli ferator response element-driven promoter in a dose-dependent fashion. Trogl itazone inhibited the growth of all four pancreatic carcinoma cell lines in a dose-dependent manner. Cell cycle analysis by flow cytometry demonstrate d that troglitazone induced G(1) arrest in PK-I cells. To examine the role of cyclin-dependent kinase inhibitors in the G(1) arrest by troglitazone, w e determined p27(Kip1), p21(Cip1/Waf1) Or p18(Ink4c) protein expression by Western blot analysis in trogtitazone-treated PK-1 cells. Troglitazone incr eased p27(Kip1) hot not p21(Cip1/Waf1) Or p18(Ink4c) protein levels in time - and dose-dependent manners. To clarify the functional importance of p27(K ip1) in the cell growth inhibition by troglitazone, we examined the effect of an antisense oligonucleotide against p27(Kip1) On the inhibition of cell proliferation by troglitazone, In PK-I cells treated with an antisense oli gonucleotide to p27(Kip1), troglitazone-induced inhibition of cell growth w as not observed. In contrast, troglitazone inhibited cell proliferation in cells that had been transfected with control mismatch oligonucleotide, Thes e results suggest that human pancreatic carcinoma cells express functional PPAR gamma and that PPAR gamma activation by troglitazone induced growth in hibition associated with G(1) cell cycle arrest in pancreatic carcinoma cel ls. It has also been indicated that p27(Kip1) may be a key molecule in the inhibition of cell growth by troglitazone. All these results suggest that P PAR gamma could be considered as a possible target molecule for treatment i n human pancreatic carcinomas.