Activation of peroxisome proliferator-activated receptor-gamma by troglitazone (TGZ) inhibits human lung cell growth

Abstract

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a member of the nuclear hormone receptor superfamily of ligand-activated transcription factors and a crucial regulator of cellular differentiation. PPAR-gamma ligands have been demonstrated to inhibit growth of several cancer cells. In this study, two human lung cancer cells (NCI-H23 and CRL-2066) and one human lung normal cell (CRL-202) were used for the experiments. The results showed that in consistence with the loss of viability, troglitazone (TGZ) induced apoptosis of CRL-2066 and NCI-H23 cells but not CCL-202 cells. TGZ upregulated PPAR-gamma expression in all the three lung cell lines, especially in the cancer cells. In association of the time-dependent inhibition of the cell proliferation, TGZ downregulated the expression of Bcl-w and Bcl-2 but activated extracellular signal-regulated kinase (ERK)1/2 and p38, suggesting that the growth-inhibitory effect of TGZ is associated with the reduction of Bcl-w and Bcl-2 and the increase of ERK1/2 and p38 activation. SAPK/JNK activation assay showed a decreased activity in all the three cell lines tested after TGZ treatment. It was also demonstrated that TGZ could activate PPAR-gamma transcriptionally. We conclude that TGZ inhibits growth of human lung cancer cells via the induction of apoptosis and the inhibition of cell growth, at least in part, in a PPAR-gamma-relevant manner. The mechanism of TGZ is associated with the activation of ERK and p38, the reduction of SAPK/JNK activity, and the alteration of Bcl-w and Bcl-2.