A Novel Peroxisome Proliferator-activated Receptor Gamma Ligand, MCC-555, Induces Apoptosis Via Posttranscriptional Regulation of NAG-1 in Colorectal Cancer Cells

Apoptosis and/or differentiation induction caused by the peroxisome proliferator-activated receptor gamma (PPARgamma) ligand is a promising approach to cancer therapy. The thiazolidinedione derivative MCC-555 has an apoptotic activity in human colorectal cancer cells, accompanied by up-regulation of a proapoptotic nonsteroidal anti-inflammatory drug-activated gene (NAG-1) in a PPARgamma-independent manner. Treatment with MCC-555 resulted in the induction of NAG-1 expression and apoptosis in HCT-116 cells. Down-regulation of NAG-1 by small interfering RNA suppressed MCC-555-induced apoptosis. MCC-555 was found to affect NAG-1 mRNA stability. To further define the underlying mechanism of RNA stability affected by MCC-555, we cloned the 3'-untranslated region (3'UTR) of human NAG-1 mRNA, which contains four copies of an AU-rich element (ARE), downstream from the luciferase gene. The reporter activity was reduced to approximately 70% by inserting the 3'UTR. In addition, deletion of ARE sequences in the 3'UTR or MCC-555 treatment substantially restored activity. This effect of MCC-555 on the ARE-mediated mRNA degradation was inhibited by extracellular signal-regulated kinase (ERK) pathway inhibitors. Subsequently, rapid phosphorylation of ERK1/2 by MCC-555 treatment was detected. Moreover, ERK small interfering RNA suppressed MCC-555-induced NAG-1 expression. These results suggest that ARE sequences in the 3'UTR of the NAG-1 gene contribute to mRNA degradation and ERK1/2 phosphorylation is responsible for the stabilization of NAG-1 mRNA. These findings may provide a novel explanation for the antitumorigenic and/or proapoptotic action of MCC-555 in human colorectal cancer and the ability of pharmacologic approaches to be used against diseases caused by alterations of RNA stability.