ABSTRACT
UCN-01, a selective inhibitor of protein kinase C, is known to inhibit the growth of cancer cells. Although it is currently undergoing clinical evaluation, information about its effect on human colon cancer is limited and the mechanism responsible is lacking. The objective of this study was to examine the cytotoxicity of UCN-01 to human colon cancer cells in vitro and its effect on the apoptotic molecules. HT-29, a radiation- and chemotherapy-resistant human colon cancer cell, was used in the study. Cell death/apoptosis was determined by the MTT assay and DNA fragmentation measurement. NF-kappaB activity was measured by an enzyme immunoassay method. Western blot was employed to examine the expression of relevant apoptotic molecules. The result showed that UCN-01 could induce apoptosis of human colon cancer cells in a time- and dose-dependent manner. It markedly reduced the expression of Bcl-xL, but enhanced the level of p38 MAPK. In addition to Bcl-xL and p38 MAPK, UCN-01 also increased both caspase-3 and peroxisome proliferator activated receptor gamma protein levels. HT-29 cells transfected with exogenous Bcl-xL showed a significant increase in NF-kappaB activity and prevented apoptosis induced by UCN-01. The overexpression of Bcl-xL also reversed other relevant molecular changes observed in UCN-01-treated cells. In conclusion, UCN-01 exerted an antitumor effect in human colon cancer cells by inducing apoptosis. The mechanism responsible appeared to be related to reduction of Bcl-xL and increased p38 MAPK. The overexpression of Bcl-xL can significantly prevent apoptosis induced by UCN-01.
Subject(s)
Apoptosis/drug effects , Protein Kinase C/antagonists & inhibitors , Staurosporine/analogs & derivatives , Staurosporine/pharmacology , Caspase 3 , Caspases/biosynthesis , Colonic Neoplasms , Dose-Response Relationship, Drug , HT29 Cells , Humans , Mitogen-Activated Protein Kinases/biosynthesis , NF-kappa B/metabolism , Proto-Oncogene Proteins c-bcl-2/antagonists & inhibitors , Receptors, Cytoplasmic and Nuclear/biosynthesis , Transcription Factors/biosynthesis , bcl-X Protein , p38 Mitogen-Activated Protein KinasesABSTRACT
Peroxisome proliferator-activated receptor gamma (PPARgamma) inhibits cell growth via promoting apoptosis. Human colorectal cancer tissues had abundant PPARgamma but the incidence of apoptosis was very low, suggesting a defect in the PPARgamma pathway. Here, we found that 15-hydroxy-eicosatetraenoic acid (15S-HETE), an endogenous ligand for PPARgamma, was significantly decreased in the serum of patients with colorectal cancer. Treatment of colon cancer cells with 15S-HETE inhibited cell proliferation and induced apoptosis, which was preceded by an increase in TGF-beta-inducible early gene (TIEG) and a decrease in Bcl-2. The action of 15S-HETE could be blocked when PPARgamma was suppressed. Overexpression of Bcl-2 prevented the apoptosis. The levels of TIEG and 15-lipoxygenase (15-LOX), the enzyme responsible for 15S-HETE production, was decreased in colorectal cancer. Therefore, colorectal cancer is associated with decreased 15S-HETE. Treatment of colon cancer cells with 15S-HETE inhibits cell proliferation and induces apoptosis in a PPARgamma-dependent pathway involving augmentation of TIEG and reduction of Bcl-2 expression.
