Involvement of p-15INK4b gene expression in oleanolic acid and ursolic acid induced apoptosis of hepG2 cells

HY Hsu, PhD

Department of Life Science, Tzu-Chi University, Hualien, Taiwan.

Two triterpene acids, oleanolic acid (OA) and ursolic acid (UA), purified components from several Chinese crude drugs with known antitumor activity such as Hedyotis corymbosa and Hedyotis diffusa, were examined for their ability and possible pathway on inhibiting the tumor growth of hepG2 cells. Cells were treated with OA and UA with doses of 100 and 200 ug/ml for 12, 24 and 36 hrs, respectively. The changes of DNA fragmentation, apoptotic bodies, DNA synthesis and the expression of cell cycle related genes were investigated after various treatments. Decrease of DNA synthesis in cells treated with both OA and UA was obviously observed at these doses for 24 and 36 hrs by using BrdU staining method. Total RNA were purified with RNA Zol B reagent and the first stranded cDNA were synthesized by AMV transcriptase. Semiquantitation of the cDNA was performed by primer dropping method. Both mRNA and protein of the CDK inhibitor of INK4 family which specifically inhibits CDK4/6 activity and then reduces the phosphorylation of RB, p-15INK4b, in hepG2 cells were greatly induced by OA and UA. However, the expression of another member in this family, p-16INK4a, was not significantly induced. Other CDK inhibitors such as p-21CIP, p-27KIP and cell cycle related genes were not induced after various OA and UA treatments. The DNA fragmentation and apoptotic bodies were also found in this study with both the time- and dose-dependent phenomena. These results suggested that the apoptosis induced by OA and UA might be partially mediated through PKC pathway and associated with p-15INK4b gene induction.

KEY WORDS: Triterpene Acids, CDKs, Cell Arrest.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Apoptosis - Molecular Mechanisms.