Triptolide inhibits colon-rectal cancer cells proliferation by induction of G1 phase arrest through upregulation of p21

Triptolide, a diterpene triepoxide compound extracted from the traditional Chinese medicine herb Tripterygium wilfordii Hook F., is a potential cancer chemotherapeutic for tumors. However, the mechanism of anti-proliferative mechanism of triptolide in colon cancer cells is not entirely clear. Triptolide markedly inhibited HT29 and SW480 cells proliferation in a dose- and time-dependent manner. Triptolide decreased ERK and AKT phosphorylation, and GABPα expression in colon cancer cells. Beta-catenin expression and phosphorylation were not altered by incubation of triptolide. However, we found that triptolide repressed expression of LEF/TCF. Although it did not significantly affect cells apoptosis, triptolide induced G1 phase arrest dose-dependently. Further detection for the expression of cell cycle-related proteins suggesting that triptolide stimulate expression of p21 and repress cyclin A1. Increased p21 binded to CDK4/CDK6, therefore blocked function of CDK4/CDK6, and subsequently contribute to the G1 arrest. These data suggested that triptolide is a potential agent for treatment of colon cancer, and its anti-proliferation effect mainly occur through G1 phase arrest.