Resveratrol-induced G₂ arrest through the inhibition of CDK7 and p34^CDC2 kinases in colon carcinoma HT29 cells

Resveratrol (3,5,4′-trihydroxystilbene), a phytoalexin found in grapes and other food products, has been shown to have cancer chemopreventive activity. However, the mechanism of the anti-carcinogenic activity is not well understood. Here, we offer a possible explanation of its anti-tumor effect. Based on flow cytometric analysis, resveratrol inhibited the proliferation of HT29 colon cancer cells and resulted in their accumulation in the G₂ phase of the cell cycle. Western blot analysis and kinase assays demonstrated that the perturbation of G₂ phase progression by resveratrol was accompanied by the inactivation of p34^CDC2 protein kinase, and an increase in the tyrosine phosphorylated (inactive) form of p34^CDC2. Kinase assays revealed that the reduction of p34^CDC2 activity by resveratrol was mediated through the inhibition of CDK7 kinase activity, while CDC25A phosphatase activity was not affected. In addition, resveratrol-treated cells were shown to have a low level of CDK7 kinase-Thr¹⁶¹-phosphorylated p34^CDC2. These results demonstrated that resveratrol induced cell cycle arrest at the G₂ phase through the inhibition of CDK7 kinase activity, suggesting that its anti-tumor activity might occur through the disruption of cell division at the G₂/M phase.