Human Leukemia U937 Cells Inhibition of Mitogenactivated Protein Kinase Activation in Bcl-2 Protein Inhibits Bufalin-induced Apoptosis through

In a previous study, we demonstrated that bufalin, which is an active principle of Chinese medicine, chan'su, caused apoptosis in human leu kemla U937 cells by anomalous activation of mitogen-activated protein kinase (MAPK) via the signaling pathway of Ras, Raf-1, and MAPK kinase-1. Here, we report the effect ofoverexpression ofbcl-2 in U937 cells on the signaling pathway of apoptosis that Is induced by bufalin. The results indicated that the apoptosis induced by bufalin in U937 cells was significantly inhibited by overexpresslon of the Bcl-2 protein. No signifi cant difference was detected in the activation of MAPK kinase-1 that is Induced by bufalin In wild-type or Bcl-2-overexpressed U937 cells; how ever, the activation of MAPK by bufalin was significantly attenuated in the cells overexpressing Bcl-2. BUfa1Intreatment activated activator pro tern-i transcriptional activity; however, this activation was decreased to 40% in bcl-2-overexpressed U937 cells. These results indicate that Bcl-2 acts downstream of MAPK kinase-1 but upstream of MAPK and suggest that, in the signaling pathway ofthe apoptotic process induced by bufalin, the transcriptional activity of activator protein-i may be down-regulated through the inhibition of MAPK activity by Bcl.2.