TAXOL-INDUCED P34(CDC2) KINASE ACTIVATION AND APOPTOSIS INHIBITED BY 12-O-TETRADECANOYLPHORBOL-13-ACETATE IN HUMAN BREAST MCF-7 CARCINOMA-CELLS

The p34(cdc2) kinase is a highly regulated serine-threonine kinase tha t, when complexed with cyclins A and B, controls cell entry into mitos is, Recently, premature activation of p34(cdc2) was shown to be requir ed for apoptosis induced by a wide variety of agents, Here, we show th at Taxol induced p34(cdc2) kinase activity with a peak at 6 h in human breast carcinoma MCF-7 cells, We subsequently observed that the activ ation of CPP32/Yama protease as well as the cleavage of its substrate poly(ADP-ribose) polymerase occurred 9 h after Taxol treatment, Olomou cine, a potent p34(cdc2) inhibitor, effectively prevented Taxol-induce d p34(cdc2) kinase activation and subsequent apoptosis, Furthermore, t he treatment of cells with cyclin B1-specific antisense oligonucleotid e also blocked Taxol-induced apoptosis, suggesting that cyclin B1-asso ciated p34(cdc2) kinase plays an important role in the induction of ap optosis by Taxol, 12-O-Tetradecanoylphorbol-13-acetate (TPA), a protei n kinase C activator, was found to exert strong protection against Tax ol-induced cell death in MCF-7 cells, TPA inhibited Taxol-mediated act ivation of p34(cdc2) kinase by preventing the dephosphorylation of the Tyr-15 residue on p34(cdc2) without altering the levels of Cdc2 and c yclin B1, In contrast, the ability of Taxol to enhance tubulin polymer ization was not inhibited by TPA, These findings suggest that modulati on of protein kinase C signaling can protect against Taxol-induced cel l death by inhibiting p34(cdc2) kinase activation.