Mitotic phosphorylation of Bcl-2 during normal cell cycle progression and Taxol-induced growth arrest.
There is increasing evidence that prolonged mitotic arrest initiates apoptosis; however, little is known about the signaling pathways involved. Several studies have associated deregulated Cdc2 activity with apoptosis. Herein, we report that the anti-apoptotic protein, Bcl-2, undergoes cell cycle-dependent phosphorylation during mitosis when there is elevated Cdc2 activity. We found that paclitaxel (Taxol(R)) treatment of epithelial tumor cells induced a prolonged mitotic arrest, elevated levels of mitotic kinase activity, hyperphosphorylation of Bcl-2, and subsequent cell death. The Taxol-induced Bcl-2 phosphorylation was dose-dependent. Furthermore, phosphorylated Bcl-2 remained complexed with Bax in Taxol-treated cells undergoing apoptosis. Immunoprecipitation experiments revealed a Bcl-2-associated kinase capable of phosphorylating histone H1 in vitro. However, the kinase was likely not cyclin B1/Cdc2, since cyclin B1/Cdc2 was not detectable in Bcl-2 immunoprecipitates, nor was recombinant Bcl-2 phosphorylated in vitro by cyclin B1/Cdc2. The results of this study further define a link between mitotic kinase activation and the apoptotic machinery in the cell. However, the role, if any, of prolonged Bcl-2 phosphorylation in Taxol-mediated apoptosis awaits further definition of Bcl-2 mechanism of action. Taxol may increase cellular susceptibility to apoptosis by amplifying the normal downstream events associated with mitotic kinase activation.
Scatena
C D
CD
Department of Biochemistry, and the Vanderbilt Cancer Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
Stewart
Z A
ZA
Mays
D
D
Tang
L J
LJ
Keefer
C J
CJ
Leach
S D
SD
Pietenpol
J A
JA
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis; D016203:CDC2 Protein Kinase / Q000378:metabolism; D016923:Cell Death; D002455:Cell Division / Q000187:drug effects; D019926:Cyclin B / Q000378:metabolism; D056744:Cyclin B1; D016195:G2 Phase; D006801:Humans; D008938:Mitosis; D017239:Paclitaxel / Q000494:pharmacology*; D010766:Phosphorylation; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D000972:Antineoplastic Agents, Phytogenic; C534699:CCNB1 protein, human; D019926:Cyclin B; D056744:Cyclin B1; D019253:Proto-Oncogene Proteins c-bcl-2; D016203:CDC2 Protein Kinase; D017239:Paclitaxel