ABSTRACT
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.
Subject(s)
Antineoplastic Agents, Phytogenic/pharmacology , Mitosis , Paclitaxel/pharmacology , Proto-Oncogene Proteins c-bcl-2/metabolism , Apoptosis , CDC2 Protein Kinase/metabolism , Cell Death , Cell Division/drug effects , Cyclin B/metabolism , Cyclin B1 , G2 Phase , Humans , Phosphorylation , Tumor Cells, CulturedABSTRACT
The G2 cell cycle checkpoint protects cells from potentially lethal mitotic entry after DNA damage. This checkpoint involves inhibitory phosphorylation of Cdc2 at the tyrosine-15 (Y15) position, mediated in part by the Wee1 protein kinase. Recent evidence suggests that p53 may accelerate mitotic entry after DNA damage and that the override of the G2 checkpoint may play a role in the induction of apoptosis by p53. To determine the biochemical mechanism by which p53 inactivates the G2 checkpoint, the effects of p53 activation on Wee1 expression, Cdc2-Y15 phosphorylation, and cyclin B1-associated Cdc2 kinase activity were examined. Under conditions of either growth arrest or apoptosis, p53 activation resulted in the down-regulation of Wee1 expression and dephosphorylation of Cdc2. A parallel increase in cyclin B1/Cdc2 kinase activity was observed during p53-mediated apoptosis. Negative regulation of the Wee1 expression and Cdc2 phosphorylation by p53 was also evident in thymus tissue from p53+/+ mice but not from p53-/- mice. Inactivation of the G2 checkpoint may contribute to the tumor suppressor activity of p53.
Subject(s)
Apoptosis/physiology , CDC2 Protein Kinase/metabolism , Cell Cycle Proteins , Nuclear Proteins , Protein-Tyrosine Kinases/biosynthesis , Tumor Suppressor Protein p53/physiology , Animals , Antineoplastic Agents/pharmacology , Blotting, Western , Cell Division/physiology , Cyclin B/metabolism , Cyclin B1 , Down-Regulation , Embryo, Mammalian , Enzyme Activation , Fibroblasts/cytology , G2 Phase/physiology , Lymphoma, T-Cell/metabolism , Mice , Nocodazole/pharmacology , Phosphorylation , Protein Conformation , Rats , Transformation, Genetic , Tumor Cells, CulturedABSTRACT
Glomangiomas, a rare variant of glomus tumors, can be mistaken for hemangiomas. Case reports of two family members are given as examples for differential diagnosis and timing of surgical intervention. Conservative excision is proposed when vital structures are involved. The use of the candela tunable pulse dye laser for the treatment of the superficial dermal component of the tumor is presented.
