Caspase inhibition in camptothecin-treated U-937 cells is coupled with a shift from apoptosis to transient G1 arrest followed by necrotic cell death.
Leukemia U-937 cells rapidly undergo characteristic morphological changes, caspase activation, and DNA fragmentation typical of apoptosis on treatment with the DNA topoisomerase I inhibitor camptothecin (CPT). In a previous report (Sané, A. T., and Bertrand, R., Cancer Res., 58: 3066-3072, 1998), we showed that, after CPT treatment, caspase inhibition by the tripeptide derivative benzyloxycarbonyl-Val-Ala-Asp(Ome)-fluoromethyl ketone (zVAD-fmk) blocked apoptosis and slowed passage of the cells through S-G2 and caused a transient accumulation of these cells at the G1 phase of the cell cycle. Accumulation of these cells at G1 is not associated with major changes in expression level of cyclin-dependent kinase (cdk)2, cdk4, and cdk6; cyclin D1 and cyclin E; or p16, p21, p27, and p57 after CPT treatment. Furthermore, cdk2, cdk4, and cdk6 kinase activities remain unaffected after CPT treatment. These results indicate that the G1 arrest of these cells does not correlate with a classical driven cell cycle checkpoint but with the known effect of CPT in mediating inhibition of DNA replication and RNA transcription after stabilization of topoisomerase I-linked DNA strand breaks. However, persistent caspase inhibition after CPT treatment also results in cells falling into necrosis after the transient G1 arrest. These results indicate that the enforced inhibition of caspase activities does not confer a survival advantage upon CPT-treated cells but is coupled with a shift from apoptosis to transient G1 arrest followed by massive necrosis.
Sané
A T
AT
Research Centre of the University of Montreal, Notre-Dame Hospital, Montreal Cancer Institute, Quebec, Canada.
Bertrand
R
R
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D002166:Camptothecin / Q000494:pharmacology*; D061945:Caspase Inhibitors; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics; D004249:DNA Damage; D053938:DNA Fragmentation; D004260:DNA Repair / Q000187:drug effects; D004261:DNA Replication / Q000187:drug effects; D004273:DNA, Neoplasm / Q000096:biosynthesis / Q000187:drug effects*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D016193:G1 Phase / Q000187:drug effects*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D009336:Necrosis; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors*; D059004:Topoisomerase I Inhibitors; D020298:U937 Cells / Q000187:drug effects*
D000590:Amino Acid Chloromethyl Ketones; D000972:Antineoplastic Agents, Phytogenic; D061945:Caspase Inhibitors; D018797:Cell Cycle Proteins; D004273:DNA, Neoplasm; D004791:Enzyme Inhibitors; D009363:Neoplasm Proteins; D059004:Topoisomerase I Inhibitors; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D002166:Camptothecin