Topoisomerase IIβ deficiency enhances camptothecin-induced apoptosis.
Camptothecin (CPT), a topoisomerase (Top) I-targeting drug that stabilizes Top1-DNA covalent adducts, can induce S-phase-specific cytotoxicity due to the arrest of progressing replication forks. However, CPT-induced non-S-phase cytotoxicity is less well characterized. In this study, we have identified topoisomerase IIβ (Top2β) as a specific determinant for CPT sensitivity, but not for many other cytotoxic agents, in non-S-phase cells. First, quiescent mouse embryonic fibroblasts (MEFs) lacking Top2β were shown to be hypersensitive to CPT with prominent induction of apoptosis. Second, ICRF-187, a Top2 catalytic inhibitor known to deplete Top2β, specifically sensitized MEFs to CPT. To explore the molecular basis for CPT hypersensitivity in Top2β-deficient cells, we found that upon CPT exposure, the RNA polymerase II large subunit (RNAP LS) became progressively depleted, followed by recovery to nearly the original level in wild-type MEFs, whereas RNAP LS remained depleted without recovery in Top2β-deficient cells. Concomitant with the reduction of the RNAP LS level, the p53 protein level was greatly induced. Interestingly, RNAP LS depletion has been well documented to lead to p53-dependent apoptosis. Altogether, our findings support a model in which Top2β deficiency promotes CPT-induced apoptosis in quiescent non-S-phase cells, possibly due to RNAP LS depletion and p53 accumulation.
Department of Pharmacology, UMDNJ-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
Ren-Kuo
RK
Lin
Chia-Wen
CW
Ho
Leroy F
LF
Liu
Yi Lisa
YL
Lyu
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D002166:Camptothecin / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004250:DNA Topoisomerases, Type II / Q000172:deficiency* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000172:deficiency* / Q000235:genetics; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D021122:Protein Subunits / Q000378:metabolism; D011929:Razoxane / Q000494:pharmacology; D059004:Topoisomerase I Inhibitors / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D000970:Antineoplastic Agents; D004268:DNA-Binding Proteins; D021122:Protein Subunits; D059004:Topoisomerase I Inhibitors; D016159:Tumor Suppressor Protein p53; D011929:Razoxane; D012321:DNA-Directed RNA Polymerases; D004250:DNA Topoisomerases, Type II; D002166:Camptothecin