S phase and G2 arrests induced by topoisomerase I poisons are dependent on ATR kinase function.
ATR, a human phosphatidylinositol 3-kinase-related kinase, is an important component of the cellular response to DNA damage. In the present study, we evaluated the role of ATR in modulating the response of cells to S phase-associated DNA double-stranded breaks induced by topoisomerase poisons. Prolonged exposure to low doses of the topoisomerase I poison topotecan (TPT) resulted in S phase slowing because of diminished DNA synthesis at late-firing replicons. In contrast, brief TPT exposure, as well as prolonged exposure to the topoisomerase II poison etoposide, resulted in subsequent G(2) arrest. These responses were associated with phosphorylation of the checkpoint kinase Chk1. The cell cycle responses and phosphorylation of Chk1 were markedly diminished by forced overexpression of a dominant negative, kinase-inactive allele of ATR. In contrast, deficiency of the related kinase ATM had no effect on these events. The loss of ATR-dependent checkpoint function sensitized GM847 human fibroblasts to the cytotoxic effects of the topoisomerase I poisons TPT and 7-ethyl-10-hydroxycamptothecin, as assessed by inhibition of colony formation, increased trypan blue uptake, and development of apoptotic morphological changes. Expression of kdATR also sensitized GM847 cells to the cytotoxic effects of prolonged low dose etoposide and doxorubicin, albeit to a smaller extent. Collectively, these results not only suggest that ATR is important in responding to the replication-associated DNA damage from topoisomerase poisons, but also support the view that ATM and ATR have unique roles in activating the downstream kinases that participate in cell cycle checkpoints.
Cliby
William A
WA
Department of Obstetrics and Gynecology, Mayo Clinic, Rochester, Minnesota 55905, USA. cliby.william@mayo.edu
Lewis
Kriste A
KA
Lilly
Kia K
KK
Kaufmann
Scott H
SH
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins; D002460:Cell Line; D000071877:Checkpoint Kinase 1; D004260:DNA Repair; D004317:Doxorubicin / Q000494:pharmacology; D004318:Doxycycline / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005047:Etoposide; D005434:Flow Cytometry; D016195:G2 Phase / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D017239:Paclitaxel / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D016196:S Phase / Q000187:drug effects* / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D059004:Topoisomerase I Inhibitors; D019772:Topotecan / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D019384:Nucleic Acid Synthesis Inhibitors; D059004:Topoisomerase I Inhibitors; D005047:Etoposide; D019772:Topotecan; D004317:Doxorubicin; D011494:Protein Kinases; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases; D004318:Doxycycline; D017239:Paclitaxel