title: Mechanism of cancer cell death induced by depletion of an essential replication regulator.
abstract: BACKGROUND
  Depletion of replication factors often causes cell death in cancer cells. Depletion of Cdc7, a kinase essential for initiation of DNA replication, induces cancer cell death regardless of its p53 status, but the precise pathways of cell death induction have not been characterized.
  
  
  RESULTS
  We have used the recently-developed cell cycle indicator, Fucci, to precisely characterize the cell death process induced by Cdc7 depletion. We have also generated and utilized similar fluorescent cell cycle indicators using fusion with other cell cycle regulators to analyze modes of cell death in live cells in both p53-positive and -negative backgrounds. We show that distinct cell-cycle responses are induced in p53-positive and -negative cells by Cdc7 depletion. p53-negative cells predominantly arrest temporally in G2-phase, accumulating CyclinB1 and other mitotic regulators. Prolonged arrest at G2-phase and abrupt entry into aberrant M-phase in the presence of accumulated CyclinB1 are followed by cell death at the post-mitotic state. Abrogation of cytoplasmic CyclinB1 accumulation partially decreases cell death. The ATR-MK2 pathway is responsible for sequestration of CyclinB1 with 14-3-3σ protein. In contrast, p53-positive cancer cells do not accumulate CyclinB1, but appear to die mostly through entry into aberrant S-phase after Cdc7 depletion. The combination of Cdc7 inhibition with known anti-cancer agents significantly stimulates cell death effects in cancer cells in a genotype-dependent manner, providing a strategic basis for future combination therapies.
  
  
  CONCLUSIONS
  Our results show that the use of Fucci, and similar fluorescent cell cycle indicators, offers a convenient assay system with which to identify cell cycle events associated with cancer cell death. They also indicate genotype-specific cell death modes induced by deficient initiation of DNA replication in cancer cells and its potential exploitation for development of efficient cancer therapies.
authors.affiliation: Genome Dynamics Project, Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, Setagaya-ku, Tokyo, Japan.
authors.forename: Sayuri
authors.initials: S
authors.lastname: Ito
authors.forename: Ai
authors.initials: A
authors.lastname: Ishii
authors.forename: Naoko
authors.initials: N
authors.lastname: Kakusho
authors.forename: Chika
authors.initials: C
authors.lastname: Taniyama
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yamazaki
authors.forename: Rino
authors.initials: R
authors.lastname: Fukatsu
authors.forename: Asako
authors.initials: A
authors.lastname: Sakaue-Sawano
authors.forename: Atsushi
authors.initials: A
authors.lastname: Miyawaki
authors.forename: Hisao
authors.initials: H
authors.lastname: Masai
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology; D014408:Biomarkers, Tumor / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D056744:Cyclin B1 / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D004261:DNA Replication / Q000187:drug effects / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects / Q000235:genetics; D005092:Exonucleases / Q000378:metabolism; D005095:Exoribonucleases; D016195:G2 Phase / Q000187:drug effects / Q000235:genetics; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D000099190:MAP-Kinase-Activated Kinase 2
chemical_list: D048948:14-3-3 Proteins; D000970:Antineoplastic Agents; D014408:Biomarkers, Tumor; D018797:Cell Cycle Proteins; D056744:Cyclin B1; D005092:Exonucleases; D005095:Exoribonucleases; D047908:Intracellular Signaling Peptides and Proteins; D017346:Protein Serine-Threonine Kinases; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D000099190:MAP-Kinase-Activated Kinase 2; C068619:CDC7 protein, human; C413442:SFN protein, human