title: Modulating ICBP90 to suppress human ribonucleotide reductase M2 induction restores sensitivity to hydroxyurea cytotoxicity.
abstract: BACKGROUND
  Ribonucleotide reductase (RR) inhibition by hydroxyurea (HU) causes deoxyribonucleotide (dNTP) depletion, which activates the replication checkpoint, a part of the S-phase checkpoint that responds to DNA damage by inhibiting late origin firing. It also transactivates RR and other genes involved in DNA replication and repair. ICBP90 (overexpressed in breast cancer) is a novel Rb-associating transactivator for the human topoisomerase IIalpha gene and responds to DNA damage-induced checkpoint signaling.
  
  
  METHODS
  ICBP90 expression was monitored by Western blot. Promoter activity was detected via the luciferase assay and gene silencing via siRNA. Cell death was monitored by the MTT assay.
  
  
  RESULTS
  dNTP depletion by HU induced ICBP90, ICBP90 transactivated RR's M2 subunit gene, and ICBP90 induction was necessary for HU-induced M2 accumulation. Blocking the M2 accumulation via anti-ICBP90 siRNA caused greater sensitivity in HU-resistant human cancer.
  
  
  CONCLUSIONS
  A transcriptional intervention strategy is presented through which HU-resistant cancers may be eradicated without dose escalation.
authors.affiliation: Department of Clinical and Molecular Pharmacology, City of Hope National Medical Center, Duarte, CA 90101, USA.
authors.forename: Frank
authors.initials: F
authors.lastname: Un
authors.forename: Christina
authors.initials: C
authors.lastname: Qi
authors.forename: Megan
authors.initials: M
authors.lastname: Prosser
authors.forename: Norby
authors.initials: N
authors.lastname: Wang
authors.forename: Bingsen
authors.initials: B
authors.lastname: Zhou
authors.forename: Christian
authors.initials: C
authors.lastname: Bronner
authors.forename: Yun
authors.initials: Y
authors.lastname: Yen
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D022762:CCAAT-Enhancer-Binding Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D003854:Deoxyribonucleotides / Q000378:metabolism; D004790:Enzyme Induction; D020868:Gene Silencing; D006258:Head and Neck Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006918:Hydroxyurea / Q000494:pharmacology*; D007624:KB Cells; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering / Q000235:genetics; D012262:Ribonucleoside Diphosphate Reductase / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000378:metabolism; D015533:Transcriptional Activation; D044767:Ubiquitin-Protein Ligases
chemical_list: D000970:Antineoplastic Agents; D022762:CCAAT-Enhancer-Binding Proteins; D003854:Deoxyribonucleotides; D034741:RNA, Small Interfering; C093713:ribonucleotide reductase M2; D012262:Ribonucleoside Diphosphate Reductase; C406364:UHRF1 protein, human; D044767:Ubiquitin-Protein Ligases; D006918:Hydroxyurea