title: The small-molecule inhibitor BI 2536 reveals novel insights into mitotic roles of polo-like kinase 1.
abstract: BACKGROUND
  The mitotic kinases, Cdk1, Aurora A/B, and Polo-like kinase 1 (Plk1) have been characterized extensively to further understanding of mitotic mechanisms and as potential targets for cancer therapy. Cdk1 and Aurora kinase studies have been facilitated by small-molecule inhibitors, but few if any potent Plk1 inhibitors have been identified.
  
  
  RESULTS
  We describe the cellular effects of a novel compound, BI 2536, a potent and selective inhibitor of Plk1. The fact that BI 2536 blocks Plk1 activity fully and instantaneously enabled us to study controversial and unknown functions of Plk1. Cells treated with BI 2536 are delayed in prophase but eventually import Cdk1-cyclin B into the nucleus, enter prometaphase, and degrade cyclin A, although BI 2536 prevents degradation of the APC/C inhibitor Emi1. BI 2536-treated cells lack prophase microtubule asters and thus polymerize mitotic microtubules only after nuclear-envelope breakdown and form monopolar spindles that do not stably attach to kinetochores. Mad2 accumulates at kinetochores, and cells arrest with an activated spindle-assembly checkpoint. BI 2536 prevents Plk1's enrichment at kinetochores and centrosomes, and when added to metaphase cells, it induces detachment of microtubules from kinetochores and leads to spindle collapse.
  
  
  CONCLUSIONS
  Our results suggest that Plk1's accumulation at centrosomes and kinetochores depends on its own activity and that this activity is required for maintaining centrosome and kinetochore function. Our data also show that Plk1 is not required for prophase entry, but delays transition to prometaphase, and that Emi1 destruction in prometaphase is not essential for APC/C-mediated cyclin A degradation.
authors.affiliation: Research Institute of Molecular Pathology, A-1030 Vienna, Austria.
authors.forename: Péter
authors.initials: P
authors.lastname: Lénárt
authors.forename: Mark
authors.initials: M
authors.lastname: Petronczki
authors.forename: Martin
authors.initials: M
authors.lastname: Steegmaier
authors.forename: Barbara
authors.initials: B
authors.lastname: Di Fiore
authors.forename: Jesse J
authors.initials: JJ
authors.lastname: Lipp
authors.forename: Matthias
authors.initials: M
authors.lastname: Hoffmann
authors.forename: Wolfgang J
authors.initials: WJ
authors.lastname: Rettig
authors.forename: Norbert
authors.initials: N
authors.lastname: Kraut
authors.forename: Jan-Michael
authors.initials: JM
authors.lastname: Peters
mesh_terms: D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000378:metabolism / Q000494:pharmacology*; D044783:F-Box Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007091:Image Processing, Computer-Assisted; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D008870:Microtubules / Q000187:drug effects* / Q000378:metabolism; D008938:Mitosis / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011621:Pteridines / Q000378:metabolism / Q000494:pharmacology*; D008941:Spindle Apparatus / Q000187:drug effects* / Q000378:metabolism; D000097869:Polo-Like Kinase 1
chemical_list: D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D044783:F-Box Proteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D011621:Pteridines; D000097869:Polo-Like Kinase 1; C518477:BI 2536; C498960:FBXO5 protein, human