title: Caffeine promotes apoptosis in mitotic spindle checkpoint-arrested cells.
abstract: The spindle assembly checkpoint arrests cells in mitosis when defects in mitotic spindle assembly or partitioning of the replicated genome are detected. This checkpoint blocks exit from mitosis until the defect is rectified or the cell initiates apoptosis. In this study we have used caffeine to identify components of the mechanism that signals apoptosis in mitotic checkpoint-arrested cells. Addition of caffeine to spindle checkpoint-arrested cells induced >40% apoptosis within 5 h. It also caused proteasome-mediated destruction of cyclin B1, a corresponding reduction in cyclin B1/cdk1 activity, and reduction in MPM-2 reactivity. However, cells retained MAD2 staining at the kinetochores, an indication of continued spindle checkpoint function. Blocking proteasome activity did not block apoptosis, but continued spindle checkpoint function was essential for apoptosis. After systematically eliminating all known targets, we have identified p21-activated kinase PAK1, which has an anti-apoptotic function in spindle checkpoint-arrested cells, as a target for caffeine inhibition. Knockdown of PAK1 also increased apoptosis in spindle checkpoint-arrested cells. This study demonstrates that the spindle checkpoint not only regulates mitotic exit but apoptosis in mitosis through the activity of PAK1.
authors.affiliation: Cancer Biology Program, Centre for Immunology and Cancer Research, University of Queensland, Brisbane, Queensland 4102, Australia. bgabrielli@cicr.uq.edu.au
authors.forename: Brian
authors.initials: B
authors.lastname: Gabrielli
authors.forename: Yu Qian
authors.initials: YQ
authors.lastname: Chau
authors.forename: Nichole
authors.initials: N
authors.lastname: Giles
authors.forename: Angus
authors.initials: A
authors.lastname: Harding
authors.forename: Frankie
authors.initials: F
authors.lastname: Stevens
authors.forename: Heather
authors.initials: H
authors.lastname: Beamish
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001549:Benzamides / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology*; D002460:Cell Line; D016195:G2 Phase; D006801:Humans; D008938:Mitosis / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D011799:Quinazolines / Q000494:pharmacology; D008941:Spindle Apparatus / Q000502:physiology*; D054462:p21-Activated Kinases
chemical_list: C474722:4-(4-(N-benzoylamino)anilino)-6-methoxy-7-(3-(1-morpholino)propoxy)quinazoline; D001549:Benzamides; D011799:Quinazolines; D002110:Caffeine; C515903:PAK1 protein, human; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases