title: KNL1-Bubs and RZZ Provide Two Separable Pathways for Checkpoint Activation at Human Kinetochores.
abstract: The spindle assembly checkpoint (SAC) ensures the accurate segregation of sister chromatids during mitosis. Activation of the SAC occurs through a series of ordered molecular events that result in recruitment of Mad1:Mad2 complexes to improperly attached kinetochores. The current model involves sequential phospho-dependent recruitment of Bub3:Bub1 to KNL1 followed by binding of Mad1:Mad2 to Bub1. Here, we show in non-transformed diploid human cells that the KNL1-Bub3-Bub1 (KBB) pathway is required during normal mitotic progression when kinetochores are misaligned but is nonessential for SAC activation and Mad2 loading when kinetochores are unattached from microtubules. We provide evidence that the Rod-ZW10-Zwilch (RZZ) complex is necessary to recruit Mad1:Mad2 to, and delay anaphase onset in response to, unattached kinetochores independently of the KBB pathway. These data suggest that the KBB and RZZ complexes provide two distinct kinetochore receptors for Mad1:Mad2 and reveal mechanistic differences between SAC activation by unattached and improperly attached kinetochores.
authors.affiliation: Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: Virginia
authors.initials: V
authors.lastname: Silió
authors.affiliation: Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK. Electronic address: a.d.mcainsh@warwick.ac.uk.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: McAinsh
authors.affiliation: Division of Biomedical Cell Biology, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK. Electronic address: j.millar@warwick.ac.uk.
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: Millar
mesh_terms: D000705:Anaphase; D059447:Cell Cycle Checkpoints / Q000235:genetics; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D004171:Diploidy; D005786:Gene Expression Regulation; D016678:Genome; D006367:HeLa Cells; D006801:Humans; D018386:Kinetochores / Q000378:metabolism*; D064246:Mad2 Proteins / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D008938:Mitosis; D009687:Nuclear Proteins / Q000378:metabolism; D000075223:Poly-ADP-Ribose Binding Proteins; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction; D008941:Spindle Apparatus / Q000378:metabolism
chemical_list: C489444:BUB3 protein, human; D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; C472643:Knl1 protein, human; C501384:MAD1L1 protein, human; C577697:MAD2L1 protein, human; D064246:Mad2 Proteins; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins; D000075223:Poly-ADP-Ribose Binding Proteins; C488261:ZW10 protein, human; C000606356:Zwilch protein, human; C584277:BUB1 protein, human; D017346:Protein Serine-Threonine Kinases