title: Phosphorylation of the Ndc80 complex protein, HEC1, by Nek2 kinase modulates chromosome alignment and signaling of the spindle assembly checkpoint.
abstract: The spindle assemble checkpoint (SAC) is critical for accurate chromosome segregation. Hec1 contributes to chromosome segregation in part by mediating SAC signaling and chromosome alignment. However, the molecular mechanism by which Hec1 modulates checkpoint signaling and alignment remains poorly understood. We found that Hec1 serine 165 (S165) is preferentially phosphorylated at kinetochores. Phosphorylated Hec1 serine 165 (pS165) specifically localized to kinetochores of misaligned chromosomes, showing a spatiotemporal distribution characteristic of SAC molecules. Expressing an RNA interference (RNAi)-resistant S165A mutant in Hec1-depleted cells permitted normal progression to metaphase, but accelerated the metaphase-to-anaphase transition. The S165A cells were defective in Mad1 and Mad2 localization to kinetochores, regardless of attachment status. These cells often entered anaphase with lagging chromosomes and elicited increased segregation errors and cell death. In contrast, expressing S165E mutant in Hec1-depleted cells triggered defective chromosome alignment and severe mitotic arrest associated with increased Mad1/Mad2 signals at prometaphase kinetochores. A small portion of S165E cells eventually bypassed the SAC but showed severe segregation errors. Nek2 is the primary kinase responsible for kinetochore pS165, while PP1 phosphatase may dephosphorylate pS165 during SAC silencing. Taken together, these results suggest that modifications of Hec1 S165 serve as an important mechanism in modulating SAC signaling and chromosome alignment.
authors.affiliation: Department of Biological Chemistry, School of Medicine, University of California, Irvine, Irvine, CA 92697, USA.
authors.forename: Randy
authors.initials: R
authors.lastname: Wei
authors.forename: Bryan
authors.initials: B
authors.lastname: Ngo
authors.forename: Guikai
authors.initials: G
authors.lastname: Wu
authors.forename: Wen-Hwa
authors.initials: WH
authors.lastname: Lee
mesh_terms: D000595:Amino Acid Sequence; D000705:Anaphase; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D020090:Chromosome Segregation; D003598:Cytoskeletal Proteins; D006801:Humans; D018386:Kinetochores / Q000378:metabolism; D059566:M Phase Cell Cycle Checkpoints; D064246:Mad2 Proteins; D008677:Metaphase; D008938:Mitosis; D008969:Molecular Sequence Data; D000072379:NIMA-Related Kinases; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics
chemical_list: D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; C501384:MAD1L1 protein, human; C577697:MAD2L1 protein, human; D064246:Mad2 Proteins; C120529:NDC80 protein, human; D009687:Nuclear Proteins; D012097:Repressor Proteins; C089441:NEK2 protein, human; D000072379:NIMA-Related Kinases; D017346:Protein Serine-Threonine Kinases