BubR1 N terminus acts as a soluble inhibitor of cyclin B degradation by APC/C(Cdc20) in interphase

Dev Cell. 2009 Jan;16(1):118-31. doi: 10.1016/j.devcel.2008.11.004.

Abstract

BubR1 is an essential mitotic checkpoint protein with multiple functional domains. It has been implicated in mitotic checkpoint control, as an active kinase at unattached kinetochores, and as a cytosolic inhibitor of APC/C(Cdc20) activity, as well as in mitotic timing and stable chromosome-spindle attachment. Using BubR1-conditional knockout cells and BubR1 domain mutants, we demonstrate that the N-terminal Cdc20 binding domain of BubR1 is essential for all of these functions, whereas its C-terminal Cdc20-binding domain, Bub3-binding domain, and kinase domain are not. We find that the BubR1 N terminus binds to Cdc20 in a KEN box-dependent manner to inhibit APC/C activity in interphase, thereby allowing accumulation of cyclin B in G(2) phase prior to mitosis onset. Together, our results suggest that kinetochore-bound BubR1 is nonessential and that soluble BubR1 functions as a pseudosubstrate inhibitor of APC/C(Cdc20) during interphase to prevent unscheduled degradation of specific APC/C substrates.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anaphase-Promoting Complex-Cyclosome
  • Animals
  • Cdc20 Proteins
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Cell Survival
  • Cells, Cultured
  • Chromosomes / metabolism
  • Cyclin B / genetics
  • Cyclin B / metabolism*
  • Fibroblasts / cytology
  • Fibroblasts / physiology
  • Humans
  • Interphase
  • Mice
  • Mice, Knockout
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Spindle Apparatus / metabolism
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism
  • Ubiquitin-Protein Ligase Complexes / metabolism*

Substances

  • Bub1b protein, mouse
  • Cdc20 Proteins
  • Cdc20 protein, mouse
  • Cell Cycle Proteins
  • Cyclin B
  • Recombinant Fusion Proteins
  • Tumor Suppressor Protein p53
  • Ubiquitin-Protein Ligase Complexes
  • Anaphase-Promoting Complex-Cyclosome
  • BUB1 protein, human
  • Bub1 spindle checkpoint protein
  • Protein-Serine-Threonine Kinases