The orderly progression through the cell division cycle requires periodic degradation of key cell cycle regulatory proteins by the ubiquitin-proteasome system. The anaphase-promoting complex or cyclosome (APC/C) is a large multi-subunit ubiquitin ligase that controls several cell cycle transitions, including the metaphase-anaphase transition. After all sister chromatids have achieved bipolar attachment to the mitotic spindle, APC/C in conjunction with its activator Cdc20 ubiquitinates securin, an inhibitor of separase. Degradation of securin activates separase, which then cleaves a subunit of cohesin and triggers sister- chromatid separation and the onset of anaphase. The activity of APC/C-Cdc20 is tightly controlled by multiple mechanisms to prevent premature sister-chromatid separation. The spindle checkpoint is one such APC/C-regulatory mechanism. Our long-term goal is to understand how the spindle checkpoint inhibits the activity of APC/C-Cdc20 and delays the onset of anaphase in response to a single unattached kinetochore within a mitotic cell. This proposal focuses on the mechanism of assembly and disassembly of the mitotic checkpoint complex (MCC), an important checkpoint inhibitor of APC/C. MCC contains BubR1, Bub3, Cdc20, and Mad2. BubR1 and Bub3 bind to each other constitutively throughout the cell cycle whereas the BubR1-Cdc20 and Mad2-Cdc20 interactions are enhanced during mitosis.
The specific aims of this proposal are: (1) to determine the role of Mad1 -assisted conformational change of Mad2 in MCC assembly;(2) to determine the role of phosphorylation of Cdc20 by Bub1 in MCC assembly;and (3) to determine the role of Cdc20 autoubiquitination and degradation in MCC disassembly. Malfunction of the spindle checkpoint has been implicated in human cancers. The antimitotic class of anti-cancer drugs, such as Taxol, kills cancer cells by exploiting defects in this pathway. Experiments in this proposal will shed light on the molecular basis of the spindle checkpoint, which might eventually lead to new strategies to treat human cancers.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
3R01GM061542-09S2
Application #
8039723
Study Section
Nuclear Dynamics and Transport (NDT)
Program Officer
Hamlet, Michelle R
Project Start
2001-05-01
Project End
2011-03-31
Budget Start
2009-05-01
Budget End
2011-03-31
Support Year
9
Fiscal Year
2010
Total Cost
$101,631
Indirect Cost
Name
University of Texas Sw Medical Center Dallas
Department
Pharmacology
Type
Schools of Medicine
DUNS #
800771545
City
Dallas
State
TX
Country
United States
Zip Code
75390
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Kim, Soonjoung; Yu, Hongtao (2011) Mutual regulation between the spindle checkpoint and APC/C. Semin Cell Dev Biol 22:551-8
Jia, Luying; Li, Bing; Warrington, Ross T et al. (2011) Defining pathways of spindle checkpoint silencing: functional redundancy between Cdc20 ubiquitination and p31(comet). Mol Biol Cell 22:4227-35
Kim, Soonjoung; Sun, Hongbin; Ball, Haydn L et al. (2010) Phosphorylation of the spindle checkpoint protein Mad2 regulates its conformational transition. Proc Natl Acad Sci U S A 107:19772-7
Luo, Xuelian; Yu, Hongtao (2008) Protein metamorphosis: the two-state behavior of Mad2. Structure 16:1616-25
Kang, Jungseog; Yang, Maojun; Li, Bing et al. (2008) Structure and substrate recruitment of the human spindle checkpoint kinase Bub1. Mol Cell 32:394-405
Kang, Jungseog; Chen, Yue; Zhao, Yingming et al. (2007) Autophosphorylation-dependent activation of human Mps1 is required for the spindle checkpoint. Proc Natl Acad Sci U S A 104:20232-7
Yu, Hongtao (2007) Cdc20: a WD40 activator for a cell cycle degradation machine. Mol Cell 27:3-16
Qi, Wei; Yu, Hongtao (2007) KEN-box-dependent degradation of the Bub1 spindle checkpoint kinase by the anaphase-promoting complex/cyclosome. J Biol Chem 282:3672-9
Qi, Wei; Tang, Zhanyun; Yu, Hongtao (2006) Phosphorylation- and polo-box-dependent binding of Plk1 to Bub1 is required for the kinetochore localization of Plk1. Mol Biol Cell 17:3705-16

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