title: A specific form of phospho protein phosphatase 2 regulates anaphase-promoting complex/cyclosome association with spindle poles.
abstract: In early mitosis, the END (Emi1/NuMA/Dynein-dynactin) network anchors the anaphase-promoting complex/cyclosome (APC/C) to the mitotic spindle and poles. Spindle anchoring restricts APC/C activity, thereby limiting the destruction of spindle-associated cyclin B and ensuring maintenance of spindle integrity. Emi1 binds directly to hypophosphorylated APC/C, linking the APC/C to the spindle via NuMA. However, whether the phosphorylation state of the APC/C is important for its association with the spindle and what kinases and phosphatases are necessary for regulating this event remain unknown. Here, we describe the regulation of APC/C-mitotic spindle pole association by phosphorylation. We find that only hypophosphorylated APC/C associates with microtubule asters, suggesting that phosphatases are important. Indeed, a specific form of PPP2 (CA/R1A/R2B) binds APC/C, and PPP2 activity is necessary for Cdc27 dephosphorylation. Screening by RNA interference, we find that inactivation of CA, R1A, or R2B leads to delocalization of APC/C from spindle poles, early mitotic spindle defects, a failure to congress chromosomes, and decreased levels of cyclin B on the spindle. Consistently, inhibition of cyclin B/Cdk1 activity increased APC/C binding to microtubules. Thus, cyclin B/Cdk1 and PPP2 regulate the dynamic association of APC/C with spindle poles in early mitosis, a step necessary for proper spindle formation.
authors.affiliation: Department of Pathology, Stanford University School of Medicine, Stanford, CA 94305, USA. torres@chem.ucla.edu
authors.forename: Jorge Z
authors.initials: JZ
authors.lastname: Torres
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Ban
authors.forename: Peter K
authors.initials: PK
authors.lastname: Jackson
mesh_terms: D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D019926:Cyclin B / Q000378:metabolism; D000072159:Dynactin Complex; D006367:HeLa Cells; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism; D008938:Mitosis / Q000502:physiology; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D008941:Spindle Apparatus / Q000378:metabolism*; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism*
chemical_list: D019926:Cyclin B; D000072159:Dynactin Complex; D007527:Isoenzymes; D008869:Microtubule-Associated Proteins; D021122:Protein Subunits; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D054648:Protein Phosphatase 2