title: Isolation of human mitotic protein phosphatase complexes: identification of a complex between protein phosphatase 1 and the RNA helicase Ddx21.
abstract: Metazoan mitosis requires remodelling of sub-cellular structures to ensure proper division of cellular and genetic material. Faults often lead to genomic instability, cell cycle arrests and disease onset. These key structural changes are under tight spatial-temporal and post-translational control, with crucial roles for reversible protein phosphorylation. The phosphoprotein phosphatases PP1 and PP2A are paramount for the timely execution of mitotic entry and exit but their interaction partners and substrates are still largely unresolved. High throughput, mass-spectrometry based studies have limited sensitivity for the detection of low-abundance and transient complexes, a typical feature of many protein phosphatase complexes. Moreover, the limited timeframe during which mitosis takes place reduces the likelihood of identifying mitotic phosphatase complexes in asynchronous cells. Hence, numerous mitotic protein phosphatase complexes still await identification. Here we present a strategy to enrich and identify serine/threonine protein phosphatase complexes at the mitotic spindle. We thus identified a nucleolar RNA helicase, Ddx21/Gu, as a novel, direct PP1 interactor. Furthermore, our results place PP1 within the toposome, a Topoisomerase II alpha (TOPOIIα) containing complex with a key role in mitotic chromatin regulation and cell cycle progression, possibly via regulated protein phosphorylation. This study provides a strategy for the identification of further mitotic PP1 partners and the unravelling of PP1 functions during mitosis.
authors: Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
authors: Veerle
authors: V
authors: De Wever
authors: David C
authors: DC
authors: Lloyd
authors: Isha
authors: I
authors: Nasa
authors: Mhairi
authors: M
authors: Nimick
authors: Laura
authors: L
authors: Trinkle-Mulcahy
authors: Robert
authors: R
authors: Gourlay
authors: Nick
authors: N
authors: Morrice
authors: Greg B G
authors: GB
authors: Moorhead
mesh_terms: D002453:Cell Cycle / Q000502:physiology; D053487:DEAD-box RNA Helicases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008938:Mitosis / Q000502:physiology*; D010766:Phosphorylation; D054645:Protein Phosphatase 1 / Q000235:genetics / Q000378:metabolism*; D008941:Spindle Apparatus / Q000235:genetics / Q000378:metabolism*
chemical_list: D054645:Protein Phosphatase 1; C501726:DDX21 protein, human; D053487:DEAD-box RNA Helicases