Phosphorylation of PP1 Regulator Sds22 by PLK1 Ensures Accurate Chromosome Segregation

Abstract

During cell division, accurate chromosome segregation is tightly regulated by Polo-like kinase 1 (PLK1) and opposing activities of Aurora B kinase and protein phosphatase 1 (PP1). However, the regulatory mechanisms underlying the aforementioned hierarchical signaling cascade during mitotic chromosome segregation have remained elusive. Sds22 is a conserved regulator of PP1 activity, but how it regulates PP1 activity in space and time during mitosis remains elusive. Here we show that Sds22 is a novel and cognate substrate of PLK1 in mitosis, and the phosphorylation of Sds22 by PLK1 elicited an inhibition of PP1-mediated dephosphorylation of Aurora B at threonine 232 (Thr 232 ) in a dose-dependent manner. Overexpression of a phosphomimetic mutant of Sds22 causes a dramatic increase in mitotic delay, whereas overexpression of a non-phosphorylatable mutant of Sds22 results in mitotic arrest. Mechanistically, the phosphorylation of Sds22 by PLK1 strengthens the binding of Sds22 to PP1 and inhibits the dephosphorylation of Thr 232 of Aurora B to ensure a robust, error-free metaphase-anaphase transition. These findings delineate a conserved signaling hierarchy that orchestrates dynamic protein phosphorylation and dephosphorylation of critical mitotic regulators during chromosome segregation to guard chromosome stability.

Kinase and Phosphatase Cross-Talk at the Kinetochore

“…It should be noted that various other PP1 complexes have also been identified at the kinetochore (Yamashiro et al, 2008 ; Akiyoshi et al, 2009 ; Kim et al, 2010 ; Posch et al, 2010 ; Meadows et al, 2011 ; De Wever et al, 2014 ; Häfner et al, 2014 ; Tang and Toda, 2015 ; Zhang et al, 2015 ; Bokros et al, 2016 ; Duan et al, 2016 ), and three of these in particular (PP1-Sds22, PP1-Cenp-E and PP1-ASPP1/2), have been implicated in Aurora B and microtubule attachment regulation. These complexes are currently omitted from Figure 1 for various reasons: PP1-ASPP1/2 can be seen to bind to Ndc80 biochemically, but it does not appear to accumulate at kinetochores (Zhang et al, 2015 ).…”

“…These complexes are currently omitted from Figure 1 for various reasons: PP1-ASPP1/2 can be seen to bind to Ndc80 biochemically, but it does not appear to accumulate at kinetochores (Zhang et al, 2015 ). Sds22 knockdown positively and negatively regulates different Aurora B substrates at the kinetochore (Posch et al, 2010 ; Wurzenberger et al, 2012 ; Duan et al, 2016 ), but this is thought to be due to regulation in the cytoplasm that has downstream consequences for PP1-Knl1 activity (Eiteneuer et al, 2014 ). Cenp-E binds to PP1, and the Aurora kinases can dynamically regulate this interaction to promote chromosome alignment (Kim et al, 2010 ).…”

“…Bod1 localizes to Ndc80 and is able to inhibit BubR1-bound PP2A-B56 (Porter et al, 2013 ; Schleicher et al, 2017 ) (arrow 25, Figure 1 ). PP1-Knl1 activity may also be modulated by various accessory proteins (Posch et al, 2010 ; Eiteneuer et al, 2014 ; Duan et al, 2016 ), however, this regulation is omitted from Figure 1 , because it is thought to occur in the cytoplasm and not at kinetochores. It will be important in future to determine whether these, or other inhibitory pathways, are shut down following chromosome biorientation to enhance kinetochore phosphatase activity and promote SAC silencing.…”

The Greatwall kinase safeguards the genome integrity by affecting the kinome activity in mitosis

“…In parallel, our data indicated the modulation of phosphorylation of three regulators of PP1, namely, SDS22 (Ppp1r7), IASPP (Ppp1r13l), and IPP2 (Ppp1r2). Both SDS22 and IPP2 have been reported to be regulated after ionizing radiation, leading to their phosphorylation by ATM and dissociation from PP1 [ 89 , 90 ]. However, only SDS22 displayed a significantly increased phosphorylation on S12, a predicted ATM site.…”

A Kinase-Phosphatase Network that Regulates Kinetochore-Microtubule Attachments and the SAC

“…It is also regulated by cross-talk with all four of the enzymes discussed above. PLK1 can phosphorylate MPS1 substrates directly (von Schubert et al 2015;Espeut et al 2015), MPS1 itself to inhibit kinetochore-localisation (von Schubert et al 2015), the KNL1-MELT and BUBR1-KARD motifs to recruit PP2A-B56 (Suijkerbuijk et al 2012;Kruse et al 2013;Xu et al 2013;von Schubert et al 2015), and the PP1 regulator SDS22 to inhibit the dephosphorylation and inactivation of Aurora B (Duan et al 2016). Furthermore, PLK1 is itself activated and recruited to kinetochores by Aurora B (Shao et al 2015;O'Connor et al 2015;Carmena et al 2012a) and inhibited and delocalised by PP2A-B56 (Foley et al 2011).…”