Feedback control of PLK1 by Apolo1 ensures accurate chromosome segregation

Abstract

SUMMARY Stable transmission of genetic material during cell division requires accurate chromosome segregation. PLK1 dynamics at kinetochores control establishment of correct kinetochore-microtubule attachments and subsequent silencing of the spindle checkpoint. However, the regulatory mechanism responsible for PLK1 activity in prometaphase has not yet been affirmatively identified. Here we identify Apolo1, which tunes PLK1 activity for accurate kinetochore-microtubule attachments. Apolo1 localizes to kinetochores during early mitosis, and suppression of Apolo1 results in misaligned chromosomes. Using the fluorescence resonance energy transfer (FRET)-based PLK1 activity reporter, we found that Apolo1 sustains PLK1 kinase activity at kinetochores for accurate attachment during prometaphase. Apolo1 is a cognate substrate of PLK1, and the phosphorylation enables PP1γ to inactivate PLK1 by dephosphorylation. Mechanistically, Apolo1 constitutes a bridge between kinase and phosphatase, which governs PLK1 activity in prometaphase. These findings define a previously uncharacterized feedback loop by which Apolo1 provides fine-tuning for PLK1 to guide chromosome segregation in mitosis.

C1orf112 is a novel regulator of interstrand crosslink that decreases FIGNL1-RAD51 interaction

“…Alike other scaffolding proteins such as REV7, it is possible that C1orf112 forms different molecular complexes, depending on the cellular context, thereby preserving genomic stability (reviewed in 45 ). In fact, our proteomic analysis also identified ERCC6L as one of the top constitutive interactors of C1orf112, which may likely reflect a role during mitotic progression 18 .…”

“…According to this network, we found that C1orf112 behaves similarly to factors of the cellular response to ICL agent in BL cell lines. Previous reports identified C1orf112 (aka Apolo1) as a modulator of chromosome segregation through the regulation of PLK1 activity 18 . As no other genes associated with mitosis progression were enriched in our screens, we reasoned that a different function of C1orf112 may be important for the cellular response to ICL.…”

“…Two of these interactors, the Pericentriolar material 1 protein (PCM1) and the DNA excision repair protein ERCC6-like (ERCC6L, also known as PICHs), play a role in mitosis where they respectively contribute to the proper assembly of functional centrosomes and the resolution of anaphase bridges 30,31,33 . Therefore, we reasoned that they most likely play a role in the mitotic function of C1orf112 (APOLO1) (Xu et al, 2021). Interestingly, the AAA+ ATPase Fidgetin Like 1 (FIGNL1) was also identified as a constitutive interactor of C1orf112 in our mTurboID.…”

The FIGNL1-interacting protein C1orf112 is synthetic lethal with PICH and mediates RAD51 retention on chromatin

“…This suggests that regulation of RAD51 dynamics alone may not fully account for the observed synthetic lethality between C1orf112 and ERCC6L , and we cannot rule out that C1orf112 has functions beyond FIGNL1 stabilisation and RAD51 filament formation. Indeed, an additional role for C1orf112 in regulating PLK1 activity during early mitosis has been described recently (Xu et al, 2021). In fact, we identified PLK1 as a potential interactor of C1orf112 in our mitotic mass spectrometry data set (Suppl.…”

Mad2 promotes Cyclin B2 recruitment to the kinetochore for guiding accurate mitotic checkpoint

“…To execute its multiple roles, Cdk1 must phosphorylate its numerous substrates in a spatiotemporally controlled manner. Kinases adopt different mechanisms, such as the structure of the kinase catalytic cleft, the kinase docking site, localization of the kinase, and system‐level competition between substrates, to phosphorylate their substrates selectively (Ubersax & Ferrell, 2007; Xu et al , 2021). Cyclin B determines Cdk1 substrate selectivity through the docking domain and subcellular localization of Cdk1.…”