bims-micesi 2022-09-18 papers

PLoS Genet. 2022 Sep 15. 18(9): e1010397

Recovery from spindle checkpoint-mediated arrest requires a novel Dnt1-dependent APC/C activation mechanism.

Shuang Bai, Li Sun, Xi Wang, Shuang-Min Wang, Zhou-Qing Luo, Yamei Wang, Quan-Wen Jin.

The activated spindle assembly checkpoint (SAC) potently inhibits the anaphase-promoting complex/cyclosome (APC/C) to ensure accurate chromosome segregation at anaphase. Early studies have recognized that the SAC should be silenced within minutes to enable rapid APC/C activation and synchronous segregation of chromosomes once all kinetochores are properly attached, but the underlying silencers are still being elucidated. Here, we report that the timely silencing of SAC in fission yeast requires dnt1+, which causes severe thiabendazole (TBZ) sensitivity and increased rate of lagging chromosomes when deleted. The absence of Dnt1 results in prolonged inhibitory binding of mitotic checkpoint complex (MCC) to APC/C and attenuated protein levels of Slp1Cdc20, consequently slows the degradation of cyclin B and securin, and eventually delays anaphase entry in cells released from SAC activation. Interestingly, Dnt1 physically associates with APC/C upon SAC activation. We propose that this association may fend off excessive and prolonged MCC binding to APC/C and help to maintain Slp1Cdc20 stability. This may allow a subset of APC/C to retain activity, which ensures rapid anaphase onset and mitotic exit once SAC is inactivated. Therefore, our study uncovered a new player in dictating the timing and efficacy of APC/C activation, which is actively required for maintaining cell viability upon recovery from the inhibition of APC/C by spindle checkpoint.

DOI: https://doi.org/10.1371/journal.pgen.1010397

Front Cell Dev Biol. 2022 ;10 967909

Structural, enzymatic and spatiotemporal regulation of PP2A-B55 phosphatase in the control of mitosis.

Benjamin Lacroix, Thierry Lorca, Anna Castro.

Cells require major physical changes to induce a proper repartition of the DNA. Nuclear envelope breakdown, DNA condensation and spindle formation are promoted at mitotic entry by massive protein phosphorylation and reversed at mitotic exit by the timely and ordered dephosphorylation of mitotic substrates. This phosphorylation results from the balance between the activity of kinases and phosphatases. The role of kinases in the control of mitosis has been largely studied, however, the impact of phosphatases has long been underestimated. Recent data have now established that the regulation of phosphatases is crucial to confer timely and ordered cellular events required for cell division. One major phosphatase involved in this process is the phosphatase holoenzyme PP2A-B55. This review will be focused in the latest structural, biochemical and enzymatic insights provided for PP2A-B55 phosphatase as well as its regulators and mechanisms of action.

Keywords: ARPP19; ENSA; PP2A phosphatase; cyclin B/Cdk1; greatwall; mitosis

DOI: https://doi.org/10.3389/fcell.2022.967909

J Cell Biol. 2022 Nov 07. pii: e202206131. [Epub ahead of print]221(11):

Conformational transitions of the Spindly adaptor underlie its interaction with Dynein and Dynactin.

Ennio A d'Amico, Misbha Ud Din Ahmad, Verena Cmentowski, Mathias Girbig, Franziska Müller, Sabine Wohlgemuth, Andreas Brockmeyer, Stefano Maffini, Petra Janning, Ingrid R Vetter, Andrew P Carter, Anastassis Perrakis, Andrea Musacchio.

Cytoplasmic Dynein 1, or Dynein, is a microtubule minus end-directed motor. Dynein motility requires Dynactin and a family of activating adaptors that stabilize the Dynein-Dynactin complex and promote regulated interactions with cargo in space and time. How activating adaptors limit Dynein activation to specialized subcellular locales is unclear. Here, we reveal that Spindly, a mitotic Dynein adaptor at the kinetochore corona, exists natively in a closed conformation that occludes binding of Dynein-Dynactin to its CC1 box and Spindly motif. A structure-based analysis identified various mutations promoting an open conformation of Spindly that binds Dynein-Dynactin. A region of Spindly downstream from the Spindly motif and not required for cargo binding faces the CC1 box and stabilizes the intramolecular closed conformation. This region is also required for robust kinetochore localization of Spindly, suggesting that kinetochores promote Spindly activation to recruit Dynein. Thus, our work illustrates how specific Dynein activation at a defined cellular locale may require multiple factors.

DOI: https://doi.org/10.1083/jcb.202206131

Front Genet. 2022 ;13 931222

CENP-A is a potential prognostic biomarker and correlated with immune infiltration levels in glioma patients.

Yuan Yang, Mengyun Duan, Yunfei Zha, Zijun Wu.

Background: Centromeric protein A (CENP-A), an essential protein involved in chromosomal segregation during cell division, is associated with several cancer types. However, its role in gliomas remains unclear. This study examined the clinical and prognostic significance of CENP-A in gliomas. Methods: Data of patients with glioma were collected from the Cancer Genome Atlas. Logistic regression, the Kruskal-Wallis test, and the Wilcoxon signed-rank test were performed to assess the relationship between CENP-A expression and clinicopathological parameters. The Cox regression model and Kaplan-Meier curve were used to analyze the association between CENP-A and survival outcomes. A prognostic nomogram was constructed based on Cox multivariate analysis. Gene set enrichment analysis (GSEA) was conducted to identify key CENP-A-related pathways and biological processes. Results: CENP-A was upregulated in glioma samples. Increased CENP-A levels were significantly associated with the world health organization (WHO) grade [Odds ratio (OR) = 49.88 (23.52-129.06) for grade 4 vs. grades 2 and 3], primary therapy outcome [OR = 2.44 (1.64-3.68) for progressive disease (PD) and stable disease (SD) vs. partial response (PR) and complete response (CR)], isocitrate dehydrogenase (IDH) status [OR = 13.76 (9.25-20.96) for wild-type vs. mutant], 1p/19q co-deletion [OR = 5.91 (3.95-9.06) for no codeletion vs. co-deletion], and age [OR = 4.02 (2.68-6.18) for > 60 vs. ≤ 60]. Elevated CENP-A expression was correlated with shorter overall survival in both univariate [hazard ratio (HR): 5.422; 95% confidence interval (CI): 4.044-7.271; p < 0.001] and multivariate analyses (HR: 1.967; 95% CI: 1.280-3.025; p < 0.002). GSEA showed enrichment of numerous cell cycle-and tumor-related pathways in the CENP-A high expression phenotype. The calibration plot and C-index indicated the favorable performance of our nomogram for prognostic prediction in patients with glioma. Conclusion: We propose a role for CENP-A in glioma progression and its potential as a biomarker for glioma diagnosis and prognosis.

Keywords: CENP-A; biomarker; glioma; microenvironment; prognosis

DOI: https://doi.org/10.3389/fgene.2022.931222

Elife. 2022 09 12. pii: e76249. [Epub ahead of print]11

The number of cytokinesis nodes in mitotic fission yeast scales with cell size.

Wasim A Sayyad, Thomas D Pollard.

Cytokinesis nodes are assemblies of stoichiometric ratios of proteins associated with the plasma membrane, which serve as precursors for the contractile ring during cytokinesis by fission yeast. The total number of nodes is uncertain, because of the limitations of the methods used previously. Here, we used the ~140 nm resolution of Airyscan super-resolution microscopy to measure the fluorescence intensity of small, single cytokinesis nodes marked with Blt1-mEGFP in live fission yeast cells early in mitosis. The ratio of the total Blt1-mEGFP fluorescence in the broad band of cytokinesis nodes to the average fluorescence of a single node gives about 190 single cytokinesis nodes in wild-type fission yeast cells early in mitosis. Most, but not all of these nodes condense into a contractile ring. The number of cytokinesis nodes scales with cell size in four strains tested, although large diameter rga4Δ mutant cells form somewhat fewer cytokinesis nodes than expected from the overall trend. The Pom1 kinase restricts cytokinesis nodes from the ends of cells, but the surface density of Pom1 on the plasma membrane around the equators of cells is similar with a wide range of node numbers, so Pom1 does not control cytokinesis node number. However, when the concentrations of either kinase Pom1 or kinase Cdr2 were varied with the nmt1 promoter, the numbers of cytokinesis nodes increased above a baseline of about ~190 with the total cellular concentration of either kinase.

Keywords: Airyscan imaging; S. pombe; cell biology; cell size; cytokinesis; nodes

DOI: https://doi.org/10.7554/eLife.76249