bims-micesi 2023-04-30 papers

bims-micesi

Biomed News

on Mitotic cell signalling

Issue of 2023–04–30
ten papers selected by
Valentina Piano, Uniklinik Köln

Alternative CDC20 translational isoforms tune mitotic arrest duration.
Mitotic chromosomes scale to nuclear-cytoplasmic ratio and cell size in Xenopus.
Microtubule competition and cell growth recenter the nucleus after anaphase in fission yeast.
Aurora B Inhibitors as Cancer Therapeutics.
Exit from Mitosis in Budding Yeast: Protein Phosphatase 1 is Required Downstream from Cdk1 Inactivation.
The establishment of mitotic errors-driven senescence depends on autophagy.
Genome folding dynamics during the M-to-G1-phase transition.
Heat shock transcription factors demonstrate a distinct mode of interaction with mitotic chromosomes.
Augmin is a Ran-regulated spindle assembly factor.
Unique progerin C-terminal peptide ameliorates Hutchinson-Gilford progeria syndrome phenotype by rescuing BUBR1.

Nature. 2023 Apr 26.

Alternative CDC20 translational isoforms tune mitotic arrest duration.

Mary-Jane Tsang, Iain M Cheeseman.

Mitotic defects activate the spindle-assembly checkpoint, which inhibits the anaphase-promoting complex co-activator CDC20 to induce a prolonged cell cycle arrest1,2. Once errors are corrected, the spindle-assembly checkpoint is silenced, allowing anaphase onset to occur. However, in the presence of persistent unresolvable errors, cells can undergo 'mitotic slippage', exiting mitosis into a tetraploid G1 state and escaping the cell death that results from a prolonged arrest. The molecular logic that enables cells to balance these duelling mitotic arrest and slippage behaviours remains unclear. Here we demonstrate that human cells modulate the duration of their mitotic arrest through the presence of conserved, alternative CDC20 translational isoforms. Downstream translation initiation results in a truncated CDC20 isoform that is resistant to spindle-assembly-checkpoint-mediated inhibition and promotes mitotic exit even in the presence of mitotic perturbations. Our study supports a model in which the relative levels of CDC20 translational isoforms control the duration of mitotic arrest. During a prolonged mitotic arrest, new protein synthesis and differential CDC20 isoform turnover create a timer, with mitotic exit occurring once the truncated Met43 isoform achieves sufficient levels. Targeted molecular changes or naturally occurring cancer mutations that alter CDC20 isoform ratios or its translational control modulate mitotic arrest duration and anti-mitotic drug sensitivity, with potential implications for the diagnosis and treatment of human cancers.

DOI: https://doi.org/10.1038/s41586-023-05943-7
Elife. 2023 Apr 25. pii: e84360. [Epub ahead of print]12

Mitotic chromosomes scale to nuclear-cytoplasmic ratio and cell size in Xenopus.

Coral Y Zhou, Bastiaan Dekker, Ziyuan Liu, Hilda Cabrera, Joel Ryan, Job Dekker, Rebecca Heald.

  During the rapid and reductive cleavage divisions of early embryogenesis, subcellular structures such as the nucleus and mitotic spindle scale to decreasing cell size. Mitotic chromosomes also decrease in size during development, presumably to scale coordinately with mitotic spindles, but underlying mechanisms are unclear. Here we combine in vivo and in vitro approaches using eggs and embryos from the frog Xenopus laevis to show that mitotic chromosome scaling is mechanistically distinct from other forms of subcellular scaling. We found that mitotic chromosomes scale continuously with cell, spindle and nuclear size in vivo. However, unlike for spindles and nuclei, mitotic chromosome size cannot be re-set by cytoplasmic factors from earlier developmental stages. In vitro, increasing nuclear-cytoplasmic (N/C) ratio is sufficient to recapitulate mitotic chromosome scaling, but not nuclear or spindle scaling, through differential loading of maternal factors during interphase. An additional pathway involving importin a scales mitotic chromosomes to cell surface area/volume ratio (SA/V) during metaphase. Finally, single-chromosome immunofluorescence and Hi-C data suggest that mitotic chromosomes shrink during embryogenesis through decreased recruitment of condensin I, resulting in major rearrangements of DNA loop architecture to accommodate the same amount of DNA on a shorter axis. Together, our findings demonstrate how mitotic chromosome size is set by spatially and temporally distinct developmental cues in the early embryo.

Keywords:  cell biology; chromosomes; gene expression; xenopus

DOI:  https://doi.org/10.7554/eLife.84360
Mol Biol Cell. 2023 Apr 26. mbcE23010034

Microtubule competition and cell growth recenter the nucleus after anaphase in fission yeast.

Kimberly Bellingham-Johnstun, Annelise Thorn, Julio M Belmonte, Caroline Laplante.

Cells actively position their nucleus based on their activity. In fission yeast, microtubule-dependent nuclear centering is critical for symmetrical cell division. After spindle disassembly at the end of anaphase, the nucleus recenters over a ∼90 min period, approximately half of the duration of the cell cycle. Live cell and simulation experiments support the cooperation of two distinct microtubule competition mechanisms in the slow recentering of the nucleus. First, a push-push mechanism acts from spindle disassembly to septation and involves the opposing actions of the mitotic Spindle Pole Body microtubules that push the nucleus away from the ends of the cell while post-anaphase array of microtubules basket the nucleus and limit its migration toward the division plane. Second, a slow-and-grow mechanism slowly centers the nucleus in the newborn cell by a combination of microtubule competition and asymmetric cell growth. Our work underlines how intrinsic properties of microtubules differently impact nuclear positioning according to microtubule network organization and cell size. [Media: see text] [Media: see text].

DOI: https://doi.org/10.1091/mbc.E23-01-0034
Molecules. 2023 Apr 11. pii: 3385. [Epub ahead of print]28(8):

Aurora B Inhibitors as Cancer Therapeutics.

Antal H Kovacs, Dong Zhao, Jinqiang Hou.

  The Aurora kinases (A, B, and C) are a family of three isoform serine/threonine kinases that regulate mitosis and meiosis. The Chromosomal Passenger Complex (CPC), which contains Aurora B as an enzymatic component, plays a critical role in cell division. Aurora B in the CPC ensures faithful chromosome segregation and promotes the correct biorientation of chromosomes on the mitotic spindle. Aurora B overexpression has been observed in several human cancers and has been associated with a poor prognosis for cancer patients. Targeting Aurora B with inhibitors is a promising therapeutic strategy for cancer treatment. In the past decade, Aurora B inhibitors have been extensively pursued in both academia and industry. This paper presents a comprehensive review of the preclinical and clinical candidates of Aurora B inhibitors as potential anticancer drugs. The recent advances in the field of Aurora B inhibitor development will be highlighted, and the binding interactions between Aurora B and inhibitors based on crystal structures will be presented and discussed to provide insights for the future design of more selective Aurora B inhibitors.

Keywords:  Aurora B; Aurora B inhibitors; Aurora kinase; cancer; chromosomal passenger complex; crystal structures

DOI:  https://doi.org/10.3390/molecules28083385
Res Sq. 2023 Apr 12. pii: rs.3.rs-2787001. [Epub ahead of print]

Exit from Mitosis in Budding Yeast: Protein Phosphatase 1 is Required Downstream from Cdk1 Inactivation.

Jason M Keaton, Benjamin G Workman, Linfeng Xie, James R Paulson.

We show that inactivation of the protein kinase Cdk1/Cyclin B (Cdc28/Clb 2 in the budding yeast Saccharomyces cerevisiae ) is not only necessary for cells to leave mitosis, as is well known, but also sufficient to trigger mitotic exit. Cells carrying the mutation cdc28-as1 , which makes Cdc28 (Cdk1) uniquely sensitive to the ATP analog 1NM-PP1, were arrested with spindle poisons and then treated with 1NM-PP1 to inhibit Cdk1. This treatment caused the cells to exit mitosis and enter G1-phase as shown by initiation of rebudding (without cytokinesis), production of "shmoos" (when α-factor was present), stabilization of Sic1, and degradation of Clb2. This result provides a system in which to test whether particular gene products are required downstream from Cdk1 inactivation in exit from mitosis. In this system, the mutation cdc28-as1 is combined with a conditional mutation in the gene of interest. Using this approach, we demonstrate that Protein Phosphatase 1 (PPase1; Glc7 in S. cerevisiae ) is required for reestablishment of G1-phase following Cdk1 inactivation. This system could be used to test whether other protein phosphatases are also needed downstream from Cdk1 inactivation, and it could be combined with phosphoproteomics to gain information about the substrates those phosphatases act on during mitotic exit.

DOI: https://doi.org/10.21203/rs.3.rs-2787001/v1
Redox Biol. 2023 Apr 17. pii: S2213-2317(23)00102-7. [Epub ahead of print]62 102701

The establishment of mitotic errors-driven senescence depends on autophagy.

Andreas Goutas, Zozo Outskouni, Ioanna Papathanasiou, Aphrodite Georgakopoulou, Georgios E Karpetas, Efstathios S Gonos, Varvara Trachana.

  We and others have reported that senescence onset is accompanied by genomic instability that is evident by several defects, such as aneuploidy or erroneous mitosis features. Here, we report that these defects also appear in young cells upon oxidative insult. We provide evidence that these errors could be the consequence of oxidative stress (OS)- either exogenous or senescence-associated - overriding the spindle assembly checkpoint (SAC). Young cells treated with Η2Ο2 as well as older cells fail to maintain mitotic arrest in the presence of spindle poisons and a significant higher percentage of them have supernumerary centrosomes and centrosome related anomalous characteristics. We also report that aging is escorted by expression modifications of SAC components, and especially of Bub1b/BubR1. Bub1b/BubR1 has been previously reported to decrease naturally upon aging. Here, we show that there is an initial increase in Bub1b/BubR1 levels, feasibly as part of the cells' response against OS-driven genomic instability, that is followed by its autophagy dependent degradation. This provides an explanation that was missing regarding the molecular entity responsible for the downregulation of Bub1b/BubR1 upon aging, especially since it is well established, by us and others, that the proteasome function decays as cells age. These results, not only serve the previously reported notion of a shift from proteasome to autophagy-dependent degradation upon aging, but also provide a mechanistic insight for mitotic errors-driven senescence. We believe that our conclusions deepen our understanding regarding the homeostatic function of autophagy that serves the establishment of senescence as a barrier against cellular transformation.

Keywords:  Autophagy; Bub1b/BubR1; Oxidative stress; Senescence; Spindle assembly checkpoint

DOI:  https://doi.org/10.1016/j.redox.2023.102701
Curr Opin Genet Dev. 2023 Apr 24. pii: S0959-437X(23)00016-3. [Epub ahead of print]80 102036

Genome folding dynamics during the M-to-G1-phase transition.

Haoyue Zhang, Gerd A Blobel.

All measurable features of higher-order chromosomal architecture undergo drastic reorganization as cells enter and exit mitosis. During mitosis, gene transcription is temporarily halted, the nuclear envelope is dismantled, and chromosomes undergo condensation. At this time, chromatin compartments, topologically associating domains (TADs), and loops that connect enhancers with promoters as well as CTCF/cohesin loops are dissolved. Upon G1 entry, genome organization is rebuilt in the daughter nuclei to resemble that of the mother nucleus. We survey recent studies that traced these features in relation to gene expression during the mitosis-to-G1-phase transition at high temporal resolution. Dissection of fluctuating architectural features informed the hierarchical relationships of chromosomal organization, the mechanisms by which they are formed, and their mutual (in-) dependence. These studies highlight the importance of considering the cell cycle dynamics for studies of chromosomal organization.

DOI: https://doi.org/10.1016/j.gde.2023.102036
Nucleic Acids Res. 2023 Apr 28. pii: gkad304. [Epub ahead of print]

Heat shock transcription factors demonstrate a distinct mode of interaction with mitotic chromosomes.

Rachel M Price, Marek A Budzyński, Junzhou Shen, Jennifer E Mitchell, James Z J Kwan, Sheila S Teves.

A large number of transcription factors have been shown to bind and interact with mitotic chromosomes, which may promote the efficient reactivation of transcriptional programs following cell division. Although the DNA-binding domain (DBD) contributes strongly to TF behavior, the mitotic behaviors of TFs from the same DBD family may vary. To define the mechanisms governing TF behavior during mitosis in mouse embryonic stem cells, we examined two related TFs: Heat Shock Factor 1 and 2 (HSF1 and HSF2). We found that HSF2 maintains site-specific binding genome-wide during mitosis, whereas HSF1 binding is somewhat decreased. Surprisingly, live-cell imaging shows that both factors appear excluded from mitotic chromosomes to the same degree, and are similarly more dynamic in mitosis than in interphase. Exclusion from mitotic DNA is not due to extrinsic factors like nuclear import and export mechanisms. Rather, we found that the HSF DBDs can coat mitotic chromosomes, and that HSF2 DBD is able to establish site-specific binding. These data further confirm that site-specific binding and chromosome coating are independent properties, and that for some TFs, mitotic behavior is largely determined by the non-DBD regions.

DOI: https://doi.org/10.1093/nar/gkad304
J Biol Chem. 2023 Apr 20. pii: S0021-9258(23)01764-7. [Epub ahead of print] 104736

Augmin is a Ran-regulated spindle assembly factor.

Jodi Kraus, Sophie M Travis, Matthew R King, Sabine Petry.

  Mitotic spindles are composed of microtubules (MTs) that must nucleate at the right place and time. Ran regulates this process by directly controlling the release of spindle assembly factors (SAFs) from nucleocytoplasmic shuttle proteins importin-αβ and subsequently forms a biochemical gradient of SAFs localized around chromosomes. The majority of spindle MTs are generated by branching MT nucleation, which has been shown to require an eight-subunit protein complex known as augmin. InXenopus laevis, Ran can control branching through a canonical SAF, TPX2, which is non-essential in Drosophila melanogaster embryos and HeLa cells. Thus, how Ran regulates branching MT nucleation when TPX2 is not required remains unknown. Here, we use in vitro pulldowns and TIRF microscopy to show that augmin is a Ran-regulated SAF. We demonstrate that augmin directly interacts with both importin-α and importin-β through two nuclear localization sequences on the Haus8 subunit, which overlap with the MT binding site. Moreover, we show Ran controls localization of augmin to MTs in both Xenopus egg extract and in vitro. Our results demonstrate that RanGTP directly regulates augmin, which establishes a new way by which Ran controls branching MT nucleation and spindle assembly both in the absence and presence of TPX2.

Keywords:  Ran pathway; TPX2; augmin; branching microtubule nucleation; importins; spindle assembly factor

DOI:  https://doi.org/10.1016/j.jbc.2023.104736
Nat Aging. 2023 Feb;3(2): 185-201

Unique progerin C-terminal peptide ameliorates Hutchinson-Gilford progeria syndrome phenotype by rescuing BUBR1.

Na Zhang, Qianying Hu, Tingting Sui, Lu Fu, Xinglin Zhang, Yu Wang, Xiaojuan Zhu, Baiqu Huang, Jun Lu, Zhanjun Li, Yu Zhang.

An accumulating body of evidence indicates an association between mitotic defects and the aging process in Hutchinson-Gilford progeria syndrome (HGPS), which is a premature aging disease caused by progerin accumulation. Here, we found that BUBR1, a core component of the spindle assembly checkpoint, was downregulated during HGPS cellular senescence. The remaining BUBR1 was anchored to the nuclear membrane by binding with the C terminus of progerin, thus further limiting the function of BUBR1. Based on this, we established a unique progerin C-terminal peptide (UPCP) that effectively blocked the binding of progerin and BUBR1 and enhanced the expression of BUBR1 by interfering with the interaction between PTBP1 and progerin. Finally, UPCP significantly inhibited HGPS cellular senescence and ameliorated progeroid phenotypes, extending the lifespan of LmnaG609G/G609G mice. Our findings reveal an essential role for the progerin-PTBP1-BUBR1 axis in HGPS. Therapeutics designed around UPCP may be a beneficial strategy for HGPS treatment.

DOI: https://doi.org/10.1038/s43587-023-00361-w