bims-micesi 2023-08-13 papers

bims-micesi

Biomed News

on Mitotic cell signalling

Issue of 2023–08–13
seven papers selected by
Valentina Piano, Uniklinik Köln

YAP co-localizes with the mitotic spindle and midbody to safeguard mitotic division in lung-cancer cells.
Evidence of kinesin motors involved in stable kinetochore assembly during early meiosis.
Compromised Mitotic Fidelity in Human Pluripotent Stem Cells.
BRD4 directs mitotic cell division by inhibiting DNA damage.
Elasticity control of entangled chromosomes: crosstalk between condensin complexes and nucleosomes.
Efficient Formation of Single-copy Human Artificial Chromosomes.
Autophagy modulates the stability of Wee1 and cell cycle G2/M transition.

FEBS J. 2023 Aug 07.

YAP co-localizes with the mitotic spindle and midbody to safeguard mitotic division in lung-cancer cells.

Shu-Er Chow, Chia-Chi Hsu, Cheng-Ta Yang, Yaa-Jyuhn J Meir.

  YES-associated protein (YAP) is a part of the Hippo pathway, with pivotal roles in several developmental processes and dual functionality as both a tumor suppressor and an oncogene. In the present study, we identified YAP activity as a microtubular scaffold protein that maintains stability of the mitotic spindle and midbody by physically interacting with α -tubulin during mitotic progression. The interaction of YAP and α -tubulin was evident in co-immunoprecipitation assays, as well as observing their co-localization in the microtubular structure of the mitotic spindle and midbody in immunostainings. With YAP depletion, levels of ECT2, MKLP-1 and Aurora B are reduced, which is consistent with YAP functioning in midbody formation during cytokinesis. The concomitant decrease of α -tubulin and increase of acetyl-α -tubulin during YAP depletion occurred at the post-transcriptional level. This suggests that YAP maintains the stability of the mitotic spindle and midbody, which ensures appropriate chromosome segregation during mitotic division. The increase of acetyl-α -tubulin during YAP depletion may provide a lesion-halting mechanism in maintaining the microtubule structure. The depletion of YAP also results in multinuclearity and aneuploidy, which supports its role in stabilizing the mitotic spindle and midbody.

Keywords:  YAP (YES-associated protein); microtubule; midbody; mitotic division; non-small cell lung cancer

DOI:  https://doi.org/10.1111/febs.16926
Mol Biol Cell. 2023 Aug 09. mbcE22120569

Evidence of kinesin motors involved in stable kinetochore assembly during early meiosis.

Seema Shah, Priyanka Mittal, Deepanshu Kumar, Anjani Mittal, Santanu K Ghosh.

During mitosis, the budding yeast, kinetochores remain attached to microtubules, except for a brief period during S phase. Sister-kinetochores separate into two clusters (bi-lobed' organization) upon stable end-on attachment to microtubules emanating from opposite spindle poles. However, in meiosis, the outer kinetochore protein Ndc80 reassembles at the centromeres much later after prophase I, establishing new kinetochore-microtubule attachments. Perhaps due to this, despite homolog bi-orientation, we observed that the kinetochores (Ndc80) are linearly dispersed between spindle-poles during metaphase I of meiosis. The presence of end-on attachment marker Dam1 as a cluster near each pole suggests one of the other possibilities that the pole-proximal and pole-distal kinetochores are attached end-on and laterally to the microtubules, respectively. Colocalization studies of kinetochores and kinesin motors suggest that budding yeast kinesin 5, Cin8 and Kip1 perhaps localize to the end-on attached kinetochores while kinesin 8, Kip3 resides at all the kinetochores. Our findings, including kinesin 5 and Ndc80 co-appearance after prophase I and reduced Ndc80 levels in cin8 null mutant, suggest that kinesin motors are crucial for kinetochore reassembly and stability during early meiosis. Thus, this work reports yet another meiosis specific function of kinesin motors.

DOI: https://doi.org/10.1091/mbc.E22-12-0569
Int J Mol Sci. 2023 Jul 25. pii: 11933. [Epub ahead of print]24(15):

Compromised Mitotic Fidelity in Human Pluripotent Stem Cells.

Inês Milagre, Carolina Pereira, Raquel A Oliveira.

  Human pluripotent stem cells (PSCs), which include both embryonic and induced pluripotent stem cells, are widely used in fundamental and applied biomedical research. They have been instrumental for better understanding development and cell differentiation processes, disease origin and progression and can aid in the discovery of new drugs. PSCs also hold great potential in regenerative medicine to treat or diminish the effects of certain debilitating diseases, such as degenerative disorders. However, some concerns have recently been raised over their safety for use in regenerative medicine. One of the major concerns is the fact that PSCs are prone to errors in passing the correct number of chromosomes to daughter cells, resulting in aneuploid cells. Aneuploidy, characterised by an imbalance in chromosome number, elicits the upregulation of different stress pathways that are deleterious to cell homeostasis, impair proper embryo development and potentiate cancer development. In this review, we will summarize known molecular mechanisms recently revealed to impair mitotic fidelity in human PSCs and the consequences of the decreased mitotic fidelity of these cells. We will finish with speculative views on how the physiological characteristics of PSCs can affect the mitotic machinery and how their suboptimal mitotic fidelity may be circumvented.

Keywords:  aneuploidy; human pluripotent stem cells; mitotic fidelity

DOI:  https://doi.org/10.3390/ijms241511933
bioRxiv. 2023 Jul 25. pii: 2023.07.02.547436. [Epub ahead of print]

BRD4 directs mitotic cell division by inhibiting DNA damage.

Tiyun Wu, Haitong Hou, Anup Dey, Mahesh Bachu, Xiongfong Chen, Jan Wisniewski, Fuki Kudoh, Chao Chen, Sakshi Chauhan, Hua Xiao, Richard Pan, Keiko Ozato.

BRD4 binds to acetylated histones to regulate transcription and drive cancer cell proliferation. However, the role of BRD4 in normal cell growth remains to be elucidated. Here we investigated the question by using mouse embryonic fibroblasts with conditional Brd4 knockout (KO). We found that Brd4KO cells grow more slowly than wild type cells: they do not complete replication, fail to achieve mitosis, and exhibit extensive DNA damage throughout all cell cycle stages. BRD4 was required for expression of more than 450 cell cycle genes including genes encoding core histones and centromere/kinetochore proteins that are critical for genome replication and chromosomal segregation. Moreover, we show that many genes controlling R-loop formation and DNA damage response (DDR) require BRD4 for expression. Finally, BRD4 constitutively occupied genes controlling R-loop, DDR and cell cycle progression. We suggest that BRD4 epigenetically marks those genes and serves as a master regulator of normal cell growth.

DOI: https://doi.org/10.1101/2023.07.02.547436
Biophys J. 2023 Aug 10. pii: S0006-3495(23)00506-4. [Epub ahead of print]

Elasticity control of entangled chromosomes: crosstalk between condensin complexes and nucleosomes.

Tetsuya Yamamoto, Kazuhisa Kinoshita, Tatsuya Hirano.

Condensin-mediated loop extrusion is now considered as the main driving force of mitotic chromosome assembly. Recent experiments have shown, however, that a class of mutant condensin complexes deficient in loop extrusion can assemble chromosome-like structures in Xenopus egg extracts, although these structures are somewhat different from those assembled by wild-type condensin complexes. In the absence of topoisomerase II (topo II), the mutant condensin complexes produce an unusual round-shaped structure termed a 'bean', which consists of a DNA-dense central core surrounded by a DNA-sparse halo. The mutant condensin complexes accumulate in the core whereas histones are more concentrated in the halo than in the core. We consider that this peculiar structure serves as a model system to study how DNA entanglements, nucleosomes, and condensin functionally crosstalk with each other. To gain insight into how the bean structure is formed, here we construct a theoretical model. Our theory predicts that the core is formed by attractive interactions between mutant condensin complexes whereas the halo is stabilized by the energy reduction through the selective accumulation of nucleosomes. The formation of the halo increases the elastic free energy due to the DNA entanglement in the core, but the latter free energy is compensated by condensin complexes that suppress the assembly of nucleosomes.

DOI: https://doi.org/10.1016/j.bpj.2023.08.006
bioRxiv. 2023 Jun 30. pii: 2023.06.30.547284. [Epub ahead of print]

Efficient Formation of Single-copy Human Artificial Chromosomes.

Craig W Gambogi, Elie Mer, David M Brown, George Yankson, Janardan N Gavade, Glennis A Logsdon, Patrick Heun, John I Glass, Ben E Black.

Large DNA assembly methodologies underlie milestone achievements in synthetic prokaryotic and budding yeast chromosomes. While budding yeast control chromosome inheritance through ∼125 bp DNA sequence-defined centromeres, mammals and many other eukaryotes use large, epigenetic centromeres. Harnessing centromere epigenetics permits human artificial chromosome (HAC) formation but is not sufficient to avoid rampant multimerization of the initial DNA molecule upon introduction to cells. Here, we describe an approach that efficiently forms single-copy HACs. It employs a ∼750 kb construct that is sufficiently large to house the distinct chromatin types present at the inner and outer centromere, obviating the need to multimerize. Delivery to mammalian cells is streamlined by employing yeast spheroplast fusion. These developments permit faithful chromosome engineering in the context of metazoan cells.
One-Sentence Summary: A quarter century after the first human artificial chromosomes, a solution to their uncontrolled multimerization is achieved.

DOI: https://doi.org/10.1101/2023.06.30.547284
Biochem Biophys Res Commun. 2023 Aug 04. pii: S0006-291X(23)00942-7. [Epub ahead of print]677 63-69

Autophagy modulates the stability of Wee1 and cell cycle G2/M transition.

Biwei Han, Yajing Chen, Chen Song, Yali Chen, Yong Chen, Daniel Ferguson, Yunzhi Yang, Anyuan He.

The mammalian cell cycle is divided into four sequential phases, namely G1 (Gap 1), S (synthesis), G2 (Gap 2), and M (mitosis). Wee1, whose turnover is tightly and finely regulated, is a well-known kinase serving as a gatekeeper for the G2/M transition. However, the mechanism underlying the turnover of Wee1 is not fully understood. Autophagy, a highly conserved cellular process, maintains cellular homeostasis by eliminating intracellular aggregations, damaged organelles, and individual proteins. In the present study, we found autophagy deficiency in mouse liver caused G2/M arrest in two mouse models, namely Fip200 and Atg7 liver-specific knockout mice. To uncover the link between autophagy deficiency and G2/M transition, we combined transcriptomic and proteomic analysis for liver samples from control and Atg7 liver-specific knockout mice. The data suggest that the inhibition of autophagy increases the protein level of Wee1 without any alteration of its mRNA abundance. Serum starvation, an autophagy stimulus, downregulates the protein level of Wee1 in vitro. In addition, the half-life of Wee1 is extended by the addition of chloroquine, an autophagy inhibitor. LC3, a central autophagic protein functioning in autophagy substrate selection and autophagosome biogenesis, interacts with Wee1 as assessed by co-immunoprecipitation assay. Furthermore, overexpression of Wee1 leads to G2/M arrest both in vitro and in vivo. Collectively, our data indicate that autophagy could degrade Wee1-a gatekeeper of the G2/M transition, whereas the inhibition of autophagy leads to the accumulation of Wee1 and causes G2/M arrest in mouse liver.

DOI: https://doi.org/10.1016/j.bbrc.2023.08.010