bims-micesi Biomed News
on Mitotic cell signalling
Issue of 2025–11–09
eight papers selected by
Valentina Piano, Uniklinik Köln
  1. Pre-rRNAs control mitosis by maintaining chromosomal segregation through protecting SMC2 from AURKA-mediated phosphorylation.
  2. Mitotic Phosphorylation of Swi6/HP1 Regulates Its Chromatin Binding and Chromosome Segregation.
  3. Designing protein-based artificial kinetochores as decoys to prevent meiotic errors in oocytes.
  4. The composition and structure of the outer kinetochore KMN complex is conserved across kingdoms.
  5. Coordinated Remodeling of Ca2+ Signaling and Intracellular Organelles During Cell Division.
  6. Optimization of Mitotic Index Quantification Using the Amnis ImageStream Imaging Flow Cytometer.
  7. MRTF-dependent cytoskeletal dynamics drive efficient cell cycle progression.
  8. Drug target proteome profiling identifies HES1-driven mitotic catastrophe in ovarian serous carcinoma.
  1. Cell Death Dis. 2025 Nov 07. 16(1): 812
    Pre-rRNAs control mitosis by maintaining chromosomal segregation through protecting SMC2 from AURKA-mediated phosphorylation.
    Shiqi Sun, Kunqi Su, Yang Jiang, Yuying Wang, Yang Hu, Chang Wang, Zhuochen Zhao, Chunfeng Zhang, Baocai Xing, Xiaojuan Du.
      In interphase, 47S pre-rRNA is transcribed by RNA polymerase I (Pol I) and processed to form intermediate pre-rRNAs and finally produce mature rRNAs in the nucleolus. During mitosis, nucleolus disassembles and pre-rRNAs including 45S, 30S and 32S pre-rRNAs relocate in the peri-chromosomal region (PR). Inhibition of pre-rRNA transcription impairs chromosome dispersion in prometaphase. However, how pre-rRNAs regulate mitosis remains elusive. Here, we unravel a novel mechanism for pre-rRNAs to control mitosis. Inhibition of Pol I prolongs the mitotic process and induces defective chromosomal segregation, resulting in mitotic catastrophe. We isolated chromosome and determined the chromosome-binding proteins by mass-spectrometry. Using quantitative proteomics analysis, immunoprecipitation and immunofluorescent staining, we found that AURKA approaches chromosome when Pol I is inhibited. The AURKA-binding proteins on the chromosome were determined by immunoprecipitation and mass-spectrometry after cells were treated with Act D, BMH-21 or CX5461, respectively, and the chromosomal segregation controlling proteins were selected. When Pol I was inhibited, the binding of AURKA with SMC2, the crucial component of Condensin, is significantly enhanced. Importantly, SMC2 is phosphorylated by AURKA only when Pol I was inhibited. Alignment of SMC2 amino acid sequence with substrates of AURKA shows that SMC2 possesses the consensus R/K/N-R-X-S/T-B, and T574 is the only potential AURKA-catalyzed phosphorylation site. Indeed, SMC2 T574 is phosphorylated by AURKA in cell and in vitro. Thereafter, we generated SMC2 T574-P specific antibody, and confirmed that endogenous SMC2 T574 is phosphorylated by AURKA in mitosis in the absence of pre-rRNAs. Consequently, phosphorylation of SMC2 T574 disrupts the SMC2/SMC4 binding and the binding of SMC2 and SMC4 to chromosomal DNA, leading to chromosomal segregation defect. The phosphorylation deficient Flag-SMC2 T574A reverses the mitotic catastrophe caused by Pol I inhibition. Collectively, we demonstrate that pre-rRNAs protect SMC2 from the AURKA-mediated phosphorylation to maintain normal mitosis.
    DOI:  https://doi.org/10.1038/s41419-025-08169-9
  2. FASEB J. 2025 Nov 15. 39(21): e71190
    Mitotic Phosphorylation of Swi6/HP1 Regulates Its Chromatin Binding and Chromosome Segregation.
    Yuriko Yoshimura, Aki Hayashi, Mayo Tanaka, Mieko Suzuki-Matsubara, Reiko Nakagawa, Gohei Nishibuchi, Hideaki Tagami, Masaya Oki, Jun-Ichi Nakayama.
      In eukaryotic cells, heterochromatin assembly is critical for chromosome segregation and transcriptional gene silencing. Heterochromatin protein 1 (HP1) is a conserved chromosomal protein that plays an important role in heterochromatin assembly. We have previously shown that mammalian HP1α and Schizosaccharomyces pombe Swi6 are phosphorylated by casein kinase II (CK2) and that this phosphorylation is essential for their function in heterochromatin assembly. In addition to CK2-mediated phosphorylation, several studies have shown that HP1 proteins undergo additional phosphorylation during mitosis. However, functional significance of the mitotic phosphorylation of HP1 remains unclear. Here, we identified mitotic phosphorylation sites within fission yeast Swi6 and showed that this phosphorylation is involved in chromosome segregation. Using an Escherichia coli co-expression system, we showed that Swi6 is phosphorylated by Ark1, a solo Aurora kinase in S. pombe, and mutational analyses revealed that serine residues in the conserved N-terminal region of Swi6 are the primary targets of Ark1. By expressing mutant Swi6, we confirmed that these serine residues are phosphorylated during mitosis in vivo. Although non-phosphorylatable or phosphomimic mutations in Swi6 had little effect on heterochromatic silencing, they caused defects in early chromosome segregation and modulated the temperature-sensitive growth of mutant cells for chromosome passenger complex components. These results suggest that the Ark1-mediated mitotic phosphorylation of Swi6 is involved in chromosome segregation during mitosis and implicates a conserved regulatory role for the mitotic phosphorylation of HP1 proteins.
    Keywords:  fission yeast; heterochromatin; heterochromatin protein 1; mitosis; phosphorylation
    DOI:  https://doi.org/10.1096/fj.202500384R
  3. Nat Cell Biol. 2025 Nov 04.
    Designing protein-based artificial kinetochores as decoys to prevent meiotic errors in oocytes.
    Yuanzhuo Zhou, Kohei Asai, Hirohisa Kyogoku, Tomoya S Kitajima.
      Chromosome mis-segregation during meiosis in oocytes causes miscarriages and congenital diseases. Ageing-associated premature chromosome separation is a major cause of mis-segregation. Effective prevention of premature chromosome separation has not yet been achieved. Here we design protein-based artificial kinetochores that act as decoys to prevent premature chromosome separation. Designed artificial kinetochore-like decoys are submicroscale clusters of NDC80-NUF2-tethered protein particles that can establish a biorientation-like state by competing with chromosomal kinetochores for HURP-decorated microtubules. This competition reduces excessive bipolar microtubule pulling forces exerted on chromosomes, thereby effectively preventing premature chromosome separation during meiosis I and II in aged mouse oocytes. These effects suppress egg aneuploidy. This study provides a decoy strategy with biocompatible artificial kinetochores to prevent ageing-associated meiotic errors in oocytes.
    DOI:  https://doi.org/10.1038/s41556-025-01792-w
  4. Commun Biol. 2025 Nov 07. 8(1): 1543
    The composition and structure of the outer kinetochore KMN complex is conserved across kingdoms.
    Dipesh Kumar Singh, Birgit Walkemeier, Anjali Nayini, Jelle Van Leene, Stéphanie Durand, Geert De Jaeger, Raphael Guerois, Raphael Mercier.
      In eukaryotes, chromosome segregation relies on attachment to the spindle, ensured by the kinetochore. The outer kinetochore attaches to the microtubules and is named after three sub-complexes KNL1C, MIS12C, and NDC80C (KMN). While the KMN complex comprises ten proteins in humans S. cerevisiae, its conservation in more distant eukaryotes is unclear. Here, we aimed to define the KMN complex in the plant Arabidopsis using affinity purification and identified thirteen KMN proteins. Seven were previously known to have a conserved function (atMIS12, atNNF1, atNDC80, atSPC24, atSPC25, atNUF2, and atKNL1) and six were uncharacterized. These six proteins show remote similarity to yeast/human KMN-associated proteins, whose homologs have not yet been characterized in plants. We named them atDSN1, atCSM1, atNSL1.1/.2, and atZWINT1.1/.2. We confirmed kinetochore localization for atDSN1, atCSM1, atNSL1.1, and atZWINT1.1 in planta. In addition, atDSN1, atCSM1, and ZWINT1.1/.2 are essential, further supporting their kinetochore function. AlphaFold3 predicts an alike3D organization of the KMN complex in plants and mammals. We conclude that the KMN complex is globally conserved with a matching composition and similar organization in distant eukaryotes, with some local variations, suggesting its presence in the common ancestors of all living eukaryotes.
    DOI:  https://doi.org/10.1038/s42003-025-09120-6
  5. Annu Rev Physiol. 2025 Nov 07.
    Coordinated Remodeling of Ca2+ Signaling and Intracellular Organelles During Cell Division.
    Fang Yu, Lama Assaf, Khaled Machaca.
      Cell division is essential for organismal growth and development and is associated with changes in signaling dynamics, including Ca2+ signaling, to meet structural, functional, and energetic needs. The process of cell division must ensure equal separation of both the genetic material and cellular organelles. Organelle segregation to the daughter cells is in most cases associated with their remodeling to support equal distribution. Here, we review the concurrent remodeling of organelles and Ca2+ signaling during cell division. Interesting patterns emerge, showing that organelle dynamics, specifically the plasma membrane, endoplasmic reticulum, and mitochondria, underlie Ca2+ signaling remodeling during cell division.
    DOI:  https://doi.org/10.1146/annurev-physiol-061324-091825
  6. Bull Exp Biol Med. 2025 Nov 07.
    Optimization of Mitotic Index Quantification Using the Amnis ImageStream Imaging Flow Cytometer.
    I V Kholodenko, K N Yarygin, Y S Kim.
      The mitotic index is a critical indicator of the proliferative activity of cell populations and is widely used in oncology and stem cell research. One of the most promising methods for its assessment is imaging flow cytometry implemented on the Amnis ImageStream platform using the IDEAS software. A critical evaluation of the built-in Wizards, Cell Cycle-Mitosis algorithm revealed several limitations, including a high degree of operator-dependent variability in gate setting and difficulties in identifying the mitotic population in the absence of distinct peaks on the cell cycle histogram. An alternative approach, the Mean + xSD algorithm, was proposed. This method is based on automated quantitative assessment of the Bright Detail Intensity R3 parameter and excludes the need for manual gating and histogram interpretation. Using the Caco2 and HT-29 cell lines, we demonstrated that the proposed algorithm exhibits accuracy comparable to the classical IDEAS algorithm, and in some cases provides even more reproducible quantification of the mitotic index. These results demonstrate the potential of the new algorithm as a more objective and robust tool for analyzing mitotic activity in cultured cells.
    Keywords:  mitotic index; cell proliferative activity; imaging flow cytometry
    DOI:  https://doi.org/10.1007/s10517-025-06525-5
  7. J Cell Sci. 2025 Nov 07. pii: jcs.264444. [Epub ahead of print]
    MRTF-dependent cytoskeletal dynamics drive efficient cell cycle progression.
    Julie C Nielsen, Maria Benito-Jardon, Noel Christo Petrela, Jessica Diring, Sofie Bellamy, Richard Treisman.
      Serum response factor (SRF) and its cofactors, Myocardin-related transcription factors A/B (MRTF-A/B), regulate transcription of numerous cytoskeletal structural and regulatory genes, and most MRTF/SRF inactivation phenotypes reflect deficits in cytoskeletal dynamics. We show that MRTF-SRF activity is required for effective proliferation of both primary and immortalised fibroblast and epithelial cells. Cells lacking the MRTFs or SRF proliferate very slowly, express elevated levels of SASP factors and SA-b-galactosidase activity, and inhibit proliferation of co-cultured primary wildtype cells. They exhibit decreased levels of CDK1 and CKS2 proteins, and elevated levels of CDK inhibitors, usually CDKN1B/p27. These phenotypes, which can be fully reversed by re-expression of MRTF-A, are also seen in wildtype cells arrested by serum deprivation. Moreover, in wildtype cells direct interference with cytoskeletal dynamics through inhibition of ROCKs or myosin ATPase induces a similar proliferative defect to that seen in MRTF-null cells. MRTF-null cells exhibit multiple cytoskeletal defects, and markedly reduced contractility. We propose that MRTF-SRF signalling will be required for cell proliferation in cell types and environments where physical progression through cell cycle transitions requires high contractility.
    Keywords:  Cell cycle; Cytoskeleton; MKL1; MRTF-A; MRTF-B; Quiescence; SRF; Senescence
    DOI:  https://doi.org/10.1242/jcs.264444
  8. Biomed Pharmacother. 2025 Nov 06. pii: S0753-3322(25)00910-2. [Epub ahead of print]193 118716
    Drug target proteome profiling identifies HES1-driven mitotic catastrophe in ovarian serous carcinoma.
    Jie Bao, Sanna Pikkusaari, Jun Dai, Samuel Leppiniemi, Wenjun Huang, Weiming Yang, Anu Anil, Mirva Pääkkönen, Chuqi Lei, Eva Daniela Mendoza-Ortiz, Ezgi Karagöz, Johanna Eriksson, Min Li, Johanna Hynninen, Otto Kauko, Anniina Färkkilä, Anna Vähärautio, Sampsa Hautaniemi, Liisa Kauppi, Jing Tang.
      Ovarian high-grade serous cancer (HGSC) is the most aggressive ovarian cancer subtype with limited treatment options. We identify the PDPK1 inhibitor BX-912 as a promising candidate, showing strong single-agent activity and synergy with the PARP inhibitor olaparib, independent of BRCA status. Unexpectedly, BX-912 induces multinucleation, a phenotype not seen with other PDPK1 inhibitors. Proteome Integral Solubility Alteration (PISA) assay reveals HES1 as a functional off-target, while structural modeling suggested BX-912 acts as a protein-protein interaction modulator, driving nuclear accumulation of HES1 complexes and hence inducing mitotic catastrophe. Cell-cycle analyses confirm enhanced DNA damage response and G2/M arrest when combined with olaparib. These findings uncover a novel mechanism for BX-912, establish HES1 inhibition as a therapeutic strategy in HGSC, demonstrate proteomics' power to reveal hidden drug activities, and propose sequential cell-cycle targeting to improve treatment efficacy.
    Keywords:  Cell division; Ovarian high-grade serous cancer; Protein-protein interaction; Proteomics; drug off-target
    DOI:  https://doi.org/10.1016/j.biopha.2025.118716
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