bims-micesi 2023-07-02 papers

bims-micesi

Biomed News

on Mitotic cell signalling

Issue of 2023–07–02
seven papers selected by
Valentina Piano, Uniklinik Köln

CDC6 as a Key Inhibitory Regulator of CDK1 Activation Dynamics and the Timing of Mitotic Entry and Progression.
Dynamic phosphorylation of CENP-N by CDK1 guides accurate chromosome segregation in mitosis.
Microtubule binding of the human augmin complex is directly controlled by importins and Ran-GTP.
Shattered Chromosomes Undergo Mitotic Tethering during Chromothripsis.
Delayed abscission in animal cells - from development to defects.
Differential translation of mRNA isoforms underlies oncogenic activation of cell cycle kinase Aurora A.
MLL methyltransferases regulate H3K4 methylation to ensure CENP-A assembly at human centromeres.

Biology (Basel). 2023 Jun 14. pii: 855. [Epub ahead of print]12(6):

CDC6 as a Key Inhibitory Regulator of CDK1 Activation Dynamics and the Timing of Mitotic Entry and Progression.

Mohammed El Dika, Damian Dudka, Malgorzata Kloc, Jacek Z Kubiak.

  Timely mitosis is critically important for early embryo development. It is regulated by the activity of the conserved protein kinase CDK1. The dynamics of CDK1 activation must be precisely controlled to assure physiologic and timely entry into mitosis. Recently, a known S-phase regulator CDC6 emerged as a key player in mitotic CDK1 activation cascade in early embryonic divisions, operating together with Xic1 as a CDK1 inhibitor upstream of the Aurora A and PLK1, both CDK1 activators. Herein, we review the molecular mechanisms that underlie the control of mitotic timing, with special emphasis on how CDC6/Xic1 function impacts CDK1 regulatory network in the Xenopus system. We focus on the presence of two independent mechanisms inhibiting the dynamics of CDK1 activation, namely Wee1/Myt1- and CDC6/Xic1-dependent, and how they cooperate with CDK1-activating mechanisms. As a result, we propose a comprehensive model integrating CDC6/Xic1-dependent inhibition into the CDK1-activation cascade. The physiological dynamics of CDK1 activation appear to be controlled by the system of multiple inhibitors and activators, and their integrated modulation ensures concomitantly both the robustness and certain flexibility of the control of this process. Identification of multiple activators and inhibitors of CDK1 upon M-phase entry allows for a better understanding of why cells divide at a specific time and how the pathways involved in the timely regulation of cell division are all integrated to precisely tune the control of mitotic events.

Keywords:  CDC25; CDC6; CDK1; Xic1; cell cycle; cyclins; mitotic entry; time of mitosis

DOI:  https://doi.org/10.3390/biology12060855
J Mol Cell Biol. 2023 Jun 26. pii: mjad041. [Epub ahead of print]

Dynamic phosphorylation of CENP-N by CDK1 guides accurate chromosome segregation in mitosis.

Ran Liu, Zhen Dou, Tian Tian, Xinjiao Gao, Lili Chen, Xiao Yuan, Chunyue Wang, Jiahe Hao, Ping Gui, McKay Mullen, Felix Aikhionbare, Liwen Niu, Guoqiang Bi, Peng Zou, Xuan Zhang, Chuanhai Fu, Xuebiao Yao, Jianye Zang, Xing Liu.

In mitosis, accurate chromosome segregation depends on super-molecular machinery kinetochore that couples dynamic spindle microtubules to centromeric chromatin. However, the structure-activity relationship of the constitutive centromere-associated network (CCAN), during mitosis remains uncharacterized. Building on our recent cryo-electron microscopy structure of human CCAN, here we reveal the molecular basis of how dynamic phosphorylation of human CENP-N regulates accurate chromosome segregation. Our mass spectrometric analyses revealed mitotic phosphorylation of CENP-N by CDK1 kinase, which modulates the CENP-L-CENP-N interaction for accurate chromosome segregation and CCAN organization. Perturbation of CENP-N phosphorylation is shown to prevent proper chromosome alignment and activate the spindle assembly checkpoint. These analyses provide mechanistic insight into a previously undefined link between the centromere-kinetochore network and accurate chromosome segregation.

DOI: https://doi.org/10.1093/jmcb/mjad041
J Cell Sci. 2023 06 15. pii: jcs261096. [Epub ahead of print]136(12):

Microtubule binding of the human augmin complex is directly controlled by importins and Ran-GTP.

Kseniya Ustinova, Felix Ruhnow, Maria Gili, Thomas Surrey.

  Mitotic spindle assembly during cell division is a highly regulated process. Ran-GTP produced around chromosomes controls the activity of a multitude of spindle assembly factors by releasing them from inhibitory interaction with importins. A major consequence of Ran-GTP regulation is the local stimulation of branched microtubule nucleation around chromosomes, which is mediated by the augmin complex (composed of the eight subunits HAUS1-HAUS8), a process that is crucially important for correct spindle assembly. However, augmin is not known to be a direct target of the Ran-GTP pathway, raising the question of how its activity is controlled. Here, we present the in vitro reconstitution of Ran-GTP-regulated microtubule binding of the human augmin complex. We demonstrate that importins directly bind to augmin, which prevents augmin from binding to microtubules. Ran-GTP relieves this inhibition. Therefore, the augmin complex is a direct target of the Ran-GTP pathway, suggesting that branching microtubule nucleation is directly regulated by the Ran-GTP gradient around chromosomes in dividing cells.

Keywords:   In vitro reconstitution; HAUS complex; Importins; Microtubule nucleation; NLS; Ran

DOI:  https://doi.org/10.1242/jcs.261096
Cancer Discov. 2023 Jun 30. OF1

Shattered Chromosomes Undergo Mitotic Tethering during Chromothripsis.

Tethering of shattered chromosomes is mediated by a complex containing MDC1, TOPBP1, and CIP2A.

DOI: https://doi.org/10.1158/2159-8290.CD-RW2023-104
J Cell Sci. 2023 Jul 01. pii: jcs260520. [Epub ahead of print]136(13):

Delayed abscission in animal cells - from development to defects.

Snježana Kodba, Agathe Chaigne.

  Cell division involves separating the genetic material and cytoplasm of a mother cell into two daughter cells. The last step of cell division, abscission, consists of cutting the cytoplasmic bridge, a microtubule-rich membranous tube connecting the two cells, which contains the midbody, a dense proteinaceous structure. Canonically, abscission occurs 1-3 h after anaphase. However, in certain cases, abscission can be severely delayed or incomplete. Abscission delays can be caused by mitotic defects that activate the abscission 'NoCut' checkpoint in tumor cells, as well as when cells exert abnormally strong pulling forces on the bridge. Delayed abscission can also occur during normal organism development. Here, we compare the mechanisms triggering delayed and incomplete abscission in healthy and disease scenarios. We propose that NoCut is not a bona fide cell cycle checkpoint, but a general mechanism that can control the dynamics of abscission in multiple contexts.

Keywords:  Abscission; Aurora B; Cytoplasmic bridges; NoCut checkpoint

DOI:  https://doi.org/10.1242/jcs.260520
Elife. 2023 Jun 29. pii: RP87253. [Epub ahead of print]12

Differential translation of mRNA isoforms underlies oncogenic activation of cell cycle kinase Aurora A.

Roberta Cacioppo, Hesna Begum Akman, Taner Tuncer, Ayse Elif Erson-Bensan, Catherine Lindon.

  Aurora Kinase A (AURKA) is an oncogenic kinase with major roles in mitosis, but also exerts cell cycle- and kinase-independent functions linked to cancer. Therefore, control of its expression, as well as its activity, is crucial. A short and a long 3'UTR isoform exist for AURKA mRNA, resulting from alternative polyadenylation (APA). We initially observed that in triple-negative breast cancer, where AURKA is typically overexpressed, the short isoform is predominant and this correlates with faster relapse times of patients. The short isoform is characterized by higher translational efficiency since translation and decay rate of the long isoform are targeted by hsa-let-7a tumor-suppressor miRNA. Additionally, hsa-let-7a regulates the cell cycle periodicity of translation of the long isoform, whereas the short isoform is translated highly and constantly throughout interphase. Finally, disrupted production of the long isoform led to an increase in proliferation and migration rates of cells. In summary, we uncovered a new mechanism dependent on the cooperation between APA and miRNA targeting likely to be a route of oncogenic activation of human AURKA.

Keywords:  3′ UTR; AURKA; cell biology; cell cycle; chromosomes; gene expression; human; miRNA; translation

DOI:  https://doi.org/10.7554/eLife.87253
PLoS Biol. 2023 Jun 28. 21(6): e3002161

MLL methyltransferases regulate H3K4 methylation to ensure CENP-A assembly at human centromeres.

Kausika Kumar Malik, Sreerama Chaitanya Sridhara, Kaisar Ahmad Lone, Payal Deepakbhai Katariya, Deepshika Pulimamidi, Shweta Tyagi.

The active state of centromeres is epigenetically defined by the presence of CENP-A interspersed with histone H3 nucleosomes. While the importance of dimethylation of H3K4 for centromeric transcription has been highlighted in various studies, the identity of the enzyme(s) depositing these marks on the centromere is still unknown. The MLL (KMT2) family plays a crucial role in RNA polymerase II (Pol II)-mediated gene regulation by methylating H3K4. Here, we report that MLL methyltransferases regulate transcription of human centromeres. CRISPR-mediated down-regulation of MLL causes loss of H3K4me2, resulting in an altered epigenetic chromatin state of the centromeres. Intriguingly, our results reveal that loss of MLL, but not SETD1A, increases co-transcriptional R-loop formation, and Pol II accumulation at the centromeres. Finally, we report that the presence of MLL and SETD1A is crucial for kinetochore maintenance. Altogether, our data reveal a novel molecular framework where both the H3K4 methylation mark and the methyltransferases regulate stability and identity of the centromere.

DOI: https://doi.org/10.1371/journal.pbio.3002161