Phosphorylation of CENP-R by Aurora B regulates kinetochore-microtubule attachment for accurate chromosome segregation

Condensation-dependent multivalent interactions of EB1 and CENP-R regulate chromosome oscillations in mitosis

Mitotic chromosomes oscillate between the spindle poles upon the establishment of bi-orientation, which is essential for chromosome alignment and subsequent synchronous segregation. However, the molecular mechanisms underlying the oscillatory movement remain unclear. Recent studies revealed that phase separation of the end-binding protein 1 (EB1) is essential for eukaryotic cell division. Here, we show that EB1 interacts with CENP-R and that the phase separation-defective EB1 mutant fails to power the chromosome oscillations. Biochemical analyses reveal a co-condensation of EB1 and CENP-R, a subunit of the constitutive centromere-associated network. Nuclear magnetic resonance assays reveal that the interaction and co-condensation are largely mediated by the structured end-binding homology domain of EB1 and the non-structured N-terminal intrinsic disorder region of CENP-R. Chromosome oscillation is perturbed in cells expressing the EB1-binding-defective CENP-R mutant. Thus, phase-separated EB1 binding to CENP-R forms a physical link between inner kinetochore and dynamic spindle microtubule plus-ends to guide accurate chromosome oscillations.

LncRNA NR_045147 modulates osteogenic differentiation and migration in PDLSCs via ITGB3BP degradation and mitochondrial dysfunction

Periodontitis is an inflammation of the alveolar bone and soft tissue surrounding the teeth. Although mesenchymal stem cells (MSCs) have been implicated in periodontal regeneration, the mechanisms by which they promote osteogenesis remain unclear. We examined whether epigenetic modifications mediated by the long-noncoding RNA (lncRNA) NR_045147, which plays a crucial role in cancer, influence the osteogenic differentiation of periodontal ligament stem cells (PDLSCs). Alkaline phosphatase staining, alizarin red staining, and western blotting were used to detect the effects of NR_045147 on PDLSC osteogenic differentiation. Scratch migration and transwell chemotaxis assays were used to evaluate the effects of NR_045147 on PDLSC migration. Mitochondrial function was evaluated via Seahorse XF analysis to measure changes in cellular respiration upon manipulation of NR_045147 expression. Ubiquitination assays were performed to examine the protein stability and degradation pathways affected by the NR_045147-MDM2 interaction. An in vivo nude rat calvarial defect model was established and gene-edited PDLSCs were re-implanted to examine the osteogenic effects of NR_045147. NR_045147 significantly reduced PDLSC osteogenic differentiation and migration ability both in vitro and in vivo. Under inflammatory conditions, the loss of NR_045147 rescued osteogenesis. NR_045147 significantly blocked the expression of integrin beta3-binding protein (ITGB3BP). Mechanistically, NR_045147 promoted the ITGB3BP-MDM2 interaction, thus increasing ITGB3BP ubiquitination and degradation. NR_045147 regulated PDLSC mitochondrial respiration and ITGB3BP upregulation efficiently promoted their osteogenic differentiation and migration ability. Concluding, NR_045147 downregulation enhances PDLSC osteogenic differentiation and migration, connects changes in cellular metabolism to functional outcomes via mitochondrial respiration, and promotes ITGB3BP degradation by mediating its interaction with MDM2.

LncRNA NR_045147 modulates osteogenic differentiation and migration in PDLSCs via ITGB3BP degradation and mitochondrial dysfunction

Periodontitis is an inflammation of the alveolar bone and soft tissue surrounding the teeth. Although mesenchymal stem cells (MSCs) have been implicated in periodontal regeneration, the mechanisms by which they promote osteogenesis remain unclear. We examined whether epigenetic modifications mediated by the long-noncoding RNA (lncRNA) NR_045147, which plays a crucial role in cancer, influence the osteogenic differentiation of periodontal ligament stem cells (PDLSCs). Alkaline phosphatase staining, alizarin red staining, and western blotting were used to detect the effects of NR_045147 on PDLSC osteogenic differentiation. Scratch migration and transwell chemotaxis assays were used to evaluate the effects of NR_045147 on PDLSC migration. Mitochondrial function was evaluated via Seahorse XF analysis to measure changes in cellular respiration upon manipulation of NR_045147 expression. Ubiquitination assays were performed to examine the protein stability and degradation pathways affected by the NR_045147–MDM2 interaction. An in vivo nude rat calvarial defect model was established and gene-edited PDLSCs were re-implanted to examine the osteogenic effects of NR_045147. NR_045147 significantly reduced PDLSC osteogenic differentiation and migration ability both in vitro and in vivo. Under inflammatory conditions, the loss of NR_045147 rescued osteogenesis. NR_045147 significantly blocked the expression of integrin beta3-binding protein (ITGB3BP). Mechanistically, NR_045147 promoted the ITGB3BP-MDM2 interaction, thus increasing ITGB3BP ubiquitination and degradation. NR_045147 regulated PDLSC mitochondrial respiration and ITGB3BP upregulation efficiently promoted their osteogenic differentiation and migration ability. Concluding, NR_045147 downregulation enhances PDLSC osteogenic differentiation and migration, connects changes in cellular metabolism to functional outcomes via mitochondrial respiration, and promotes ITGB3BP degradation by mediating its interaction with MDM2.

Delineation of the CENP-LN sub-complex dissociation mechanism upon multisite phosphorylation during mitosis

Phosphorylation is the most prevalent form of regulation in cells, organizing virtually all cellular functions, including survival, motility, differentiation, proliferation, and metabolism. This regulatory function has been largely conserved from the primitive single-cell to the more complex multicellular organisms. More than a third of proteins in eukaryotes are phosphorylated, and essentially every class of protein undergoes regulation by phosphorylation. A decline in the cellular level of CENP-L and CENP-N (components of the constitutive centromere associated network) has earlier been reported and linked to cyclin-dependent kinase (CDK) phosphorylation upon transition into mitosis. Given the importance of posttranslational modifications in cell cycle regulation, mechanistic comprehension of the impact of phosphorylation on both proteins (CENP-L and CENP-N) is of high significance. Through the application of diverse computational analytical techniques, including atomistic molecular dynamics simulations, the mechanism of kinetochore mis-localization and dissociation of the CENP-LN sub-complex in mitosis was delineated. We showed that the phosphorylation of both components of the sub-complex induces global conformational destabilizing effects on the proteins, combined with changes in the electrostatic potential and increase in steric clashes around the protein-protein interaction interface. This, consistent with earlier experimental reports, suggest that the multisite phosphorylation of the CENP-LN sub-complex plays a crucial role in the regulation of cell division.Communicated by Ramaswamy H. Sarma.

Golgi protein ACBD3 downregulation sensitizes cells to ferroptosis

Ferroptosis, a form of cell death driven by iron-dependent lipid peroxidation, is emerging as a promising target in cancer therapy. It is regulated by a network of molecules and pathways that modulate lipid metabolism, iron homeostasis and redox balance, and related processes. However, there are still numerous regulatory molecules intricately involved in ferroptosis that remain to be identified. Here, we indicated that suppression of Golgi protein acyl-coenzyme A binding domain A containing 3 (ACBD3) increased the sensitivity of Henrieta Lacks and PANC1 cells to ferroptosis. ACBD3 knockdown increases labile iron levels by promoting ferritinophagy. This increase in free iron, coupled with reduced levels of glutathione peroxidase 4 due to ACBD3 knockdown, leads to the accumulation of reactive oxygen species and lipid peroxides. Moreover, ACBD3 knockdown also results in elevated levels of polyunsaturated fatty acid-containing glycerophospholipids through mechanisms that remain to be elucidated. Furthermore, inhibition of ferrtinophagy in ACBD3 downregulated cells by knocking down the nuclear receptor co-activator 4 or Bafilomycin A1 treatment impeded ferroptosis. Collectively, our findings highlight the pivotal role of ACBD3 in governing cellular resistance to ferroptosis and suggest that pharmacological manipulation of ACBD3 levels is a promising strategy for cancer therapy.

Chromothripsis: an emerging crossroad from aberrant mitosis to therapeutic opportunities

Chromothripsis, a type of complex chromosomal rearrangement originally known as chromoanagenesis, has been a subject of extensive investigation due to its potential role in various diseases, particularly cancer. Chromothripsis involves the rapid acquisition of tens to hundreds of structural rearrangements within a short period, leading to complex alterations in one or a few chromosomes. This phenomenon is triggered by chromosome mis-segregation during mitosis. Errors in accurate chromosome segregation lead to formation of aberrant structural entities such as micronuclei or chromatin bridges. The association between chromothripsis and cancer has attracted significant interest, with potential implications for tumorigenesis and disease prognosis. This review aims to explore the intricate mechanisms and consequences of chromothripsis, with a specific focus on its association with mitotic perturbations. Herein, we discuss a comprehensive analysis of crucial molecular entities and pathways, exploring the intricate roles of the CIP2A-TOPBP1 complex, micronuclei formation, chromatin bridge processing, DNA damage repair, and mitotic checkpoints. Moreover, the review will highlight recent advancements in identifying potential therapeutic targets and the underlying molecular mechanisms associated with chromothripsis, paving the way for future therapeutic interventions in various diseases.

A non-canonical role of the inner kinetochore in regulating sister-chromatid cohesion at centromeres

The 16-subunit Constitutive Centromere-associated Network (CCAN)-based inner kinetochore is well-known for connecting centromeric chromatin to the spindle-binding outer kinetochore. Here, we report a non-canonical role for the inner kinetochore in directly regulating sister-chromatid cohesion at centromeres. We provide biochemical, X-ray crystal structure, and intracellular ectopic localization evidence that the inner kinetochore directly binds cohesin, a ring-shaped multi-subunit complex that holds sister chromatids together from S-phase until anaphase onset. This interaction is mediated by binding of the 5-subunit CENP-OPQUR sub-complex of CCAN to the Scc1-SA2 sub-complex of cohesin. Mutation in the CENP-U subunit of the CENP-OPQUR complex that abolishes its binding to the composite interface between Scc1 and SA2 weakens centromeric cohesion, leading to premature separation of sister chromatids during delayed metaphase. We further show that CENP-U competes with the cohesin release factor Wapl for binding the interface of Scc1-SA2, and that the cohesion-protecting role for CENP-U can be bypassed by depleting Wapl. Taken together, this study reveals an inner kinetochore-bound pool of cohesin, which strengthens centromeric sister-chromatid cohesion to resist metaphase spindle pulling forces.

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

In mitosis, accurate chromosome segregation depends on the kinetochore, a supermolecular machinery 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 microscopic analyses of human CCAN structure, we investigated how dynamic phosphorylation of human CENP-N regulates accurate chromosome segregation. Our mass spectrometric analyses revealed mitotic phosphorylation of CENP-N by CDK1, 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.