Cell biology. Reversible centriole depletion with an inhibitor of Polo-like kinase 4

Gradual centriole maturation associates with the mitotic surveillance pathway in mouse development

Centrosomes, composed of two centrioles and pericentriolar material, organize mitotic spindles during cell division and template cilia during interphase. The first few divisions during mouse development occur without centrioles, which form around embryonic day (E) 3. However, disruption of centriole biogenesis in Sas-4 null mice leads to embryonic arrest around E9. Centriole loss in Sas-4^-/- embryos causes prolonged mitosis and p53-dependent cell death. Studies in vitro discovered a similar USP28-, 53BP1-, and p53-dependent mitotic surveillance pathway that leads to cell cycle arrest. In this study, we show that an analogous pathway is conserved in vivo where 53BP1 and USP28 are upstream of p53 in Sas-4^-/- embryos. The data indicate that the pathway is established around E7 of development, four days after the centrioles appear. Our data suggest that the newly formed centrioles gradually mature to participate in mitosis and cilia formation around the beginning of gastrulation, coinciding with the activation of mitotic surveillance pathway upon centriole loss.

Polo-like kinase 1 independently controls microtubule-nucleating capacity and size of the centrosome

Centrosomes are composed of a centriolar core surrounded by a pericentriolar material (PCM) matrix that docks microtubule-nucleating γ-tubulin complexes. During mitotic entry, the PCM matrix increases in size and nucleating capacity in a process called centrosome maturation. Polo-like kinase 1 (PLK1) is recruited to centrosomes and phosphorylates PCM matrix proteins to drive their self-assembly, which leads to PCM expansion. Here, we show that in addition to controlling PCM expansion, PLK1 independently controls the generation of binding sites for γ-tubulin complexes on the PCM matrix. Selectively preventing the generation of PLK1-dependent γ-tubulin docking sites led to spindle defects and impaired chromosome segregation without affecting PCM expansion, highlighting the importance of phospho-regulated centrosomal γ-tubulin docking sites in spindle assembly. Inhibiting both γ-tubulin docking and PCM expansion by mutating substrate target sites recapitulated the effects of loss of centrosomal PLK1 on the ability of centrosomes to catalyze spindle assembly.

Centrosome defects cause microcephaly by activating the 53BP1-USP28-TP53 mitotic surveillance pathway

Mutations in centrosome genes deplete neural progenitor cells (NPCs) during brain development, causing microcephaly. While NPC attrition is linked to TP53-mediated cell death in several microcephaly models, how TP53 is activated remains unclear. In cultured cells, mitotic delays resulting from centrosome loss prevent the growth of unfit daughter cells by activating a pathway involving 53BP1, USP28, and TP53, termed the mitotic surveillance pathway. Whether this pathway is active in the developing brain is unknown. Here, we show that the depletion of centrosome proteins in NPCs prolongs mitosis and increases TP53-mediated apoptosis. Cell death after a delayed mitosis was rescued by inactivation of the mitotic surveillance pathway. Moreover, 53BP1 or USP28 deletion restored NPC proliferation and brain size without correcting the upstream centrosome defects or extended mitosis. By contrast, microcephaly caused by the loss of the non-centrosomal protein SMC5 is also TP53-dependent but is not rescued by loss of 53BP1 or USP28. Thus, we propose that mutations in centrosome genes cause microcephaly by delaying mitosis and pathologically activating the mitotic surveillance pathway in the developing brain.

Identification of compounds that bind the centriolar protein SAS-6 and inhibit its oligomerization

Centrioles are key eukaryotic organelles that are responsible for the formation of cilia and flagella, and for organizing the microtubule network and the mitotic spindle in animals. Centriole assembly requires oligomerization of the essential protein spindle assembly abnormal 6 (SAS-6), which forms a structural scaffold templating the organization of further organelle components. A dimerization interaction between SAS-6 N-terminal "head" domains was previously shown to be essential for protein oligomerization in vitro and for function in centriole assembly. Here, we developed a pharmacophore model allowing us to assemble a library of low-molecular-weight ligands predicted to bind the SAS-6 head domain and inhibit protein oligomerization. We demonstrate using NMR spectroscopy that a ligand from this family binds at the head domain dimerization site of algae, nematode, and human SAS-6 variants, but also that another ligand specifically recognizes human SAS-6. Atomistic molecular dynamics simulations starting from SAS-6 head domain crystallographic structures, including that of the human head domain which we now resolve, suggest that ligand specificity derives from favorable Van der Waals interactions with a hydrophobic cavity at the dimerization site.

Autophosphorylation-induced self-assembly and STIL-dependent reinforcement underlie Plk4's ring-to-dot localization conversion around a human centriole

Polo-like kinase 4 (Plk4) is a key regulator of centriole biogenesis. Studies have shown that Plk4 undergoes dynamic relocalization from a ring-like pattern around a centriole to a dot-like morphology at the procentriole assembly site and this event is central for inducing centriole biogenesis. However, the detailed mechanisms underlying Plk4's capacity to drive its symmetry-breaking ring-to-dot relocalization remain largely unknown. Here, we showed that Plk4 self-initiates this process in an autophosphorylation-dependent manner and that STIL, its downstream target, is not required for this event. Time-dependent analyses with mEOS-fused photoconvertible Plk4 revealed that a portion of ring-state Plk4 acquires a capacity, presumably through autophosphorylation, to linger around a centriole, ultimately generating a dot-state morphology. Interestingly, Plk4 WT, but not its catalytically inactive mutant, showed the ability to form a nanoscale spherical assembly in the cytosol of human cells or heterologous E. coli, demonstrating its autophosphorylation-dependent self-organizing capacity. At the biochemical level, Plk4 - unlike its N-terminal βTrCP degron motif - robustly autophosphorylated the PC3 SSTT motif within its C-terminal cryptic polo-box, an event critical for inducing its physical clustering. Additional in vivo experiments showed that although STIL was not required for Plk4's initial ring-to-dot conversion, coexpressed STIL greatly enhanced Plk4's ability to generate a spherical condensate and recruit Sas6, a major component of the centriolar cartwheel structure. We propose that Plk4's autophosphorylation-induced clustering is sufficient to induce its ring-to-dot localization conversion and that subsequently recruited STIL potentiates this process to generate a procentriole assembly body critical for Plk4-dependent centriole biogenesis.

Centrosome organization and functions

The centrosome, discovered near 1875, was named by Boveri when proposing the chromosomal theory of heredity. After a long eclipse, a considerable amount of molecular data has been accumulated on the centrosome and its biogenesis in the last 30 years, summarized regularly in excellent reviews. Major questions are still at stake in 2021 however, as we lack a comprehensive view of the centrosome functions. I will first try to see how progress towards a unified view of the role of centrosomes during evolution is possible, and then review recent data on only some of the many important questions raised by this organelle.

Use of the Polo-like kinase 4 (PLK4) inhibitor centrinone to investigate intracellular signalling networks using SILAC-based phosphoproteomics

Polo-like kinase 4 (PLK4) is the master regulator of centriole duplication in metazoan organisms. Catalytic activity and protein turnover of PLK4 are tightly coupled in human cells, since changes in PLK4 concentration and catalysis have profound effects on centriole duplication and supernumerary centrosomes, which are associated with aneuploidy and cancer. Recently, PLK4 has been targeted with a variety of small molecule kinase inhibitors exemplified by centrinone, which rapidly induces inhibitory effects on PLK4 and leads to on-target centrosome depletion. Despite this, relatively few PLK4 substrates have been identified unequivocally in human cells, and PLK4 signalling outside centriolar networks remains poorly characterised. We report an unbiased mass spectrometry (MS)-based quantitative analysis of cellular protein phosphorylation in stable PLK4-expressing U2OS human cells exposed to centrinone. PLK4 phosphorylation was itself sensitive to brief exposure to the compound, resulting in PLK4 stabilisation. Analysing asynchronous cell populations, we report hundreds of centrinone-regulated cellular phosphoproteins, including centrosomal and cell cycle proteins and a variety of likely 'non-canonical' substrates. Surprisingly, sequence interrogation of ∼300 significantly down-regulated phosphoproteins reveals an extensive network of centrinone-sensitive [Ser/Thr]Pro phosphorylation sequence motifs, which based on our analysis might be either direct or indirect targets of PLK4. In addition, we confirm that NMYC and PTPN12 are PLK4 substrates, both in vitro and in human cells. Our findings suggest that PLK4 catalytic output directly controls the phosphorylation of a diverse set of cellular proteins, including Pro-directed targets that are likely to be important in PLK4-mediated cell signalling.

Centriole-independent mitotic spindle assembly relies on the PCNT-CDK5RAP2 pericentriolar matrix

Centrosomes, composed of centrioles that recruit a pericentriolar material (PCM) matrix assembled from PCNT and CDK5RAP2, catalyze mitotic spindle assembly. Here, we inhibit centriole formation and/or remove PCNT-CDK5RAP2 in RPE1 cells to address their relative contributions to spindle formation. While CDK5RAP2 and PCNT are normally dispensable for spindle formation, they become essential when centrioles are absent. Acentriolar spindle assembly is accompanied by the formation of foci containing PCNT and CDK5RAP2 via a microtubule and Polo-like kinase 1-dependent process. Foci formation and spindle assembly require PCNT-CDK5RAP2-dependent matrix assembly and the ability of CDK5RAP2 to recruit γ-tubulin complexes. Thus, the PCM matrix can self-organize independently of centrioles to generate microtubules for spindle assembly; conversely, an alternative centriole-anchored mechanism supports spindle assembly when the PCM matrix is absent. Extension to three cancer cell lines revealed similar results in HeLa cells, whereas DLD1 and U2OS cells could assemble spindles in the absence of centrioles and PCNT-CDK5RAP2, suggesting cell type variation in spindle assembly mechanisms.

Phase separation of the Cep63•Cep152 complex underlies the formation of dynamic supramolecular self-assemblies at human centrosomes

The centrosome is a unique membraneless organelle that plays a pivotal role in the orderly progression of the cell cycle in animal cells. It has been shown that two pericentriolar scaffold proteins, Cep63 and Cep152, generate a heterotetrameric complex to self-assemble into a higher-order cylindrical architecture around a centriole. However, the mechanisms underlying how they reach their threshold concentrations in the vast intracellular space and generate a self-assembled architecture remain mysterious. Here we demonstrate that, like liquid-like assemblies, Cep63 and Cep152 cooperatively generate amorphous aggregates capable of undergoing dynamic turnover and inter-aggregate fusion in vivo and a significant level of internal rearrangemefnt within a condensate in vitro. Consistently, 1,6-hexanediol, a liquid-liquid phase separation disruptor, greatly diminished the ability of endogenous Cep63 and Cep152 to localize to centrosomes. Interestingly, a purified Cep63•Cep152 complex generated either a cylindrical structure or a vesicle-like hollow sphere in a spatially controlled manner. It also formed condensate-like solid spheres in the presence of a macromolecular crowder. At the molecular level, two hydrophobic motifs, one each from Cep63 and Cep152, were required for generating phase-separating condensates and a high molecular-weight assembly. Thus, we propose that the self-assembly of the Cep63•Cep152 complex is triggered by an intrinsic property of the complex undergoing density transition through the hydrophobic-motif-mediated phase separation. Abbreviations: PCM, pericentriolar material; LLPS, liquid-liquid phase separation; MW, molecular-weight; CLEM, correlative light and electron microscopy; WT, wild-type; CMV, cytomegalovirus; FRAP, fluorescence recovery after photobleaching; FITC, fluorescein isothiocyanate; PCR, polymerase chain reaction; 3D-SIM, three-dimensional structured illumination microscopy; DMEM, Dulbecco's Modified Eagle Medium; PEI Max, Polyethylenimine Max; PBS, phosphate-buffered saline; RT, room temperature; DAPI, 4', 6-diamidino-2-phenylindole; AOTF, acousto-optic tunable filter; LB, Luria broth; OD, optical density; IPTG, isopropyl β-D-1-thiogalactopyranoside; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

PLK1- and PLK4-Mediated Asymmetric Mitotic Centrosome Size and Positioning in the Early Zebrafish Embryo

Factors that regulate mitotic spindle positioning remain unclear within the confines of extremely large embryonic cells, such as the early divisions of the vertebrate embryo, Danio rerio (zebrafish). We find that the mitotic centrosome, a structure that assembles the mitotic spindle [1], is notably large in the zebrafish embryo (246.44 ± 11.93 μm2 in a 126.86 ± 0.35 μm diameter cell) compared to a C. elegans embryo (5.78 ± 0.18 μm2 in a 55.83 ± 1.04 μm diameter cell). During embryonic cell divisions, cell size changes rapidly in both C. elegans and zebrafish [2, 3], where mitotic centrosome area scales more closely with changes in cell size compared to changes in spindle length. Embryonic zebrafish spindles contain asymmetrically sized mitotic centrosomes (2.14 ± 0.13-fold difference between the two), with the larger mitotic centrosome placed toward the embryo center in a polo-like kinase (PLK) 1- and PLK4-dependent manner. We propose a model in which uniquely large zebrafish embryonic centrosomes direct spindle placement within disproportionately large cells.

Centrosomes in disease: how the same music can sound so different?

Centrosomes are the major microtubule organizing center of animal cells. Centrosomes contribute to timely bipolar spindle assembly during mitosis and participate in the regulation of other processes such as polarity establishment and cell migration. Centrosome numbers are tightly controlled during the cell cycle to ensure that mitosis is initiated with only two centrosomes. Deviations in centrosome number or structure are known to impact cell or tissue homeostasis and can impact different processes as diverse as proliferation, death or disease. Interestingly, defects in centrosome number seem to culminate with common responses, which depend on p53 activation even in different contexts such as development or cancer. p53 is a tumor suppressor gene with essential roles in the maintenance of genetic stability normally stimulated by various cellular stresses. Here, we review current knowledge and discuss how defects in centrosome structure and number can lead to different human pathologies.

Basal Feet: Walking to the Discovery of a Novel Hybrid Cilium

Cilia are important cell structures found on nearly all cells. In this issue of Developmental Cell, Mennella and colleagues investigate the molecular architecture of basal foot proteins in cells with primary or motile cilia and discover a hybrid cilium with a unique assembly that regulates polarity in multiciliated cells.

Centrosome Reduction Promotes Terminal Differentiation of Human Cardiomyocytes

Centrosome reduction and redistribution of pericentriolar material (PCM) coincides with cardiomyocyte transitions to a post-mitotic and matured state. However, it is unclear whether centrosome changes are a cause or consequence of terminal differentiation. We validated that centrosomes were intact and functional in proliferative human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs), consistent with their immature phenotype. We generated acentrosomal hPSC-CMs, through pharmacological inhibition of centriole duplication, and showed that centrosome loss was sufficient to promote post-mitotic transitions and aspects of cardiomyocyte maturation. As Hippo kinases are activated during post-natal cardiac maturation, we pharmacologically activated the Hippo pathway using C19, which was sufficient to trigger centrosome disassembly and relocalization of PCM components to perinuclear membranes. This was due to specific activation of Hippo kinases, as direct inhibition of YAP-TEAD interactions with verteporfin had no effect on centrosome organization. This suggests that Hippo kinase-centrosome remodeling may play a direct role in cardiac maturation.

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Centrosomes are intact and functional in immature human cardiomyocytes

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Centrosome loss promotes maturation of human cardiomyocytes

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Centrosomes are returned with cell cycle reinitiation in post-natal cardiomyocytes

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Hippo kinases promote disassembly and redistribution of centrosomal proteins

Super-Resolution Microscopy and FIB-SEM Imaging Reveal Parental Centriole-Derived, Hybrid Cilium in Mammalian Multiciliated Cells

Motile cilia are cellular beating machines that play a critical role in mucociliary clearance, cerebrospinal fluid movement, and fertility. In the airways, hundreds of motile cilia present on the surface of a multiciliated epithelia cell beat coordinately to protect the epithelium from bacteria, viruses, and harmful particulates. During multiciliated cell differentiation, motile cilia are templated from basal bodies, each extending a basal foot-an appendage linking motile cilia together to ensure coordinated beating. Here, we demonstrate that among the many motile cilia of a multiciliated cell, a hybrid cilium with structural features of both primary and motile cilia is harbored. The hybrid cilium is conserved in mammalian multiciliated cells, originates from parental centrioles, and its cellular position is biased and dependent on ciliary beating. Furthermore, we show that the hybrid cilium emerges independently of other motile cilia and functions in regulating basal body alignment.

The centriole protein CEP76 negatively regulates PLK1 activity in the cytoplasm for proper mitotic progression

Polo-like kinase 1 (PLK1) dynamically changes its localization and plays important roles in proper mitotic progression. In particular, strict control of cytoplasmic PLK1 is needed to prevent mitotic defects. However, the regulation of cytoplasmic PLK1 is not fully understood. In this study, we show that CEP76, a centriolar protein, physically interacts with PLK1 and tightly controls the activation of cytoplasmic PLK1 during mitosis in human cells. We found that removal of centrosomes induced ectopic aggregation of PLK1, which is highly phosphorylated, in the cytoplasm during mitosis. Importantly, a targeted RNAi screen revealed that depletion of CEP76 resulted in a similar phenotype. In addition, depletion of CEP76 caused defective spindle orientation and mitotic delay. Moreover, the formation of ectopic PLK1 aggregates and defective spindle orientation were significantly suppressed by the inhibition of PLK1 kinase activity. Overall, these results demonstrate that CEP76 suppresses the aberrant activation of cytoplasmic PLK1 for proper mitotic progression.This article has an associated First Person interview with the first author of the paper.

Growth disadvantage associated with centrosome amplification drives population-level centriole number homeostasis

The centriole duplication cycle normally ensures that centriole number is maintained at two centrioles per G1 cell. However, some circumstances can result in an aberrant increase in centriole number—a phenotype that is particularly prevalent in several types of cancer. Following an artificial increase in centriole number without tetraploidization due to transient overexpression of the kinase PLK4, human cells return to a normal centriole number during the proliferation of the population. We examine the mechanisms responsible for this return to normal centriole number at the population level in human retinal pigment epithelial cells. We find that the return to normal centriole number in the population of induced cells cannot be explained by limited duplication of centrioles, instability of extra centrioles, or by grossly asymmetric segregation of extra centrioles in mitosis. However, cells with extra centrioles display heterogenous phenotypes including extended cell cycle arrest, longer interphase durations, and death, which overall results in a proliferative disadvantage relative to normal cells in the population. Although about half of cells with extra centrioles in a population were able to divide, the extent of the disadvantages conferred by other fates is sufficient to account for the observed rate of return to normal centriole number. These results suggest that only under conditions of positive selection for cells with extra centrioles, continuous generation of such centrioles, or alleviation of the disadvantageous growth phenotypes would they be maintained in a population.

TRIM37 controls cancer-specific vulnerability to PLK4 inhibition

Centrosomes catalyze microtubule formation for mitotic spindle assembly¹. Centrosomes duplicate once per cell cycle in a process controlled the kinase PLK4^2,3. Following chemical PLK4 inhibition, cell division in the absence of centrosome duplication generates centrosome-less cells that exhibit delayed, acentrosomal spindle assembly⁴. Whether PLK4 inhibitors can be leveraged for cancer treatment is not yet clear. Here, we show that acentrosomal spindle assembly following PLK4 inhibition depends on levels of the centrosomal ubiquitin ligase TRIM37. Low TRIM37 accelerates acentrosomal spindle assembly and improves proliferation following PLK4 inhibition, whereas high TRIM37 inhibits acentrosomal spindle assembly, leading to mitotic failure and cessation of proliferation. The Chr17q region containing the TRIM37 gene is frequently amplified in neuroblastoma and in breast cancer^5–8, which renders these cancer types highly sensitive to PLK4 inhibition. TRIM37 inactivation improves acentrosomal mitosis because TRIM37 prevents PLK4 self-assembly into centrosome-independent condensates that serve as ectopic microtubule-organizing centers. By contrast, elevated TRIM37 expression inhibits acentrosomal spindle assembly via a distinct mechanism that involves degradation of the centrosomal component CEP192. Thus, TRIM37 is a critical determinant of mitotic vulnerability to PLK4 inhibition. Linkage of TRIM37 to prevalent cancer-associated genomic changes, including 17q gain in neuroblastoma and 17q23 amplification in breast cancer, may offer an opportunity to use PLK4 inhibition to trigger selective mitotic failure and provide new avenues to treatments for these cancers.

RACK1 regulates centriole duplication through promoting the activation of polo-like kinase 1 by Aurora A

Breast cancer gene 1 (BRCA1) contributes to the regulation of centrosome number. We previously identified receptor for activated C kinase 1 (RACK1) as a BRCA1-interacting partner. RACK1, a scaffold protein that interacts with multiple proteins through its seven WD40 domains, directly binds to BRCA1 and localizes to centrosomes. RACK1 knockdown suppresses centriole duplication, whereas RACK1 overexpression causes centriole overduplication in a subset of mammary gland-derived cells. In this study, we showed that RACK1 binds directly to polo-like kinase 1 (PLK1) and Aurora A, and promotes the Aurora A-PLK1 interaction. RACK1 knockdown decreased phosphorylated PLK1 (p-PLK1) levels and the centrosomal localization of Aurora A and p-PLK1 in S phase, whereas RACK1 overexpression increased p-PLK1 level and the centrosomal localization of Aurora A and p-PLK1 in interphase, resulting in an increase of cells with abnormal centriole disengagement. Overexpression of cancer-derived RACK1 variants failed to enhance the Aurora A-PLK1 interaction, PLK1 phosphorylation and the centrosomal localization of p-PLK1. These results suggest that RACK1 functions as a scaffold protein that promotes the activation of PLK1 by Aurora A in order to promote centriole duplication.This article has an associated First Person interview with the first author of the paper.

Loss of polycystins suppresses deciliation via the activation of the centrosomal integrity pathway

The primary cilium is a microtubule-based, antenna-like organelle housing several signaling pathways. It follows a cyclic pattern of assembly and deciliation (disassembly and/or shedding), as cells exit and re-enter the cell cycle, respectively. In general, primary cilia loss leads to kidney cystogenesis. However, in animal models of autosomal dominant polycystic kidney disease, a major disease caused by mutations in the polycystin genes (Pkd1 or Pkd2), primary cilia ablation or acceleration of deciliation suppresses cystic growth, whereas deceleration of deciliation enhances cystogenesis. Here, we show that deciliation is delayed in the cystic epithelium of a mouse model of postnatal deletion of Pkd1 and in Pkd1- or Pkd2-null cells in culture. Mechanistic experiments show that PKD1 depletion activates the centrosomal integrity/mitotic surveillance pathway involving 53BP1, USP28, and p53 leading to a delay in deciliation. Reduced deciliation rate causes prolonged activation of cilia-based signaling pathways that could promote cystic growth. Our study links polycystins to cilia dynamics, identifies cellular deciliation downstream of the centrosomal integrity pathway, and helps explain pro-cystic effects of primary cilia in autosomal dominant polycystic kidney disease.

Targeting TRIM37-driven centrosome dysfunction in 17q23-amplified breast cancer

Genomic instability is a hallmark of cancer, and has a central role in the initiation and development of breast cancer1,2. The success of poly-ADP ribose polymerase inhibitors in the treatment of breast cancers that are deficient in homologous recombination exemplifies the utility of synthetically lethal genetic interactions in the treatment of breast cancers that are driven by genomic instability3. Given that defects in homologous recombination are present in only a subset of breast cancers, there is a need to identify additional driver mechanisms for genomic instability and targeted strategies to exploit these defects in the treatment of cancer. Here we show that centrosome depletion induces synthetic lethality in cancer cells that contain the 17q23 amplicon, a recurrent copy number aberration that defines about 9% of all primary breast cancer tumours and is associated with high levels of genomic instability4-6. Specifically, inhibition of polo-like kinase 4 (PLK4) using small molecules leads to centrosome depletion, which triggers mitotic catastrophe in cells that exhibit amplicon-directed overexpression of TRIM37. To explain this effect, we identify TRIM37 as a negative regulator of centrosomal pericentriolar material. In 17q23-amplified cells that lack centrosomes, increased levels of TRIM37 block the formation of foci that comprise pericentriolar material-these foci are structures with a microtubule-nucleating capacity that are required for successful cell division in the absence of centrosomes. Finally, we find that the overexpression of TRIM37 causes genomic instability by delaying centrosome maturation and separation at mitotic entry, and thereby increases the frequency of mitotic errors. Collectively, these findings highlight TRIM37-dependent genomic instability as a putative driver event in 17q23-amplified breast cancer and provide a rationale for the use of centrosome-targeting therapeutic agents in treating these cancers.

FAM46C/TENT5C functions as a tumor suppressor through inhibition of Plk4 activity

Polo like kinase 4 (Plk4) is a tightly regulated serine threonine kinase that governs centriole duplication. Increased Plk4 expression, which is a feature of many common human cancers, causes centriole overduplication, mitotic irregularities, and chromosomal instability. Plk4 can also promote cancer invasion and metastasis through regulation of the actin cytoskeleton. Herein we demonstrate physical interaction of Plk4 with FAM46C/TENT5C, a conserved protein of unknown function until recently. FAM46C localizes to centrioles, inhibits Plk4 kinase activity, and suppresses Plk4-induced centriole duplication. Interference with Plk4 function by FAM46C was independent of the latter's nucleotidyl transferase activity. In addition, FAM46C restrained cancer cell invasion and suppressed MDA MB-435 cancer growth in a xenograft model, opposing the effect of Plk4. We demonstrate loss of FAM46C in patient-derived colorectal cancer tumor tissue that becomes more profound with advanced clinical stage. These results implicate FAM46C as a tumor suppressor that acts by inhibiting Plk4 activity.

Anticancer effects of the PLK4 inhibitors CFI-400945 and centrinone in Ewing's sarcoma cells

Purpose

Polo-like kinase 4 (PLK4) inhibitors, such as CFI-400945 and centrinone, are emerging as promising antineoplastic agents. However, their effectiveness against Ewing’s sarcoma, a highly aggressive childhood cancer, remains to be established.

Methods

CFI-400945 and centrinone were tested in three Ewing’s sarcoma cell lines with different TP53 status. Effects were assessed by flow-cytometric analyses of cell death, dissipation of the mitochondrial transmembrane potential and cell cycle distribution, by cell viability assay as well as by caspase 3/7 activity measurement, by immunoblotting and by immunofluorescence microscopy.

Results

CFI-400945 and centrinone elicited cell death in p53 wild-type and mutant Ewing’s sarcoma cells. Both agents induced mitochondrial membrane depolarisation, caspase 3/7 activation, PARP1 cleavage and DNA fragmentation, indicating an apoptotic form of cell death. In addition, the PLK4 inhibitors induced a G2/M cell cycle arrest, particularly when cell killing was attenuated by the pan-caspase inhibitor z-VAD-fmk. Moreover, CFI-400945 treatment produced polyploidy.

Conclusion

Our findings show that PLK4 inhibitors were effective against Ewing’s sarcoma cells in vitro and thus provide a rationale for their evaluation in vivo.

Electronic supplementary material

The online version of this article (10.1007/s00432-020-03346-z) contains supplementary material, which is available to authorized users.

Screening and Identification of Therapeutic Targets for Pulmonary Arterial Hypertension Through Microarray Technology

Pulmonary arterial hypertension (PAH) is a rare but fatal disease characterized by vascular cell proliferation; the pathogenesis of PAH has yet to be fully elucidated. Publicly available genetic data were downloaded from the Gene Expression Omnibus (GEO) database, and gene set enrichment analysis (GSEA) was used to determine significant differences in gene expression between tissues with PAH and healthy lung tissues. Differentially expressed genes (DEGs) were identified using the online tool, GEO2R, and functional annotation of DEGs was performed using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Next, the construction and module analysis of the protein–protein interaction (PPI) network and verification of the expression level of hub genes was performed. Finally, prediction and enrichment analysis of microRNAs associated with the hub genes was carried out. A total of 110 DEGs were detected by screening PAH and healthy lung samples. The expression of nine genes [polo-like kinase 4 (PLK4), centromere protein U, kinesin family member 20B, structural maintenance of chromosome 2 (SMC2), abnormal spindle microtubule assembly, Fanconi Anemia complementation group I, kinesin family member 18A, spindle apparatus coiled-coil protein 1, and MIS18 binding protein 1] was elevated in PAH; this was statistically significant compared with their expression in healthy lung tissue, and they were identified as hub genes. GO and KEGG analysis showed that the variations in DEGs were abundant in DNA-templated transcription, sister chromatid cohesion, mitotic nuclear division, cell proliferation, and regulation of the actin cytoskeleton. In conclusion, this study has successfully identified hub genes and key pathways of PAH, with a total of 110 DEGs and nine hub genes related to PAH, especially the PLK4 and SMC2 genes, thus providing important clues for the in-depth understanding of the molecular mechanism of PAH and providing potential therapeutic targets.

Analysis of the "centrosome-ome" identifies MCPH1 deletion as a cause of centrosome amplification in human cancer

The centrosome is the microtubule organizing center of human cells and facilitates a myriad of cellular functions including organization of the mitotic spindle to ensure faithful chromosome segregation during mitosis, cell polarization and migration, and primary cilia formation. A numerical increase in centrosomes, or centrosome amplification (CA), is common in cancer and correlates with more aggressive clinical features and worse patient outcomes. However, the causes of CA in human cancer are unclear. Many previous studies have identified mechanisms of CA in cellulo, such as overexpression of PLK4, but it is unclear how often these are the primary mechanism in human disease. To identify a primary cause of CA, we analyzed The Cancer Genome Atlas (TCGA) genomic and transcriptomic data for genes encoding the 367 proteins that localize to the centrosome (the "centrosome-ome"). We identified the following candidates for primary causes of CA: gain-of-function alterations of CEP19, CEP72, CTNNB1, PTK2, NDRG1, SPATC1, TBCCD1; and loss-of-function alterations of CEP76, MCPH1, NEURL4, and NPM1. In cellulo analysis of these candidates revealed that loss of MCPH1/microcephalin caused the most robust increase in centriole number. MCPH1 deep gene deletions are seen in 5-15% of human cancers, depending on the anatomic site of the tumor. Mechanistic experiments demonstrated that loss of MCPH1 caused a CDK2-dependent increase in STIL levels at the centrosome to drive CA. We conclude that loss of MCPH1 is common in human cancer and is likely to be a cause of CA.

Genetic relationship between Hashimoto`s thyroiditis and papillary thyroid carcinoma with coexisting Hashimoto`s thyroiditis

Hashimoto's thyroiditis (HT) is present in the background of around 30% of papillary thyroid carcinomas (PTCs). The genetic predisposition effect of this autoimmune condition is not thoroughly understood. We analyzed the microarray expression profiles of 13 HT, eight PTCs with (w/) coexisting HT, six PTCs without (w/o) coexisting HT, six micro PTCs (mPTCs), and three normal thyroid (TN) samples. Based on a false discovery rate (FDR)-adjusted p-value ≤ 0.05 and a fold change (FC) > 2, four comparison groups were defined, which were HT vs. TN; PTC w/ HT vs. TN; PTC w/o HT vs. TN; and mPTC vs. TN. A Venn diagram displayed 15 different intersecting and non-intersecting differentially expressed gene (DEG) sets, of which a set of 71 DEGs, shared between the two comparison groups HT vs. TN ∩ PTC w/ HT vs. TN, harbored the relatively largest number of genes related to immune and inflammatory functions; oxidative stress and reactive oxygen species (ROS); DNA damage and DNA repair; cell cycle; and apoptosis. The majority of the 71 DEGs were upregulated and the most upregulated DEGs included a number of immunoglobulin kappa variable genes, and other immune-related genes, e.g., CD86 molecule (CD86), interleukin 2 receptor gamma (IL2RG), and interferon, alpha-inducible protein 6 (IFI6). Upregulated genes preferentially associated with other gene ontologies (GO) were, e.g., STAT1, MMP9, TOP2A, and BRCA2. Biofunctional analysis revealed pathways related to immunogenic functions. Further data analysis focused on the set of non-intersecting 358 DEGs derived from the comparison group of HT vs. TN, and on the set of 950 DEGs from the intersection of all four comparison groups. In conclusion, this study indicates that, besides immune/inflammation-related genes, also genes associated with oxidative stress, ROS, DNA damage, DNA repair, cell cycle, and apoptosis are comparably more deregulated in a data set shared between HT and PTC w/ HT. These findings are compatible with the conception of a genetic sequence where chronic inflammatory response is accompanied by deregulation of genes and biofunctions associated with oncogenic transformation. The generated data set may serve as a source for identifying candidate genes and biomarkers that are practical for clinical application.

Loss of CPAP in developing mouse brain and its functional implication for human primary microcephaly

Primary microcephaly (MCPH) is a neurodevelopmental disorder characterized by small brain size with mental retardation. CPAP (also known as CENPJ), a known microcephaly-associated gene, plays a key role in centriole biogenesis. Here, we generated a previously unreported conditional knockout allele in the mouse Cpap gene. Our results showed that conditional Cpap deletion in the central nervous system preferentially induces formation of monopolar spindles in radial glia progenitors (RGPs) at around embryonic day 14.5 and causes robust apoptosis that severely disrupts embryonic brains. Interestingly, microcephalic brains with reduced apoptosis are detected in conditional Cpap gene-deleted mice that lose only one allele of p53 (also known as Trp53), while simultaneous removal of p53 and Cpap rescues RGP death. Furthermore, Cpap deletion leads to cilia loss, RGP mislocalization, junctional integrity disruption, massive heterotopia and severe cerebellar hypoplasia. Together, these findings indicate that complete CPAP loss leads to severe and complex phenotypes in developing mouse brain, and provide new insights into the causes of MCPH.

Homogeneous multifocal excitation for high-throughput super-resolution imaging

Super-resolution microscopies have become an established tool in biological research. However, imaging throughput remains a main bottleneck in acquiring large datasets required for quantitative biology. Here we describe multifocal flat illumination for field-independent imaging (mfFIFI). By integrating mfFIFI into an instant structured illumination microscope (iSIM), we extend the field of view (FOV) to >100 × 100 µm² while maintaining high-speed, multicolor, volumetric imaging at double the diffraction-limited resolution. We further extend the effective FOV by stitching adjacent images for fast live-cell super-resolution imaging of dozens of cells. Finally, we combine our flat-fielded iSIM with ultrastructure expansion microscopy to collect three-dimensional (3D) images of hundreds of centrioles in human cells, or thousands of purified Chlamydomonas reinhardtii centrioles, per hour at an effective resolution of ~35 nm. Classification and particle averaging of these large datasets enables 3D mapping of posttranslational modifications of centriolar microtubules, revealing differences in their coverage and positioning.

Centrosomes are required for proper β-catenin processing and Wnt response

The Wnt/β-catenin signaling pathway is central to metazoan development and routinely dysregulated in cancer. Wnt/β-catenin signaling initiates transcriptional reprogramming upon stabilization of the transcription factor β-catenin, which is otherwise posttranslationally processed by a destruction complex and degraded by the proteasome. Since various Wnt signaling components are enriched at centrosomes, we examined the functional contribution of centrosomes to Wnt signaling, β-catenin regulation, and posttranslational modifications. In HEK293 cells depleted of centrosomes we find that β-catenin synthesis and degradation rates are unaffected but that the normal accumulation of β-catenin in response to Wnt signaling is attenuated. This is due to accumulation of a novel high-molecular-weight form of phosphorylated β-catenin that is constitutively degraded in the absence of Wnt. Wnt signaling operates by inhibiting the destruction complex and thereby reducing destruction complex–phosphorylated β-catenin, but high-molecular-weight β-catenin is unexpectedly increased by Wnt signaling. Therefore these studies have identified a pool of β-catenin effectively shielded from regulation by Wnt. We present a model whereby centrosomes prevent inappropriate β-catenin modifications that antagonize normal stabilization by Wnt signals.

Tetrahymena Poc5 is a transient basal body component that is important for basal body maturation

Basal bodies (BBs) are microtubule-based organelles that act as a template for and stabilize cilia at the cell surface. Centrins ubiquitously associate with BBs and function in BB assembly, maturation and stability. Human POC5 (hPOC5) is a highly conserved centrin-binding protein that binds centrins through Sfi1p-like repeats and is required for building full-length, mature centrioles. Here, we use the BB-rich cytoskeleton of Tetrahymena thermophila to characterize Poc5 BB functions. Tetrahymena Poc5 (TtPoc5) uniquely incorporates into assembling BBs and is then removed from mature BBs prior to ciliogenesis. Complete genomic knockout of TtPOC5 leads to a significantly increased production of BBs, yet a markedly reduced ciliary density, both of which are rescued by reintroduction of TtPoc5. A second Tetrahymena POC5-like gene, SFR1, is similarly implicated in modulating BB production. When TtPOC5 and SFR1 are co-deleted, cell viability is compromised and BB overproduction is exacerbated. Overproduced BBs display defective transition zone formation and a diminished capacity for ciliogenesis. This study uncovers a requirement for Poc5 in building mature BBs, providing a possible functional link between hPOC5 mutations and impaired cilia.This article has an associated First Person interview with the first author of the paper.

Microtubule Organization in Striated Muscle Cells

Distinctly organized microtubule networks contribute to the function of differentiated cell types such as neurons, epithelial cells, skeletal myotubes, and cardiomyocytes. In striated (i.e., skeletal and cardiac) muscle cells, the nuclear envelope acts as the dominant microtubule-organizing center (MTOC) and the function of the centrosome—the canonical MTOC of mammalian cells—is attenuated, a common feature of differentiated cell types. We summarize the mechanisms known to underlie MTOC formation at the nuclear envelope, discuss the significance of the nuclear envelope MTOC for muscle function and cell cycle progression, and outline potential mechanisms of centrosome attenuation.

Prolonged mitosis results in structurally aberrant and over-elongated centrioles

Centrioles are precisely built microtubule-based structures that assemble centrosomes and cilia. Aberrations in centriole structure are common in tumors, yet how these aberrations arise is unknown. Analysis of centriole structure is difficult because it requires demanding electron microscopy. Here we employ expansion microscopy to study the origins of centriole structural aberrations in large populations of human cells. We discover that centrioles do not have an elongation monitoring mechanism, which renders them prone to over-elongation, especially during prolonged mitosis induced by various factors, importantly including supernumerary centrioles. We identify that mitotic centriole over-elongation is dependent on mitotic Polo-like kinase 1, which we uncover as a novel regulator of centriole elongation in human cycling cells. While insufficient Plk1 levels lead to the formation of shorter centrioles lacking a full set of microtubule triplets, its overactivity results in over-elongated and structurally aberrant centrioles. Our data help explain the origin of structurally aberrant centrioles and why centriole numerical and structural defects coexist in tumors.

Structural and Functional Analyses of the FAM46C/Plk4 Complex

FAM46C, a non-canonical poly(A) polymerase, is frequently mutated in multiple myeloma. Loss of function of FAM46C promotes cell survival of multiple myeloma, suggesting a tumor-suppressive role. FAM46C is also essential for fastening sperm head and flagellum, indispensable for male fertility. The molecular mechanisms of these functions of FAM46C remain elusive. We report the crystal structure of FAM46C to provide the basis for its poly(A) polymerase activity and rationalize mutations associated with multiple myeloma. In addition, we found that FAM46C interacts directly with the serine/threonine kinase Plk4, the master regulator of centrosome duplication. We present the structure of FAM46C in complex with the Cryptic Polo-Box 1-2 domains of Plk4. Our structure-based mutational analyses show that the interaction with Plk4 recruits FAM46C to centrosomes. Our data suggest that Plk4-mediated localization of FAM46C enables its regulation of centrosome structure and functions, which may underlie the roles for FAM46C in cell proliferation and sperm development.

Phosphorylation of multiple proteins involved in ciliogenesis by Tau Tubulin kinase 2

Primary cilia are organelles necessary for proper implementation of developmental and homeostasis processes. To initiate their assembly, coordinated actions of multiple proteins are needed. Tau tubulin kinase 2 (TTBK2) is a key player in the cilium assembly pathway, controlling the final step of cilia initiation. The function of TTBK2 in ciliogenesis is critically dependent on its kinase activity; however, the precise mechanism of TTBK2 action has so far not been fully understood due to the very limited information about its relevant substrates. In this study, we demonstrate that CEP83, CEP89, CCDC92, Rabin8, and DVL3 are substrates of TTBK2 kinase activity. Further, we characterize a set of phosphosites of those substrates and CEP164 induced by TTBK2 in vitro and in vivo. Intriguingly, we further show that identified TTBK2 phosphosites and consensus sequence delineated from those are distinct from motifs previously assigned to TTBK2. Finally, we show that TTBK2 is also required for efficient phosphorylation of many S/T sites in CEP164 and provide evidence that TTBK2-induced phosphorylations of CEP164 modulate its function, which in turn seems relevant for the process of cilia formation. In summary, our work provides important insight into the substrates-TTBK2 kinase relationship and suggests that phosphorylation of substrates on multiple sites by TTBK2 is probably involved in the control of ciliogenesis in human cells.

Cell Cycle-Dependent Dynamics of the Golgi-Centrosome Association in Motile Cells

Here, we characterize spatial distribution of the Golgi complex in human cells. In contrast to the prevailing view that the Golgi compactly surrounds the centrosome throughout interphase, we observe characteristic differences in the morphology of Golgi ribbons and their association with the centrosome during various periods of the cell cycle. The compact Golgi complex is typical in G1; during S-phase, Golgi ribbons lose their association with the centrosome and extend along the nuclear envelope to largely encircle the nucleus in G2. Interestingly, pre-mitotic separation of duplicated centrosomes always occurs after dissociation from the Golgi. Shortly before the nuclear envelope breakdown, scattered Golgi ribbons reassociate with the separated centrosomes restoring two compact Golgi complexes. Transitions between the compact and distributed Golgi morphologies are microtubule-dependent. However, they occur even in the absence of centrosomes, which implies that Golgi reorganization is not driven by the centrosomal microtubule asters. Cells with different Golgi morphology exhibit distinct differences in the directional persistence and velocity of migration. These data suggest that changes in the radial distribution of the Golgi around the nucleus define the extent of cell polarization and regulate cell motility in a cell cycle-dependent manner.

Direct interaction between CEP85 and STIL mediates PLK4-driven directed cell migration

PLK4 has emerged as a prime target for cancer therapeutics, and its overexpression is frequently observed in various types of human cancer. Recent studies have further revealed an unexpected oncogenic activity of PLK4 in regulating cancer cell migration and invasion. However, the molecular basis behind the role of PLK4 in these processes still remains only partly understood. Our previous work has demonstrated that an intact CEP85-STIL binding interface is necessary for robust PLK4 activation and centriole duplication. Here, we show that CEP85 and STIL are also required for directional cancer cell migration. Mutational and functional analyses reveal that the interactions between CEP85, STIL and PLK4 are essential for effective directional cell motility. Mechanistically, we show that PLK4 can drive the recruitment of CEP85 and STIL to the leading edge of cells to promote protrusive activity, and that downregulation of CEP85 and STIL leads to a reduction in ARP2 (also known as ACTR2) phosphorylation and reorganization of the actin cytoskeleton, which in turn impairs cell migration. Collectively, our studies provide molecular insight into the important role of the CEP85-STIL complex in modulating PLK4-driven cancer cell migration.This article has an associated First Person interview with the first author of the paper.

Loss of AMPKalpha1 Triggers Centrosome Amplification via PLK4 Upregulation in Mouse Embryonic Fibroblasts

Recent evidence indicates that activation of adenosine monophosphate-activated protein kinase (AMPK), a highly conserved sensor and modulator of cellular energy and redox, regulates cell mitosis. However, the underlying molecular mechanisms for AMPKα subunit regulation of chromosome segregation remain poorly understood. This study aimed to ascertain if AMPKα1 deletion contributes to chromosome missegregation by elevating Polo-like kinase 4 (PLK4) expression. Centrosome proteins and aneuploidy were monitored in cultured mouse embryonic fibroblasts (MEFs) isolated from wild type (WT, C57BL/6J) or AMPKα1 homozygous deficient (AMPKα1^−/−) mice by Western blotting and metaphase chromosome spread. Deletion of AMPKα1, the predominant AMPKα isoform in immortalized MEFs, led to centrosome amplification and chromosome missegregation, as well as the consequent aneuploidy (34–66%) and micronucleus. Furthermore, AMPKα1 null cells exhibited a significant induction of PLK4. Knockdown of nuclear factor kappa B2/p52 ameliorated the PLK4 elevation in AMPKα1-deleted MEFs. Finally, PLK4 inhibition by Centrinone reversed centrosome amplification of AMPKα1-deleted MEFs. Taken together, our results suggest that AMPKα1 plays a fundamental role in the maintenance of chromosomal integrity through the control of p52-mediated transcription of PLK4, a trigger of centriole biogenesis.

Radiation-induced abnormal centrosome amplification and mitotic catastrophe in human cervical tumor HeLa cells and murine mammary tumor EMT6 cells

Mitotic catastrophe is a form of cell death linked to aberrant mitosis caused by improper or uncoordinated mitotic progression. Abnormal centrosome amplification and mitotic catastrophe occur simultaneously, and some cells with amplified centrosomes enter aberrant mitosis, but it is not clear whether abnormal centrosome amplification triggers mitotic catastrophe. Here, to investigate whether radiation-induced abnormal centrosome amplification is essential for induction of radiation-induced mitotic catastrophe, centrinone-B, a highly selective inhibitor of polo-like kinase 4, was utilized to inhibit centrosome amplification, since polo-like kinase 4 is an essential kinase in centrosome duplication. When human cervical tumor HeLa cells and murine mammary tumor EMT6 cells were irradiated with 2.5 Gy of X-rays, cells with morphological features of mitotic catastrophe and the number of cells having >2 centrosomes increased in both cell lines. Although centrinone-B significantly inhibited radiation-induced abnormal centrosome amplification in both cell lines, such treatment did not change cell growth and significantly enhanced mitotic catastrophe in HeLa cells exposed to X-rays. In contrast, inhibition of centrosome amplification reduced cell growth and mitotic catastrophe in EMT6 cells exposed to X-rays. These results indicated that the role of radiation-induced abnormal centrosome amplification in radiation-induced mitotic catastrophe changes, depending on the cell type.

Mechanisms of spindle bipolarity establishment in acentrosomal human cells

Centrosomes are not absolutely essential for cell division; acentrosomal bipolar spindles can be established in oocytes and centrosome-eliminated somatic cells. However, the detailed mechanisms describing how spindle bipolarity is established without centrosomes are not completely understood. We have recently demonstrated that in acentrosomal human cells, nuclear mitotic apparatus protein (NuMA) assemblies-mediated microtubule asters and EG5 promote spindle bipolarization in early mitosis.

A liquid-like spindle domain promotes acentrosomal spindle assembly in mammalian oocytes

Mammalian oocytes segregate chromosomes with a microtubule spindle that lacks centrosomes, but the mechanisms by which acentrosomal spindles are organized and function are largely unclear. In this study, we identify a conserved subcellular structure in mammalian oocytes that forms by phase separation. This structure, which we term the liquid-like meiotic spindle domain (LISD), permeates the spindle poles and forms dynamic protrusions that extend well beyond the spindle. The LISD selectively concentrates multiple microtubule regulatory factors and allows them to diffuse rapidly within the spindle volume. Disruption of the LISD via different means disperses these factors and leads to severe spindle assembly defects. Our data suggest a model whereby the LISD promotes meiotic spindle assembly by serving as a reservoir that sequesters and mobilizes microtubule regulatory factors in proximity to spindle microtubules.

Centrosomes: The good and the bad for brain development

Centrosomes nucleate and organise the microtubule cytoskeleton in animal cells. These membraneless organelles are key structures for tissue organisation, polarity and growth. Centrosome dysfunction, defined as deviation in centrosome numbers and/or structural integrity, has major impact on brain size and functionality, as compared with other tissues of the organism. In this review, we discuss the contribution of centrosomes to brain growth during development. We discuss in particular the impact of centrosome dysfunction in Drosophila and mammalian neural stem cell division and fitness, which ultimately underlie brain growth defects.

Targeting centrosome amplification, an Achilles' heel of cancer

Due to cell-cycle dysregulation, many cancer cells contain more than the normal compliment of centrosomes, a state referred to as centrosome amplification (CA). CA can drive oncogenic phenotypes and indeed can cause cancer in flies and mammals. However, cells have to actively manage CA, often by centrosome clustering, in order to divide. Thus, CA is also an Achilles' Heel of cancer cells. In recent years, there have been many important studies identifying proteins required for the management of CA and it has been demonstrated that disruption of some of these proteins can cause cancer-specific inhibition of cell growth. For certain targets therapeutically relevant interventions are being investigated, for example, small molecule inhibitors, although none are yet in clinical trials. As the field is now poised to move towards clinically relevant interventions, it is opportune to summarise the key work in targeting CA thus far, with particular emphasis on recent developments where small molecule or other strategies have been proposed. We also highlight the relatively unexplored paradigm of reversing CA, and thus its oncogenic effects, for therapeutic gain.

Zika virus NS5 localizes at centrosomes during cell division

Zika virus (ZIKV) nonstructural protein 5 (NS5) plays a critical role in viral RNA replication and mediates key virus-host cell interactions. As with other flavivirus NS5 proteins, ZIKV NS5 is primarily found in the nucleus. We previously reported that the NS5 protein of dengue virus, another flavivirus, localized to centrosomes during cell division. Here we show that ZIKV NS5 also relocalizes from the nucleus to centrosomes during mitosis. In infected cells with supernumerary centrosomes, NS5 was present at all centrosomes. Transient expression of NS5 in uninfected cells confirmed that centrosomal localization was independent of other viral proteins. Live-cell imaging demonstrated that NS5-GFP accumulated at centrosomes shortly after break down of nuclear membrane and remained there through mitosis. Cells expressing NS5-GFP took longer to complete mitosis than control cells. Finally, an analysis of ZIKV NS5 binding partners revealed several centrosomal proteins, providing potential direct links between NS5 and centrosomes.

Centrioles control the capacity, but not the specificity, of cytotoxic T cell killing

Immunological synapse formation between cytotoxic T lymphocytes (CTLs) and the target cells they aim to destroy is accompanied by reorientation of the CTL centrosome to a position beneath the synaptic membrane. Centrosome polarization is thought to enhance the potency and specificity of killing by driving lytic granule fusion at the synapse and thereby the release of perforin and granzymes toward the target cell. To test this model, we employed a genetic strategy to delete centrioles, the core structural components of the centrosome. Centriole deletion altered microtubule architecture as expected but surprisingly had no effect on lytic granule polarization and directional secretion. Nevertheless, CTLs lacking centrioles did display substantially reduced killing potential, which was associated with defects in both lytic granule biogenesis and synaptic actin remodeling. These results reveal an unexpected role for the intact centrosome in controlling the capacity but not the specificity of cytotoxic killing.

Golgi-associated microtubules are fast cargo tracks and required for persistent cell migration

Microtubules derived from the Golgi (Golgi MTs) have been implicated to play critical roles in persistent cell migration, but the underlying mechanisms remain elusive, partially due to the lack of direct observation of Golgi MT-dependent vesicular trafficking. Here, using super-resolution stochastic optical reconstruction microscopy (STORM), we discovered that post-Golgi cargos are more enriched on Golgi MTs and also surprisingly move much faster than on non-Golgi MTs. We found that, compared to non-Golgi MTs, Golgi MTs are morphologically more polarized toward the cell leading edge with significantly fewer inter-MT intersections. In addition, Golgi MTs are more stable and contain fewer lattice repair sites than non-Golgi MTs. Our STORM/live-cell imaging demonstrates that cargos frequently pause at the sites of both MT intersections and MT defects. Furthermore, by optogenetic maneuvering of cell direction, we demonstrate that Golgi MTs are essential for persistent cell migration but not for cells to change direction. Together, our study unveils the role of Golgi MTs in serving as a group of "fast tracks" for anterograde trafficking of post-Golgi cargos.

NuMA assemblies organize microtubule asters to establish spindle bipolarity in acentrosomal human cells

In most animal cells, mitotic spindle formation is mediated by coordination of centrosomal and acentrosomal pathways. At the onset of mitosis, centrosomes promote spindle bipolarization. However, the mechanism through which the acentrosomal pathways facilitate the establishment of spindle bipolarity in early mitosis is not completely understood. In this study, we show the critical roles of nuclear mitotic apparatus protein (NuMA) in the generation of spindle bipolarity in acentrosomal human cells. In acentrosomal human cells, we found that small microtubule asters containing NuMA formed at the time of nuclear envelope breakdown. In addition, these asters were assembled by dynein and the clustering activity of NuMA. Subsequently, NuMA organized the radial array of microtubules, which incorporates Eg5, and thus facilitated spindle bipolarization. Importantly, in cells with centrosomes, we also found that NuMA promoted the initial step of spindle bipolarization in early mitosis. Overall, these data suggest that canonical centrosomal and NuMA-mediated acentrosomal pathways redundantly promote spindle bipolarity in human cells.

PLK4 deubiquitination by Spata2-CYLD suppresses NEK7-mediated NLRP3 inflammasome activation at the centrosome

The innate immune sensor NLRP3 assembles an inflammasome complex with NEK7 and ASC to activate caspase-1 and drive the maturation of proinflammatory cytokines IL-1β and IL-18. NLRP3 inflammasome activity must be tightly controlled, as its over-activation is involved in the pathogenesis of inflammatory diseases. Here, we show that NLRP3 inflammasome activation is suppressed by a centrosomal protein Spata2. Spata2 deficiency enhances NLRP3 inflammasome activity both in the macrophages and in an animal model of peritonitis. Mechanistically, Spata2 recruits the deubiquitinase CYLD to the centrosome for deubiquitination of polo-like kinase 4 (PLK4), the master regulator of centrosome duplication. Deubiquitination of PLK4 facilitates its binding to and phosphorylation of NEK7 at Ser204. NEK7 phosphorylation in turn attenuates NEK7 and NLRP3 interaction, which is required for NLRP3 inflammasome activation. Pharmacological or shRNA-mediated inhibition of PLK4, or mutation of the NEK7 Ser204 phosphorylation site, augments NEK7 interaction with NLRP3 and causes increased NLRP3 inflammasome activation. Our study unravels a novel centrosomal regulatory pathway of inflammasome activation and may provide new therapeutic targets for the treatment of NLRP3-associated inflammatory diseases.

Centriolar satellite biogenesis and function in vertebrate cells

Centriolar satellites are non-membranous cytoplasmic granules that concentrate in the vicinity of the centrosome, the major microtubule-organizing centre (MTOC) in animal cells. Originally assigned as conduits for the transport of proteins towards the centrosome and primary cilium, the complexity of satellites is starting to become apparent. Recent studies defined the satellite proteome and interactomes, placing hundreds of proteins from diverse pathways in association with satellites. In addition, studies on cells lacking satellites have revealed that the centrosome can assemble in their absence, whereas studies on acentriolar cells have demonstrated that satellite assembly is independent from an intact MTOC. A role for satellites in ciliogenesis is well established; however, their contribution to other cellular functions is poorly understood. In this Review, we discuss the developments in our understanding of centriolar satellite assembly and function, and why satellites are rapidly becoming established as governors of multiple cellular processes. We highlight the composition and biogenesis of satellites and what is known about the regulation of these aspects. Furthermore, we discuss the evolution from thinking of satellites as mere facilitators of protein trafficking to the centrosome to thinking of them being key regulators of protein localization and cellular proteostasis for a diverse set of pathways, making them of broader interest to fields beyond those focused on centrosomes and ciliogenesis.

TRIGGERING ANAPHASE CATASTROPHE TO COMBAT ANEUPLOID CANCERS

Cancer cells are genetically unstable and often have supernumerary centrosomes. When supernumerary centrosome clustering is inhibited at mitosis, multipolar cell division is forced, triggering apoptosis in daughter cells. This proapoptotic pathway is called anaphase catastrophe. Cyclin-dependent kinase 1 (CDK1) or CDK2 inhibitors can antagonize centrosome clustering and cause anaphase catastrophe to occur in lung cancer and other types of cancer. The centrosome protein CP110, a CDK1 and CDK2 phosphorylation substrate, engages anaphase catastrophe. Intriguingly, CP110 is downregulated by the KRAS oncoprotein, enhancing sensitivity of KRAS-driven cancers to CDK2 inhibitors. Anaphase catastrophe eradicates aneuploid cancer cells while relatively sparing normal diploid cells with two centrosomes. This therapeutic window discriminates between normal and neoplastic cells and can be exploited in the cancer clinic. The work reviewed here establishes that pharmacologically-induced anaphase catastrophe is useful to combat aneuploid cancers, especially when the KRAS oncoprotein is activated. This addresses an unmet medical need in oncology.

Massive centriole production can occur in the absence of deuterosomes in multiciliated cells

Multiciliated cells (MCCs) amplify large numbers of centrioles, which convert into basal bodies that are required for producing multiple motile cilia. Most centrioles amplified by MCCs grow on the surface of organelles called deuterosomes, while a smaller number grow through the centriolar pathway in association with the two parent centrioles. Here we show that MCCs lacking deuterosomes amplify the correct number of centrioles with normal step-wise kinetics. This is achieved through a massive production of centrioles on the surface and in the vicinity of parent centrioles. Therefore, deuterosomes may have evolved to relieve, rather than supplement, the centriolar pathway during multiciliogenesis. Remarkably, MCCs lacking parent centrioles and deuterosomes also amplify the appropriate number of centrioles inside a cloud of pericentriolar and fibrogranular material. These data show that centriole number is set independently of their nucleation platforms and that massive centriole production in MCCs is a robust process that can self-organize.

p53 mitotic centrosome localization preserves centrosome integrity and works as sensor for the mitotic surveillance pathway

Centrosomal p53 has been described for three decades but its role is still unclear. We previously reported that, in proliferating human cells, p53 transiently moves to centrosomes at each mitosis. Such p53 mitotic centrosome localization (p53-MCL) occurs independently from DNA damage but requires ATM-mediated p53Ser15 phosphorylation (p53Ser15^P) on discrete cytoplasmic p53 foci that, through MT dynamics, move to centrosomes during the mitotic spindle formation. Here, we show that inhibition of p53-MCL, obtained by p53 depletion or selective impairment of p53 centrosomal localization, induces centrosome fragmentation in human nontransformed cells. In contrast, tumor cells or mouse cells tolerate p53 depletion, as expected, and p53-MCL inhibition. Such tumor- and species-specific behavior of centrosomal p53 resembles that of the recently identified sensor of centrosome-loss, whose activation triggers the mitotic surveillance pathway in human nontransformed cells but not in tumor cells or mouse cells. The mitotic surveillance pathway prevents the growth of human cells with increased chance of making mitotic errors and accumulating numeral chromosome defects. Thus, we evaluated whether p53-MCL could work as a centrosome-loss sensor and contribute to the activation of the mitotic surveillance pathway. We provide evidence that centrosome-loss triggered by PLK4 inhibition makes p53 orphan of its mitotic dock and promotes accumulation of discrete p53Ser15^P foci. These p53 foci are required for the recruitment of 53BP1, a key effector of the mitotic surveillance pathway. Consistently, cells from patients with constitutive impairment of p53-MCL, such as ATM- and PCNT-mutant carriers, accumulate numeral chromosome defects. These findings indicate that, in nontransformed human cells, centrosomal p53 contributes to safeguard genome integrity by working as sensor for the mitotic surveillance pathway.