IFT proteins interact with HSET to promote supernumerary centrosome clustering in mitosis

Positioning centrioles and centrosomes

Centrosomes are the primary microtubule organizer in eukaryotic cells. In addition to shaping the intracellular microtubule network and the mitotic spindle, centrosomes are responsible for positioning cilia and flagella. To fulfill these diverse functions, centrosomes must be properly located within cells, which requires that they undergo intracellular transport. Importantly, centrosome mispositioning has been linked to ciliopathies, cancer, and infertility. The mechanisms by which centrosomes migrate are diverse and context dependent. In many cells, centrosomes move via indirect motor transport, whereby centrosomal microtubules engage anchored motor proteins that exert forces on those microtubules, resulting in centrosome movement. However, in some cases, centrosomes move via direct motor transport, whereby the centrosome or centriole functions as cargo that directly binds molecular motors which then walk on stationary microtubules. In this review, we summarize the mechanisms of centrosome motility and the consequences of centrosome mispositioning and identify key questions that remain to be addressed.

The emerging functions of intraflagellar transport 52 in ciliary transport and ciliopathies

Ciliary transport in eukaryotic cells is an intricate and conserved process involving the coordinated assembly and functioning of a multiprotein intraflagellar transport (IFT) complex. Among the various IFT proteins, intraflagellar transport 52 (IFT52) plays a crucial role in ciliary transport and is implicated in various ciliopathies. IFT52 is a core component of the IFT-B complex that facilitates movement of cargoes along the ciliary axoneme. Stable binding of the IFT-B1 and IFT-B2 subcomplexes by IFT52 in the IFT-B complex regulates recycling of ciliary components and maintenance of ciliary functions such as signal transduction and molecular movement. Mutations in the IFT52 gene can disrupt ciliary trafficking, resulting in dysfunctional cilia and affecting cellular processes in ciliopathies. Such ciliopathies caused by IFT52 mutations exhibit a wide range of clinical features, including skeletal developmental abnormalities, retinal degeneration, respiratory failure and neurological abnormalities in affected individuals. Therefore, IFT52 serves as a promising biomarker for the diagnosis of various ciliopathies, including short-rib thoracic dysplasia 16 with or without polydactyly. Here, we provide an overview of the IFT52-mediated molecular mechanisms underlying ciliary transport and describe the IFT52 mutations that cause different disorders associated with cilia dysfunction.

Centrosome linker diversity and its function in centrosome clustering and mitotic spindle formation

The centrosome linker joins the two interphase centrosomes of a cell into one microtubule organizing center. Despite increasing knowledge on linker components, linker diversity in different cell types and their role in cells with supernumerary centrosomes remained unexplored. Here, we identified Ninein as a C-Nap1-anchored centrosome linker component that provides linker function in RPE1 cells while in HCT116 and U2OS cells, Ninein and Rootletin link centrosomes together. In interphase, overamplified centrosomes use the linker for centrosome clustering, where Rootletin gains centrosome linker function in RPE1 cells. Surprisingly, in cells with centrosome overamplification, C-Nap1 loss prolongs metaphase through persistent activation of the spindle assembly checkpoint indicated by BUB1 and MAD1 accumulation at kinetochores. In cells lacking C-Nap1, the reduction of microtubule nucleation at centrosomes and the delay in nuclear envelop rupture in prophase probably cause mitotic defects like multipolar spindle formation and chromosome mis-segregation. These defects are enhanced when the kinesin HSET, which normally clusters multiple centrosomes in mitosis, is partially inhibited indicating a functional interplay between C-Nap1 and centrosome clustering in mitosis.

The fate of extra centrosomes in newly formed tetraploid cells: should I stay, or should I go?

An increase in centrosome number is commonly observed in cancer cells, but the role centrosome amplification plays along with how and when it occurs during cancer development is unclear. One mechanism for generating cancer cells with extra centrosomes is whole genome doubling (WGD), an event that occurs in over 30% of human cancers and is associated with poor survival. Newly formed tetraploid cells can acquire extra centrosomes during WGD, and a generally accepted model proposes that centrosome amplification in tetraploid cells promotes cancer progression by generating aneuploidy and chromosomal instability. Recent findings, however, indicate that newly formed tetraploid cells in vitro lose their extra centrosomes to prevent multipolar cell divisions. Rather than persistent centrosome amplification, this evidence raises the possibility that it may be advantageous for tetraploid cells to initially restore centrosome number homeostasis and for a fraction of the population to reacquire additional centrosomes in the later stages of cancer evolution. In this review, we explore the different evolutionary paths available to newly formed tetraploid cells, their effects on centrosome and chromosome number distribution in daughter cells, and their probabilities of long-term survival. We then discuss the mechanisms that may alter centrosome and chromosome numbers in tetraploid cells and their relevance to cancer progression following WGD.

Computational benchmarking of putative KIFC1 inhibitors

The centrosome in animal cells is instrumental in spindle pole formation, nucleation, proper alignment of microtubules during cell division, and distribution of chromosomes in each daughter cell. Centrosome amplification involving structural and numerical abnormalities in the centrosome can cause chromosomal instability and dysregulation of the cell cycle, leading to cancer development and metastasis. However, disturbances caused by centrosome amplification can also limit cancer cell survival by activating mitotic checkpoints and promoting mitotic catastrophe. As a smart escape, cancer cells cluster their surplus of centrosomes into pseudo-bipolar spindles and progress through the cell cycle. This phenomenon, known as centrosome clustering (CC), involves many proteins and has garnered considerable attention as a specific cancer cell-targeting weapon. The kinesin-14 motor protein KIFC1 is a minus end-directed motor protein that is involved in CC. Because KIFC1 is upregulated in various cancers and modulates oncogenic signaling cascades, it has emerged as a potential chemotherapeutic target. Many molecules have been identified as KIFC1 inhibitors because of their centrosome declustering activity in cancer cells. Despite the ever-increasing literature in this field, there have been few efforts to review the progress. The current review aims to collate and present an in-depth analysis of known KIFC1 inhibitors and their biological activities. Additionally, we present computational docking data of putative KIFC1 inhibitors with their binding sites and binding affinities. This first-of-kind comparative analysis involving experimental biology, chemistry, and computational docking of different KIFC1 inhibitors may help guide decision-making in the selection and design of potent inhibitors.

Whole-Genome Duplication and Genome Instability in Cancer Cells: Double the Trouble

Whole-genome duplication (WGD) is one of the most common genomic abnormalities in cancers. WGD can provide a source of redundant genes to buffer the deleterious effect of somatic alterations and facilitate clonal evolution in cancer cells. The extra DNA and centrosome burden after WGD is associated with an elevation of genome instability. Causes of genome instability are multifaceted and occur throughout the cell cycle. Among these are DNA damage caused by the abortive mitosis that initially triggers tetraploidization, replication stress and DNA damage associated with an enlarged genome, and chromosomal instability during the subsequent mitosis in the presence of extra centrosomes and altered spindle morphology. Here, we chronicle the events after WGD, from tetraploidization instigated by abortive mitosis including mitotic slippage and cytokinesis failure to the replication of the tetraploid genome, and finally, to the mitosis in the presence of supernumerary centrosomes. A recurring theme is the ability of some cancer cells to overcome the obstacles in place for preventing WGD. The underlying mechanisms range from the attenuation of the p53-dependent G₁ checkpoint to enabling pseudobipolar spindle formation via the clustering of supernumerary centrosomes. These survival tactics and the resulting genome instability confer a subset of polyploid cancer cells proliferative advantage over their diploid counterparts and the development of therapeutic resistance.

KIF24 depletion induces clustering of supernumerary centrosomes in PDAC cells

Depletion of the centrosomal kinesin KIF24, known to restrain the assembly of primary cilia, suppresses multipolar spindle formation by clustering centrosomes in centrosome-amplified PDAC cells.

Clustering of supernumerary centrosomes, which potentially leads to cell survival and chromosomal instability, is frequently observed in cancers. However, the molecular mechanisms that control centrosome clustering remain largely unknown. The centrosomal kinesin KIF24 was previously shown to restrain the assembly of primary cilia in mammalian cells. Here, we revealed that KIF24 depletion suppresses multipolar spindle formation by clustering centrosomes in pancreatic ductal adenocarcinoma (PDAC) cells harboring supernumerary centrosomes. KIF24 depletion also induced hyper-proliferation and improved mitotic progression in PDAC cells. In contrast, disruption of primary cilia failed to affect the proliferation and spindle formation in KIF24-depleted cells. These results suggest a novel role for KIF24 in suppressing centrosome clustering independent of primary ciliation in centrosome-amplified PDAC cells.

Emerging roles of centrosome cohesion

The centrosome, consisting of centrioles and the associated pericentriolar material, is the main microtubule-organizing centre (MTOC) in animal cells. During most of interphase, the two centrosomes of a cell are joined together by centrosome cohesion into one MTOC. The most dominant element of centrosome cohesion is the centrosome linker, an interdigitating, fibrous network formed by the protein C-Nap1 anchoring a number of coiled-coil proteins including rootletin to the proximal end of centrioles. Alternatively, centrosomes can be kept together by the action of the minus end directed kinesin motor protein KIFC3 that works on interdigitating microtubules organized by both centrosomes and probably by the actin network. Although cells connect the two interphase centrosomes by several mechanisms into one MTOC, the general importance of centrosome cohesion, particularly for an organism, is still largely unclear. In this article, we review the functions of the centrosome linker and discuss how centrosome cohesion defects can lead to diseases.

Kinesin-14 HSET may not oppose kinesin-5 Eg5 activity in RPE-1 cells

Human retinal pigment epithelium RPE-1 cells are immortalized diploid wild-type cells. RPE-1 is increasingly used for studies of spindle assembly dynamics and chromosome segregation. Here, we imaged living RPE-1 cells using the spinning disk confocal microscope and report their complete spindle assembly dynamic parameters. Live-cell experiments enabled ascribing precise timing of function of the kinesin-5 Eg5 and kinesin-14 HSET throughout different phases of mitosis. Eg5 functions at prophase and metaphase, to assemble and maintain spindle bipolarity, respectively. Eg5 inhibition results in spindle collapse during prophase and metaphase, resulting in monoastral/monopolar spindles. HSET functions throughout mitosis to maintain spindle length. HSET degradation results in shorter spindles through all phases of mitosis. Double-inhibition of Eg5 and HSET produces only monoastral/monopolar spindles, indicating that Eg5 and HSET may not be antagonistic in wild-type RPE-1 cells, contrary to previous studies using cancer cells. In the context of spindle assembly, our results highlight potential important differences between RPE-1 and other cancer-derived cell lines.

Comparative investigation of toxicity induced by UV-A and UV-C radiation using Allium test

Organisms are increasingly exposed to ultraviolet (UV) rays of sunlight, due to the thinning of the ozone layer and its widespread use in sterilization processes, especially against the SARS-CoV-2 virus. The present study was conducted with the purpose of evaluating the damages of UV-A and UV-C radiations in Allium cepa L. roots. The effects of two different types of UV on some physiological, biochemical, cytogenotoxic, and anatomical parameters were investigated in a multifaceted study. Three groups were formed from Allium bulbs, one of which was the control group. One of the other groups was exposed to 254 nm (UV-C) and the other to 365 nm (UV-A) UV. Growth retardation effect of UV was investigated with respect to germination percentage, total weight gain, and root elongation, while cytogenotoxicity arisen from UV exposure was analyzed using mitotic index (MI) and chromosomal aberration (CA) and micronucleus (MN) frequency. Oxidative stress due to UV application was investigated based on the accumulation of malondialdehyde (MDA) and the total activities of superoxide dismutase (SOD) and catalase (CAT) enzymes. Also, anatomical changes induced by UV-A and UV-C were analyzed in root meristematic cells. UV treatments caused significant reductions in growth-related parameters. Both UV treatments caused a significant increase in MDA levels and induction of SOD and CAT enzymes in root meristematic cells. A decrease in MI and an increase in the frequency of MN and CAs were observed in root tip cells, indicating the cytogenotoxic effect of UV application. Anatomical damages such as epidermis cell damage, cortex cell damage, necrotic zones, giant cell nucleus, and indistinct transmission tissue occurred in cells exposed to UV. All of the physiological, biochemical, cytogenetic, and anatomical damages observed in this study were more severe in cells treated with UV-C compared to UV-A. This study suggested that UV exposure triggered growth inhibition, cytogenotoxicity, oxidative stress, and meristematic cell damages in A. cepa roots depending on the wavelength.

Up-Regulated MISP Is Associated With Poor Prognosis and Immune Infiltration in Pancreatic Ductal Adenocarcinoma

Background

Pancreatic ductal adenocarcinoma (PDAC) is a highly malignant disease with a poor prognosis. More effective biomarkers and treatment options remain to be discovered. Mitotic Spindle Positioning (MISP), also called C19orf21, has been reported to be upregulated in several malignancies. However, the effects of MISP on PDAC have yet to be investigated.

Materials and Methods

The differential expression of MISP at the mRNA and protein levels were evaluated using Gene Expression Profiling Interactive Analysis 2 (GEPIA 2), Gene Expression Omnibus (GEO), and the Human Protein Atlas (HPA) databases, and was further verified by quantitative real-time PCR and western blotting in PDAC cell lines. Correlations between MISP expression and clinical characteristics were explored using Kaplan-Meier Plotter Database and clinical data from The Cancer Genome Atlas (TCGA). CCK-8 assays, Transwell assays, and immunoblotting were used to determine the role of MISP in PDAC proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) in vitro. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were executed by the R package ‘clusterProfiler’. Correlations between MISP expression and immune cell infiltration, immune checkpoints, immunophenoscore (IPS) and the tumor mutational burden (TMB) in PDAC were explored using the R package ‘CIBERSORT’, the Tumor Immune Estimation Resource 2.0 (TIMER2.0), and The Cancer Immunome Atlas (TCIA) database based on TCGA data.

Result

MISP expression was significantly higher in pancreatic cancer tissues compared to normal pancreas tissues, which was associated with a poor prognosis. Increased expression of MISP was related to the proliferation, migration and invasion of PDAC cell lines. GO and KEGG pathway analyses determined that MISP is involved in the Ras signaling pathway and immune regulation. Higher expression of MISP was associated with decreased infiltration levels of activated CD4+ memory T cells, CD8+ T cells, M2 macrophages and neutrophils. Furthermore, increased MISP was associated with lower expression of immune checkpoint molecules, higher gene mutation burden and IPS.

Conclusions

This study reveals that MISP, which is associated with the progression and prognosis of PDAC, may exert a potential regulatory effect on immune infiltration and predict the response to immunotherapy in PDAC.

Male infertility-associated Ccdc108 regulates multiciliogenesis via the intraflagellar transport machinery

Motile cilia on the cell surface generate movement and directional fluid flow that is crucial for various biological processes. Dysfunction of these cilia causes human diseases such as sinopulmonary disease and infertility. Here, we show that Ccdc108, a protein linked to male infertility, has an evolutionarily conserved requirement in motile multiciliation. Using Xenopus laevis embryos, Ccdc108 is shown to be required for the migration and docking of basal bodies to the apical membrane in epidermal multiciliated cells (MCCs). We demonstrate that Ccdc108 interacts with the IFT‐B complex, and the ciliation requirement for Ift74 overlaps with Ccdc108 in MCCs. Both Ccdc108 and IFT‐B proteins localize to migrating centrioles, basal bodies, and cilia in MCCs. Importantly, Ccdc108 governs the centriolar recruitment of IFT while IFT licenses the targeting of Ccdc108 to the cilium. Moreover, Ccdc108 is required for the centriolar recruitment of Drg1 and activated RhoA, factors that help establish the apical actin network in MCCs. Together, our studies indicate that Ccdc108 and IFT‐B complex components cooperate in multiciliogenesis.

Mechanism of spindle pole organization and instability in human oocytes

Human oocytes are prone to assembling meiotic spindles with unstable poles, which can favor aneuploidy in human eggs. The underlying causes of spindle instability are unknown. We found that NUMA (nuclear mitotic apparatus protein)-mediated clustering of microtubule minus ends focused the spindle poles in human, bovine, and porcine oocytes and in mouse oocytes depleted of acentriolar microtubule-organizing centers (aMTOCs). However, unlike human oocytes, bovine, porcine, and aMTOC-free mouse oocytes have stable spindles. We identified the molecular motor KIFC1 (kinesin superfamily protein C1) as a spindle-stabilizing protein that is deficient in human oocytes. Depletion of KIFC1 recapitulated spindle instability in bovine and aMTOC-free mouse oocytes, and the introduction of exogenous KIFC1 rescued spindle instability in human oocytes. Thus, the deficiency of KIFC1 contributes to spindle instability in human oocytes.

Intraflagellar Transport Complex B Proteins Regulate the Hippo Effector Yap1 during Cardiogenesis

Cilia and the intraflagellar transport (IFT) proteins involved in ciliogenesis are associated with congenital heart diseases (CHDs). However, the molecular links between cilia, IFT proteins, and cardiogenesis are yet to be established. Using a combination of biochemistry, genetics, and live-imaging methods, we show that IFT complex B proteins (Ift88, Ift54, and Ift20) modulate the Hippo pathway effector YAP1 in zebrafish and mouse. We demonstrate that this interaction is key to restrict the formation of the proepicardium and the myocardium. In cellulo experiments suggest that IFT88 and IFT20 interact with YAP1 in the cytoplasm and functionally modulate its activity, identifying a molecular link between cilia-related proteins and the Hippo pathway. Taken together, our results highlight a noncanonical role for IFT complex B proteins during cardiogenesis and shed light on a mechanism of action for ciliary proteins in YAP1 regulation.

Non-ciliary Roles of IFT Proteins in Cell Division and Polycystic Kidney Diseases

Cilia are small organelles present at the surface of most differentiated cells where they act as sensors for mechanical or biochemical stimuli. Cilia assembly and function require the Intraflagellar Transport (IFT) machinery, an intracellular transport system that functions in association with microtubules and motors. If IFT proteins have long been studied for their ciliary roles, recent evidences indicate that their functions are not restricted to the cilium. Indeed, IFT proteins are found outside the ciliary compartment where they are involved in a variety of cellular processes in association with non-ciliary motors. Recent works also provide evidence that non-ciliary roles of IFT proteins could be responsible for the development of ciliopathies related phenotypes including polycystic kidney diseases. In this review, we will discuss the interactions of IFT proteins with microtubules and motors as well as newly identified non-ciliary functions of IFT proteins, focusing on their roles in cell division. We will also discuss the potential contribution of non-ciliary IFT proteins functions to the etiology of kidney diseases.

IFT proteins interact with HSET to promote supernumerary centrosome clustering in mitosis

Centrosome amplification is a hallmark of cancer, and centrosome clustering is essential for cancer cell survival. The mitotic kinesin HSET is an essential contributor to this process. Recent studies have highlighted novel functions for intraflagellar transport (IFT) proteins in regulating motors and mitotic processes. Here, using siRNA knock‐down of various IFT proteins or AID‐inducible degradation of endogenous IFT88 in combination with small‐molecule inhibition of HSET, we show that IFT proteins together with HSET are required for efficient centrosome clustering. We identify a direct interaction between the kinesin HSET and IFT proteins, and we define how IFT proteins contribute to clustering dynamics during mitosis using high‐resolution live imaging of centrosomes. Finally, we demonstrate the requirement of IFT88 for efficient centrosome clustering in a variety of cancer cell lines naturally harboring supernumerary centrosomes and its importance for cancer cell proliferation. Overall, our data unravel a novel role for the IFT machinery in centrosome clustering during mitosis in cells harboring supernumerary centrosomes.