PCM1 Depletion Inhibits Glioblastoma Cell Ciliogenesis and Increases Cell Death and Sensitivity to Temozolomide

Aurora kinase A inhibition plus Tumor Treating Fields suppress glioma cell proliferation in a cilium-independent manner

Tumor Treating Fields (TTFields) extend the survival of glioblastoma (GBM) patients by interfering with a broad range of tumor cellular processes. Among these, TTFields disrupt primary cilia stability on GBM cells. Here we asked if concomitant treatment of TTFields with other agents that interfere with GBM ciliogenesis further suppress GBM cell proliferation in vitro. Aurora kinase A (AURKA) promotes both cilia disassembly and GBM growth. Inhibitors of AURKA, such as Alisertib, inhibit cilia disassembly and increase ciliary frequency in various cell types. However, we found that Alisertib treatment significantly reduced GBM cilia frequency in gliomaspheres across multiple patient derived cell lines, and in patient biopsies treated ex vivo. This effect appeared glioma cell-specific as it did not reduce normal neuronal or glial cilia frequencies. Alisertib-mediated depletion of glioma cilia appears specific to AURKA and not AURKB inhibition, and attributable in part to autophagy pathway activation. Treatment of two different GBM patient-derived cell lines with TTFields and Alisertib resulted in a significant reduction in cell proliferation compared to either treatment alone. However, this effect was not cilia-dependent as the combined treatment reduced proliferation in cilia-depleted cell lines lacking, ARL13B, or U87MG cells which are naturally devoid of ARL13B+ cilia. Thus, Alisertib-mediated effects on glioma cilia may be a useful biomarker of drug efficacy within tumor tissue. Considering Alisertib can cross the blood brain barrier and inhibit intracranial growth, our data warrant future studies to explore whether concomitant Alisertib and TTFields exposure prolongs survival of brain tumor-bearing animals in vivo.

PCM1 conveys centrosome asymmetry to polarized endosome dynamics in regulating daughter cell fate

Vertebrate radial glia progenitors (RGPs), the principal neural stem cells, balance self-renewal and differentiation through asymmetric cell division (ACD), during which unequal inheritance of centrosomes is observed. Mechanistically, how centrosome asymmetry leads to distinct daughter cell fate remains largely unknown. Here we find that the centrosome protein Pericentriolar Material 1 (Pcm1), asymmetrically distributed at the centrosomes, regulates polarized endosome dynamics and RGP fate. In vivo time-lapse imaging and nanoscale-resolution expansion microscopy of zebrafish embryonic RGPs detect Pcm1 on Notch ligand-containing endosomes, in a complex with the polarity regulator Par-3 and dynein motor. Loss of pcm1 disrupts endosome dynamics, with clonal analysis uncovering increased neuronal production at the expense of progenitors. Pcm1 facilitates an exchange of Rab5b (early) for Rab11a (recycling) endosome markers and promotes the formation of Par-3 and dynein macromolecular complexes on recycling endosomes. Finally, in human-induced pluripotent stem cell-derived brain organoids, PCM1 shows asymmetry and co-localization with PARD3 and RAB11A in mitotic neural progenitors. Our data reveal a new mechanism by which centrosome asymmetry is conveyed by Pcm1 to polarize endosome dynamics and Notch signaling in regulating ACD and progenitor fate.

Tumor-treating fields in cancer therapy: advances of cellular and molecular mechanisms

Tumor-Treating Fields (TTFields) use intermediate-frequency and low-intensity electric fields to inhibit tumor cells. However, their mechanisms are still not well understood. This article reviews their key antitumor mechanisms at the cellular and molecular levels, including inhibition of proliferation, induction of death, disturbance of migration, and activation of the immune system. The multifaceted biological effects in combination with other cancer treatments are also summarized. The deep insight into their mechanism will help develop more potential antitumor treatments.

Navigating centriolar satellites: the role of PCM1 in cellular and organismal processes

Centriolar satellites are ubiquitous membrane-less organelles that play critical roles in numerous cellular and organismal processes. They were initially discovered through electron microscopy as cytoplasmic granules surrounding centrosomes in vertebrate cells. These structures remained enigmatic until the identification of pericentriolar material 1 protein (PCM1) as their molecular marker, which has enabled their in-depth characterization. Recently, centriolar satellites have come into the spotlight due to their links to developmental and neurodegenerative disorders. This review presents a comprehensive summary of the major advances in centriolar satellite biology, with a focus on studies that investigated their biology associated with the essential scaffolding protein PCM1. We begin by exploring the molecular, cellular, and biochemical properties of centriolar satellites, laying the groundwork for a deeper understanding of their functions and mechanisms at both cellular and organismal levels. We then examine the implications of their dysregulation in various diseases, particularly highlighting their emerging roles in neurodegenerative and developmental disorders, as revealed by organismal models of PCM1. We conclude by discussing the current state of knowledge and posing questions about the adaptable nature of these organelles, thereby setting the stage for future research.

Glioblastoma may evade immune surveillance through primary cilia-dependent signaling in an IL-6 dependent manner

Glioblastoma is the most common, malignant primary brain tumor in adults and remains universally fatal. While immunotherapy has vastly improved the treatment of several solid cancers, efficacy in glioblastoma is limited. These challenges are due in part to the propensity of glioblastoma to recruit tumor-suppressive immune cells, which act in conjunction with tumor cells to create a pro-tumor immune microenvironment through secretion of several soluble factors. Glioblastoma-derived EVs induce myeloid-derived suppressor cells (MDSCs) and non-classical monocytes (NCMs) from myeloid precursors leading to systemic and local immunosuppression. This process is mediated by IL-6 which contributes to the recruitment of tumor-associated macrophages of the M2 immunosuppressive subtype, which in turn, upregulates anti-inflammatory cytokines including IL-10 and TGF-β. Primary cilia are highly conserved organelles involved in signal transduction and play critical roles in glioblastoma proliferation, invasion, angiogenesis, and chemoradiation resistance. In this perspectives article, we provide preliminary evidence that primary cilia regulate intracellular release of IL-6. This ties primary cilia mechanistically to tumor-mediated immunosuppression in glioblastomas and potentially, in additional neoplasms which have a shared mechanism for cancer-mediated immunosuppression. We propose potentially testable hypotheses of the cellular mechanisms behind this finding.

Establishment and Comprehensive Molecular Characterization of an Immortalized Glioblastoma Cell Line from a Brazilian Patient

Glioblastoma (GBM) is the most common and aggressive primary brain tumor in adults, with few effective treatment strategies. The research on the development of new treatments is often constrained by the limitations of preclinical models, which fail to accurately replicate the disease's essential characteristics. Herein, we describe the obtention, molecular, and functional characterization of the GBM33 cell line. This cell line belongs to the GBM class according to the World Health Organization 2021 Classification of Central Nervous System Tumors, identified by methylation profiling. GBM33 expresses the astrocytic marker GFAP, as well as markers of neuronal origin commonly expressed in GBM cells, such as βIII-tubulin and neurofilament. Functional assays demonstrated an increased growth rate when compared to the U87 commercial cell line and a similar sensitivity to temozolamide. GBM33 cells retained response to serum starvation, with reduced growth and diminished activation of the Akt signaling pathway. Unlike LN-18 and LN-229 commercial cell lines, GBM33 is able to produce primary cilia upon serum starvation. In summary, the successful establishment and comprehensive characterization of this GBM cell line provide researchers with invaluable tools for studying GBM biology, identifying novel therapeutic targets, and evaluating the efficacy of potential treatments.

NKD1 targeting PCM1 regulates the therapeutic effects of homoharringtonine on colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is the most common primary malignancy. Recently, antineoplastic attributes of homoharringtonine (HHT) have attracted lots of attention. This study investigated the molecular target and underlying mechanism of HHT in the CRC process by using a cellular and animal models.

METHODS

This study first detected the effects of HHT on the proliferation, cell cycle and apoptosis ability of CRC cells using CCK-8, Edu staining, flow cytometry and Western blotting assay. In vitro recovery experiment and in vivo tumorigenesis experiment were used to detect the targeted interaction between HHT and NKD1. After that, the downstream target and mechanism of action of HHT targeting NKD1 was determined using quantitative proteomics combined with co-immunoprecipitation/immunofluorescence assay.

RESULTS

HHT suppressed CRC cells proliferation by inducing cell cycle arrest and apoptosis in vitro and vivo. HHT inhibited NKD1 expression in a concentration and time dependent manner. NKD1 was overexpressed in CRC and its depletion enhanced the therapeutic sensitivity of HHT on CRC, which indicating that NKD1 plays an important role in the development of CRC as the drug delivery target of HHT. Furthermore, proteomic analysis revealed that PCM1 participated the process of NKD1-regulated cell proliferation and cell cycle. NKD1 interacted with PCM1 and promoted PCM1 degradation through the ubiquitin-proteasome pathway. The overexpression of PCM1 effectively reversed the inhibition of siNKD1 on cell cycle.

CONCLUSIONS

The present findings revealed that HHT blocked NKD1 expression to participate in inhibiting cell proliferation and inducing cell apoptosis, ultimately leading to obstruction of CRC development through NKD1/PCM1 dependent mechanism. Our research provide evidence for clinical application of NKD1-targeted therapy in improving HHT sensitivity for CRC treatment.

Cilia at the Crossroads of Tumor Treating Fields and Chemotherapy

Glioblastoma (GBM), the most common and lethal primary brain tumor in adults, requires multi-treatment intervention which unfortunately barely shifts the needle in overall survival. The treatment options after diagnosis and surgical resection (if possible) include irradiation, temozolomide (TMZ) chemotherapy, and now tumor treating fields (TTFields). TTFields are electric fields delivered locoregionally to the head/tumor via a wearable medical device (Optune®). Overall, the concomitant treatment of TTFields and TMZ target tumor cells but spare normal cell types in the brain. Here, we examine whether primary cilia, microtubule-based "antennas" found on both normal brain cells and GBM cells, play specific roles in sensitizing tumor cells to treatment. We discuss evidence supporting GBM cilia being exploited by tumor cells to promote their growth and treatment resistance. We review how primary cilia on normal brain and GBM cells are affected by GBM treatments as monotherapy or concomitant modalities. We also focus on latest findings indicating a differential regulation of GBM ciliogenesis by TTFields and TMZ. Future studies await arrival of intracranial TTFields models to determine if GBM cilia carry a prognostic capacity.

Patterns of Ciliation and Ciliary Signaling in Cancer

Among the factors that have been strongly implicated in regulating cancerous transformation, the primary monocilium (cilium) has gained increasing attention. The cilium is a small organelle extending from the plasma membrane, which provides a localized hub for concentration of transmembrane receptors. These receptors transmit signals from soluble factors (including Sonic hedgehog (SHH), platelet-derived growth factor (PDGF-AA), WNT, TGFβ, NOTCH, and others) that regulate cell growth, as well as mechanosensory cues provided by flow or extracellular matrix. Ciliation is regulated by cell cycle, with most cells that are in G0 (quiescent) or early G1 ciliation and cilia typically absent in G2/M cells. Notably, while most cells organized in solid tissues are ciliated, cancerous transformation induces significant changes in ciliation. Most cancer cells lose cilia; medulloblastomas and basal cell carcinomas, dependent on an active SHH pathway, rely on ciliary maintenance. Changes in cancer cell ciliation are driven by core oncogenic pathways (EGFR, KRAS, AURKA, PI3K), and importantly ciliation status regulates functionality of those pathways. Ciliation is both influenced by targeted cancer therapies and linked to therapeutic resistance; recent studies suggest ciliation may also influence cancer cell metabolism and stem cell identity. We review recent studies defining the relationship between cilia and cancer.

Crosstalk between cilia and autophagy: implication for human diseases

Macroautophagy/autophagy is a self-degradative process necessary for cells to maintain their energy balance during development and in response to nutrient deprivation. Autophagic processes are tightly regulated and have been found to be dysfunctional in several pathologies. Increasing experimental evidence points to the existence of an interplay between autophagy and cilia. Cilia are microtubule-based organelles protruding from the cell surface of mammalian cells that perform a variety of motile and sensory functions and, when dysfunctional, result in disorders known as ciliopathies. Indeed, selective autophagic degradation of ciliary proteins has been shown to control ciliogenesis and, conversely, cilia have been reported to control autophagy. Moreover, a growing number of players such as lysosomal and mitochondrial proteins are emerging as actors of the cilia-autophagy interplay. However, some of the published data on the cilia-autophagy axis are contradictory and indicate that we are just starting to understand the underlying molecular mechanisms. In this review, the current knowledge about this axis and challenges are discussed, as well as the implication for ciliopathies and autophagy-associated disorders.

Shedding of ciliary vesicles at a glance

Cilia sense and transduce sensory stimuli, homeostatic cues and developmental signals by orchestrating signaling reactions. Extracellular vesicles (EVs) that bud from the ciliary membrane have well-studied roles in the disposal of excess ciliary material, most dramatically exemplified by the shedding of micrometer-sized blocks by photoreceptors. Shedding of EVs by cilia also affords cells with a powerful means to shorten cilia. Finally, cilium-derived EVs may enable cell-cell communication in a variety of organisms, ranging from single-cell parasites and algae to nematodes and vertebrates. Mechanistic understanding of EV shedding by cilia is an active area of study, and future progress may open the door to testing the function of ciliary EV shedding in physiological contexts. In this Cell Science at a Glance and the accompanying poster, we discuss the molecular mechanisms that drive the shedding of ciliary material into the extracellular space, the consequences of shedding for the donor cell and the possible roles that ciliary EVs may have in cell non-autonomous contexts.

Centromere protein J is overexpressed in human glioblastoma and promotes cell proliferation and migration

Glioblastoma is the most common and malignant type of primary brain tumor. Previous studies have shown that alterations in centrosome amplification and its components are frequently found in treatment-resistant tumors and may be associated with tumor progression. A centrosome protein essential for centrosome biogenesis is the centromere protein J (CENPJ), known to control the proliferation of neural progenitors and hepatocarcinoma cells, and also neuronal migration. However, it remains unknown the role of CENPJ in glioblastoma. Here we show that CENPJ is overexpressed in human glioblastoma cell lines in comparison to human astrocytes. Using bioinformatics analysis, we find that high Cenpj expression is associated with poor prognosis in glioma patients. Examining Cenpj loss of function in glioblastoma by siRNA transfection, we find impairments in cell proliferation and migration. Using a Cenpj mutant version with the deleted PN2-3 or TCP domain, we found that a conserved PN2-3 region is required for glioblastoma migration. Moreover, Cenpj downregulation modulates glioblastoma morphology resulting in microtubules stabilization and actin filaments depolymerization. Altogether, our findings indicate that CENPJ controls relevant aspects of glioblastoma progression and might be a target for therapeutic intervention and a biomarker for glioma malignancy.

Aggresome assembly at the centrosome is driven by CP110–CEP97–CEP290 and centriolar satellites

Protein degradation is critical to maintaining cellular homeostasis, and perturbation of the ubiquitin proteasome system leads to the accumulation of protein aggregates. These aggregates are either directed towards autophagy for destruction or sequestered into an inclusion, termed the aggresome, at the centrosome. Utilizing high-resolution quantitative analysis, here, we define aggresome assembly at the centrosome in human cells. Centriolar satellites are proteinaceous granules implicated in the trafficking of proteins to the centrosome. During aggresome assembly, satellites were required for the growth of the aggresomal structure from an initial ring of phosphorylated HSP27 deposited around the centrioles. The seeding of this phosphorylated HSP27 ring depended on the centrosomal proteins CP110, CEP97 and CEP290. Owing to limiting amounts of CP110, senescent cells, which are characterized by the accumulation of protein aggregates, were defective in aggresome formation. Furthermore, satellites and CP110–CEP97–CEP290 were required for the aggregation of mutant huntingtin. Together, these data reveal roles for CP110–CEP97–CEP290 and satellites in the control of cellular proteostasis and the aggregation of disease-relevant proteins.

Prosser et al. report that centriolar satellite and centrosomal proteins seed aggresomes, perinuclear inclusions of misfolded proteins, and may play a role in aggresome formation during senescence and huntingtin aggregation.

Tumor Treating Fields Suppression of Ciliogenesis Enhances Temozolomide Toxicity

Tumor Treating Fields (TTFields) are low-intensity, alternating intermediate-frequency (200 kHz) electrical fields that extend survival of glioblastoma patients receiving maintenance temozolomide (TMZ) chemotherapy. How TTFields exert efficacy on cancer over normal cells or interact with TMZ is unclear. Primary cilia are microtubule-based organelles triggered by extracellular ligands, mechanical and electrical field stimulation and are capable of promoting cancer growth and TMZ chemoresistance. We found in both low- and high-grade patient glioma cell lines that TTFields ablated cilia within 24 h. Halting TTFields treatment led to recovered frequencies of elongated cilia. Cilia on normal primary astrocytes, neurons, and multiciliated/ependymal cells were less affected by TTFields. The TTFields-mediated loss of glioma cilia was partially rescued by chloroquine pretreatment, suggesting the effect is in part due to autophagy activation. We also observed death of ciliated cells during TTFields by live imaging. Notably, TMZ and TTFields have opposing effects on glioma ciliogenesis. TMZ-induced stimulation of ciliogenesis in both adherent cells and gliomaspheres was blocked by TTFields. Surprisingly, the inhibitory effects of TTFields and TMZ on tumor cell recurrence are linked to the relative timing of TMZ exposure to TTFields and ARL13B⁺ cilia. Finally, TTFields disrupted cilia in patient tumors treated ex vivo. Our findings suggest that the efficacy of TTFields may depend on the degree of tumor ciliogenesis and relative timing of TMZ treatment.

Primary Cilia-Related Pathways Moderate the Development and Therapy Resistance of Glioblastoma

As microtubule-based structures, primary cilia are typically present on the cells during the G0 or G1-S/G2 phase of the cell cycle and are closely related to the development of the central nervous system. The presence or absence of this special organelle may regulate the central nervous system tumorigenesis (e.g., glioblastoma) and several degenerative diseases. Additionally, the development of primary cilia can be regulated by several pathways. Conversely, primary cilia are able to regulate a few signaling transduction pathways. Therefore, development of the central nervous system tumors in conjunction with abnormal cilia can be regulated by up- or downregulation of the pathways related to cilia and ciliogenesis. Here, we review some pathways related to ciliogenesis and tumorigenesis, aiming to provide a potential target for developing new therapies at genetic and molecular levels.

Applications of CRISPR-Cas9 Technology to Genome Editing in Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is an aggressive malignancy of the brain and spinal cord with a poor life expectancy. The low survivability of GBM patients can be attributed, in part, to its heterogeneity and the presence of multiple genetic alterations causing rapid tumor growth and resistance to conventional therapy. The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-CRISPR associated (Cas) nuclease 9 (CRISPR-Cas9) system is a cost-effective and reliable gene editing technology, which is widely used in cancer research. It leads to novel discoveries of various oncogenes that regulate autophagy, angiogenesis, and invasion and play important role in pathogenesis of various malignancies, including GBM. In this review article, we first describe the principle and methods of delivery of CRISPR-Cas9 genome editing. Second, we summarize the current knowledge and major applications of CRISPR-Cas9 to identifying and modifying the genetic regulators of the hallmark of GBM. Lastly, we elucidate the major limitations of current CRISPR-Cas9 technology in the GBM field and the future perspectives. CRISPR-Cas9 genome editing aids in identifying novel coding and non-coding transcriptional regulators of the hallmarks of GBM particularly in vitro, while work using in vivo systems requires further investigation.

2-IPMA Ameliorates PM2.5-Induced Inflammation by Promoting Primary Ciliogenesis in RPE Cells

Primary cilia mediate the interactions between cells and external stresses. Thus, dysregulation of primary cilia is implicated in various ciliopathies, e.g., degeneration of the retina caused by dysregulation of the photoreceptor primary cilium. Particulate matter (PM) can cause epithelium injury and endothelial dysfunction by increasing oxidative stress and inflammatory responses. Previously, we showed that PM disrupts the formation of primary cilia in retinal pigment epithelium (RPE) cells. In the present study, we identified 2-isopropylmalic acid (2-IPMA) as a novel inducer of primary ciliogenesis from a metabolite library screening. Both ciliated cells and primary cilium length were increased in 2-IPMA-treated RPE cells. Notably, 2-IPMA strongly promoted primary ciliogenesis and restored PM2.5-induced dysgenesis of primary cilia in RPE cells. Both excessive reactive oxygen species (ROS) generation and activation of a stress kinase, JNK, by PM2.5 were reduced by 2-IPMA. Moreover, 2-IPMA inhibited proinflammatory cytokine production, i.e., IL-6 and TNF-α, induced by PM2.5 in RPE cells. Taken together, our data suggest that 2-IPMA ameliorates PM2.5-induced inflammation by promoting primary ciliogenesis in RPE cells.

Oleuropein Activates Neonatal Neocortical Proteasomes, but Proteasome Gene Targeting by AAV9 Is Variable in a Clinically Relevant Piglet Model of Brain Hypoxia-Ischemia and Hypothermia

Cerebral hypoxia-ischemia (HI) compromises the proteasome in a clinically relevant neonatal piglet model. Protecting and activating proteasomes could be an adjunct therapy to hypothermia. We investigated whether chymotrypsin-like proteasome activity differs regionally and developmentally in the neonatal brain. We also tested whether neonatal brain proteasomes can be modulated by oleuropein, an experimental pleiotropic neuroprotective drug, or by targeting a proteasome subunit gene using recombinant adeno-associated virus-9 (AAV). During post-HI hypothermia, we treated piglets with oleuropein, used AAV-short hairpin RNA (shRNA) to knock down proteasome activator 28γ (PA28γ), or enforced PA28γ using AAV-PA28γ with green fluorescent protein (GFP). Neonatal neocortex and subcortical white matter had greater proteasome activity than did liver and kidney. Neonatal white matter had higher proteasome activity than did juvenile white matter. Lower arterial pH 1 h after HI correlated with greater subsequent cortical proteasome activity. With increasing brain homogenate protein input into the assay, the initial proteasome activity increased only among shams, whereas HI increased total kinetic proteasome activity. OLE increased the initial neocortical proteasome activity after hypothermia. AAV drove GFP expression, and white matter PA28γ levels correlated with proteasome activity and subunit levels. However, AAV proteasome modulation varied. Thus, neonatal neocortical proteasomes can be pharmacologically activated. HI slows the initial proteasome performance, but then augments ongoing catalytic activity. AAV-mediated genetic manipulation in the piglet brain holds promise, though proteasome gene targeting requires further development.

Therapeutic Perspective of Temozolomide Resistance in Glioblastoma Treatment

Glioblastoma (GB) is the most lethal form of primary brain neoplasm. TMZ is the first-line standard treatment, but the strong resistance constrains the efficacy in clinical use. GB contains glioma stem cells (GSCs), which contribute to TMZ resistance, promote cell survival evolvement, and repopulate the tumor mass. This review summarizes the TMZ-resistance mechanisms and discusses several potential therapies from the conservative opinion of GSC-targeted therapy orientation to the current view of TMZ resistance-aimed efficacy, which will provide an understanding of the role of heterogeneity in drug resistance and improve therapeutic efficacy in general.

The ciliary impact of nonciliary gene mutations

Mutations in genes encoding centriolar or ciliary proteins cause diseases collectively known as 'ciliopathies'. Interestingly, the Human Phenotype Ontology database lists numerous disorders that display clinical features reminiscent of ciliopathies but do not involve defects in the centriole-cilium proteome. Instead, defects in different cellular compartments may impair cilia indirectly and cause additional, nonciliopathy phenotypes. This phenotypic heterogeneity, perhaps combined with the field's centriole-cilium-centric view, may have hindered the recognition of ciliary contributions. Identifying these diseases and dissecting how the underlying gene mutations impair cilia not only will add to our understanding of cilium assembly and function but also may open up new therapeutic avenues.

HDAC6 Signaling at Primary Cilia Promotes Proliferation and Restricts Differentiation of Glioma Cells

Simple Summary

Glioblastoma is the most common and lethal brain tumor in adults because it becomes resistant to virtually every treatment. Histone deacetylase 6 (HDAC6), which is located primarily in the cytoplasm, has a unique role in promoting the disassembly of cells’ primary cilium, a non-motile “antenna” that must be broken down before cells can progress through the cell cycle. The role of HDAC6 and its function in gliomas have not been investigated with respect to tumor cell cilia. We have found that inhibitors of HDAC6 cause rapid and specific changes inside glioma cilia, reducing tumor cell proliferative capacity and promoting cell differentiation. Importantly, the HDAC6 inhibitors did not affect the proliferation or differentiation of glioma cells that we genetically modified unable to grow cilia. Our findings reveal a conserved and critical role for HDAC6 in glioma growth that is dependent on cilia.

Abstract

Histone deacetylase 6 (HDAC6) is an emerging therapeutic target that is overexpressed in glioblastoma when compared to other HDACs. HDAC6 catalyzes the deacetylation of alpha-tubulin and mediates the disassembly of primary cilia, a process required for cell cycle progression. HDAC6 inhibition disrupts glioma proliferation, but whether this effect is dependent on tumor cell primary cilia is unknown. We found that HDAC6 inhibitors ACY-1215 (1215) and ACY-738 (738) inhibited the proliferation of multiple patient-derived and mouse glioma cells. While both inhibitors triggered rapid increases in acetylated alpha-tubulin (aaTub) in the cytosol and led to increased frequencies of primary cilia, they unexpectedly reduced the levels of aaTub in the cilia. To test whether the antiproliferative effects of HDAC6 inhibitors are dependent on tumor cell cilia, we generated patient-derived glioma lines devoid of cilia through depletion of ciliogenesis genes ARL13B or KIF3A. At low concentrations, 1215 or 738 did not decrease the proliferation of cilia-depleted cells. Moreover, the differentiation of glioma cells that was induced by HDAC6 inhibition did not occur after the inhibition of cilia formation. These data suggest HDAC6 signaling at primary cilia promotes the proliferation of glioma cells by restricting their ability to differentiate. Surprisingly, overexpressing HDAC6 did not reduce cilia length or the frequency of ciliated glioma cells, suggesting other factors are required to control HDAC6-mediated cilia disassembly in glioma cells. Collectively, our findings suggest that HDAC6 promotes the proliferation of glioma cells through primary cilia.

CRISPR/Cas9 for overcoming drug resistance in solid tumors

OBJECTIVES

In this review, we focus on the application of clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated nuclease 9 (Cas9), as a powerful genome editing system, in the identification of resistance mechanisms and in overcoming drug resistance in the most frequent solid tumors.

DATA ACQUISITION

Data were collected by conducting systematic searching of scientific English literature using specific keywords such as "cancer", "CRISPR" and related combinations.

RESULTS

The review findings revealed the importance of CRISPR/Cas9 system in understanding drug resistance mechanisms and identification of resistance-related genes such as PBRM1, SLFN11 and ATPE1 in different cancers. We also provided an overview of genes, including RSF1, CDK5, and SGOL1, whose disruption can synergize with the currently available drugs such as paclitaxel and sorafenib.

CONCLUSION

The data suggest CRISPR/Cas9 system as a useful tool in elucidating the molecular basis of drug resistance and improving clinical outcomes. Graphical abstract The mechanisms of CRISPR/Cas9-mediated genome editing and double-strand breaks (DSBs) repair.

CRISPR/Cas9 for cancer treatment: technology, clinical applications and challenges

Clustered regularly interspaced short palindromic repeats (CRISPR) is described as RNA mediated adaptive immune system defense, which is naturally found in bacteria and archaea. CRISPR-Cas9 has shown great promise for cancer treatment in cancer immunotherapy, manipulation of cancer genome and epigenome and elimination or inactivation of carcinogenic viral infections. However, many challenges remain to be addressed to increase its efficacy, including off-target effects, editing efficiency, fitness of edited cells, immune response and delivery methods. Here, we explain CRISPR-Cas classification and its general function mechanism for gene editing. Then, we summarize these preclinical CRISPR-Cas9-based therapeutic strategies against cancer. Moreover, the challenges and improvements of CRISPR-Cas9 clinical applications will be discussed.

Proneural and mesenchymal glioma stem cells display major differences in splicing and lncRNA profiles

Therapy resistance and recurrence in high-grade gliomas are driven by their populations of glioma stem cells (GSCs). Thus, detailed molecular characterization of GSCs is needed to develop more effective therapies. We conducted a study to identify differences in the splicing profile and expression of long non-coding RNAs in proneural and mesenchymal GSC cell lines. Genes related to cell cycle, DNA repair, cilium assembly, and splicing showed the most differences between GSC subgroups. We also identified genes distinctly associated with survival among patients of mesenchymal or proneural subgroups. We determined that multiple long non-coding RNAs with increased expression in mesenchymal GSCs are associated with poor survival of glioblastoma patients. In summary, our study established critical differences between proneural and mesenchymal GSCs in splicing profiles and expression of long non-coding RNA. These splicing isoforms and lncRNA signatures may contribute to the uniqueness of GSC subgroups, thus contributing to cancer phenotypes and explaining differences in therapeutic responses.

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.

Primary cilia mediate mitochondrial stress responses to promote dopamine neuron survival in a Parkinson's disease model

A primary cilium is an antenna-like structure on the cell surface that plays a crucial role in sensory perception and signal transduction. Mitochondria, the ‘powerhouse’ of the cell, control cell survival, and death. The cellular ability to remove dysfunctional mitochondria through mitophagy is important for cell survival. We show here that mitochondrial stress, caused by respiratory complex inhibitors and excessive fission, robustly stimulates ciliogenesis in different types of cells including neuronal cells. Mitochondrial stress-induced ciliogenesis is mediated by mitochondrial reactive oxygen species generation, subsequent activation of AMP-activated protein kinase and autophagy. Conversely, abrogation of ciliogenesis compromises mitochondrial stress-induced autophagy, leading to enhanced cell death. In mice, treatment with mitochondrial toxin, MPTP elicits ciliary elongation and autophagy in the substantia nigra dopamine neurons. Blockade of cilia formation in these neurons attenuates MPTP-induced autophagy but facilitates dopamine neuronal loss and motor disability. Our findings demonstrate the important role of primary cilia in cellular pro-survival responses during mitochondrial stress.

Flow stimulates drug transport in a human kidney proximal tubule-on-a-chip independent of primary cilia

BACKGROUND

Kidney disease modeling and assessment of drug-induced kidney injury can be advanced using three-dimensional (3D) microfluidic models that recapitulate in vivo characteristics. Fluid shear stress (FSS) has been depicted as main modulator improving in vitro physiology in proximal tubule epithelial cells (PTECs). We aimed to elucidate the role of FSS and primary cilia on transport activity and morphology in PTECs.

METHODS

Human conditionally immortalized PTEC (ciPTEC-parent) was cultured in a microfluidic 3D device, the OrganoPlate, under a physiological peak FSS of 2.0 dyne/cm² or low peak FSS of 0.5 dyne/cm². Upon a 9-day exposure to FSS, albumin-FITC uptake, activity of P-glycoprotein (P-gp) and multidrug resistance-associated proteins 2/4 (MRP2/4), cytotoxicity and cell morphology were determined.

RESULTS

A primary cilium knock-out cell model, ciPTEC-KIF3α^-/-, was successfully established via CRISPR-Cas9 genome editing. Under physiological peak FSS, albumin-FITC uptake (p = .04) and P-gp efflux (p = .002) were increased as compared to low FSS. Remarkably, a higher albumin-FITC uptake (p = .03) and similar trends in activity of P-gp and MRP2/4 were observed in ciPTEC-KIF3α^-/-. FSS induced cell elongation corresponding with the direction of flow in both cell models, but had no effect on cyclosporine A-induced cytotoxicity.

CONCLUSIONS

FSS increased albumin uptake, P-gp efflux and cell elongation, but this was not attributed to a mechanosensitive mechanism related to primary cilia in PTECs, but likely to microvilli present at the apical membrane.

GENERAL SIGNIFICANCE

FSS-induced improvements in biological characteristics and activity in PTECs was not mediated through a primary cilium-related mechanism.

What went wrong with variant effect predictor performance for the PCM1 challenge

The recent years have seen a drastic increase in the amount of available genomic sequences. Alongside this explosion, hundreds of computational tools were developed to assess the impact of observed genetic variation. Critical Assessment of Genome Interpretation (CAGI) provides a platform to evaluate the performance of these tools in experimentally relevant contexts. In the CAGI-5 challenge assessing the 38 missense variants affecting the human Pericentriolar material 1 protein (PCM1), our SNAP-based submission was the top performer, although it did worse than expected from other evaluations. Here, we compare the CAGI-5 submissions, and 24 additional commonly used variant effect predictors, to analyze the reasons for this observation. We identified per residue conservation, structural, and functional PCM1 characteristics, which may be responsible. As expected, predictors had a hard time distinguishing effect variants in nonconserved positions. They were also better able to call effect variants in a structurally rich region than in a less-structured one; in the latter, they more often correctly identified benign than effect variants. Curiously, most of the protein was predicted to be functionally robust to mutation-a feature that likely makes it a harder problem for generalized variant effect predictors.

The Autophagy-Cilia Axis: An Intricate Relationship

Primary cilia are microtubule-based organelles protruding from the surface of almost all vertebrate cells. This organelle represents the cell’s antenna which acts as a communication hub to transfer extracellular signals into intracellular responses during development and in tissue homeostasis. Recently, it has been shown that loss of cilia negatively regulates autophagy, the main catabolic route of the cell, probably utilizing the autophagic machinery localized at the peri-ciliary compartment. On the other side, autophagy influences ciliogenesis in a context-dependent manner, possibly to ensure that the sensing organelle is properly formed in a feedback loop model. In this review we discuss the recent literature and propose that the autophagic machinery and the ciliary proteins are functionally strictly related to control both autophagy and ciliogenesis. Moreover, we report examples of diseases associated with autophagic defects which cause cilia abnormalities, and propose and discuss the hypothesis that, at least some of the clinical manifestations observed in human diseases associated to ciliary disfunction may be the result of a perturbed autophagy.

Spatial and proteomic profiling reveals centrosome-independent features of centriolar satellites

Centriolar satellites are small electron-dense granules that cluster in the vicinity of centrosomes. Satellites have been implicated in multiple critical cellular functions including centriole duplication, centrosome maturation, and ciliogenesis, but their precise composition and assembly properties have remained poorly explored. Here, we perform in vivo proximity-dependent biotin identification (BioID) on 22 human satellite proteins, to identify 2,113 high-confidence interactions among 660 unique polypeptides. Mining this network, we validate six additional satellite components. Analysis of the satellite interactome, combined with subdiffraction imaging, reveals the existence of multiple unique microscopically resolvable satellite populations that display distinct protein interaction profiles. We further show that loss of satellites in PCM1-depleted cells results in a dramatic change in the satellite interaction landscape. Finally, we demonstrate that satellite composition is largely unaffected by centriole depletion or disruption of microtubules, indicating that satellite assembly is centrosome-independent. Together, our work offers the first systematic spatial and proteomic profiling of human centriolar satellites and paves the way for future studies aimed at better understanding the biogenesis and function(s) of these enigmatic structures.

Primary cilium and brain aging: role in neural stem cells, neurodegenerative diseases and glioblastoma

Brain aging is characterized by a progressive loss of tissue integrity and function as a consequence of impaired homeostasis and regeneration capacities. The primary cilium is a highly conserved organelle that projects from the cell surface in a single copy in virtually all mammalian cell types including neural stem/progenitors cells and neurons. Increasing evidence in the last decade points out that primary cilium could be a relevant mediator of neural stem cell activity, neurogenesis, neuronal maturation and maintenance, and brain tumorigenesis. In this review, we summarize the current knowledge about primary cilia roles in these processes. There is currently sufficient background to propose that defective primary cilia contribute to age-related cognitive decline and brain tumor development due to their critical roles in cell cycle control and signaling transduction. This might have potential applications on therapy against age-associated brain diseases.

RNA Sequencing Analysis for the Identification of a PCM1/PDGFRB Fusion Gene Responsive to Imatinib

The platelet-derived growth factor receptor β (PDGFRB) gene translocations lead to a spectrum of chronic myeloid neoplasms, frequently associated with eosinophilia. Clinical heterogeneity is associated with a molecular one. Here, we report a novel case of a patient harboring a t(5;8)(q33;p22) translocation, resulting in the PCM1/PDGFRB fusion. Conventional cytogenetics and RNA sequencing were performed to identify the chromosomes and the genes involved in the rearrangement, respectively. This study shows that the combination of different strategies is pivotal to fine-tune the diagnosis and the clinical management of the patient. After 1 year of treatment with imatinib, the patient achieves hematological and molecular remission. We present an attractive strategy to identify novel and/or cryptic fusions, which will be relevant for clinicians dealing with the diagnosis of the patients with myelodysplastic syndrome/myeloproliferative diseases with atypical manifestations.

Roles of Primary Cilia in the Developing Brain

Essential to development, primary cilia are microtubule-based cellular organelles that protrude from the surface of cells. Acting as cellular antenna, primary cilia play central roles in transducing or regulating several signaling pathways, including Sonic hedgehog (Shh) and Wnt signaling. Defects in primary cilia contribute to a group of syndromic disorders known as “ciliopathies” and can adversely affect development of the brain and other essential organs, including the kidneys, eyes, and liver. The molecular mechanisms of how defective primary cilia contribute to neurological defects, however, remain poorly understood. In this mini review, we summarize recent advances in understanding of the interactions between primary cilia and signaling pathways essential to cellular homeostasis and brain development.

Centriolar satellites are required for efficient ciliogenesis and ciliary content regulation

Centriolar satellites are ubiquitous in vertebrate cells. They have recently emerged as key regulators of centrosome/cilium biogenesis, and their mutations are linked to ciliopathies. However, their precise functions and mechanisms of action remain poorly understood. Here, we generated a kidney epithelial cell line (IMCD3) lacking satellites by CRISPR/Cas9-mediated PCM1 deletion and investigated the cellular and molecular consequences of satellite loss. Cells lacking satellites still formed full-length cilia but at significantly lower numbers, with changes in the centrosomal and cellular levels of key ciliogenesis factors. Using these cells, we identified new ciliary functions of satellites such as regulation of ciliary content, Hedgehog signaling, and epithelial cell organization in three-dimensional cultures. However, other functions of satellites, namely proliferation, cell cycle progression, and centriole duplication, were unaffected in these cells. Quantitative transcriptomic and proteomic profiling revealed that loss of satellites affects transcription scarcely, but significantly alters the proteome. Importantly, the centrosome proteome mostly remains unaltered in the cells lacking satellites. Together, our findings identify centriolar satellites as regulators of efficient cilium assembly and function and provide insight into disease mechanisms of ciliopathies.

Polo-like kinase 4 maintains centriolar satellite integrity by phosphorylation of centrosomal protein 131 (CEP131)

The centrosome, consisting of two centrioles surrounded by a dense network of proteins, is the microtubule-organizing center of animal cells. Polo-like kinase 4 (PLK4) is a Ser/Thr protein kinase and the master regulator of centriole duplication, but it may play additional roles in centrosome function. To identify additional proteins regulated by PLK4, we generated an RPE-1 human cell line with a genetically engineered "analog-sensitive" PLK4AS, which genetically encodes chemical sensitivity to competitive inhibition via a bulky ATP analog. We used this transgenic line in an unbiased multiplex phosphoproteomic screen. Several hits were identified and validated as direct PLK4 substrates by in vitro kinase assays. Among them, we confirmed Ser-78 in centrosomal protein 131 (CEP131, also known as AZI1) as a direct substrate of PLK4. Using immunofluorescence microscopy, we observed that although PLK4-mediated phosphorylation of Ser-78 is dispensable for CEP131 localization, ciliogenesis, and centriole duplication, it is essential for maintaining the integrity of centriolar satellites. We also found that PLK4 inhibition or use of a nonphosphorylatable CEP131 variant results in dispersed centriolar satellites. Moreover, replacement of endogenous WT CEP131 with an S78D phosphomimetic variant promoted aggregation of centriolar satellites. We conclude that PLK4 phosphorylates CEP131 at Ser-78 to maintain centriolar satellite integrity.

Primary Cilium in Cancer Hallmarks

The primary cilium is a solitary, nonmotile and transitory appendage that is present in virtually all mammalian cells. Our knowledge of its ultrastructure and function is the result of more than fifty years of research that has dramatically changed our perspectives on the primary cilium. The mutual regulation between ciliogenesis and the cell cycle is now well-recognized, as well as the function of the primary cilium as a cellular "antenna" for perceiving external stimuli, such as light, odorants, and fluids. By displaying receptors and signaling molecules, the primary cilium is also a key coordinator of signaling pathways that converts extracellular cues into cellular responses. Given its critical tasks, any defects in primary cilium formation or function lead to a wide spectrum of diseases collectively called "ciliopathies". An emerging role of primary cilium is in the regulation of cancer development. In this review, we seek to describe the current knowledge about the influence of the primary cilium in cancer progression, with a focus on some of the events that cancers need to face to sustain survival and growth in hypoxic microenvironment: the cancer hallmarks.

Emerging Roles of Primary Cilia in Glioma

Primary cilia are microtubule-based organelles that are typically present on cells during the G0 or G1-S/G2 phases of the cell cycle. Recent studies of glioblastoma (GBM) biopsies, a brain tumor that is notorious for its aggressive growth and resistance to treatment, show that many cells in the tumor lack cilia. At this point, it remains unclear whether primary cilia promote or suppress glioma tumorigenesis. In this review, we will discuss the different roles that have been proposed for primary cilia in glioma and how cilia may contribute to the resistance of these tumors to current therapies.

Glioma cell proliferation is enhanced in the presence of tumor-derived cilia vesicles

Background

The mechanisms by which primary cilia affect glioma pathogenesis are unclear. Depending on the glioma cell line, primary cilia can promote or inhibit tumor development. Here, we used piggyBac-mediated transgenesis to generate patient-derived glioblastoma (GBM) cell lines that stably express Arl13b:GFP in their cilia. This allowed us to visualize and analyze the behavior of cilia and ciliated cells during live GBM cell proliferation.

Results

Time-lapse imaging of Arl13b:GFP⁺ cilia revealed their dynamic behaviors, including distal tip excision into the extracellular milieu. Recent studies of non-cancerous cells indicate that this process occurs during the G0 phase, prior to cilia resorption and cell cycle re-entry, and requires ciliary recruitment of F-actin and actin regulators. Similarly, we observed ciliary buds associated with Ki67^- cells as well as scattered F-actin⁺ cilia, suggesting that quiescent GBM cells may also utilize an actin network-based mechanism for ciliary tip excision. Notably, we found that the proliferation of ciliated GBM cells was promoted by exposing them to conditioned media obtained from ciliated cell cultures when compared to conditioned media collected from cilia-defective cell cultures (depleted in either KIF3A or IFT88 using CRISPR/Cas9). These results suggest that GBM cilia may release mitogenic vesicles carrying factors that promote tumor cell proliferation. Although Arl13b is implicated in tumor growth, our data suggest that Arl13b released from GBM cilia does not mediate tumor cell proliferation.

Conclusion

Collectively, our results indicate that ciliary vesicles may represent a novel mode of intercellular communication within tumors that contributes to GBM pathogenesis. The mitogenic capacity of GBM ciliary vesicles and the molecular mediators of this phenomenon requires further investigation.

Primary cilium and glioblastoma

Glioblastoma (GBM) represents the most common, malignant and lethal primary brain tumour in adults. The primary cilium is a highly conserved and dynamic organelle that protrudes from the apical surface of virtually every type of mammalian cell. There is increasing evidence that abnormal cilia are involved in cancer progression, since primary cilia regulate cell cycle and signalling transduction. In this review, we summarize the role of primary cilium specifically with regard to GBM, where there is evidence postulating it as a critical mediator of GBM tumorigenesis and progression. This opens the way to the application of cilia-targeted therapies (‘ciliotherapy’) as a new approach in the fight against this devastating tumour.