Mixed signals from the cell's antennae: primary cilia in cancer

A pan-cancer interrogation of intronic polyadenylation and its association with cancer characteristics

3'UTR-APAs have been extensively studied, but intronic polyadenylations (IPAs) remain largely unexplored. We characterized the profiles of 22 260 IPAs in 9679 patient samples across 32 cancer types from the Cancer Genome Atlas cohort. By comparing tumor and paired normal tissues, we identified 180 ~ 4645 dysregulated IPAs in 132 ~ 2249 genes in each of 690 patient tumors from 22 cancer types that showed consistent patterns within individual cancer types. We selected 2741 genes that showed consistently patterns across cancer types, including 1834 pan-cancer tumor-enriched and 907 tumor-depleted IPA genes; the former were amply represented in the functional pathways such as deoxyribonucleic acid damage repair. Expression of IPA isoforms was associated with tumor mutation burden and patient characteristics (e.g. sex, race, cancer stages, and subtypes) in cancer-specific and feature-specific manners, and could be a more accurate prognostic marker than gene expression (summary of all isoforms). In summary, our study reveals the roles and the clinical relevance of tumor-associated IPAs.

The implication of ciliary signaling pathways for epithelial-mesenchymal transition

Epithelial-to-mesenchymal transition (EMT), which plays an essential role in development, tissue repair and fibrosis, and cancer progression, is a reversible cellular program that converts epithelial cells to mesenchymal cell states characterized by motility-invasive properties. The mostly signaling pathways that initiated and controlled the EMT program are regulated by a solitary, non-motile organelle named primary cilium. Acting as a signaling nexus, primary cilium dynamically concentrates signaling molecules to respond to extracellular cues. Recent research has provided direct evidence of connection between EMT and primary ciliogenesis in multiple contexts, but the mechanistic understanding of this relationship is complicated and still undergoing. In this review, we describe the current knowledge about the ciliary signaling pathways involved in EMT and list the direct evidence that shows the link between them, trying to figure out the intricate relationship between EMT and primary ciliogenesis, which may aid the future development of primary cilium as a novel therapeutic approach targeted to EMT.

Mebendazole preferentially inhibits cilia formation and exerts anticancer activity by synergistically augmenting DNA damage

The cilium is a microtubule-based organelle that plays a pivotal role in embryonic development and maintenance of physiological functions in the human body. In addition to their function as sensors that transduce diverse extracellular signals, including growth factors, fluid flow, and physical forces, cilia are intricately involved in cell cycle regulation and preservation of DNA integrity, as their formation and resorption dynamics are tightly linked to cell cycle progression. Recently, several studies have linked defects in specific ciliary proteins to the DNA damage response. However, it remains unclear whether and how primary cilia contribute to cancer development. Mebendazole (MBZ) is an anthelmintic drug with anticancer properties in some cancer cells. MBZ is continuously being tested for clinical studies, but the precise mechanism of its anticancer activities remains unknown. Here, using Xenopus laevis embryos as a model system, we discovered that MBZ significantly hinders cilia formation and induces DNA damage. Remarkably, primary cilium-bearing cancer cells exhibited heightened vulnerability to combined treatment with MBZ and conventional anticancer drugs. Our findings shed light on the specific influence of MBZ on cilia, rather than cytosolic microtubules, in triggering DNA damage, elucidating a previously unidentified mechanism underlying potential MBZ-mediated cancer therapy.

Primary Cilia as a Tumor Marker in Pituitary Neuroendocrine Tumors

Pituitary neuroendocrine tumors (PitNETs) account for approximately 15% of all intracranial neoplasms. Although they usually appear to be benign, some tumors display worse behavior, displaying rapid growth, invasion, refractoriness to treatment, and recurrence. Increasing evidence supports the role of primary cilia (PC) in regulating cancer development. Here, we showed that PC are significantly increased in PitNETs and are associated with increased tumor invasion and recurrence. Serial electron micrographs of PITNETs demonstrated different ciliation phenotypes (dot-like versus normal-like cilia) that represented PC at different stages of ciliogenesis. Molecular findings demonstrated that 123 ciliary-associated genes (eg, doublecortin domain containing protein 2, Sintaxin-3, and centriolar coiled-coil protein 110) were dysregulated in PitNETs, representing the upregulation of markers at different stages of intracellular ciliogenesis. Our results demonstrate, for the first time, that ciliogenesis is increased in PitNETs, suggesting that this process might be used as a potential target for therapy in the future.

CRP inhibits the osteoblastic differentiation of OPCs via the up-regulation of primary cilia and repression of the Hedgehog signaling pathway

Inflammation disrupts bone metabolism and leads to bone damage. C-reactive protein (CRP) is a typical inflammation marker. Although CRP measurement has been conducted for many decades, how osteoblastic differentiation influences molecular mechanisms remains largely unknown. The present study attempted to investigate the effects of CRP on primary cultured osteoblast precursor cells (OPCs) while elucidating the underlying molecular mechanisms. OPCs were isolated from suckling Sprague-Dawleyrats. Fewer OPCs were observed after recombinant C-reactive protein treatment. In a series of experiments, CRP inhibited OPC proliferation, osteoblastic differentiation, and the OPC gene expression of the hedgehog (Hh) signaling pathway. The inhibitory effect of CRP on OPC proliferation occurred via blockade of the G1-S transition of the cell cycle. In addition, the regulation effect of proto cilium on osteoblastic differentiation was analyzed using the bioinformatics p. This revealed the primary cilia activation of recombinant CRP effect on OPCs through in vitro experiments. A specific Sonic Hedgehog signaling agonist (SAG) rescued osteoblastic differentiation inhibited by recombinant CRP. Moreover, chloral hydrate, which removes primary cilia, inhibited the Suppressor of Fused (SUFU) formation and blocked Gli2 degradation. This counteracted osteogenesis inhibition caused by CRP. Therefore, these data depict that CRP can inhibit the proliferation and osteoblastic differentiation of OPCs. The underlying mechanism could be associated with primary cilia activation and Hh pathway repression.

EMT and primary ciliogenesis: For better or worse in sickness and in health

Epithelial-mesenchymal transition (EMT) and primary ciliogenesis are two cell-biological programs that are essential for development of multicellular organisms and whose abnormal regulation results in many diseases (i.e., developmental anomalies and cancers). Emerging studies suggest an intricate interplay between these two processes. Here, we discuss physiological and pathological contexts in which their interconnections promote normal development or disease progression. We describe underlying molecular mechanisms of the interplay and EMT/ciliary signaling axes that influence EMT-related processes (i.e., stemness, motility and invasion). Understanding the molecular and cellular mechanisms of the relationship between EMT and primary ciliogenesis may provide new insights in the etiology of diseases related to EMT and cilia dysfunction.

Emerging principles of primary cilia dynamics in controlling tissue organization and function

Primary cilia project from the surface of most vertebrate cells and are key in sensing extracellular signals and locally transducing this information into a cellular response. Recent findings show that primary cilia are not merely static organelles with a distinct lipid and protein composition. Instead, the function of primary cilia relies on the dynamic composition of molecules within the cilium, the context-dependent sensing and processing of extracellular stimuli, and cycles of assembly and disassembly in a cell- and tissue-specific manner. Thereby, primary cilia dynamically integrate different cellular inputs and control cell fate and function during tissue development. Here, we review the recently emerging concept of primary cilia dynamics in tissue development, organization, remodeling, and function.

Primary cilia: a novel research approach to overcome anticancer drug resistance

Primary cilia are cellular organelles that consist of a microtubule skeleton surrounded by a membrane filled with cell signaling receptors. Many studies have shown that primary cilia are cellular antennas, which serve as signaling hubs and their assembly and disassembly are dynamically regulated throughout the cell cycle, playing an important role in regulating cellular homeostasis. Aberrant control of primary cilia dynamics causes a number of genetic disorders known as ciliopathies and is closely associated with tumorigenesis. Anticancer drug resistance is a primary cause of chemotherapy failure, although there is no apparent remedy. The recent identification of a relationship between anticancer drug resistance and primary ciliary dynamics has made primary cilia an important target subcellular organelle for overcoming anticancer drug resistance. Therefore, the research on primary ciliary dynamics may provide new strategies to overcome anticancer drug resistance, which is urgently needed. This review aims to summarize research on the relevance of primary cilia and anticancer drug resistance, as well as future possibilities for research on overcoming anticancer drug resistance utilizing primary cilia dynamics.

Primary cilia: Structure, dynamics, and roles in cancer cells and tumor microenvironment

Despite the initiation of tumor arises from tumorigenic transformation signaling in cancer cells, cancer cell survival, invasion, and metastasis also require a dynamic and reciprocal association with extracellular signaling from tumor microenvironment (TME). Primary cilia are the antenna-like structure that mediate signaling sensation and transduction in different tissues and cells. Recent studies have started to uncover that the heterogeneous ciliation in cancer cells and cells from the TME in tumor growth impels asymmetric paracellular signaling in the TME, indicating the essential functions of primary cilia in homeostasis maintenance of both cancer cells and the TME. In this review, we discussed recent advances in the structure and assembly of primary cilia, and the role of primary cilia in tumor and TME formation, as well as the therapeutic potentials that target ciliary dynamics and signaling from the cells in different tumors and the TME.

Cilia and Cancer: From Molecular Genetics to Therapeutic Strategies

Cilia are microtubule-based organelles that project from the cell surface with motility or sensory functions. Primary cilia work as antennae to sense and transduce extracellular signals. Cilia critically control proliferation by mediating cell-extrinsic signals and by regulating cell cycle entry. Recent studies have shown that primary cilia and their associated proteins also function in autophagy and genome stability, which are important players in oncogenesis. Abnormal functions of primary cilia may contribute to oncogenesis. Indeed, defective cilia can either promote or suppress cancers, depending on the cancer-initiating mutation, and the presence or absence of primary cilia is associated with specific cancer types. Together, these findings suggest that primary cilia play important, but distinct roles in different cancer types, opening up a completely new avenue of research to understand the biology and treatment of cancers. In this review, we discuss the roles of primary cilia in promoting or inhibiting oncogenesis based on the known or predicted functions of cilia and cilia-associated proteins in several key processes and related clinical implications.

STIL/AURKA axis promotes cell proliferation by influencing primary cilia formation in bladder cancer

BACKGROUND

The primary cilia (PC) is a microtubule-based and nonmotile organelle which protrudes from the surface of almost all mammalian cells. At present, PC has been found to be a deficiency or loss in multiple cancers. Restoring PC could be a novel targeting therapy strategy. Our research showed that PC was reduced in human bladder cancer (BLCA) cells, and PC deficiency promotes cell proliferation. However, the concrete mechanisms remain unknown. SCL/TAL1 interrupting locus (STIL), a PC-related protein, was screened in our previous study and could influence the cell cycle by regulating PC in tumor cells. In this study, we aimed to elucidate the function of STIL for PC to explore the underlying mechanism of PC in BLCA.

METHODS

Public database analysis, western blot, and enzyme-linked immunosorbent assay (ELISA) were used to screen genes and explore gene expression alteration. Immunofluorescence and western blot were utilized to investigate PC. Wound healing assay, clone formation assay, and CCK-8 assay were used to explore cell migration, growth, and proliferation. The co-immunoprecipitation and western blot were employed to reveal the interaction of STIL and AURKA.

RESULTS

We found that high STIL expression is correlated with poor outcomes of BLCA patients. Further analysis revealed that STIL overexpression could inhibit PC formation, activate SHH signaling pathways, and promote cell proliferation. In contrast, STIL-knockdown could promote PC formation, inactivate SHH signaling, and inhibit cell proliferation. Furthermore, we found that the regulatory functions of STIL for PC depend on AURKA. STIL could influence proteasome activity and maintain AURKA stabilization. AURKA-knockdown could reverse PC deficiency caused by STIL overexpression for PC in BLCA cells. We observed that co-knockdown in STIL and AURKA significantly enhanced PC assembly.

CONCLUSION

In summary, our result provides a potential therapy target for BLCA based on the restoration of PC.

Primary Cilium Identifies a Quiescent Cell Population in the Human Intestinal Crypt

Primary cilia are sensory antennae located at the cell surface which mediate a variety of extracellular signals involved in development, tissue homeostasis, stem cells and cancer. Primary cilia are found in an extensive array of vertebrae cells but can only be generated when cells become quiescent. The small intestinal epithelium is a rapidly self-renewing tissue organized into a functional unit called the crypt–villus axis, containing progenitor and differentiated cells, respectively. Terminally differentiated villus cells are notoriously devoid of primary cilia. We sought to determine if intestinal crypts contain a quiescent cell population that could be identified by the presence of primary cilia. Here we show that primary cilia are detected in a subset of cells located deep in the crypts slightly above a Paneth cell population. Using a normal epithelial proliferative crypt cell model, we show that primary cilia assembly and activity correlate with a quiescent state. These results provide further evidence for the existence of a quiescent cell population in the human small intestine and suggest the potential for new modes of regulation in stem cell dynamics.

Brain heterotopia formation by ciliopathic breakdown of neuroepithelial and blood-cerebrospinal fluid barriers

The developmental functions of primary cilia and the downstream signaling pathways have been widely studied; however, the roles of primary cilia in the developing neurovascular system are not clearly understood. In this study, we found that ablation of genes encoding ciliary transport proteins such as intraflagellar transport homolog 88 (Ift88) and kinesin family member 3a (Kif3a) in cortical radial progenitors led to periventricular heterotopia during late mouse embryogenesis. Conditional mutation of primary cilia unexpectedly caused breakdown of both the neuroepithelial lining and the blood-choroid plexus barrier. Choroidal leakage was partially caused by enlargement of the choroid plexus in the cilia mutants. We found that the choroid plexus expressed platelet-derived growth factor A (Pdgf-A) and that Pdgf-A expression was ectopically increased in cilia-mutant embryos. Cortices obtained from embryos in utero electroporated with Pdgfa mimicked periventricular heterotopic nodules of the cilia mutant. These results suggest that defective ciliogenesis in both cortical progenitors and the choroid plexus leads to breakdown of cortical and choroidal barriers causing forebrain neuronal dysplasia, which may be related to developmental cortical malformation.

Primary Cilia Are Frequently Present in Small Cell Lung Carcinomas but Not in Non–Small Cell Lung Carcinomas or Lung Carcinoids

Most human malignant neoplasms show loss of primary cilia (PC). However, PC are known to be retained and involved in tumorigenesis in some types of neoplasms. The PC status in lung carcinomas remains largely uninvestigated. In this study, we comprehensively assessed the PC status in lung carcinomas. A total of 492 lung carcinomas, consisting of adenocarcinomas (ACs) (n = 319), squamous cell carcinomas (SCCs) (n = 152), and small cell lung carcinomas (SCLCs) (n = 21), were examined by immunohistochemical analysis using an antibody against ARL13B, a marker of PC. The PC-positive rate was markedly higher in SCLCs (81.0%) than in ACs (1.6%) and SCCs (7.9%). We subsequently performed analyses to characterize the PC-positive lung carcinomas further. PC-positive lung carcinomas were more numerous and had longer PC than normal cells. The presence of PC in these cells was not associated with the phase of the cell cycle. We also found that the PC were retained even in metastases from PC-positive lung carcinomas. Furthermore, the hedgehog signaling pathway was activated in PC-positive lung carcinomas. Because ARL13B immunohistochemistry of lung carcinoids (n = 10) also showed a statistically significantly lower rate (10.0%) of PC positivity than SCLCs, we searched for a gene(s) that might be upregulated in PC-positive SCLCs compared with lung carcinoids, but not in PC-negative carcinomas. This search, and further cell culture experiments, identified HYLS1 as a gene possessing the ability to regulate ciliogenesis in PC-positive lung carcinomas. In conclusion, our findings indicate that PC are frequently present in SCLCs but not in non-SCLCs (ACs and SCCs) or lung carcinoids, and their PC exhibit various specific pathobiological characteristics. This suggests an important link between lung carcinogenesis and PC.

The Male Mouse Meiotic Cilium Emanates from the Mother Centriole at Zygotene Prior to Centrosome Duplication

Cilia are hair-like projections of the plasma membrane with an inner microtubule skeleton known as axoneme. Motile cilia and flagella beat to displace extracellular fluids, playing important roles in the airways and reproductive system. On the contrary, primary cilia function as cell-type-dependent sensory organelles, detecting chemical, mechanical, or optical signals from the extracellular environment. Cilia dysfunction is associated with genetic diseases called ciliopathies and with some types of cancer. Cilia have been recently identified in zebrafish gametogenesis as an important regulator of bouquet conformation and recombination. However, there is little information about the structure and functions of cilia in mammalian meiosis. Here we describe the presence of cilia in male mouse meiotic cells. These solitary cilia formed transiently in 20% of zygotene spermatocytes and reached considerable lengths (up to 15-23 µm). CEP164 and CETN3 localization studies indicated that these cilia emanate from the mother centriole prior to centrosome duplication. In addition, the study of telomeric TFR2 suggested that cilia are not directly related to the bouquet conformation during early male mouse meiosis. Instead, based on TEX14 labeling of intercellular bridges in spermatocyte cysts, we suggest that mouse meiotic cilia may have sensory roles affecting cyst function during prophase I.

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.

Loss of primary cilia promotes inflammation and carcinogenesis

Primary cilia (PC) are important signaling hubs, and we here explored their role in colonic pathology. In the colon, PC are mostly present on fibroblasts, and exposure of mice to either chemically induced colitis-associated colon carcinogenesis (CAC) or dextran sodium sulfate (DSS)-induced acute colitis decreases PC numbers. We generated conditional knockout mice with reduced numbers of PC on colonic fibroblasts. These mice show increased susceptibility to CAC, as well as DSS-induced colitis. Secretome and immunohistochemical analyses of DSS-treated mice display an elevated production of the proinflammatory cytokine IL-6 in PC-deficient colons. An inflammatory environment diminishes PC presence in primary fibroblast cultures, which is triggered by IL-6 as identified by RNA-seq analysis together with blocking experiments. These findings suggest an activation loop between IL-6 production and PC loss. An analysis of PC presence on biopsies of patients with ulcerative colitis or colorectal cancer (CRC) reveals decreased numbers of PC on colonic fibroblasts in pathological compared with surrounding normal tissue. Taken together, we provide evidence that a decrease in colonic PC numbers promotes colitis and CRC.

Primary cilia contribute to the aggressiveness of atypical teratoid/rhabdoid tumors

Atypical teratoid/rhabdoid tumor (AT/RT) is a highly malignant brain tumor in infants that is characterized by loss of nuclear expression of SMARCB1 or SMARCA4 proteins. Recent studies show that AT/RTs comprise three molecular subgroups, namely AT/RT-TYR, AT/RT-MYC and AT/RT-SHH. The subgroups show distinct expression patterns of genes involved in ciliogenesis, however, little is known about the functional roles of primary cilia in the biology of AT/RT. Here, we show that primary cilia are present across all AT/RT subgroups with specific enrichment in AT/RT-TYR patient samples. Furthermore, we demonstrate that primary ciliogenesis contributes to AT/RT biology in vitro and in vivo. Specifically, we observed a significant decrease in proliferation and clonogenicity following disruption of primary ciliogenesis in AT/RT cell line models. Additionally, apoptosis was significantly increased via the induction of STAT1 and DR5 signaling, as detected by proteogenomic profiling. In a Drosophila model of SMARCB1 deficiency, concomitant knockdown of several cilia-associated genes resulted in a substantial shift of the lethal phenotype with more than 20% of flies reaching adulthood. We also found significantly extended survival in an orthotopic xenograft mouse model of AT/RT upon disruption of primary ciliogenesis. Taken together, our findings indicate that primary ciliogenesis or its downstream signaling contributes to the aggressiveness of AT/RT and, therefore, may constitute a novel therapeutic target.

Atypical small GTPase RABL3 interacts with RAB11 to regulate early ciliogenesis in human cells

Primary cilia are near-ubiquitously assembled on cells in the human body and are broadly associated with genetic diseases and cancers. In the early stage of ciliogenesis, the ciliary vesicle (CV) is formed on the mother centriole, which nucleates the primary cilium. However, the regulatory mechanisms underlying CV formation have not yet been fully elucidated. Here, we found that the atypical small GTPase RAB-Like 3 (RABL3) is necessary to assemble primary cilia in human cells. RABL3 directly interacts with RAB11, which is involved in CV formation. RABL3 localizes around the centrosome during early ciliogenesis, reminiscent of RAB11 dynamics. Furthermore, RABL3 positively controls the CV formation like RAB11. These findings suggest that RABL3 plays an important role, in cooperation with RAB11, in CV formation during early ciliogenesis.

EV duty vehicles: Features and functions of ciliary extracellular vesicles

The primary cilium is a microtubule-based organelle that extends from a basal body at the surface of most cells. This antenna is an efficient sensor of the cell micro-environment and is instrumental to the proper development and homeostatic control of organs. Recent compelling studies indicate that, in addition to its role as a sensor, the primary cilium also emits signals through the release of bioactive extracellular vesicles (EVs). While some primary-cilium derived EVs are released through an actin-dependent ectocytosis and are called ectosomes (or large EVs, 350–500 nm), others originate from the exocytosis of multivesicular bodies and are smaller (small EVs, 50–100 nm). Ciliary EVs carry unique signaling factors, including protein markers and microRNAs (miRNAs), and participate in intercellular communication in different organism models. This review discusses the mechanism of release, the molecular features, and functions of EVs deriving from cilia, based on the existing literature.

The intraflagellar transport protein IFT52 associated with short-rib thoracic dysplasia is essential for ciliary function in osteogenic differentiation in vitro and for sensory perception in Drosophila

Primary cilia are non-motile sensory cell-organelle that are essential for organismal development, differentiation, and postnatal homeostasis. Their biogenesis and function are mediated by the intraflagellar transport (IFT) system. Pathogenic variants in IFT52, a central component of the IFT-B complex is associated with short-rib thoracic dysplasia with or without polydactyly 16 (SRTD16), with major skeletal manifestations, in addition to other features. Here we sought to examine the role of IFT52 in osteoblast differentiation. Using lentiviral shRNA interference Ift52 was depleted in C3H10T1/2 mouse mesenchymal stem cells. This led to the disruption of the IFT-B anterograde trafficking machinery that impaired primary ciliogenesis and blocked osteogenic differentiation. In Ift52 silenced cells, Hedgehog (Hh) pathway upregulation during osteogenesis was attenuated and despite Smoothened Agonist (SAG) based Hh activation, osteogenic differentiation was incompletely restored. Further we investigated IFT52 activity in Drosophila, wherein the only ciliated somatic cells are the bipolar sensory neurons of the peripheral nervous system. Knockdown of IFT52 in Drosophila neuronal tissues reduced lifespan with the loss of embryonic chordotonal cilia, and produced severe locomotion, auditory and proprioceptive defects in larva and adults. Together these findings improve our knowledge of the role of IFT52 in various physiological contexts and its associated human disorder.

Primary cilia control translation and the cell cycle in medulloblastoma

The primary cilium, a signaling organelle projecting from the surface of a cell, controls cellular physiology and behavior. The presence or absence of primary cilia is a distinctive feature of a given tumor type; however, whether and how the primary cilium contributes to tumorigenesis are unknown for most tumors. Medulloblastoma (MB) is a common pediatric brain cancer comprising four groups: SHH, WNT, group 3 (G3), and group 4 (G4). From 111 cases of MB, we show that primary cilia are abundant in SHH and WNT MBs but rare in G3 and G4 MBs. Using WNT and G3 MB mouse models, we show that primary cilia promote WNT MB by facilitating translation of mRNA encoding β-catenin, a major oncoprotein driving WNT MB, whereas cilium loss promotes G3 MB by disrupting cell cycle control and destabilizing the genome. Our findings reveal tumor type-specific ciliary functions and underlying molecular mechanisms. Moreover, we expand the function of primary cilia to translation control and reveal a molecular mechanism by which cilia regulate cell cycle progression, thereby providing new frameworks for studying cilium function in normal and pathologic conditions.

Pathophysiology of Primary Cilia: Signaling and Proteostasis Regulation

Primary cilia are microtubule-based, non-motile sensory organelles present in most types of growth-arrested eukaryotic cells. They are transduction hubs that receive and transmit external signals to the cells in order to control growth, differentiation and development. Mutations of genes involved in the formation, maintenance or disassembly of ciliary structures cause a wide array of developmental genetic disorders, also known as ciliopathies. The primary cilium is formed during G1 in the cell cycle and disassembles at the G2/M transition. Following the completion of the cell division, the cilium reassembles in G1. This cycle is finely regulated at multiple levels. The ubiquitin-proteasome system (UPS) and the autophagy machinery, two main protein degradative systems in cells, play a fundamental role in cilium dynamics. Evidence indicate that UPS, autophagy and signaling pathways may act in synergy to control the ciliary homeostasis. However, the mechanisms involved and the links between these regulatory systems and cilium biogenesis, dynamics and signaling are not well defined yet. Here, we discuss the reciprocal regulation of signaling pathways and proteolytic machineries in the control of the assembly and disassembly of the primary cilium, and the impact of the derangement of these regulatory networks in human ciliopathies.

Ciliary signaling in stem cells in health and disease: Hedgehog pathway and beyond

The primary cilium is a hair-like sensory compartment that protrudes from the cellular surface. The primary cilium is enriched in a variety of signaling molecules that regulate cellular activities. Stem cells have primary cilia. They reside in a specialized environment, called the stem cell niche. This niche contains a variety of secreted factors, and some of their receptors are localized in the primary cilia of stem cells. Here, we summarize the current understanding of the function of cilia in compartmentalized signaling in stem cells. We describe how ciliary signaling regulates stem cells and progenitor cells during development, tissue homeostasis and tumorigenesis. We summarize our understanding of cilia regulated signaling -primary involving the hedgehog pathway- in stem cells in diverse settings that include neuroepithelial cells, radial glia, cerebellar granule neuron precursors, hematopoietic stem cells, hair follicle stem cells, bone marrow mesenchymal stem cells and mammary gland stem cells. Overall, our review highlights a variety of roles that ciliary signaling plays in regulating stem cells throughout life.

Copy number and expression of CEP89, a protein required for ciliogenesis, are increased and predict poor prognosis in patients with ovarian cancer

CEP89 (centrosomal protein 89) is required for ciliogenesis and mitochondrial metabolism, but its role in cancer has yet to be clarified. We report that CEP89 is overexpressed in ovarian cancer (OC) compared to normal ovaries. Likewise, its expression is higher in malignant ovarian tumors than in borderline ovarian tumors with low malignant potential. More than a quarter of patients with OC have copy number gains in the CEP89 gene, and patients with high expression have more than a year shorter overall survival compared to those with low expression. Moreover, we found that CEP89 can be considered as a prognostic marker for poor overall survival in patients with OC, after adjusting for tumor stage and residual tumor. Nine out of the top 10 protein interactors of CEP89 have the highest percentage of total copy number variation (CNV) events in OC among all other cancer types. Furthermore, CEP89 messenger RNA (mRNA) levels are higher in OC patients with disease recurrence compared to those with no recurrence. We also analyzed CEP89 levels in OC cell lines in terms of CNV, mRNA, and protein levels; and observed that the FUOV-1 cell line has the highest levels among cell lines that originated from primary sites. Our study suggests that CEP89 may be a valuable prognostic predictor for the overall survival of patients with OC, and it could also be a novel therapeutic target in this malignancy.

Random survival forest model identifies novel biomarkers of event-free survival in high-risk pediatric acute lymphoblastic leukemia

High-risk pediatric B-ALL patients experience 5-year negative event rates up to 25%. Although some biomarkers of relapse are utilized in the clinic, their ability to predict outcomes in high-risk patients is limited. Here, we propose a random survival forest (RSF) machine learning model utilizing interpretable genomic inputs to predict relapse/death in high-risk pediatric B-ALL patients. We utilized whole exome sequencing profiles from 156 patients in the TARGET-ALL study (with samples collected at presentation) further stratified into training and test cohorts (109 and 47 patients, respectively). To avoid overfitting and facilitate the interpretation of machine learning results, input genomic variables were engineered using a stepwise approach involving univariable Cox models to select variables directly associated with outcomes, genomic coordinate-based analysis to select mutational hotspots, and correlation analysis to eliminate feature co-linearity. Model training identified 7 genomic regions most predictive of relapse/death-free survival. The test cohort error rate was 12.47%, and a polygenic score based on the sum of the top 7 variables effectively stratified patients into two groups, with significant differences in time to relapse/death (log-rank P = 0.001, hazard ratio = 5.41). Our model outperformed other EFS modeling approaches including an RSF using gold-standard prognostic variables (error rate = 24.35%). Validation in 174 standard-risk patients and 3 patients who failed to respond to induction therapy confirmed that our RSF model and polygenic score were specific to high-risk disease. We propose that our feature selection/engineering approach can increase the clinical interpretability of RSF, and our polygenic score could be utilized for enhance clinical decision-making in high-risk B-ALL.

Using mammary organoids to study cilia

Cilia are hair-like projections that assemble at the surface of cells in various tissues of multicellular organisms through a complex cell biological process called ciliogenesis. Cilia can assemble as single structures per cell (i.e. non-motile primary cilia), which act as cell signaling centers that dictate cell fate, or can be assembled in distinct cell types as many copies per cell (i.e. motile cilia) that beat to move fluids at the cell surface. The mechanisms that orchestrate formation and function of cilia, which are dysregulated in pathological settings such as ciliopathies, remain incompletely understood. Stem cell-derived organoids represent valuable models to study the mechanisms of ciliogenesis, ciliary signaling, and ciliary beating that collectively promote tissue development and homeostasis. Here, we present a comprehensive protocol for the growth of mammary organoids derived from mouse mammary stem cells and for immunofluorescence staining of primary cilia in these three-dimensional structures.

Stromal cells of giant cell tumor of bone show primary cilia in giant cell tumor of bone

Giant cell tumor of bone (GCTB) is a locally aggressive primary bone neoplasm composed by tumoral stromal cells (SCs) and a reactive component that consists of monocytic/histiocytic cells that give rise by fusion to osteoclast-like multinucleated cells. Recently, specific Histone 3.3 mutations have been demonstrated in SCs of GCTB. Many of the pathways related to bone proliferation and regulation depend on the primary cilium, a microtubule-based organelle that protrudes outside the cell and acts as a sensorial antenna. In the present work, we aimed to study the presence and role of primary cilia in GCTB. Ultrastructural, immunohistochemical, and immunofluorescence studies were performed in order to demonstrate, for the first time, that the primary cilium is located in spindle-shaped SCs of GCTB. Moreover, we showed Hedgehog (Hh) signaling pathway activation in these cells. Hence, primary cilia may play a relevant role in GCTB tumorogenesis through Hh signaling activation in SCs. RESEARCH HIGHLIGHTS: Transmission electron microscopy allows describing and differentiating cellular subpopulations in giant cell tumor of bone (GCTB). The primary cilium is present in some tumoral stromal cells of GCTB. Hedgehog signalling is activated in these cells.

MAPK15 Controls Hedgehog Signaling in Medulloblastoma Cells by Regulating Primary Ciliogenesis

In medulloblastomas, genetic alterations resulting in over-activation and/or deregulation of proteins involved in Hedgehog (HH) signaling lead to cellular transformation, which can be prevented by inhibition of primary ciliogenesis. Here, we investigated the role of MAPK15 in HH signaling and, in turn, in HH-mediated cellular transformation. We first demonstrated, in NIH3T3 mouse fibroblasts, the ability of this kinase of controlling primary ciliogenesis and canonical HH signaling. Next, we took advantage of transformed human medulloblastoma cells belonging to the SHH-driven subtype, i.e., DAOY and ONS-76 cells, to ascertain the role for MAPK15 in HH-mediated cellular transformation. Specifically, medullo-spheres derived from these cells, an established in vitro model for evaluating progression and malignancy of putative tumor-initiating medulloblastoma cells, were used to demonstrate that MAPK15 regulates self-renewal of these cancer stem cell-like cells. Interestingly, by using the HH-related oncogenes SMO-M2 and GLI2-DN, we provided evidences that disruption of MAPK15 signaling inhibits oncogenic HH overactivation in a specific cilia-dependent fashion. Ultimately, we show that pharmacological inhibition of MAPK15 prevents cell proliferation of SHH-driven medulloblastoma cells, overall suggesting that oncogenic HH signaling can be counteracted by targeting the ciliary gene MAPK15, which could therefore be considered a promising target for innovative "smart" therapies in medulloblastomas.

Proteomic profiling of the oncogenic septin 9 reveals isoform-specific interactions in breast cancer cells

Septins are a family of multimeric GTP-binding proteins, which are abnormally expressed in cancer. Septin 9 (SEPT9) is an essential and ubiquitously expressed septin with multiple isoforms, which have differential expression patterns and effects in breast cancer cells. It is unknown, however, if SEPT9 isoforms associate with different molecular networks and functions. Here, we performed a proteomic screen in MCF-7 breast cancer cells to identify the interactome of GFP-SEPT9 isoforms 1, 4 and 5, which vary significantly in their N-terminal extensions. While all three isoforms associated with SEPT2 and SEPT7, the truncated SEPT9_i4 and SEPT9_i5 interacted with septins of the SEPT6 group more promiscuously than SEPT9_i1, which bound predominately SEPT8. Spatial mapping and functional clustering of non-septin partners showed isoform-specific differences in interactions with proteins of distinct subcellular organelles (e.g., nuclei, centrosomes, cilia) and functions such as cell signalling and ubiquitination. The interactome of the full length SEPT9_i1 was more enriched in cytoskeletal regulators, while the truncated SEPT9_i4 and SEPT9_i5 exhibited preferential and isoform-specific interactions with nuclear, signalling, and ubiquitinating proteins. These data provide evidence for isoform-specific interactions, which arise from truncations in the N-terminal extensions of SEPT9, and point to novel roles in the pathogenesis of breast cancer.

A PDZ Protein GIPC3 Positively Modulates Hedgehog Signaling and Melanoma Growth

The Hedgehog (Hh) pathway is essential for animal development but aberrant activation promotes cancer growth. Here we show that GIPC3, a PDZ domain-containing protein with putative adaptor protein function, positively modulates Hh target gene expression in normal fibroblasts and melanoma cells and supports melanoma tumor growth. Using overexpression and epistasis studies, we show that Gipc3 potentiates Hh transcriptional output and it modulates GLI-dependent transcription independently of Sufu. While we find GIPC3 protein does not interact with Hh pathway components, Ingenuity Pathway Analyses of GIPC3-interacting proteins identified by co-immunoprecipitation and mass spectrometry show an association with cancer pathogenesis. Subsequent interrogation of TCGA and The Human Protein Atlas databases reveals GIPC3 upregulation in many cancers. Using expression screens in selected groups of GIPC3-upregulated cancers with reported Hh pathway activation, we find a significant positive correlation of GIPC3 expression with Hh pathway components GLI1, GLI2, and GPR161, in melanoma lines. Consistently, GIPC3 knockdown in melanoma lines significantly reduces GLI1 and GLI2 expression, cell viability, colony formation, and allograft tumor growth. Our findings highlight previously unidentified roles of Gipc3 in potentiating Hh response and melanoma tumorigenesis, and suggest that GIPC3 modulation on Hh signaling may be targeted to reduce melanoma growth.

Primary Cilium Is Involved in Stem Cell Differentiation and Renewal through the Regulation of Multiple Signaling Pathways

Signaling networks guide stem cells during their lineage specification and terminal differentiation. Primary cilium, an antenna-like protrusion, directly or indirectly plays a significant role in this guidance. All stem cells characterized so far have primary cilia. They serve as entry- or check-points for various signaling events by controlling the signal transduction and stability. Thus, defects in the primary cilia formation or dynamics cause developmental and health problems, including but not limited to obesity, cardiovascular and renal anomalies, hearing and vision loss, and even cancers. In this review, we focus on the recent findings of how primary cilium controls various signaling pathways during stem cell differentiation and identify potential gaps in the field for future research.

Identification and characterization of primary cilia-positive salivary gland tumours exhibiting basaloid/myoepithelial differentiation

Primary cilia (PC) are non-motile, antenna-like structures on the cell surface. Many types of neoplasms exhibit PC loss, whereas in some neoplasms PC are retained and involved in tumourigenesis. To elucidate the PC status and characteristics of major salivary gland tumours (SGTs), we examined 100 major SGTs encompassing eight histopathological types by immunohistochemical analysis. PC were present in all (100%) of the pleomorphic adenomas (PAs), basal cell adenomas (BCAs), adenoid cystic carcinomas (AdCCs), and basal cell adenocarcinomas (BCAcs) examined, but absent in all (0%) of the Warthin tumours, salivary duct carcinomas, mucoepidermoid carcinomas, and acinic cell carcinomas examined. PC were also detected by electron-microscopic analysis using the NanoSuit method. It is worthy of note that the former category and latter category of tumours contained and did not contain a basaloid/myoepithelial differentiation component, respectively. The four types of PC-positive SGTs showed longer PC than normal and exhibited a characteristic distribution pattern of the PC in the ductal and basaloid/neoplastic myoepithelial components. Two PC-positive carcinomas (AdCC and BCAc) still possessed PC in their recurrent/metastatic sites. Interestingly, activation of the Hedgehog signalling pathway, shown by predominantly nuclear GLI1 expression, was significantly more frequently observed in PC-positive SGTs. Finally, we identified tau tubulin kinase 2 (TTBK2) as being possibly involved in the production of PC in SGTs. Taken together, our findings indicate that SGTs that exhibit basaloid/myoepithelial differentiation (PA, BCA, AdCC, and BCAc) are ciliated, and their PC exhibit tumour-specific characteristics, are involved in activation of the Hedgehog pathway, and are associated with TTBK2 upregulation, providing a significant and important link between SGT tumourigenesis and PC. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Cobalt chloride-simulated hypoxia elongates primary cilia in immortalized human retina pigment epithelial-1 cells

Primary cilia are microtubule-based organelles that are involved in sensing micro-environmental cues and regulating cellular homeostasis via triggering signaling cascades. Hypoxia is one of the most common environmental stresses that organ and tissue cells may often encounter during embryogenesis, cell differentiation, infection, inflammation, injury, cerebral and cardiac ischemia, or tumorigenesis. Although hypoxia has been reported to promote or inhibit primary ciliogenesis in different tissues or cultured cell lines, the role of hypoxia in ciliogenesis is controversial and still unclear. Here we investigated the primary cilia change under cobalt chloride (CoCl₂)-simulated hypoxia in immortalized human retina pigment epithelial-1 (hTERT RPE-1) cells. We found CoCl₂ treatment elongated primary cilia in a time- and dose-dependent manner. The prolonged cilia recovered back to near normal length when CoCl₂ was washed out from the cell culture medium. Under CoCl₂-simulated hypoxia, the protein expression levels of HIF-1/2α and acetylated-α-tubulin (cilia marker) were increased, while the protein expression level of Rabaptin-5 is decreased during hypoxia. Taken together, our results suggest that hypoxia may elongate primary cilia by downregulating Rabaptin-5 involved endocytosis. The coordination between endocytosis and ciliogenesis may be utilized by cells to adapt to hypoxia.

Primary cilia presence and implications in bladder cancer progression and invasiveness

Urothelial bladder cancer is the tenth most common cancer worldwide. It is divided into muscle and non-muscle invading bladder cancer. Primary cilia have been related to several cancer hallmarks such as proliferation, epithelial-to-mesenchymal transition (EMT) or tumoral progression mainly through signaling pathways as Hedgehog (Hh). In the present study, we used immunohistochemical and ultrastructural techniques in human tissues of healthy bladder, non-muscle-invasive bladder cancer (NMIBC) and muscle-invasive bladder cancer (MIBC) to study and clarify the activation of epithelial-to-mesenchymal transition and Hedgehog signaling pathway and the presence of primary cilia. Thus, we found a clear correlation between EMT and Hedgehog activation and bladder cancer stage and progression. Moreover, we identified the presence of primary cilia in these tissues. Interestingly, we found that in NMIBC, some ciliated cells cross the basement membrane and localized in lamina propria, near blood vessels. These results show a correlation between EMT beginning from urothelial basal cells and primary cilia assembly and suggest a potential implication of this structure in tumoral migration and invasiveness (likely in a Hh-dependent way). Hence, primary cilia may play a fundamental role in urothelial bladder cancer progression and suppose a potential therapeutic target.

Targeting the Mevalonate Pathway in Cancer

The mevalonate synthesis inhibitors, statins, are mainstay therapeutics for cholesterol management and cardiovascular health. Thirty years of research have uncovered supportive roles for the mevalonate pathway in numerous cellular processes that support oncogenesis, most recently macropinocytosis. Central to the diverse mechanisms of statin sensitivity is an acquired dependence on one mevalonate pathway output, protein geranylgeranylation. New chemical prenylation probes and the discovery of a novel geranylgeranyl transferase hold promise to deepen our understanding of statin mechanisms of action. Further, insights into statin selection and the counterproductive role of dietary geranylgeraniol highlight how we should assess statins in the clinic. Lastly, rational combination strategies preview how statins will enter the oncology toolbox.

Kif3a deletion prevents primary cilia assembly on oligodendrocyte progenitor cells, reduces oligodendrogenesis and impairs fine motor function

Primary cilia are small microtubule‐based organelles capable of transducing signals from growth factor receptors embedded in the cilia membrane. Developmentally, oligodendrocyte progenitor cells (OPCs) express genes associated with primary cilia assembly, disassembly, and signaling, however, the importance of primary cilia for adult myelination has not been explored. We show that OPCs are ciliated in vitro and in vivo, and that they disassemble their primary cilia as they progress through the cell cycle. OPC primary cilia are also disassembled as OPCs differentiate into oligodendrocytes. When kinesin family member 3a (Kif3a), a gene critical for primary cilium assembly, was conditionally deleted from adult OPCs in vivo (Pdgfrα‐CreER™:: Kif3a^fl/fl transgenic mice), OPCs failed to assemble primary cilia. Kif3a‐deletion was also associated with reduced OPC proliferation and oligodendrogenesis in the corpus callosum and motor cortex and a progressive impairment of fine motor coordination.

Crosstalk between the COX2-PGE2-EP4 signaling pathway and primary cilia in osteoblasts after mechanical stimulation

Primary cilia have been found to function as mechanosensors in low-magnitude high-frequency vibration (LMHFV)-induced osteogenesis. The PGE2 also regulates bone homeostasis and mechanical osteogenesis through its receptor EP4 signaling, but its involvement in LMHFV-induced or in primary cilia-induced osteogenesis has not been investigated. We hypothesized that LMHFV stimulates osteoblast (OB) differentiation by activating the COX2-PGE2-EP pathway in a manner dependent on primary cilia and that primary cilia are also affected by the PGE2 pathway. In this study, through western blot analysis, RNA interference, enzyme-linked immunosorbent assay, real-time quantitative polymerase chain reaction, and cytochemical staining, we observed that COX2, mPGES-1, and PGE2 levels were markedly elevated in cells treated with LMHFV and were greatly decreased in LMHFV-treated cells following IFT88 silencing. EP4 expression was significantly increased in OBs following LMHFV treatment, but IFT88 silencing significantly blocked this increase. EP4 localized to the bases of primary cilia. LMHFV reduced the length and abundance of primary cilia, but the cells could self-repair their primary cilia after mechanical damage. EP4 antagonism significantly blocked the LMHFV-induced increase in IFT88 expression and blocked the recovery of primary cilia length and the proportion of cells with primary cilia. In addition, COX2 or EP4 antagonism disrupted LMHFV-induced osteogenesis. These results demonstrate the integration of and crosstalk between primary cilia and the COX2-PGE2-EP4 signaling pathway under mechanical stimulation.

CEP164 Deficiency Causes Hyperproliferation of Pancreatic Cancer Cells

Primary cilia are hair-like projections that protrude from most mammalian cells and mediate various extracellular signaling pathways. Pancreatic ductal adenocarcinoma (PDAC) cells are known to lose their primary cilia, but the relevance of this phenomenon remains unclear. In this study, we generated PDAC-originated Panc1 cells devoid of primary cilia by mutating a centriolar protein, centrosomal protein 164 (CEP164), which is required for ciliogenesis. CEP164 depletion enhanced the clonogenicity of Panc1 cells, along with chemically induced elimination of primary cilia, suggesting that a lack of these organelles promotes PDAC cells proliferation. In addition, the loss of CEP164 altered the cell cycle progression irrespective of absence of primary cilia. We found that CEP164 was co-localized with the GLI2 transcription factor at the mother centriole and controlled its activation, thus inducing Cyclin D-CDK6 expression. Furthermore, CEP164-mutated Panc1 cells were significantly tolerant to KRAS depletion-dependent growth inhibition. This study suggests that CEP164 deficiency is advantageous for PDAC cells proliferation due to not only lack of ciliation but also cilia-independent GLI2-Cyclin D/CDK6 activation, and that CEP164 is a potential therapeutic target for PDAC.

Primary Ciliary Signaling in the Skin-Contribution to Wound Healing and Scarring

Primary cilia (PC) are solitary, post-mitotic, microtubule-based, and membrane-covered protrusions that are found on almost every mammalian cell. PC are specialized cellular sensory organelles that transmit environmental information to the cell. Signaling through PC is involved in the regulation of a variety of cellular processes, including proliferation, differentiation, and migration. Conversely, defective, or abnormal PC signaling can contribute to the development of various pathological conditions. Our knowledge of the role of PC in organ development and function is largely based on ciliopathies, a family of genetic disorders with mutations affecting the structure and function of PC. In this review, we focus on the role of PC in their major signaling pathways active in skin cells, and their contribution to wound healing and scarring. To provide comprehensive insights into the current understanding of PC functions, we have collected data available in the literature, including evidence across cell types, tissues, and animal species. We conclude that PC are underappreciated subcellular organelles that significantly contribute to both physiological and pathological processes of the skin development and wound healing. Thus, PC assembly and disassembly and PC signaling may serve as attractive targets for antifibrotic and antiscarring therapies.

The Primary Cilium of Adipose Progenitors Is Necessary for Their Differentiation into Cancer-Associated Fibroblasts that Promote Migration of Breast Cancer Cells In Vitro

Cancer associated fibroblasts (CAFs) are central elements of the microenvironment that control tumor development. In breast cancer, CAFs can originate from adipose progenitors (APs). We, and others, have shown that the primary cilium, an antenna-shaped organelle, controls several aspects of APs’ biology. We studied the conversion of human APs into CAFs by breast cancer cell lines (BCCs). Deletion of the cilium of APs by a pharmacological inhibitor, or by siRNA, allow us to demonstrate that the cilium is necessary for the differentiation of APs into CAFs. BCCs increase production of TGF-β1 by APs, which is a known inducer of CAFs. Pharmacological inhibition of TGF-β1 signaling in APs prevents their conversion into CAFs. Since we previously showed that deletion of the APs’ cilium inhibits TGF-β1 signaling, we propose that BCCs induce TGF-β1 production in Aps, which binds to the primary cilium of Aps and leads to their differentiation into CAFs. Inhibition of APs conversion into CAFs induces a loss in some of the biological effects of CAFs since deletion of the cilium of APs decreases their effect on the migration of BCCs. This is the first observation of a function of the cilium of APs in their conversion into CAFs, and its consequences on BCCs.

Targeting Primary Ciliogenesis with Small-Molecule Inhibitors

The primary cilium is generally a non-motile solitary organelle that protrudes from a basal body at the cell surface in various cell types in multicellular organisms. This microtubule-based structure acts as a cell signaling platform to control key cellular processes, including cell proliferation and differentiation in development and in adult tissues. Elongated and/or dysfunctional primary cilia cause developmental disorders termed ciliopathies and cancers. The genetic inhibition of ciliogenesis inducers can block the progression of these diseases in model organisms. Thus, pharmacological inhibition of primary ciliogenesis has emerged as a potential strategy to treat these pathological conditions. Pharmacological inhibitors that affect cilium assembly, and have an impact on other cellular processes, have been identified. Here, we review some of these tools and discuss their value and limitations in the study of primary cilium biology, as well as for the treatment of some ciliopathies and cancers.

Ciliation Index Is a Useful Diagnostic Tool in Challenging Spitzoid Melanocytic Neoplasms

The loss of primary cilia on melanocytes is a useful biomarker for the distinction of melanoma from conventional melanocytic nevi. It is unknown whether ciliation status is beneficial for diagnosing spitzoid tumors-a subclass of melanomas that present inherently ambiguous histology and are challenging to classify. We evaluated the Ciliation Index (CI) in 68 cases of spitzoid tumors ranging from Spitz nevi and atypical Spitz tumors to spitzoid melanoma. We found a significant decrease in CI within the spitzoid melanoma group when compared with either the Spitz nevi or atypical Spitz tumors groups. In addition, we used a machine-learning-based algorithm to determine the value of CI when considered in combination with other histopathologic and molecular features commonly used for diagnosis. We found that a low CI was consistently ranked as a top predictive feature in the diagnosis of malignancy. Predictive models trained on only the top four predictive features (CI, asymmetry, hyperchromatism, and cytologic atypia) outperformed standard histologic assessment in an independent validation cohort of 56 additional cases. The results provide an alternative approach to evaluate diagnostically challenging melanocytic lesions, and further support the use of CI as an ancillary diagnostic test.

Long-Pentraxin 3 Affects Primary Cilium in Zebrafish Embryo and Cancer Cells via the FGF System

Primary cilium drives the left-right asymmetry process during embryonic development. Moreover, its dysregulation contributes to cancer progression by affecting various signaling pathways. The fibroblast growth factor (FGF)/FGF receptor (FGFR) system modulates primary cilium length and plays a pivotal role in embryogenesis and tumor growth. Here, we investigated the impact of the natural FGF trap long-pentraxin 3 (PTX3) on the determination of primary cilium extension in zebrafish embryo and cancer cells. The results demonstrate that down modulation of the PTX3 orthologue ptx3b causes the shortening of primary cilium in zebrafish embryo in a FGF-dependent manner, leading to defects in the left-right asymmetry determination. Conversely, PTX3 upregulation causes the elongation of primary cilium in FGF-dependent cancer cells. Previous observations have identified the PTX3-derived small molecule NSC12 as an orally available FGF trap with anticancer effects on FGF-dependent tumors. In keeping with the non-redundant role of the FGF/FGR system in primary cilium length determination, NSC12 induces the elongation of primary cilium in FGF-dependent tumor cells, thus acting as a ciliogenic anticancer molecule in vitro and in vivo. Together, these findings demonstrate the ability of the natural FGF trap PTX3 to exert a modulatory effect on primary cilium in embryonic development and cancer. Moreover, they set the basis for the design of novel ciliogenic drugs with potential implications for the therapy of FGF-dependent tumors.

NRF2 and Primary Cilia: An Emerging Partnership

When not dividing, many cell types target their centrosome to the plasma membrane, where it nucleates assembly of a primary cilium, an antenna-like signaling structure consisting of nine concentric microtubule pairs surrounded by membrane. Primary cilia play important pathophysiological roles in many tissues, their dysfunction being associated with cancer and ciliopathies, a diverse group of congenital human diseases. Several recent studies have unveiled functional connections between primary cilia and NRF2 (nuclear factor erythroid 2-related factor 2), the master transcription factor orchestrating cytoprotective responses to oxidative and other cellular stresses. These NRF2-cilia relationships are reciprocal: primary cilia, by promoting autophagy, downregulate NRF2 activity. In turn, NRF2 transcriptionally regulates genes involved in ciliogenesis and Hedgehog (Hh) signaling, a cilia-dependent pathway with major roles in embryogenesis, stem cell function and tumorigenesis. Nevertheless, while we found that NRF2 stimulates ciliogenesis and Hh signaling, a more recent study reported that NRF2 negatively affects these processes. Herein, we review the available evidence linking NRF2 to primary cilia, suggest possible explanations to reconcile seemingly contradictory data, and discuss what the emerging interplay between primary cilia and NRF2 may mean for human health and disease.

Rapamycin treatment correlates changes in primary cilia expression with cell cycle regulation in epithelial cells

Primary cilia are sensory organelles that regulate cell cycle and signaling pathways. In addition to its association with cancer, dysfunction of primary cilia is responsible for the pathogenesis of polycystic kidney disease (PKD) and other ciliopathies. Because the association between cilia formation or length and cell cycle or division is poorly understood, we here evaluated their correlation in this study. Using Spectral Karyotyping (SKY) technique, we showed that PKD and the cancer/tumorigenic epithelial cells PC3, DU145, and NL20-TA were associated with abnormal ploidy. We also showed that PKD and the cancer epithelia were highly proliferative. Importantly, the cancer epithelial cells had a reduction in the presence and/or length of primary cilia relative to the normal kidney (NK) cells. We then used rapamycin to restore the expression and length of primary cilia in these cells. Our subsequent analyses indicated that both the presence and length of primary cilia were inversely correlated with cell proliferation. Collectively, our data suggest that restoring the presence and/or length of primary cilia may serve as a novel approach to inhibit cancer cell proliferation.

The primary cilium dampens proliferative signaling and represses a G2/M transcriptional network in quiescent myoblasts

BACKGROUND

Reversible cell cycle arrest (quiescence/G0) is characteristic of adult stem cells and is actively controlled at multiple levels. Quiescent cells also extend a primary cilium, which functions as a signaling hub. Primary cilia have been shown to be important in multiple developmental processes, and are implicated in numerous developmental disorders. Although the association of the cilium with G0 is established, the role of the cilium in the control of the quiescence program is still poorly understood.

RESULTS

Primary cilia are dynamically regulated across different states of cell cycle exit in skeletal muscle myoblasts: quiescent myoblasts elaborate a primary cilium in vivo and in vitro, but terminally differentiated myofibers do not. Myoblasts where ciliogenesis is ablated using RNAi against a key ciliary assembly protein (IFT88) can exit the cell cycle but display an altered quiescence program and impaired self-renewal. Specifically, the G0 transcriptome in IFT88 knockdown cells is aberrantly enriched for G2/M regulators, suggesting a focused repression of this network by the cilium. Cilium-ablated cells also exhibit features of activation including enhanced activity of Wnt and mitogen signaling and elevated protein synthesis via inactivation of the translational repressor 4E-BP1.

CONCLUSIONS

Taken together, our results show that the primary cilium integrates and dampens proliferative signaling, represses translation and G2/M genes, and is integral to the establishment of the quiescence program.

The primary cilium: Its role as a tumor suppressor organelle

The primary cilium is an organelle that nearly all cells within the body contain. Its function is to sense the extracellular environment through its abundance of receptors and linked signaling pathways, working as an antenna. Ciliary defects lead to different pathologies. In particular, many tumors lose primary cilia, and this is linked with negative implications for the cell such as an increase in malignancy. In this work we will go through the knowledge of the role of primary cilia in normal conditions, how it is involved in diverse signaling pathways, and in disease, particularly in cancer, highlighting its tumor suppressor properties.