Primary cilia in gastric gastrointestinal stromal tumours (GISTs): an ultrastructural study

Spheresomes are the main extracellular vesicles in low-grade gliomas

Cancer progression and its impact on treatment response and prognosis is deeply regulated by tumour microenvironment (TME). Cancer cells are in constant communication and modulate TME through several mechanisms, including transfer of tumour-promoting cargos through extracellular vesicles (EVs) or oncogenic signal detection by primary cilia. Spheresomes are a specific EV that arise from rough endoplasmic reticulum-Golgi vesicles. They accumulate beneath cell membrane and are released to the extracellular medium through multivesicular spheres. This study describes spheresomes in low-grade gliomas using electron microscopy. We found that spheresomes are more frequent than exosomes in these tumours and can cross the blood-brain barrier. Moreover, the distinct biogenesis processes of these EVs result in unique cargo profiles, suggesting different functional roles. We also identified primary cilia in these tumours. These findings collectively contribute to our understanding of glioma progression and metastasis.

Cholesterol in the ciliary membrane as a therapeutic target against cancer

Primary cilium is a non-motile, antenna-like structure that develops in the quiescent G0 phase-cell surface. It is composed of an array of axonemal microtubules polymerized from the centrosome/basal body. The plasma membrane surrounding the primary cilium, which is called the ciliary membrane, contains a variety of receptors and ion channels, through which the cell receives extracellular chemical and physical stimuli to initiate signal transduction. In general, primary cilia disappear when cells receive the proliferative signals to re-enter the cell cycle. Primary cilia thus cannot be identified in many malignant and proliferative tumors. In contrast, some cancers, including basal cell carcinoma, medulloblastoma, gastrointestinal stromal tumor, and other malignancies, retain their primary cilia. Importantly, it has been reported that the primary cilia-mediated oncogenic signals of Hedgehog, Wnt, and Aurora kinase A are involved in the tumorigenesis and tumor progression of basal cell carcinoma and some types of medulloblastoma. It has also been demonstrated that cholesterol is significantly more enriched in the ciliary membrane than in the rest of the plasma membrane to ensure Sonic hedgehog signaling. A series of epidemiological studies on statin drugs (cholesterol-lowering medication) demonstrated that they prevent recurrence in a wide range of cancers. Taken together, ciliary cholesterol could be a potential therapeutic target in primary cilia-dependent progressive cancers.

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.

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.

Functional inhibition of fatty acid binding protein 4 ameliorates impaired ciliogenesis in GCs

Ciliogenesis is often impaired in some cancer cells, leading to acceleration of cancer phenotypes such as cell migration and proliferation. From the investigation of primary cilia of 16 gastric cancer cells (GCs), we found that GCs could be grouped into four primary cilia (PC)-positive GCs and 12 PC-negative GCs. The proliferation of the PC-positive GCs was lower than that of PC-negative GCs. To explore the role of fatty acid binding protein 4 (FABP4), which is a known oncogenic factor, in ciliogenesis, FABP4 expression and function were inhibited by transfection of cells with short interfering RNA targeting FABP4 (siFABP4) or FABP4 inhibitor treatment. Notably, the proliferation and migration of the cilia-forming GCs was effectively suppressed by inhibition of FABP4. In addition, the primary cilia in GCs were restored by a factor greater than two, suggesting a negative role of FABP4 in ciliogenesis in these GCs and FABP4 as a potential anticancer target.

Functional aspects of primary cilium in signaling, assembly and microenvironment in cancer

The primary cilium is an antennae‐like structure extent outside the cell surface. It has an important role in regulating cell‐signaling transduction to affect proliferation, differentiation and migration. Evidence is accumulating that ciliary defects lead to ciliopathies and ciliary deregulation also play crucial roles in cancer formation and progression. Interestingly, restoring the cilia can suppress proliferation in some cancer cell. However, t he role of primary cilia in cancer still be debated. In this article, we review the role of the primary cilium in cancer through architecture, signaling pathways, cilia assembly and disassembly regulators, and summarized the new findings of the primary cilium in tumor microenvironments and different cancers, highlighting novel possibilities for therapeutic target in cancer.

Hedgehog signalling pathway activation in gastrointestinal stromal tumours is mediated by primary cilia

BACKGROUND

Gastrointestinal stromal tumour (GIST) is a mesenchymal cancer which derives from interstitial cells of Cajal. To determine whether a relationship between Hedgehog (Hh) signalling pathway and primary cilia exists in GIST tumours is intended here.

METHODS

Immunohistochemical, immunofluorescence and ultrastructural techniques were performed in this study.

RESULTS

We show that GIST cells present primary cilia (an antenna-like structure based on microtubules). But, moreover, we prove Hedgehog signalling pathway activation in these tumours (a pathway related with tumoural features such as proliferation, migration or stemness) and we show for the first time that this signalling pathway activation in GIST is mediated by primary cilia, likely in a paracrine way.

CONCLUSION

Thus, primary cilia and Hedgehog signalling would be fundamental in tumoural microenvironment control of GIST cells for their maintenance, differentiation and proliferation.

The Roles of Primary Cilia in Cardiovascular Diseases

Primary cilia are microtubule-based organelles found in most mammalian cell types. Cilia act as sensory organelles that transmit extracellular clues into intracellular signals for molecular and cellular responses. Biochemical and molecular defects in primary cilia are associated with a wide range of diseases, termed ciliopathies, with phenotypes ranging from polycystic kidney disease, liver disorders, mental retardation, and obesity to cardiovascular diseases. Primary cilia in vascular endothelia protrude into the lumen of blood vessels and function as molecular switches for calcium (Ca²⁺) and nitric oxide (NO) signaling. As mechanosensory organelles, endothelial cilia are involved in blood flow sensing. Dysfunction in endothelial cilia contributes to aberrant fluid-sensing and thus results in vascular disorders, including hypertension, aneurysm, and atherosclerosis. This review focuses on the most recent findings on the roles of endothelial primary cilia within vascular biology and alludes to the possibility of primary cilium as a therapeutic target for cardiovascular disorders.

Primary Cilia in Tumor Biology: The Primary Cilium as a Therapeutic Target in Cholangiocarcinoma

Cilia are microtubule-based organelles, which are ubiquitously expressed in epithelial cells. Cholangiocytes, the epithelial cells lining the biliary tree, have primary cilia extending from their apical plasma membrane into the ductal lumen, where the cilia function as multisensory organelles transducing environmental cues into the cell interior. The decrease or loss of primary cilia has been described in several malignancies, including cholangiocarcinoma, suggesting that the loss of cilia is a common occurrence in neoplastic transformation. In this short review, we describe the expression of cilia in several cancers, explore the mechanisms and consequences of ciliary loss, and discuss the potential use of the primary cilia as therapeutic targets.

Hedgehog pathway dysregulation contributes to the pathogenesis of human gastrointestinal stromal tumors via GLI-mediated activation of KIT expression

Gastrointestinal stromal tumors (GIST) arise within the interstitial cell of Cajal (ICC) lineage due to activating KIT/PDGFRA mutations. Both ICC and GIST possess primary cilia (PC), which coordinate PDGFRA and Hedgehog signaling, regulators of gastrointestinal mesenchymal development. Therefore, we hypothesized that Hedgehog signaling may be altered in human GIST and controls KIT expression. Quantitative RT-PCR, microarrays, and next generation sequencing were used to describe Hedgehog/PC-related genes in purified human ICC and GIST. Genetic and pharmacologic approaches were employed to investigate the effects of GLI manipulation on KIT expression and GIST cell viability. We report that Hedgehog pathway and PC components are expressed in ICC and GIST and subject to dysregulation during GIST oncogenesis, irrespective of KIT/PDGFRA mutation status. Using genomic profiling, 10.2% of 186 GIST studied had potentially deleterious genomic alterations in 5 Hedgehog-related genes analyzed, including in the PTCH1 tumor suppressor (1.6%). Expression of the predominantly repressive GLI isoform, GLI3, was inversely correlated with KIT mRNA levels in GIST cells and non-KIT/non-PDGFRA mutant GIST. Overexpression of the 83-kDa repressive form of GLI3 or small interfering RNA-mediated knockdown of the activating isoforms GLI1/2 reduced KIT mRNA. Treatment with GLI1/2 inhibitors, including arsenic trioxide, significantly increased GLI3 binding to the KIT promoter, decreased KIT expression, and reduced viability in imatinib-sensitive and imatinib-resistant GIST cells. These data offer new evidence that genes necessary for Hedgehog signaling and PC function in ICC are dysregulated in GIST. Hedgehog signaling activates KIT expression irrespective of mutation status, offering a novel approach to treat imatinib-resistant GIST.

Primary Cilia and Coordination of Receptor Tyrosine Kinase (RTK) and Transforming Growth Factor β (TGF-β) Signaling

Since the beginning of the millennium, research in primary cilia has revolutionized our way of understanding how cells integrate and organize diverse signaling pathways during vertebrate development and in tissue homeostasis. Primary cilia are unique sensory organelles that detect changes in their extracellular environment and integrate and transmit signaling information to the cell to regulate various cellular, developmental, and physiological processes. Many different signaling pathways have now been shown to rely on primary cilia to function properly, and mutations that lead to ciliary dysfunction are at the root of a pleiotropic group of diseases and syndromic disorders called ciliopathies. In this review, we present an overview of primary cilia-mediated regulation of receptor tyrosine kinase (RTK) and transforming growth factor β (TGF-β) signaling. Further, we discuss how defects in the coordination of these pathways may be linked to ciliopathies.

Neoexpression of a functional primary cilium in colorectal cancer cells

The Hedgehog (HH) signaling pathway is involved in the maintenance of numerous cell types both during development and in the adult. Often deregulated in cancers, its involvement in colorectal cancer has come into view during the last few years, although its role remains poorly defined. In most tissues, the HH pathway is highly connected to the primary cilium (PC), an organelle that recruits functional components and regulates the HH pathway. However, normal epithelial cells of the colon display an inactive HH pathway and lack a PC. In this study, we report the presence of the PC in adenocarcinoma cells of primary colorectal tumors at all stages. Using human colorectal cancer cell lines we found a clear correlation between the presence of the PC and the expression of the final HH effector, GLI1, and provide evidence of a functional link between the two by demonstrating the recruitment of the SMO receptor to the membrane of the primary cilium. We conclude that the primary cilium directly participates in the HH pathway in colorectal cancer cells.

PDGFRβ and oncogenic mutant PDGFRα D842V promote disassembly of primary cilia through a PLCγ- and AURKA-dependent mechanism

Primary cilia are microtubule-based sensory organelles projecting from most quiescent mammalian cells, which disassemble in cells cultured in serum-deprived conditions upon re-addition of serum or growth factors. Platelet-derived growth factors (PDGF) are implicated in deciliation, but the specific receptor isoforms and mechanisms involved are unclear. We report that PDGFRβ promotes deciliation in cultured cells and provide evidence implicating PLCγ and intracellular Ca(2+) release in this process. Activation of wild-type PDGFRα alone did not elicit deciliation. However, expression of constitutively active PDGFRα D842V mutant receptor, which potently activates PLCγ (also known as PLCG1), caused significant deciliation, and this phenotype was rescued by inhibiting PDGFRα D842V kinase activity or AURKA. We propose that PDGFRβ and PDGFRα D842V promote deciliation through PLCγ-mediated Ca(2+) release from intracellular stores, causing activation of calmodulin and AURKA-triggered deciliation.

Comparative proteomic analysis of human lung telocytes with fibroblasts

Telocytes (TCs) were recently described as interstitial cells with very long prolongations named telopodes (Tps; http://www.telocytes.com). Establishing the TC proteome is a priority to show that TCs are a distinct type of cells. Therefore, we examined the molecular aspects of lung TCs by comparison with fibroblasts (FBs). Proteins extracted from primary cultures of these cells were analysed by automated 2-dimensional nano-electrospray ionization liquid chromatography tandem mass spectrometry (2D Nano-ESI LC-MS/MS). Differentially expressed proteins were screened by two-sample t-test (P < 0.05) and fold change (>2), based on the bioinformatics analysis. We identified hundreds of proteins up- or down-regulated, respectively, in TCs as compared with FBs. TC proteins with known identities are localized in the cytoskeleton (87%) and plasma membrane (13%), while FB up-regulated proteins are in the cytoskeleton (75%) and destined to extracellular matrix (25%). These identified proteins were classified into different categories based on their molecular functions and biological processes. While the proteins identified in TCs are mainly involved in catalytic activity (43%) and as structural molecular activity (25%), the proteins in FBs are involved in catalytic activity (24%) and in structural molecular activity, particularly synthesis of collagen and other extracellular matrix components (25%). Anyway, our data show that TCs are completely different from FBs. In conclusion, we report here the first extensive identification of proteins from TCs using a quantitative proteomics approach. Protein expression profile shows many up-regulated proteins e.g. myosin-14, periplakin, suggesting that TCs might play specific roles in mechanical sensing and mechanochemical conversion task, tissue homoeostasis and remodelling/renewal. Furthermore, up-regulated proteins matching those found in extracellular vesicles emphasize TCs roles in intercellular signalling and stem cell niche modulation. The novel proteins identified in TCs will be an important resource for further proteomic research and it will possibly allow biomarker identification for TCs. It also creates the premises for understanding the pathogenesis of some lung diseases involving TCs.