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Functional aspects of primary cilia in signaling, cell cycle and tumorigenesis
Abstract and Figures
Dysfunctional cilia underlie a broad range of cellular and tissue phenotypes and can eventually result in the development of ciliopathies: pathologically diverse diseases that range from clinically mild to highly complex and severe multi-organ failure syndromes incompatible with neonatal life. Given that virtually all cells of the human body have the capacity to generate cilia, it is likely that clinical manifestations attributed to ciliary dysfunction will increase in the years to come. Disputed but nevertheless enigmatic is the notion that at least a subset of tumor phenotypes fit within the ciliopathy disease spectrum and that cilia loss may be required for tumor progression. Contending for the centrosome renders ciliation and cell division mutually exclusive; a regulated tipping of balance promotes either process. The mechanisms involved, however, are complex. If the hypothesis that tumorigenesis results from dysfunctional cilia is true, then why do the classic ciliopathies only show limited hyperplasia at best? Although disassembly of the cilium is a prerequisite for cell proliferation, it does not intrinsically drive tumorigenesis per se. Alternatively, we will explore the emerging evidence suggesting that some tumors depend on ciliary signaling. After reviewing the structure, genesis and signaling of cilia, the various ciliopathy syndromes and their genetics, we discuss the current debate of tumorigenesis as a ciliopathy spectrum defect, and describe recent advances in this fascinating field.
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... Primary cilia play a significant role in regulating cell behavior, particularly in influencing cell cycle progression and suppressing proliferative signaling. [35][36][37] The disassembly of primary cilia facilitates cell proliferation, and their absence is linked to excessive cell proliferation observed in conditions like cancer. 35,36 Signaling pathways like Shh and Notch, known regulators of cell proliferation and differentiation across various tissues and cell types, are influenced by primary cilia. ...
... [35][36][37] The disassembly of primary cilia facilitates cell proliferation, and their absence is linked to excessive cell proliferation observed in conditions like cancer. 35,36 Signaling pathways like Shh and Notch, known regulators of cell proliferation and differentiation across various tissues and cell types, are influenced by primary cilia. 23,38,39 Deletion of Ift88 or Kif3a in different contexts results in hyperproliferation in the epidermis or myoblasts. ...
Purpose:
Intraflagellar transport 46 (IFT46) is an integral subunit of the IFT-B complex, playing a key role in the assembly and maintenance of primary cilia responsible for transducing signaling pathways. Despite its predominant expression in the basal body of cilia, the precise role of Ift46 in ocular development remains undetermined. This study aimed to elucidate the impact of neural crest (NC)-specific deletion of Ift46 on ocular development.
Methods:
NC-specific conditional knockout mice for Ift46 (NC-Ift46F/F) were generated by crossing Ift46F mice with Wnt1-Cre2 mice, enabling the specific deletion of Ift46 in NC-derived cells (NCCs). Sonic Hedgehog (Shh) and Notch signaling activities in NC-Ift46F/F mice were evaluated using Gli1lacZ and CBF:H2B-Venus reporter mice, respectively. Cell fate mapping was conducted using ROSAmTmG reporter mice.
Results:
The deletion of Ift46 in NCCs resulted in a spectrum of ocular abnormalities, including thickened corneal stroma, hypoplasia of the anterior chamber, irregular iris morphology, and corneal neovascularization. Notably, this deletion led to reduced Shh signal activity in the periocular mesenchyme, sustained expression of key transcription factors Foxc1, Foxc2 and Pitx2, along with persistent cell proliferation. Additionally, it induced increased Notch signaling activity and the development of ectopic neovascularization within the corneal stroma.
Conclusions:
The absence of primary cilia due to Ift46 deficiency in NCCs is associated with anterior segment dysgenesis (ASD) and corneal neovascularization, suggesting a potential link to Axenfeld-Rieger syndrome, a disorder characterized by ASD. This underscores the pivotal role of primary cilia in ensuring proper anterior segment development and maintaining an avascular cornea.
... Various cancer cells have been shown to lack cilia expression (Menzl et al., 2014;Cao and Zhong, 2016;Higgins et al., 2019). Changes in primary cilia have been noted in renal, prostate, cholangiocarcinoma, pancreatic, skin, brain and breast cancers (Seeley et al., 2009;Basten and Giles, 2013;Hassounah et al., 2013;Seeger-Nukpezah et al., 2013;Menzl et al., 2014;Snedecor et al., 2015;Higgins et al., 2019). Renal epithelial and human primary melanoma cells demonstrate significant losses of cilia in response to carcinogens Snedecor et al., 2015;Higgins et al., 2019). ...
Cilia are cellular signaling hubs. Given that human kinases are central regulators of signaling, it is not surprising that kinases are key players in cilia biology. In fact, many kinases modulate ciliogenesis, which is the generation of cilia, and distinct ciliary pathways. Several of these kinases are understudied with few publications dedicated to the interrogation of their function. Recent efforts to develop chemical probes for members of the cyclin-dependent kinase like (CDKL), never in mitosis gene A (NIMA) related kinase (NEK), and tau tubulin kinase (TTBK) families either have delivered or are working toward delivery of high-quality chemical tools to characterize the roles that specific kinases play in ciliary processes. A better understanding of ciliary kinases may shed light on whether modulation of these targets will slow or halt disease onset or progression. For example, both understudied human kinases and some that are more well-studied play important ciliary roles in neurons and have been implicated in neurodevelopmental, neurodegenerative, and other neurological diseases. Similarly, subsets of human ciliary kinases are associated with cancer and oncological pathways. Finally, a group of genetic disorders characterized by defects in cilia called ciliopathies have associated gene mutations that impact kinase activity and function. This review highlights both progress related to the understanding of ciliary kinases as well as in chemical inhibitor development for a subset of these kinases. We emphasize known roles of ciliary kinases in diseases of the brain and malignancies and focus on a subset of poorly characterized kinases that regulate ciliary biology.
... Although this is not completely deterministic, mutations in genes encoding ciliary TZ proteins often lead to neurodevelopmental ciliopathies such as Joubert Syndrome (JS) and the embryonically lethal Meckel Gruber syndrome (MKS) (1,3). It was demonstrated that primary cilia are present throughout the neuronal lineage, from neural stem to progenitor cells, mature neurons and glia, where they play an essential role in CNS formation by modulating signaling pathways and cell cycle progression (4)(5)(6)(7)(8)(9)(10). ...
Studying developmental processes in the context of the human central nervous system is essential to understand neurodevelopmental diseases. In this paper we perform a comparative functional study of the ciliopathy gene RPGRIP1L in human and mouse spinal development using in vitro 3D differentiation of pluripotent stem cells. RGPRIP1L, a causal gene of severe neurodevelopmental ciliopathies such as Joubert and Meckel syndromes, encodes a scaffolding protein of the ciliary transition zone involved in ciliary gating. Previous work has identified a major role for Rpgrip1l in mouse brain and spinal cord development, via controlling the Sonic Hedgehog (SHH)/GLI pathway. We show that spinal organoids derived from Rpgrip1l mutant mouse embryonic stem cells faithfully recapitulate the loss of motoneurons and the strong reduction of SHH signaling observed in the mutant mice. In contrast, human induced pluripotent stem cells mutant for RPGRIP1L produce motoneurons and activate the SHH pathway at levels similar to wild types. Moreover, we show that, in human RPGRIP1L mutant organoids, MNs acquire a more anterior identity, expressing HOX genes and proteins normally present in the hindbrain while motoneurons from wild type organoids strictly display spinal identity. By performing a temporal transcriptome analysis throughout the differentiation process, we find that the anteroposterior specification defect arises in early axial progenitors. Thus, this study uncovers distinct functions in humans and mice for a ciliopathy protein and a novel role for RPGRIP1L in human spinal anteroposterior patterning. These findings have important implications for understanding the role of cilia in human spinal cord development and the pathogenic mechanisms of neurodevelopmental ciliopathies.
... Since microtubules are a critical component of primary cilia, primary cilia regulate cell cycle processes. They can prevent abnormal cell growth by restricting the cell cycle in studies of the CRP effect on the primary cilia of OPCs [2,12]. The present study showed more primary cilia on recombinant CRP-treated OPCs than on control OPCs, indicating that CRP abnormally activated primary cilia formation (Fig. 3C-E). ...
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.
... Ciliogenesis in cancer cells is dependent on the cancer type. Unsurprisingly, most cancer cells lack cilia because they serve as gatekeepers to stop cell cycle re-entry [116][117][118]. Nevertheless, several others exhibit increased numbers of primary cilia [119]. ...
Cancer whose major problems are metastasis, treatment resistance, and recurrence is the leading cause of death worldwide. Tumor-initiating stem cells (TiSCs) are a subset of the tumor population responsible for tumor resistance and relapse. Understanding the characteristics and shared features between tumor-initiating stem cells (TiSCs) and long-lived postmitotic cells may hold a key to better understanding the biology of cancer. Postmitotic cells have exited the cell cycle and are transitioned into a non-dividing and terminally differentiated state with a specialized function within a tissue. Conversely, a cancer cell with TiSC feature can divide and produce a variety of progenies, and is responsible for disease progression, tumor resistance to therapy and immune system and disease relapse. Surprisingly, our comprehensive evaluation of TiSCs suggests common features with long-lived post-mitotic cells. They are similar in structure (primary cilia, high mitochondrial content, and being protected by a barrier), metabolism (autophagy and senescence), and function (immunoescape and/or immune-privileged by a blood barrier). In-depth exploration showed how mitochondrial metabolism contributes to these shared features, including high energy demands arising from ciliary and microtubular functionality, increased metabolic activity, and movement. These findings can assist in decoding the remaining properties which offer insights into the biology of TiSCs, with potential implications for enhancing cancer treatment strategies and patient prognosis. Keywords: blood barrier; cilium; immunity; postmitotic cells; tumor-initiating stem cells; tumor microenvironment
Primary cilia are present on renal tubules and are implicated to play pivotal role in transducing signals during development; however, the oncogenic role of cilia in clear cell renal cell carcinoma (ccRCC) has not been examined. Here we show that VHL wild-type ccRCC cell lines have high incidence of primary cilia, and high frequency of primary cilia is positively correlated with VHL expression and poor prognosis. Besides, depletion Kif3a or Ift88, genes required for ciliogenesis, significantly inhibited tumor proliferation and metastasis in vitro and in vivo. Further analysis found that mutations of key genes in hedgehog signaling are enriched in VHL wild ccRCC, its downstream signaling activation depends on ciliogenesis. Moreover, depletion of primary cilia or suppression of hedgehog pathway activation with inhibitor induced robust autophagic cell death. Collectively, our findings revealed that primary cilia could serve as a diagnostic tool and provide new insights into the mechanism of VHL wild-type ccRCC progression. Targeting primary cilia-hedgehog pathway may represent an effective therapeutic strategy for VHL wild-type ccRCC.
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.
Cilia beating influences bio-fluid flow, and conduits with ciliated surfaces serve numerous purposes. Cilia are hair-like adjuncts that produce liquid drive and cell locomotion. This novel research integrates magnetohydrodynamics, Hall effects, and porous medium with the cilia-driven flow. The developed problem is further simplified by utilizing famous assumptions, i.e., low Reynolds number and large wavelength. The bvp5c function in MATLAB (2023a) is adopted to achieve a convergent solution. The graphical illustrations of streamlines, pressure drop, and axial velocity under the influence of pertinent parameters are thoroughly examined. The findings suggest that when a high magnetic field (Hall current) and porous media are combined with the Carreau–Yasuda fluid, the pumping equipment operates better than the viscous liquid. In addition, fluid movement in biological organs is improved by metachronal ciliary motion. Furthermore, it is predicted that this study will make a significant contribution to biomedical engineering in terms of the upgrading and advancement of various types of drug-delivery technologies.
Phosphotidylinositol (PtdIns) signaling is tightly regulated both spatially and temporally by subcellularly localized PtdIns kinases and phosphatases that dynamically alter downstream signaling events. Joubert syndrome is characterized by a specific midbrain-hindbrain malformation ('molar tooth sign'), variably associated retinal dystrophy, nephronophthisis, liver fibrosis and polydactyly and is included in the newly emerging group of 'ciliopathies'. In individuals with Joubert disease genetically linked to JBTS1, we identified mutations in the INPP5E gene, encoding inositol polyphosphate-5-phosphatase E, which hydrolyzes the 5-phosphate of PtdIns(3,4,5)P3 and PtdIns(4,5)P2. Mutations clustered in the phosphatase domain and impaired 5-phosphatase activity, resulting in altered cellular PtdIns ratios. INPP5E localized to cilia in major organs affected by Joubert syndrome, and mutations promoted premature destabilization of cilia in response to stimulation. These data link PtdIns signaling to the primary cilium, a cellular structure that is becoming increasingly recognized for its role in mediating cell signals and neuronal function.
Background
Lithium (Li) is an invaluable drug for the treatment of bipolar disorder. Long-term Li use is associated with renal complications including the formation of uncomplicated renal cysts caused by proliferation and expansion of collecting duct (CD) cells. We report six patients with complicated renal cysts in the context of Li nephropathy.Methods
Over a time period of 15 years, we have identified six patients with one or more solid renal tumours in our population of approximately 50 patients with chronic Li nephropathy. In this study we describe the clinical and pathological characteristics of these Li-related tumours.ResultsAll patients were on Li therapy for over 10 years and suffered from varying degrees of Li nephropathy. The tumours were all of CD origin and comprised both oncocytomas and collecting duct carcinomas. The CD carcinomas differed from the very rare "classical" CD cell carcinomas in histological appearance, multifocal presentation and non-aggressive clinical behaviourConclusions
The increased incidence of CD derived tumours and atypical presentation of CD cell carcinomas in patients with chronic Li nephropathy suggests that Li predisposes to the development of these tumours. We hypothesize that prolonged stimulation of CD cell proliferation and expansion by Li not only causes cyst formation, but can eventually induce the formation of adenomas and carcinomas. Increased awareness of a possible relationship between chronic Li therapy and renal neoplasms, will enhance the knowledge on epidemiology, clinical behavior and optimal therapy for the Li-related renal neoplasms. © 2012 The Author. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved.
Centrosomes organize the microtubule cytoskeleton for both interphase and mitotic functions. They are implicated in cell-cycle progression but the mechanism is unknown. Here, we show that depletion of 14 out of 15 centrosome proteins arrests human diploid cells in G1 with reduced Cdk2–cyclin A activity and that expression of a centrosome-disrupting dominant-negative construct gives similar results. Cell-cycle arrest is always accompanied by defects in centrosome structure and function (for example, duplication and primary cilia assembly). The arrest occurs from within G1, excluding contributions from mitosis and cytokinesis. The arrest requires p38, p53 and p21, and is preceded by p38-dependent activation and centrosomal recruitment of p53. p53-deficient cells fail to arrest, leading to centrosome and spindle dysfunction and aneuploidy. We propose that loss of centrosome integrity activates a checkpoint that inhibits G1–S progression. This model satisfies the definition of a checkpoint in having three elements: a perturbation that is sensed, a transducer (p53) and a receiver (p21).
Familial adenomatous polyposis (FAP) is an autosomal dominant form of intestinal polyposis and colorectal cancer caused by germ-line mutations in the adenomatous polyposis coli (APC) gene. The term Gardner's syndrome is used to describe extracolonic manifestations, such as osteomas, skin cysts, congenital hypertrophy of the retinal pigmented epithelium (CHRPE), and desmoid tumours (aggressive fibromatosis), that are especially prominent in families with FAP. We postulate that a ciliary dysfunction is the underlying pathogenetic mechanism of extraintestinal manifestations in patients with FAP. This postulation is based on the presence of common clinical manifestations (ie, cysts, retinal abnormalities, and fibrosis) in Gardner's syndrome and cilia-related disorders. Additionally, both APC and the cilia have degradation of beta-catenin as the common downstream target in the Wnt-signalling pathway. Mutations in APC causing Gardner's syndrome are clustered in a region encoding a series of amino-acid repeats responsible for the binding to beta-catenin. Proofs of principle that beta-catenin could be the key mediator of the ciliary disorder also rely in the findings that overexpression of beta-catenin induces polycystic kidney disease, and CHRPE phenotypes in animal models. Other candidates for the common link between Gardner's syndrome and cilia-related disorders are the APC-binding proteins: end-binding protein 1 (EB1) and kinesin-family-member 3a (KIF3a), both of which are ciliary proteins involved in intraflagellar transport. Finally, pathogenetic similarities between some ciliopathies and extraintestinal tumours in FAP suggest a cilia defect. Understanding extracolonic manifestations in the context of FAP as a ciliary disorder might add new therapeutic options for patients with Gardner's syndrome.
We analysed the expression profiles of 70 kidney tumors of different histological subtypes to determine if these subgroups can be distinguished by their gene expression profiles, and to gain insights into the molecular mechanisms underlying each subtype. In all, 39 clear cell renal cell carcinomas (RCC), seven primary and one metastatic papillary RCC, six granular RCC from old classification, five chromophobe RCC, five sarcomatoid RCC, two oncocytomas, three transitional cell carcinomas (TCC) of the renal pelvis and five Wilms' tumors were compared with noncancerous kidney tissues using microarrays containing 19 968 cDNAs. Based on global gene clustering of 3560 selected cDNAs, we found distinct molecular signatures in clear cell, papillary, chromophobe RCC/ oncocytoma, TCC and Wilms' subtypes. The close clustering in each of these subtypes points to different tumorigenic pathways as reflected by their histological characteristics. In the clear cell RCC clustering, two subgroups emerged that correlated with clinical outcomes, confirming the potential use of gene expression signatures as a predictor of survival. In the so-called granular cell RCC (terminology for a subtype that is no longer preferred), none of the six cases clusters together, supporting the current view that they do not represent a single entity. Blinded histological re-evaluation of four cases of 'granular RCC' led to their reassignment to other existing histological subtypes, each compatible with our molecular classification. Finally, we found gene sets specific to each subtype. In order to establish the use of some of these genes as novel subtype markers, we selected four genes and performed immunohistochemical analysis on 40 cases of primary kidney tumors. The results were consistent with the gene expression micro-array data: glutathione S-transferase α was highly expressed in clear cell RCC, α methylacyl racemase in papillary RCC, carbonic anhydrase II in chromophobe RCC and K19 in TCC. In conclusion, we demonstrated that molecular profiles of kidney cancers closely correlated with their histological subtypes. We have also identified in these subtypes differentially expressed genes that could have important diagnostic and therapeutic implications.
Nephronophthisis (NPHP), Joubert (JBTS), and Meckel-Gruber (MKS) syndromes are autosomal-recessive ciliopathies presenting with cystic kidneys, retinal degeneration, and cerebellar/neural tube malformation. Whether defects in kidney, retinal, or neural disease primarily involve ciliary, Hedgehog, or cell polarity pathways remains unclear. Using high-confidence proteomics, we identified 850 interactors copurifying with nine NPHP/JBTS/MKS proteins and discovered three connected modules: "NPHP1-4-8" functioning at the apical surface, "NPHP5-6" at centrosomes, and "MKS" linked to Hedgehog signaling. Assays for ciliogenesis and epithelial morphogenesis in 3D renal cultures link renal cystic disease to apical organization defects, whereas ciliary and Hedgehog pathway defects lead to retinal or neural deficits. Using 38 interactors as candidates, linkage and sequencing analysis of 250 patients identified ATXN10 and TCTN2 as new NPHP-JBTS genes, and our Tctn2 mouse knockout shows neural tube and Hedgehog signaling defects. Our study further illustrates the power of linking proteomic networks and human genetics to uncover critical disease pathways.
Eukaryotic cilia and flagella, including primary cilia and sensory cilia, are highly conserved organelles that project from the surfaces of many cells. The assembly and maintenance of these nearly ubiquitous structures are dependent on a transport system--known as 'intraflagellar transport' (IFT)--which moves non-membrane-bound particles from the cell body out to the tip of the cilium or flagellum, and then returns them to the cell body. Recent results indicate that defects in IFT might be a primary cause of some human diseases.