Epithelial to Stromal Re-Distribution of Primary Cilia during Pancreatic Carcinogenesis

Diminution of Primary Cilia in the Stromal Cells at the Tumor-stromal Interface Correlates With an Aggressive Tumor Biology in the Urothelial Carcinoma of the Urinary Bladder

BACKGROUND AND AIMS

Primary cilia (PC) are cellular organelles that regulate the cellular homeostasis. They are the seats of many oncogenic pathways and indirectly regulate the epithelial-mesenchymal transition (EMT) and extracellular matrix, both critical for the tumor microenvironment (TME). Though there are a few studies highlighting the alteration of PC in the tumor cells of various malignancies, none depict the PC in the stromal cells in the urothelial carcinoma of the urinary bladder (UC), the stromal cells being an essential component of TME. Therefore, we intend to evaluate the PC in the stromal cells at the tumor-stromal interface in UC.

METHODS

Immunohistochemistry for acetylated-α-tubulin (for PC), Ki67, E-cadherin, and SNAI1 was performed in 141 cases of UC and 5 normal controls, and primary cilium: nucleus (C:N) ratio was counted in the stromal cells at the tumor-stromal interface. The C:N ratio was correlated with various clinical and histopathological parameters.

RESULTS

The C:N ratio showed significant diminution from normal control (mean=0.75) to low-grade UC (mean=0.24) ( P =0.001) to high-grade UC (mean value=0.17) ( P =0.001). There was a significant diminution of the C:N ratio from the noninvasive to invasive UC ( P =0.025). The C:N ratio did not show any correlation with EMT although negatively correlated with the Ki67 index ( r =-0.32; P =0.001), and a higher ratio showed a trend with a higher recurrence-free survival ( P =0.07).

CONCLUSIONS

The diminution of the PC in the stromal cells at the tumor-stromal interface is an early event and correlates with an aggressive tumor biology of UC.

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.

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.

Increase in primary cilia number and length upon VDAC1 depletion contributes to attenuated proliferation of cancer cells

Primary cilia (PCs) that are present in most human cells and perform sensory function or signal transduction are lost in many solid tumors. Previously, we identified VDAC1, best known to regulate mitochondrial bioenergetics, to negatively regulate ciliogenesis. Here, we show that downregulation of VDAC1 in pancreatic cancer-derived Panc1 and glioblastoma-derived U-87MG cells significantly increased ciliation. Those PCs were significantly longer than the control cells. Such increased ciliation possibly inhibited cell cycle, which contributed to reduced proliferation of these cells. VDAC1-depletion also led to longer PCs in quiescent RPE1 cells. Therefore, serum-induced PC disassembly was slower in VDAC1-depleted RPE1 cells. Overall, this study reiterates the importance of VDAC1 in modulating tumorigenesis, due to its novel role in regulating PC disassembly and cilia length.

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.

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.

Primary cilia regulate gastric cancer-induced bone loss via cilia/Wnt/β-catenin signaling pathway

Cancer-associated bone disease is a frequent occurrence in cancer patients and is associated with pain, bone fragility, loss, and fractures. However, whether primary or non-bone metastatic gastric cancer induces bone loss remains unclear. Here, we collected clinical evidence of bone loss by analyzing serum and X-rays of 25 non-bone metastatic gastric cancer patients. In addition, C57BL mice were injected with the human gastric cancer cell line HGC27 and its effect on bone mass was analyzed by Micro-CT, immunoblotting, and immunohistochemistry. Furthermore, the degree of the proliferation and osteogenic differentiation of mesenchymal stem cells (MSCs) co-cultured with HGC-27 or SGC-7901 cells was analyzed by colony-formation assay, alizarin red staining, immunofluorescence, qPCR, immunoblotting, and alkaline phosphatase activity assay. These indicated that gastric cancer could damage bone tissue before the occurrence of bone metastases. We also found that cilia formation of MSCs was increased in the presence of HGC27 cells, which was associated with abnormal activation of the Wnt/β-catenin pathway. Expression of DKK1 inhibited the Wnt/β-catenin signaling pathway and partially rescued osteogenic differentiation of MSCs. In summary, our results suggest that gastric cancer cells might cause bone damage prior to the occurrence of bone metastasis via cilia-dependent activation of the Wnt/β-catenin signaling pathway.

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.

Silica Perturbs Primary Cilia and Causes Myofibroblast Differentiation during Silicosis by Reduction of the KIF3A-Repressor GLI3 Complex

The purpose of this study was to determine the effects of Kinesin family member 3A (KIF3A) on primary cilia and myofibroblast differentiation during silicosis by regulating Sonic hedgehog (SHH) signalling. Methods: Changes in primary cilia during silicosis and myofibroblast differentiation were detected in silicotic patients, experimental silicotic rats, and a myofibroblast differentiation model induced by SiO₂. We also explored the mechanisms underlying KIF3A regulation of Glioma-associated oncogene homologs (GLIs) involved in myofibroblast differentiation. Results: Primary cilia (marked by ARL13B and Ac-α-Tub) and ciliary-related proteins (IFT 88 and KIF3A) were increased initially and then decreased as silicosis progressed. Loss and shedding of primary cilia were also found during silicosis. Treatment of MRC-5 fibroblasts with silica and then transfection of KIF3A-siRNA blocked activation of SHH signalling, but increased GLI2^FL as a transcriptional activator of SRF, and reduced the inhibitory effect of GLI3^R on ACTA2. Conclusion: Our findings indicate that primary cilia are markedly altered during silicosis and the loss of KIF3A may promote myofibroblast differentiation induced by SiO₂.

Ciliary signalling in cancer

Although tumours initiate from oncogenic changes in a cancer cell, subsequent tumour progression and therapeutic response depend on interactions between the cancer cells and the tumour microenvironment (TME). The primary monocilium, or cilium, provides a spatially localized platform for signalling by Hedgehog, Notch, WNT and some receptor tyrosine kinase pathways and mechanosensation. Changes in ciliation of cancer cells and/or cells of the TME during tumour development enforce asymmetric intercellular signalling in the TME. Growing evidence indicates that some oncogenic signalling pathways as well as some targeted anticancer therapies induce ciliation, while others repress it. The links between the genomic profile of cancer cells, drug treatment and ciliary signalling in the TME likely affect tumour growth and therapeutic response.