HDAC6 inhibition restores ciliary expression and decreases tumor growth

The regulation of cilium assembly and disassembly in development and disease

The primary cilium is an antenna-like organelle assembled on most types of quiescent and differentiated mammalian cells. This immotile structure is essential for interpreting extracellular signals that regulate growth, development and homeostasis. As such, ciliary defects produce a spectrum of human diseases, termed ciliopathies, and deregulation of this important organelle also plays key roles during tumor formation and progression. Recent studies have begun to clarify the key mechanisms that regulate ciliary assembly and disassembly in both normal and tumor cells, highlighting new possibilities for therapeutic intervention. Here, we review these exciting new findings, discussing the molecular factors involved in cilium formation and removal, the intrinsic and extrinsic control of cilium assembly and disassembly, and the relevance of these processes to mammalian cell growth and disease.

HDAC6 inhibitor TST strengthens the antiproliferative effects of PI3K/mTOR inhibitor BEZ235 in breast cancer cells via suppressing RTK activation

NVP-BEZ235 (BEZ235), an available dual PI3K/mTOR inhibitor, showed antitumor effect and provided a therapy strategy in carcinomas. However, the acquired upregulation of multiple receptor tyrosine kinases (RTKs) by NVP-BEZ235 in tumors limits its clinical efficacy. HDAC6, a class II histone deacetylase, is associated with expressions of multiple RTKs. The aim of this study was to detect whether co-treatment with HDAC6 inhibitor Tubastatin A (TST) would enhance the anticancer effects of BEZ235 in breast cancer cells. In this study, we described that treatment of breast cancer cell lines (T47D, BT474, and MDA-MB-468) with BEZ235 significantly triggered PI3K/mTOR signaling inactivation and increased multiple RTK expression, including EGFR, HER2, HER3, IGF-1 receptor, insulin receptor, and their phosphorylation levels. The adding of TST destabilized these RTKs in those breast cancer cells. Co-treatment with BEZ235 and TST reduced cell proliferative rate by strengthening Akt inactivation. In addition, the combination of these two drugs also cooperatively arrested cell cycle and DNA synthesis. In conclusion, the co-treatment with PI3K/mTOR inhibitor BEZ235 and HDAC6 inhibitor TST displayed additive antiproliferative effects on breast cancer cells through inactivating RTKs and established a rationable combination therapy to treat breast cancer.

MicroRNA (miR)-433 and miR-22 dysregulations induce histone-deacetylase-6 overexpression and ciliary loss in cholangiocarcinoma

Cholangiocytes normally express primary cilia, a multisensory organelle that detects signals from the cellular environment. Cilia are significantly reduced in cholangiocarcinoma (CCA) by a mechanism involving overexpression of histone deacetylase 6 (HDAC6). Despite HDAC6 overexpression in CCA, we found no differences in its mRNA level, suggesting a posttranscriptional regulation, possibly involving microRNAs (miRNAs). Here, we describe that at least two HDAC6-targeting miRNAs, miR-433 and miR-22, are down-regulated in CCA both in vitro and in vivo. Experimental restoration of these miRNAs in CCA cells reduced HDAC6 expression, induced ciliary restoration, and decreased the malignant phenotype. Furthermore, in contrast to the mature forms, levels of precursor forms of these miRNAs were higher in CCA compared to normal cholangiocytes and accumulated in the nuclei, suggesting a defective nuclear export. We assessed the expression of Exportin-5, the protein responsible for transporting miRNA precursors out of the nucleus, and found it to be reduced by 50% in CCA compared to normal cholangiocytes. Experimental overexpression of Exportin-5 in CCA cells restored precursor and mature forms of these miRNAs to normal levels, inducing a decrease in the expression of HDAC6 and a decrease in the malignant phenotype. Conversely, short hairpin RNA (shRNA) depletion of Exportin-5 in normal cholangiocytes resulted in increased nuclear retention of precursor miRNAs, decreased mature miRNAs, increased cell proliferation, and shorter cilia.

CONCLUSION

These data suggest that down-regulated Exportin-5 impairs the nuclear export of miR-433 and miR-22 precursor forms, causing a decrease in levels of mature miR-433 and miR-22 forms, and leading to overexpression of HDAC6 and ciliary loss in CCA. (Hepatology 2018).

Cilium structure, assembly, and disassembly regulated by the cytoskeleton

The cilium, once considered a vestigial structure, is a conserved, microtubule-based organelle critical for transducing extracellular chemical and mechanical signals that control cell polarity, differentiation, and proliferation. The cilium undergoes cycles of assembly and disassembly that are controlled by complex inter-relationships with the cytoskeleton. Microtubules form the core of the cilium, the axoneme, and are regulated by post-translational modifications, associated proteins, and microtubule dynamics. Although actin and septin cytoskeletons are not major components of the axoneme, they also regulate cilium organization and assembly state. Here, we discuss recent advances on how these different cytoskeletal systems­ affect cilium function, structure, and organization.

Role of HDAC6 in primary digestive system malignancies

Cancer has become the second leading cause of death around the world following cardiovascular disease. The morbidity and mortality of digestive system malignancies rank among the top in malignant tumors. Cancer occurrence and development are a multi-factor and multi-stage process. Acetylation and deacetylation play an important role in the development of cancer. Deacetylation of proteins is regulated by histone deacetylases (HDACs). A total of 18 human HDACs have been discovered, among which HDAC6 is the most widely studied. It has been demonstrated that HDAC6 is highly expressed in a variety of tumor tissues and associated with the clinicopathological characteristics of these tumors. What's more, HDAC6 selective inhibitors can inhibit the growth of many cancer cells. In the present review, we summarize the role of HDAC6 in primary digestive system malignancies.

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.

FAM65B controls the proliferation of transformed and primary T cells

Cell quiescence is controlled by regulated genome-encoded programs that actively express genes which are often down-regulated or inactivated in transformed cells. Among them is FoxO1, a transcription factor that imposes quiescence in several cell types, including T lymphocytes. In these cells, the FAM65B encoding gene is a major target of FOXO1. Here, we show that forced expression of FAM65B in transformed cells blocks their mitosis because of a defect of the mitotic spindle, leading to G2 cell cycle arrest and apoptosis. Upon cell proliferation arrest, FAM65B is engaged in a complex containing two proteins well known to be involved in cell proliferation i.e. the HDAC6 deacetylase and the 14.3.3 scaffolding protein. In primary T cells, FAM65B is down-regulated upon T cell receptor engagement, and maintaining its expression blocks their proliferation, establishing that the decrease of FAM65B expression is required for proliferation. Conversely, inhibiting FAM65B expression in naive T lymphocytes decreases their activation threshold. These results identify FAM65B as a potential new target for controlling proliferation of both transformed and normal cells.

Pathobiology of biliary epithelia

Cholangiocytes are epithelial cells that line the intra- and extrahepatic biliary tree. They serve predominantly to mediate the content of luminal biliary fluid, which is controlled via numerous signaling pathways influenced by endogenous (e.g., bile acids, nucleotides, hormones, neurotransmitters) and exogenous (e.g., microbes/microbial products, drugs etc.) molecules. When injured, cholangiocytes undergo apoptosis/lysis, repair and proliferation. They also become senescent, a form of cell cycle arrest, which may prevent propagation of injury and/or malignant transformation. Senescent cholangiocytes can undergo further transformation to a senescence-associated secretory phenotype (SASP), where they begin secreting pro-inflammatory and pro-fibrotic signals that may contribute to disease initiation and progression. These and other concepts related to cholangiocyte pathobiology will be reviewed herein. This article is part of a Special Issue entitled: Cholangiocytes in Health and Disease edited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

The cholangiocyte primary cilium in health and disease

Cholangiocytes, like most cells, express primary cilia extending from their membranes. These organelles function as antennae which detect stimuli from bile and transmit the information into cells regulating several signaling pathways involved in secretion, proliferation and apoptosis. The ability of primary cilia to detect different signals is provided by ciliary associated proteins which are expressed in its membrane. Defects in the structure and/or function of these organelles lead to cholangiociliopathies that result in cholangiocyte hyperproliferation, altered fluid secretion and absorption. Since primary cilia dysfunction has been observed in several epithelial tumors, including cholangiocarcinoma (CCA), primary cilia have been proposed as tumor suppressor organelles. In addition, the loss of cilia is associated with dysregulation of several molecular pathways resulting in CCA development and progression. Thus, restoration of the primary cilia may be a potential therapeutic approach for several ciliopathies and CCA.

LPA signaling is regulated through the primary cilium: a novel target in glioblastoma

The primary cilium is a ubiquitous organelle presented on most human cells. It is a crucial signaling hub for multiple pathways including growth factor and G-protein coupled receptors. Loss of primary cilia, observed in various cancers, has been shown to affect cell proliferation. Primary cilia formation is drastically decreased in glioblastoma (GBM), however, the role of cilia in normal astrocyte or glioblastoma proliferation has not been explored. Here, we report that loss of primary cilia in human astrocytes stimulates growth rate in a lysophosphatidic acid (LPA)-dependent manner. We show that lysophosphatidic acid receptor 1 (LPAR1) is accumulated in primary cilia. LPAR1 signaling through Gα12/Gαq was previously reported to be responsible for cancer cell proliferation. We found that in ciliated cells, Gα12 and Gαq are excluded from the cilium, creating a barrier against unlimited proliferation, one of the hallmarks of cancer. Upon loss of primary cilia, LPAR1 redistributes to the plasma membrane with a concomitant increase in LPAR1 association with Gα12 and Gαq. Inhibition of LPA signaling with the small molecule compound Ki16425 in deciliated highly proliferative astrocytes or glioblastoma patient-derived cells/xenografts drastically suppresses their growth both in vitro and in vivo. Moreover, Ki16425 brain delivery via PEG-PLGA nanoparticles inhibited tumor progression in an intracranial glioblastoma PDX model. Overall, our findings establish a novel mechanism by which primary cilium restricts proliferation and indicate that loss of primary cilia is sufficient to increase mitogenic signaling, and is important for the maintenance of a highly proliferative phenotype. Clinical application of LPA inhibitors may prove beneficial to restrict glioblastoma growth and ensure local control of disease.

Effect of Tubastatin A on the Functional Recovery of Cauda Equina Injury in Rats

OBJECTIVE

To explore the effect of the inhibitor of histone deacetylase (6HDAC6), tubastatin A, on the functional recovery of injured central branch of dorsal root ganglia (cauda equina).

METHODS

A total of 30 Sprague-Dawley rats (n = 10 for each group) were divided randomly into sham operation (sham group), cauda equina compression control (CEC control group), and cauda equina compression plus tubastatin A treatment (tubastatin A group). The tail-flick test was performed to detect the sense of pain and warmth as well as motor function. Immunoblotting/immunofluorescence experiments, terminal deoxynucleotidyl transferase dUTP nick end labeling staining, and hematoxylin-eosin staining were performed to detect the amount of HDAC6 in dorsal root ganglion (DRG) neurons, degree of apoptosis in DRG neurons, and degree of cauda equina injury, respectively.

RESULTS

The ratio of apoptotic cells in the CEC control group was greater than that in the sham group, whereas it decreased in the tubastatin A group. Hematoxylin-eosin staining revealed that the fibers of cauda equina in the tubastatin A group were more compact compared with those in the CEC control group. The expression of HDAC6 was not different between the sham and CEC control groups, whereas it decreased significantly in the tubastatin A group. Tubastatin A administration shortened tail-flick latency on the seventh day after operation compared with the CEC control group.

CONCLUSIONS

Tubastatin A significantly decreased the expression of HDAC6 in DRG neurons with injured cauda equina, inhibited the apoptosis of neural cells and axonal demyelinating changes in cauda equina, and partially promoted the recovery of neural function.

Combination of a Histone Deacetylase 6 Inhibitor and a Somatostatin Receptor Agonist Synergistically Reduces Hepatorenal Cystogenesis in an Animal Model of Polycystic Liver Disease

Hepatic cystogenesis in polycystic liver disease (PLD) is associated with abnormalities in multiple cellular processes, including elevated cAMP and overexpression of histone deacetylase 6 (HDAC6). Disease progression in polycystic kidney (PCK) rats (an animal model of PLD) is attenuated by inhibition of either cAMP production or HDAC6. Therefore, we hypothesized that concurrent targeting of HDAC6 and cAMP would synergistically reduce cyst growth. Changes in hepatorenal cystogenesis were examined in PCK rats treated with a pan-HDAC inhibitor, panobinostat; three specific HDAC6 inhibitors, ACY-1215, ACY-738, and ACY-241; and a combination of ACY-1215 and the somatostatin receptor analogue, pasireotide. We also assessed effects of ACY-1215 and pasireotide alone and in combination on cell proliferation, cAMP production, and expression of acetylated α-tubulin in vitro in cultured cholangiocytes and the length of primary cilia and the frequency of ciliated cholangiocytes in vivo in PCK rats. Panobinostat and all three HDAC6 inhibitors decreased hepatorenal cystogenesis in PCK rats. ACY-1215 was more effective than other HDAC inhibitors and was chosen for combinational treatment. ACY-1215 + pasireotide combination synergistically reduced cyst growth and increased length of primary cilia in PCK rats. In cultured cystic cholangiocytes, ACY-1215 + pasireotide combination concurrently decreased cell proliferation and inhibited cAMP levels. These data suggest that the combination of drugs that inhibit HDAC6 and cAMP may be an effective therapy for PLD.

A synthetic combinatorial approach to disabling deviant Hedgehog signaling

Mutations in components of the Hedgehog (HH) signal transduction pathway are found in the majority of basal cell carcinoma (BCC) and medulloblastoma incidents. Cancerous cells with intrinsic or acquired resistance to antagonists targeting the seven transmembrane effector Smoothened (SMO) frequently invoke alternative mechanisms for maintaining deviant activity of the GLI DNA binding proteins. Here we introduce a chemical agent that simultaneously achieves inhibition of SMO and GLI activity by direct targeting of the SMO heptahelical domain and the GLI-modifying enzymes belonging to the histone deacetylase (HDAC) family. We demonstrate a small molecule SMO-HDAC antagonist (IHR-SAHA) retains inhibitory activity for GLI transcription induced by SMO-dependent and -independent mechanisms frequently associated with cancer biogenesis. Synthetic combinatorial therapeutic agents such as IHR-SAHA that a priori disable cancer drivers and anticipated mechanisms of drug resistance could extend the duration of disease remission, and provide an alternative clinical development path for realizing combinatorial therapy modalities.

Functional interplay between cylindromatosis and histone deacetylase 6 in ciliary homeostasis revealed by phenotypic analysis of double knockout mice

Cilia are present in most vertebrate tissues with a wide variety of functions, and abnormalities of cilia are linked to numerous human disorders. However, the molecular events underlying ciliary homeostasis are poorly understood. In this study, we generated double knockout (DKO) mice for the deubiquitinase cylindromatosis (CYLD) and histone deacetylase 6 (HDAC6), two critical ciliary regulators. The Cyld/Hdac6 DKO mice were phenotypically normal and showed no obvious variances in weight or behavior compared with their wild-type littermates. Strikingly, Cyld loss-induced ciliary defects in the testis, trachea, and kidney were abrogated in the Cyld/Hdac6 DKO mice. In addition, the diminished α-tubulin acetylation and impaired sonic hedgehog signaling caused by loss of Cyld were largely restored by simultaneous deletion of Hdac6. We further found by immunofluorescence microscopy a colocalization of CYLD and HDAC6 at the centrosome/basal body and, interestingly, loss of Cyld promoted the localization of HDAC6 at the centrosome/basal body. These findings provide physiological insight into the ciliary role of the CYLD/HDAC6 axis and suggest a functional interplay between these two proteins in ciliary homeostasis.

Primary Cilia in Brain Development and Diseases

The primary cilium, a sensory appendage that is present in most mammalian cells, plays critical roles in signaling pathways and cell cycle progression. Mutations that affect the structure or function of primary cilia result in ciliopathies, a group of developmental and degenerative diseases that affect almost all organs and tissues. Our understanding of the constituents, development, and function of primary cilia has advanced considerably in recent years, revealing pathogenic mechanisms that potentially underlie ciliopathies. In the brain, the primary cilia are crucial for early patterning, neurogenesis, neuronal maturation and survival, and tumorigenesis, mostly through regulating cell cycle progression, Hedgehog signaling, and WNT signaling. We review these advances in our knowledge of primary cilia, focusing on brain development, and discuss the mechanisms that may underlie brain abnormalities in ciliopathies.

Critical role of the HDAC6-cortactin axis in human megakaryocyte maturation leading to a proplatelet-formation defect

Thrombocytopenia is a major side effect of a new class of anticancer agents that target histone deacetylase (HDAC). Their mechanism is poorly understood. Here, we show that HDAC6 inhibition and genetic knockdown lead to a strong decrease in human proplatelet formation (PPF). Unexpectedly, HDAC6 inhibition-induced tubulin hyperacetylation has no effect on PPF. The PPF decrease induced by HDAC6 inhibition is related to cortactin (CTTN) hyperacetylation associated with actin disorganization inducing important changes in the distribution of megakaryocyte (MK) organelles. CTTN silencing in human MKs phenocopies HDAC6 inactivation and knockdown leads to a strong PPF defect. This is rescued by forced expression of a deacetylated CTTN mimetic. Unexpectedly, unlike human-derived MKs, HDAC6 and CTTN are shown to be dispensable for mouse PPF in vitro and platelet production in vivo. Our results highlight an unexpected function of HDAC6–CTTN axis as a positive regulator of human but not mouse MK maturation.

Histone deacetylase (HDAC) inhibitors, a class of cancer therapeutics, cause thrombocytopenia via an unknown mechanism. Here, the authors show that HDAC6 inhibition impairs proplatelet formation in human megakaryocytes, and show that this is linked to hyperacetylation of the actin-binding protein cortactin.

Maintaining centrosomes and cilia

Centrosomes and cilia are present in organisms from all branches of the eukaryotic tree of life. These structures are composed of microtubules and various other proteins, and are required for a plethora of cell processes such as structuring the cytoskeleton, sensing the environment, and motility. Deregulation of centrosome and cilium components leads to a wide range of diseases, some of which are incompatible with life. Centrosomes and cilia are thought to be very stable and can persist over long periods of time. However, these structures can disappear in certain developmental stages and diseases. Moreover, some centrosome and cilia components are quite dynamic. While a large body of knowledge has been produced regarding the biogenesis of these structures, little is known about how they are maintained. In this Review, we propose the existence of specific centrosome and cilia maintenance programs, which are regulated during development and homeostasis, and when deregulated can lead to disease.

Anti-cancer effects of naturally derived compounds targeting histone deacetylase 6-related pathways

Alterations of the epigenetic machinery, affecting multiple biological functions, represent a major hallmark enabling the development of tumors. Among epigenetic regulatory proteins, histone deacetylase (HDAC)6 has emerged as an interesting potential therapeutic target towards a variety of diseases including cancer. Accordingly, this isoenzyme regulates many vital cellular regulatory processes and pathways essential to physiological homeostasis, as well as tumor multistep transformation involving initiation, promotion, progression and metastasis. In this review, we will consequently discuss the critical implications of HDAC6 in distinct mechanisms relevant to physiological and cancerous conditions, as well as the anticancer properties of synthetic, natural and natural-derived compounds through the modulation of HDAC6-related pathways.

Primary cilia: Cell and molecular mechanosensors directing whole tissue function

Primary cilia are immotile, microtubule-based organelles extending from the surface of nearly every mammalian cell. Mechanical stimulation causes deflection of the primary cilium, initiating downstream signaling cascades to the rest of the cell. The cilium forms a unique subcellular microdomain, and defects in ciliary protein composition or physical structure have been associated with a myriad of human pathologies. In this review, we discuss the importance of ciliary mechanotransduction at the cell and tissue level, and how furthering our molecular understanding of primary cilia mechanobiology may lead to therapeutic strategies to treat human diseases.

Vorinostat-eluting poly(DL-lactide-co-glycolide) nanofiber-coated stent for inhibition of cholangiocarcinoma cells

Purpose

The aim of this study was to fabricate a vorinostat (Zolinza™)-eluting nanofiber membrane-coated gastrointestinal (GI) stent and to study its antitumor activity against cholangiocarcinoma (CCA) cells in vitro and in vivo.

Methods

Vorinostat and poly(DL-lactide-co-glycolide) dissolved in an organic solvent was sprayed onto a GI stent to make a nanofiber-coated stent using an electro-spinning machine. Intact vorinostat and vorinostat released from nanofibers was used to assess anticancer activity in vitro against various CCA cells. The antitumor activity of the vorinostat-eluting nanofiber membrane-coated stent was evaluated using HuCC-T1 bearing mice.

Results

A vorinostat-incorporated polymer nanofiber membrane was formed on the surface of the GI stent. Vorinostat was continuously released from the nanofiber membrane over 10 days, and its release rate was higher in cell culture media than in phosphate-buffered saline. Released vorinostat showed similar anticancer activity against various CCA cells in vitro compared to that of vorinostat. Like vorinostat, vorinostat released from nanofibers induced acetylation of histone H4 and inhibited histone deacetylases 1⋅3⋅4/5/7 expression in vitro and in vivo. Furthermore, vorinostat nanofibers showed a higher tumor growth inhibition rate in HuCC-T1 bearing mice than vorinostat injections.

Conclusion

Vorinostat-eluting nanofiber membranes showed significant antitumor activity against CCA cells in vitro and in vivo. We suggest the vorinostat nanofiber-coated stent may be a promising candidate for CCA treatment.

Chlamydomonas FAP265 is a tubulin polymerization promoting protein, essential for flagellar reassembly and hatching of daughter cells from the sporangium

Tubulin polymerization promoting proteins (TPPPs) belong to a family of neomorphic moon lighting proteins, involved in various physiological and pathological conditions. In physiological conditions, TPPPs play an important role in microtubule dynamics regulating mitotic spindle assembly and in turn cell proliferation. In pathological situations, TPPPs interact with α-synuclein and β-amyloid and promote their aggregation leading to Parkinson’s disease and multiple system atrophy. Orthologs of TPPP family proteins were identified in ciliary proteomes from various organisms including Chlamydomonas but their role in ciliogenesis was not known. Here we showed that Flagellar Associated Protein, FAP265, a Chlamydomonas homologue of TPPP family proteins, localizes in the cytosol, at the basal bodies and in the flagella of vegetative Chlamydomonas cells. During cell division, the protein was found as a distinct spot in the nucleus and at the cleavage furrow which forms between the daughter cells. Further null mutants of Chlamydomonas FAP265 protein, fap265, showed severe defects in hatching from the mother sporangium. Daughter cells of fap265 were significantly larger in size compared with wild type cells. Moreover, the daughter cells present within the mother sporangium failed to form flagella before hatching. They reassembled their flagella only after hatching from the sporangium suggesting that FAP265 plays an important role in flagellar reassembly after cell division.

The search for novel diagnostic and prognostic biomarkers in cholangiocarcinoma

The poor prognosis of cholangiocarcinoma (CCA) is in part due to late diagnosis, which is currently achieved by a combination of clinical, radiological and histological approaches. Available biomarkers determined in serum and biopsy samples to assist in CCA diagnosis are not sufficiently sensitive and specific. Therefore, the identification of new biomarkers, preferably those obtained by minimally invasive methods, such as liquid biopsy, is important. The development of innovative technologies has permitted to identify a significant number of genetic, epigenetic, proteomic and metabolomic CCA features with potential clinical usefulness in early diagnosis, prognosis or prediction of treatment response. Potential new candidates must be rigorously evaluated prior to entering routine clinical application. Unfortunately, to date, no such biomarker has achieved validation for these purposes. This review is an up-to-date of currently used biomarkers and the candidates with promising characteristics that could be included in the clinical practice in the next future. This article is part of a Special Issue entitled: Cholangiocytes in Health and Disease edited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

SOX17 regulates cholangiocyte differentiation and acts as a tumor suppressor in cholangiocarcinoma

BACKGROUND & AIMS

Cholangiocarcinoma (CCA) is a biliary malignancy linked to genetic and epigenetic abnormalities, such as hypermethylation of SOX17 promoter. Here, the role of SOX17 in cholangiocyte differentiation and cholangiocarcinogenesis was studied.

METHODS

SOX17 expression/function was evaluated along the differentiation of human induced pluripotent stem cells (iPSC) into cholangiocytes, in the dedifferentiation process of normal human cholangiocytes (NHC) in culture and in cholangiocarcinogenesis. Lentiviruses for SOX17 overexpression or knockdown were used. Gene expression and DNA methylation profiling were performed.

RESULTS

SOX17 expression is induced in the last stage of cholangiocyte differentiation from iPSC and regulates the acquisition of biliary markers. SOX17 becomes downregulated in NHC undergoing dedifferentiation; experimental SOX17 knockdown in differentiated NHC downregulated biliary markers and promoted baseline and Wnt-dependent proliferation. SOX17 expression is lower in human CCA than in healthy tissue, which correlates with worse survival after tumor resection. In CCA cells, SOX17 overexpression decreased their tumorigenic capacity in murine xenograft models, which was related to increased oxidative stress and apoptosis. In contrast, SOX17 overexpression in NHC did not affect their survival but inhibited their baseline proliferation. In CCA cells, SOX17 inhibited migration, anchorage-independent growth and Wnt/β-catenin-dependent proliferation, and restored the expression of biliary markers and primary cilium length. In human CCA, SOX17 promoter was found hypermethylated and its expression inversely correlates with the methylation grade. In NHC, Wnt3a decreased SOX17 expression in a DNMT-dependent manner, whereas in CCA, DNMT1 inhibition or silencing upregulated SOX17.

CONCLUSIONS

SOX17 regulates the differentiation and maintenance of the biliary phenotype and functions as a tumor suppressor for CCA, being a potential prognostic marker and a promising therapeutic target.

LAY SUMMARY

Understanding the molecular mechanisms involved in the pathogenesis of CCA is key in finding new valuable diagnostic and prognostic biomarkers, as well as therapeutic targets. This study provides evidence that SOX17 regulates the differentiation and maintenance of the biliary phenotype, and its downregulation promotes their tumorigenic transformation. SOX17 acts as a tumor suppressor in CCA and its genetic, molecular and/or pharmacological restoration may represent a new promising therapeutic strategy. Moreover, SOX17 expression correlates with the outcome of patients after tumor resection, being a potential prognostic biomarker.

The Fungal Metabolite Brefeldin A Inhibits Dvl2-Plk1-Dependent Primary Cilium Disassembly

The primary cilium is a non-motile microtubule-based organelle that protrudes from the surface of most human cells and works as a cellular antenna to accept extracellular signals. Primary cilia assemble from the basal body during the resting stage (G0 phase) and simultaneously disassemble with cell cycle re-entry. Defective control of assembly or disassembly causes diverse human diseases including ciliopathy and cancer. To identify the effective compounds for studying primary cilium disassembly, we have screened 297 natural compounds and identified 18 and 17 primary cilium assembly and disassembly inhibitors, respectively. Among them, the application of KY-0120, identified as Brefeldin A, disturbed Dvl2-Plk1-mediated cilium disassembly via repression of the interaction of CK1ɛ-Dvl2 and the expression of Plk1 mRNA. Therefore, our study may suggest useful compounds for studying the cellular mechanism of primary cilium disassembly to prevent ciliopathy and cancer.

Inhibition of Ciliogenesis Promotes Hedgehog Signaling, Tumorigenesis, and Metastasis in Breast Cancer

Primary cilia are chemosensors that play a dual role to either activate or repress Hedgehog signaling, depending on presence or absence of ligand, respectively. While inhibition of ciliogenesis has been shown to be characteristic of breast cancers, the functional consequence is unknown. Here, for the first time, inhibition of ciliogenesis led to earlier tumor formation, faster tumor growth rate, higher grade tumor formation, and increased metastasis in the polyoma middle T (PyMT) mouse model of breast cancer. In in vitro model systems, inhibition of ciliogenesis resulted in increased expression of Hedgehog-target genes through a mechanism involving loss of the repressor form of the GLI transcription factor (GLIR) and activation of Hedgehog target gene expression through cross-talk with TGF-alpha (TGFA) signaling. Bioinformatics analysis revealed that increased Hedgehog signaling is frequently associated with increased TGFA; signaling in patients with triple-negative breast cancers (TNBC), a particularly aggressive breast cancer subtype. These results identify a previously unrecognized role for inhibition of ciliogenesis in breast cancer progression. This study identifies inhibition of ciliogenesis as an important event for activation of Hedgehog signaling and progression of breast cancer to a more aggressive, metastatic disease.Implications: These findings change the way we understand how cancer cells turn on a critical signaling pathways and a provide rationale for developing novel therapeutic approaches to target noncanonical Hedgehog signaling for the treatment of breast cancer. Mol Cancer Res; 15(10); 1421-30. ©2017 AACR.

HDAC6 inhibition suppresses chondrosarcoma by restoring the expression of primary cilia

Chondrosarcoma is a bone tumor characterized by the secretion of a cartilage-like extracellular matrix. It has been proved to lack extracellular sensor primary cilia. This study aimed to illustrate a feasible therapeutic method for chondrosarcoma by regulating primary cilia assembly through inhibiting histone deacetylases 6 (HDAC6) activation. In order to detect the interaction between primary cilia and HDAC6 in human chondrosarcoma, Tubastatin A and small interfering RNA (siRNA) were used to inhibit the endogenous expression of HDAC6. Cell viability test and Transwell assay were applied to evaluate the effects of malignant biological properties. Primary cilia staining and related proteins were detected. The abnormal expression of HDAC6 and cilia intraflagellar transport protein 88 (IFT88) was found in chondrosarcoma tissues. The inhibition of HDAC6 could downregulate the proliferation of chondrosarcoma cells in a concentration- and time-dependent manner and suppress the invasion capacity of tumor cells. Besides, the downregulation of HDAC6 exhibited a negative effect on the proliferation of relevant proteins but a positive effect on the primary cilia-related expression of IFT88 and acetylated α-tubulin. Primary cilia restoration could be observed after HDAC6 siRNA transfection. The Aurora A-HDAC6 cascade was involved in regulating primary cilia resorption by affecting α-tubulin deacetylation and Tubastatin A could inhibit chondrosarcoma cell growth in vivo. These results indicate that restricting HDAC6 can restore primary cilia assembly accompanied with suppressed chondrosarcoma cell proliferation and invasion capacities. Thus, promoting primary cilia restoration by targeting HDAC6 may be a feasible potential therapeutic method for chondro-sarcoma treatment.

The daughter centriole controls ciliogenesis by regulating Neurl-4 localization at the centrosome

During ciliogenesis, the daughter centriole is found next to the mother, but its role in this process is not known. Loukil et al. show that a daughter centriole is necessary for primary cilia formation by promoting Neurl-4–dependent removal of the negative ciliogenesis regulator CP110 from the mother.

The two centrioles of the centrosome differ in age and function. Although the mother centriole mediates most centrosome-dependent processes, the role of the daughter remains poorly understood. A recent study has implicated the daughter centriole in centriole amplification in multiciliated cells, but its contribution to primary ciliogenesis is unclear. We found that manipulations that prevent daughter centriole formation or induce its separation from the mother abolish ciliogenesis. This defect was caused by stabilization of the negative ciliogenesis regulator CP110 and was corrected by CP110 depletion. CP110 dysregulation may be caused by effects on Neurl-4, a daughter centriole–associated ubiquitin ligase cofactor, which was required for ciliogenesis. Centrosome-targeted Neurl-4 was sufficient to restore ciliogenesis in cells with manipulated daughter centrioles. Interestingly, early during ciliogenesis, Neurl-4 transiently associated with the mother centriole in a process that required mother–daughter centriole proximity. Our data support a model in which the daughter centriole promotes ciliogenesis through Neurl-4–dependent regulation of CP110 levels at the mother centriole.

HDAC2 promotes loss of primary cilia in pancreatic ductal adenocarcinoma

Loss of primary cilia is frequently observed in tumor cells, including pancreatic ductal adenocarcinoma (PDAC) cells, suggesting that the absence of this organelle may promote tumorigenesis through aberrant signal transduction and the inability to exit the cell cycle. However, the molecular mechanisms that explain how PDAC cells lose primary cilia are still ambiguous. In this study, we found that inhibition or silencing of histone deacetylase 2 (HDAC2) restores primary cilia formation in PDAC cells. Inactivation of HDAC2 results in decreased Aurora A expression, which promotes disassembly of primary cilia. We further showed that HDAC2 controls ciliogenesis independently of Kras, which facilitates Aurora A expression. These studies suggest that HDAC2 is a novel regulator of primary cilium formation in PDAC cells.

Primary cilia: a link between hormone signalling and endocrine-related cancers?

Primary cilia are sensory organelles that play a role as signalling hubs. Disruption of primary cilia structure and function is increasingly recognised in a range of cancers, with a growing body of evidence suggesting that ciliary disruption contributes to tumourigenesis. This review considers the role of primary cilia in the pathogenesis of endocrine-related cancers.

A Glasgow Tipple-transjugular intrahepatic portosystemic shunt insertion prior to Whipple resection

Abdominal surgery performed in patients with significant liver disease and portal hypertension is associated with high mortality rates, with even poorer outcomes associated with complex pancreaticobiliary operations. We report on a patient requiring portal decompression via transjugular intrahepatic portosystemic shunt (TIPS) prior to a pancreaticoduodenectomy. The 49-year-old patient presented with pain, jaundice and weight loss. At ERCP an edematous ampulla was biopsied, revealing high-grade dysplasia within a distal bile duct adenoma. Liver biopsy was performed to investigate portal hypertension, confirming congenital hepatic fibrosis (CHF). A TIPS was performed to enable a pancreaticoduodenectomy. Prophylactic TIPS can be performed for preoperative portal decompression for patients requiring pancreatic resection. A potentially curative resection was performed when abdominal surgery was initially thought impossible. Notably, CHF has been associated with the development of cholangiocarcinoma in only four previous instances, with this case being only the second reported distal bile duct cholangiocarcinoma.

Expert consensus document: Cholangiocarcinoma: current knowledge and future perspectives consensus statement from the European Network for the Study of Cholangiocarcinoma (ENS-CCA)

Cholangiocarcinoma (CCA) is a heterogeneous group of malignancies with features of biliary tract differentiation. CCA is the second most common primary liver tumour and the incidence is increasing worldwide. CCA has high mortality owing to its aggressiveness, late diagnosis and refractory nature. In May 2015, the "European Network for the Study of Cholangiocarcinoma" (ENS-CCA: www.enscca.org or www.cholangiocarcinoma.eu) was created to promote and boost international research collaboration on the study of CCA at basic, translational and clinical level. In this Consensus Statement, we aim to provide valuable information on classifications, pathological features, risk factors, cells of origin, genetic and epigenetic modifications and current therapies available for this cancer. Moreover, future directions on basic and clinical investigations and plans for the ENS-CCA are highlighted.

HDAC6-mediated EGFR stabilization and activation restrict cell response to sorafenib in non-small cell lung cancer cells

Sorafenib is a multi-targeted kinase inhibitor and has been the subject of extensive clinical research in advanced non-small cell lung cancer (NSCLC). However, sorafenib fails to improve overall survival of patients with advanced NSCLC. The molecular mechanisms that account for this phenomenon are unclear. Here we show that sorafenib treatment stabilizes epidermal growth factor receptor (EGFR) and activates EGFR pathway. Moreover, this is partly mediated by stabilization of histone deacetylase 6 (HDAC6), which has been shown to regulate EGFR endocytic trafficking and degradation. Overexpression of HDAC6 confers resistance to sorafenib in NSCLC cells. Inhibition of HDAC6 with selective inhibitors synergizes with sorafenib to kill NSCLC cells via inhibition of sorafenib-mediated EGFR pathway activation. Taken together, our findings might partly explain the failure of Phase III trial of sorafenib in improving overall survival of advanced NSCLC patients and bear possible implications for the improvement on the efficacy of sorafenib in treatment of NSCLC.

A Hippo and Fibroblast Growth Factor Receptor Autocrine Pathway in Cholangiocarcinoma

Herein, we have identified cross-talk between the Hippo and fibroblast growth factor receptor (FGFR) oncogenic signaling pathways in cholangiocarcinoma (CCA). Yes-associated protein (YAP) nuclear localization and up-regulation of canonical target genes was observed in CCA cell lines and a patient-derived xenograft (PDX). Expression of FGFR1, -2, and -4 was identified in human CCA cell lines, driven, in part, by YAP coactivation of TBX5. In turn, FGFR signaling in a cell line with minimal basal YAP expression induced its cellular protein expression and nuclear localization. Treatment of YAP-positive CCA cell lines with BGJ398, a pan-FGFR inhibitor, resulted in a decrease in YAP activation. FGFR activation of YAP appears to be driven largely by FGF5 activation of FGFR2, as siRNA silencing of this ligand or receptor, respectively, inhibited YAP nuclear localization. BGJ398 treatment of YAP-expressing cells induced cell death due to Mcl-1 depletion. In a YAP-associated mouse model of CCA, expression of FGFR 1, 2, and 4 was also significantly increased. Accordingly, BGJ398 treatment was tumor-suppressive in this model and in a YAP-positive PDX model. These preclinical data suggest not only that the YAP and Hippo signaling pathways culminate in an Mcl-1-regulated tumor survival pathway but also that nuclear YAP expression may be a biomarker to employ in FGFR-directed therapy.

Cilia in autophagy and cancer

Cancer cells are distinguished from normal cells by increased proliferation and metabolism, loss of polarity control, and the potential to invade other tissues of the body. As hubs of signaling transduction, primary cilia have been linked to diverse developmental and degenerative disorders. Interestingly, loss of cilia has been observed in multiple malignant tumors, suggesting a potential suppressive role of cilia in cancer development. More recently, emerging studies began to unveil the bidirectional interaction of cilia and autophagy, a basic cellular clearance and recycling mechanism to regulate cell homeostasis. Here, we summarize the interplay between cilia and autophagy and discuss the roles of cilia in both autophagy and cancer.

Ciliopathies: Does HDAC6 Represent a New Therapeutic Target?

Cilia are cellular appendages with critical roles in sensing and transducing environmental signals and guiding fluid flow. Consistent with these diverse activities, defects in ciliary structure or function have been implicated in a variety of human diseases, collectively known as 'ciliopathies'. Histone deacetylase 6 (HDAC6) is a unique cytoplasmic enzyme that regulates many biological processes through its deacetylase and ubiquitin-binding activities. There is accumulating evidence that HDAC6 is a major driver of ciliary disassembly. Small-molecule compounds that inhibit HDAC6 have been demonstrated to restore ciliary structure and function in several different ciliopathies. Here, we discuss recent findings that highlight the important role for HDAC6 in mediating ciliary disassembly and the potential for HDAC6-selective inhibitors as therapeutics for specific ciliopathies.

RhoA Ambivalently Controls Prominent Myofibroblast Characteritics by Involving Distinct Signaling Routes

Introduction

RhoA has been shown to be beneficial in cardiac disease models when overexpressed in cardiomyocytes, whereas its role in cardiac fibroblasts (CF) is still poorly understood. During cardiac remodeling CF undergo a transition towards a myofibroblast phenotype thereby showing an increased proliferation and migration rate. Both processes involve the remodeling of the cytoskeleton. Since RhoA is known to be a major regulator of the cytoskeleton, we analyzed its role in CF and its effect on myofibroblast characteristics in 2 D and 3D models.

Results

Downregulation of RhoA was shown to strongly affect the actin cytoskeleton. It decreased the myofibroblast marker α-sm-actin, but increased certain fibrosis-associated factors like TGF-β and collagens. Also, the detailed analysis of CTGF expression demonstrated that the outcome of RhoA signaling strongly depends on the involved stimulus. Furthermore, we show that proliferation of myofibroblasts rely on RhoA and tubulin acetylation. In assays accessing three different types of migration, we demonstrate that RhoA/ROCK/Dia1 are important for 2D migration and the repression of RhoA and Dia1 signaling accelerates 3D migration. Finally, we show that a downregulation of RhoA in CF impacts the viscoelastic and contractile properties of engineered tissues.

Conclusion

RhoA positively and negatively influences myofibroblast characteristics by differential signaling cascades and depending on environmental conditions. These include gene expression, migration and proliferation. Reduction of RhoA leads to an increased viscoelasticity and a decrease in contractile force in engineered cardiac tissue.

The hallmarks of cancer: relevance to the pathogenesis of polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a progressive inherited disorder in which renal tissue is gradually replaced with fluid-filled cysts, giving rise to chronic kidney disease (CKD) and progressive loss of renal function. ADPKD is also associated with liver ductal cysts, hypertension, chronic pain and extra-renal problems such as cerebral aneurysms. Intriguingly, improved understanding of the signalling and pathological derangements characteristic of ADPKD has revealed marked similarities to those of solid tumours, even though the gross presentation of tumours and the greater morbidity and mortality associated with tumour invasion and metastasis would initially suggest entirely different disease processes. The commonalities between ADPKD and cancer are provocative, particularly in the context of recent preclinical and clinical studies of ADPKD that have shown promise with drugs that were originally developed for cancer. The potential therapeutic benefit of such repurposing has led us to review in detail the pathological features of ADPKD through the lens of the defined, classic hallmarks of cancer. In addition, we have evaluated features typical of ADPKD, and determined whether evidence supports the presence of such features in cancer cells. This analysis, which places pathological processes in the context of defined signalling pathways and approved signalling inhibitors, highlights potential avenues for further research and therapeutic exploitation in both diseases.

Deacetylation of α-tubulin and cortactin is required for HDAC6 to trigger ciliary disassembly

Cilia play important roles in sensing extracellular signals and directing fluid flow. Ciliary dysfunction is associated with a variety of diseases known as ciliopathies. Histone deacetylase 6 (HDAC6) has recently emerged as a major driver of ciliary disassembly, but little is known about the downstream players. Here we provide the first evidence that HDAC6-mediated deacetylation of α-tubulin and cortactin is critical for its induction of ciliary disassembly. HDAC6 is localized in the cytoplasm and enriched at the centrosome and basal body. Overexpression of HDAC6 decreases the levels of acetylated α-tubulin and cortactin without affecting the expression or localization of known ciliary regulators. We also find that overexpression of α-tubulin or cortactin or their acetylation-deficient mutants enhances the ability of HDAC6 to induce ciliary disassembly. In addition, acetylation-mimicking mutants of α-tubulin and cortactin counteract HDAC6-induced ciliary disassembly. Furthermore, HDAC6 stimulates actin polymerization, and inhibition of actin polymerization abolishes the activity of HDAC6 to trigger ciliary disassembly. These findings provide mechanistic insight into the ciliary role of HDAC6 and underscore the importance of reversible acetylation in regulating ciliary homeostasis.

Proteasome inhibition reverses hedgehog inhibitor and taxane resistance in ovarian cancer

The goal of this study was to determine whether combined targeted therapies, specifically those against the Notch, hedgehog and ubiquitin-proteasome pathways, could overcome ovarian cancer chemoresistance. Chemoresistant ovarian cancer cells were exposed to gamma-secretase inhibitors (GSI-I, Compound E) or the proteasome inhibitor bortezomib, alone and in combination with the hedgehog antagonist, LDE225. Bortezomib, alone and in combination with LDE225, was evaluated for effects on paclitaxel efficacy. Cell viability and cell cycle analysis were assessed by MTT assay and propidium iodide staining, respectively. Proteasome activity and gene expression were determined by luminescence assay and qPCR, respectively. Studies demonstrated that GSI-I, but not Compound E, inhibited proteasome activity, similar to bortezomib. Proteasome inhibition decreased hedgehog target genes (PTCH1, GLI1 and GLI2) and increased LDE225 sensitivity in vitro. Bortezomib, alone and in combination with LDE225, increased paclitaxel sensitivity through apoptosis and G2/M arrest. Expression of the multi-drug resistance gene ABCB1/MDR1 was decreased and acetylation of α-tubulin, a marker of microtubule stabilization, was increased following bortezomib treatment. HDAC6 inhibitor tubastatin-a demonstrated that microtubule effects are associated with hedgehog inhibition and sensitization to paclitaxel and LDE225. These results suggest that proteasome inhibition, through alteration of microtubule dynamics and hedgehog signaling, can reverse taxane-mediated chemoresistance.

Histone deacetylase 6 represents a novel drug target in the oncogenic Hedgehog signaling pathway

Uncontrolled Hedgehog (Hh) signaling is the cause of several malignancies, including the pediatric cancer medulloblastoma, a neuroectodermal tumor affecting the cerebellum. Despite the development of potent Hh pathway antagonists, medulloblastoma drug resistance is still an unresolved issue that requires the identification of novel drug targets. Following up on our observation that histone deacetylase 6 (HDAC6) expression was increased in Hh-driven medulloblastoma, we found that this enzyme is essential for full Hh pathway activation. Intriguingly, these stimulatory effects of HDAC6 are partly integrated downstream of primary cilia, a known HDAC6-regulated structure. In addition, HDAC6 is also required for the complete repression of basal Hh target gene expression. These contrasting effects are mediated by HDAC6's impact on Gli2 mRNA and GLI3 protein expression. As a result of this complex interaction with Hh signaling, global transcriptome analysis revealed that HDAC6 regulates only a subset of Smoothened- and Gli-driven genes, including all well-established Hh targets such as Ptch1 or Gli1. Importantly, medulloblastoma cell survival was severely compromised by HDAC6 inhibition in vitro and pharmacologic HDAC6 blockade strongly reduced tumor growth in an in vivo allograft model. In summary, our data describe an important role for HDAC6 in regulating the mammalian Hh pathway and encourage further studies focusing on HDAC6 as a novel drug target in medulloblastoma.

TGR5 in the Cholangiociliopathies

A plasma membrane-bound G protein-coupled receptor, TGR5, that transmits bile acid signaling into a cellular response primarily via the cAMP pathway is expressed in human and rodent cholangiocytes and is localized to multiple, diverse subcellular compartments, including primary cilia. Ciliary-associated TGR5 plays an important role in cholangiocyte physiology and may contribute to a group of liver diseases referred to as the 'cholangiociliopathies', which include polycystic liver disease (PLD) and, possibly, cholangiocarcinoma and primary sclerosing cholangitis. Based on our observations that (1) ciliated and nonciliated cholangiocytes respond to TGR5 activation differently (i.e. the level of cAMP increases in nonciliated cholangiocytes but decreases in ciliated cells) and (2) hepatic cysts are derived from cholangiocytes that are characterized by both malformed cilia and increased cAMP levels, we hypothesized that TGR5-mediated cAMP signaling in cystic cholangiocytes contributes to hepatic cystogenesis. Indeed, our studies show that TGR5 is overexpressed and mislocalized in cystic cholangiocytes, and when activated by ligands, results in increased intracellular cAMP levels, cholangiocyte hyperproliferation and cyst growth. Our studies also show that genetic elimination of TGR5 in an animal model of PLD inhibits hepatic cystogenesis. Collectively, these data suggest the involvement of TGR5 in PLD and that TGR5 targeting in cystic cholangiocytes may have therapeutic potential.

14-3-3ε functions as an oncogene in SGC7901 gastric cancer cells through involvement of cyclin E and p27kip1

Investigation into the highly conserved 14‑3‑3ε protein has become increasingly important in cell biology due to its involvement in cell survival signaling, cell cycle control and apoptosis. The 14‑3‑3ε protein has been found to exert an impact on the development of various tumor types. However, the functional role and the possible mechanism of 14‑3‑3ε in gastric cancer remains to be elucidated. A previous study by our group indicated a negative correlation between 14‑3‑3ε expression levels and gastric cancer tissue differentiation and a positive correlation between 14‑3‑3ε expression levels and tumor infiltration, lymph node metastasis and tumor, nodes and metastasis staging. In the present study, 14‑3‑3ε suppression in the SGC7901 gastric cancer cell line was demonstrated to inhibit cell proliferation in vitro and tumor growth in vivo and the cell cycle‑associated proteins cyclin E and p27kip1 may have contributed to this antitumor effect. The present study showed for the first time that reducing the expression of 14‑3‑3ε may inhibit the proliferation and progression of gastric cancer and inhibition of this protein may provide a potential strategy for gastric cancer therapy in the future.

Loss of primary cilia occurs early in breast cancer development

BACKGROUND

Primary cilia are microtubule-based organelles that protrude from the cell surface. Primary cilia play a critical role in development and disease through regulation of signaling pathways including the Hedgehog pathway. Recent mouse models have also linked ciliary dysfunction to cancer. However, little is known about the role of primary cilia in breast cancer development. Primary cilia expression was characterized in cancer cells as well as their surrounding stromal cells from 86 breast cancer patients by counting cilia and measuring cilia length. In addition, we examined cilia expression in normal epithelial and stromal cells from reduction mammoplasties as well as histologically normal adjacent tissue for comparison.

RESULTS

We observed a statistically significant decrease in the percentage of ciliated cells on both premalignant lesions as well as in invasive cancers. This loss of cilia does not correlate with increased proliferative index (Ki67-positive cells). However, we did detect rare ciliated cancer cells present in patients with invasive breast cancer and found that these express a marker of basaloid cancers that is associated with poor prognosis (Cytokeratin 5). Interestingly, the percentage of ciliated stromal cells associated with both premalignant and invasive cancers decreased when compared to stromal cells associated with normal tissue. To understand how cilia may be lost during cancer development we analyzed the expression of genes required for ciliogenesis and/or ciliary function and compared their expression in normal versus breast cancer samples. We found that expression of ciliary genes were frequently downregulated in human breast cancers.

CONCLUSIONS

These data suggest that primary cilia are lost early in breast cancer development on both the cancer cells and their surrounding stromal cells.

Primary cilia in stem cells and neural progenitors are regulated by neutral sphingomyelinase 2 and ceramide

Human embryonic stem and induced pluripotent stem cell–derived neuroprogenitors (NPs) develop primary cilia. Ciliogenesis depends on the sphingolipid ceramide and its interaction with atypical PKC, both of which distribute to the primary cilium and the apicolateral cell membrane in NP rosettes.

We show here that human embryonic stem (ES) and induced pluripotent stem cell–derived neuroprogenitors (NPs) develop primary cilia. Ciliogenesis depends on the sphingolipid ceramide and its interaction with atypical PKC (aPKC), both of which distribute to the primary cilium and the apicolateral cell membrane in NP rosettes. Neural differentiation of human ES cells to NPs is concurrent with a threefold elevation of ceramide—in particular, saturated, long-chain C_16:0 ceramide (N-palmitoyl sphingosine) and nonsaturated, very long chain C_24:1 ceramide (N-nervonoyl sphingosine). Decreasing ceramide levels by inhibiting ceramide synthase or neutral sphingomyelinase 2 leads to translocation of membrane-bound aPKC to the cytosol, concurrent with its activation and the phosphorylation of its substrate Aurora kinase A (AurA). Inhibition of aPKC, AurA, or a downstream target of AurA, HDAC6, restores ciliogenesis in ceramide-depleted cells. Of importance, addition of exogenous C_24:1 ceramide reestablishes membrane association of aPKC, restores primary cilia, and accelerates neural process formation. Taken together, these results suggest that ceramide prevents activation of HDAC6 by cytosolic aPKC and AurA, which promotes acetylation of tubulin in primary cilia and, potentially, neural processes. This is the first report on the critical role of ceramide generated by nSMase2 in stem cell ciliogenesis and differentiation.

Primary cilia disassembly down-regulates mechanosensitive hedgehog signalling: a feedback mechanism controlling ADAMTS-5 expression in chondrocytes

OBJECTIVE

Hedgehog signalling is mediated by the primary cilium and promotes cartilage degeneration in osteoarthritis. Primary cilia are influenced by pathological stimuli and cilia length and prevalence are increased in osteoarthritic cartilage. This study aims to investigate the relationship between mechanical loading, hedgehog signalling and cilia disassembly in articular chondrocytes.

METHODS

Primary bovine articular chondrocytes were subjected to cyclic tensile strain (CTS; 0.33 Hz, 10% or 20% strain). Hedgehog pathway activation (Ptch1, Gli1) and A Disintegrin And Metalloproteinase with Thrombospondin Motifs 5 (ADAMTS-5) expression were assessed by real-time PCR. A chondrocyte cell line generated from the Tg737(ORPK) mouse was used to investigate the role of the cilium in this response. Cilia length and prevalence were quantified by immunocytochemistry and confocal microscopy.

RESULTS

Mechanical strain upregulates Indian hedgehog expression and activates hedgehog signalling. Ptch1, Gli1 and ADAMTS-5 expression were increased following 10% CTS, but not 20% CTS. Pathway activation requires a functioning primary cilium and is not observed in Tg737(ORPK) cells lacking cilia. Mechanical loading significantly reduced cilium length such that cilia became progressively shorter with increasing strain magnitude. Inhibition of histone deacetylase 6 (HDAC6), a tubulin deacetylase, prevented cilia disassembly and restored mechanosensitive hedgehog signalling and ADAMTS-5 expression at 20% CTS.

CONCLUSIONS

This study demonstrates for the first time that mechanical loading activates primary cilia-mediated hedgehog signalling and ADAMTS-5 expression in adult articular chondrocytes, but that this response is lost at high strains due to HDAC6-mediated cilia disassembly. The study provides new mechanistic insight into the role of primary cilia and mechanical loading in articular cartilage.