Primary Cilia In Cells Research Articles

Therapeutically actionable signaling node to rescue AURKA driven loss of primary cilia in VHL-deficient cells

Loss of primary cilia in cells deficient for the tumor suppressor von Hippel Lindau (VHL) arise from elevated Aurora Kinase A (AURKA) levels. VHL in its role as an E3 ubiquitin ligase targets AURKA for degradation and in the absence of VHL, high levels of AURKA result in destabilization of the primary cilium. We identified NVP-BEZ235, a dual PI3K/AKT and mTOR inhibitor, in an image-based high throughput screen, as a small molecule that restored primary cilia in VHL-deficient cells. We identified the ability of AKT to modulate AURKA expression at the transcript and protein level. Independent modulation of AKT and mTOR signaling decreased AURKA expression in cells confirming AURKA as a new signaling node downstream of the PI3K cascade. Corroborating these data, a genetic knockdown of AKT in cells deficient for VHL rescued the ability of these cells to ciliate. Finally, inhibition of AKT/mTOR using NVP-BEZ235 was efficacious in reducing tumor burden in a 786-0 xenograft model of renal cell carcinoma. These data highlight a previously unappreciated signaling node downstream of the AKT/mTOR pathway via AURKA that can be targeted in VHL-null cells to restore ciliogenesis.

Roles for IFT172 and Primary Cilia in Cell Migration, Cell Division, and Neocortex Development.

The cilium of a cell translates varied extracellular cues into intracellular signals that control embryonic development and organ function. The dynamic maintenance of ciliary structure and function requires balanced bidirectional cargo transport involving intraflagellar transport (IFT) complexes. IFT172 is a member of the IFT complex B, and IFT172 mutation is associated with pathologies including short rib thoracic dysplasia, retinitis pigmentosa and Bardet-Biedl syndrome, but how it underpins these conditions is not clear. We used the WIM cell line, derived from embryonic fibroblasts of Wimple mice (carrying homozygous Leu1564Pro mutation in Ift172), to probe roles of Ift172 and primary cilia in cell behavior. WIM cells had ablated cilia and deficiencies in directed migration (electrotaxis), cell proliferation and intracellular signaling. Additionally, WIM cells displayed altered cell cycle progression, with increased numbers of chromatids, highlighting dysfunctional centrosome status. Exposure to a physiological electric field promoted a higher percentage of primary cilia in wild-type cells. Interestingly, in situ hybridization revealed an extensive and dynamic expression profile of Ift172 in both developing and adult mouse cortex. In vivo manipulation of Ift172 expression in germinal regions of embryonic mouse brains perturbed neural progenitor proliferation and radial migration of post-mitotic neurons, revealing a regulatory role of Ift172 in cerebral morphogenesis. Our data suggest that Ift172 regulates a range of fundamental biological processes, highlighting the pivotal roles of the primary cilium in cell physiology and brain development.

Centrosome-derived microtubule radial array, PCM-1 protein, and primary cilia formation.

In animal cells, the centrosome nucleates and anchors microtubules (MT), forming their radial array. During interphase centrosome-derived MT, aster can either team up with other MT network or function in an autonomous manner. What is the function of the centrosome-derived MT aster? We suggested that it might play an important role in the formation of the primary cilium, the organelle obligatorily associated with the centrosome. PCM-1 (PeriCentriolar Matrix 1) protein, which participates in the organization of the primary cilium, is a part of pericentiolar satellites. They are transported to the centrosome along MTs by the motor protein dynein in a complex with its cofactor dynactin. Previously, we showed that SLK/LOSK phosphorylated the p150Glued subunit of dynactin, thus promoting its centrosomal targeting followed by its participation in the retention of microtubules. Here, we found that under the repression of SLK/LOSK activity, the PCM-1 protein lost its pericentrosomal localization and was being dispersed throughout the cytoplasm. Despite that the alanine and glutamine mutants of p150Glued had opposite effects on PCM-1 localization, they associated with PCM-1 to the same extent. The occurrence of primary cilia also significantly decreased when SLK/LOSK was repressed. These defects also correlated with a disturbance of the long-range transport in cells, whereas dynein-depending motility was intact. Treatment with the GSK-3β kinase inhibitor also resulted in the loss of the centrosome-derived MT aster, dispersion of PCM-1 over the cytoplasm, and reduction of primary cilia occurrence. Thus, kinases involved in the centrosome-derived MT aster regulation can indirectly control the formation of primary cilia in cells.

Measurement of mechanical properties of primary cilia in cells by atomic force microscopy

Measurement of mechanical properties of primary cilia in cells by atomic force microscopy

Measurement of mechanical properties of primary cilia in cells by micro-tensile tester

Measurement of mechanical properties of primary cilia in cells by micro-tensile tester

Adenylate Cyclase Type III Is Not a Ubiquitous Marker for All Primary Cilia during Development.

Adenylate cyclase type III (AC3) is localized in plasma membrane of neuronal primary cilium and can be used as a marker of this cilium. AC3 has also been detected in some other primary cilia such as those of fibroblasts, synoviocytes or astrocytes. Despite the presence of a cilium in almost all cell types, we show that AC3 is not a common marker of all primary cilia of different human and mouse tissues during development. In peripheral organs, AC3 is present mainly in primary cilia in cells of the mesenchymal lineage (fibroblasts, chondroblasts, osteoblasts-osteocytes, odontoblasts, muscle cells and endothelial cells). In epithelia, the apical cilium of renal and pancreatic tubules and of ductal plate in liver is AC3-negative whereas the cilium of basal cells of stratified epithelia is AC3-positive. Using fibroblasts cell culture, we show that AC3 appears at the plasma membrane of the primary cilium as soon as this organelle develops. The functional significance of AC3 localization at the cilium membrane in some cells but not others has to be investigated in relationship with cell physiology and expression at the cilium plasma membrane of specific upstream receptors.

Primary cilia are present on human blood and bone marrow cells and mediate Hedgehog signaling.

Primary cilia are nonmotile, microtubule-based organelles that are present on the cellular membrane of all eukaryotic cells. Functional cilia are required for the response to developmental signaling pathways such as Hedgehog (Hh) and Wnt/β-catenin. Although the Hh pathway has been shown to be active in leukemia and other blood cancers, there have been no reports describing the presence of primary cilia in human blood or leukemia cells. In the present study, we show that nearly all human blood and bone marrow cells have primary cilia (97-99%). In contrast, primary cilia on AML cell lines (KG1, KG1a, and K562) were less frequent (10-36% of cells) and were often shorter and dysmorphic, with less well-defined basal bodies. Finally, we show that treatment of blood cells with the Hh pathway ligand Sonic Hedgehog (SHh) causes translocation of Smoothened (SMO) to the primary cilia and activation of Hh target genes, demonstrating that primary cilia in blood cells are functional and participate in Hh signaling. Loss of primary cilia on leukemia cells may have important implications for aberrant pathway activation and response to SMO inhibitors currently in clinical development.

P-005 Prognostic significance of the frequency of primary cilia in cells of small bowel and colorectal adenocarcinoma

Purpose: The primary cilium is a solitary, sensory, immotile microtubule-based structure that arises from the centrosome and is projected from the surface of most human cell types. It has been hypothesized that primary cilia could serve as a tumor suppressor organelle. The objective of this pilot study was to investigate the presence and frequency of primary cilia in cells of small bowel and colorectal adenocarcinoma and to evaluate the prognostic significance of their frequency. Methods: The presence of primary cilia in cells in samples of small bowel (8 patients) and colorectal adenocarcinoma (32 patiens) was evaluated. The primary cilia of cells were immunofluorescently labeled using primary monoclonal anti-acetylated alpha-tubulin antibody and cell nuclei were labeled using DAPI. Results: Primary cilia were identified in all examined specimens. The median frequency of primary cilia was 0.49% in cells of small bowel cancer and 0.22% in cells in colorectal cancer. Overall survival according to frequency of primary cilia in all intestinal adenocarcinomas was significantly longer in patients with higher frequency (>= 0.187) than in patients with lower frequency of primary cilia ( = 0.187) than in patients with lower frequency of primary cilia (< 0.187) (p=0.028). Conclusions: The present pilot study provides the first evidence of the prognostic significance of the frequency of primary cilia in small bowel and colorectal adenocarcinoma. Because of significantly higher median frequency of primary cilia in the rare small bowel adenocarcinoma than in the frequent colorectal adenocarcinoma (p<0.001), the results of this study support a potential role for primary cilia as a biomarker in these types of cancer.

Primary cilia in gastrointestinal stromal tumors.

The primary cilium is a solitary, sensory, non-motile microtubule-based structure that arises from the centrosome and is projected from the surface of most human cells. The objective of the current pilot study was to conduct an investigation of presence and frequency of cilia in gastrointestinal stromal tumors (GIST).The presence of primary cilia in GIST was evaluated in 9 patients, including 8 primary tumors and 1 liver metastasis. In 2 patients the presence of primary cilia was evaluated not only in the primary tumor, but also in recurrence: in 1 patient in recurrence without previous treatment with imatinib and in 1 patient in recurrence after treatment with imatinib. The primary cilia of GIST cells were immunofluorescently stained with primary monoclonal anti-acetylated tubulin alpha antibody and cell nuclei with DAPI.We observed 9985 nuclei of cells of GISTs and 425 primary cilia in total. The median of frequency of primary cilia in cells of GISTs in all examined samples was 4.26%, in primary tumors was 4.32% and in metastases was 3.64%, respectively. This pilot study provides the evidence of the presence of primary cilia in GISTs in different organs. Primary cilia were identified in all examined cases of GIST, including primary tumors, metastases and recurrent lesions without and with previous treatment with imatinib.

Variation of medium osmolalities induces changes in cilia related signalling pathways in primary cultured renal inner medullary collecting duct cells

Compared to other organs the cells of the renal inner medulla are challenged with an environment of highly variable osmolality. Cellular adaption to changing osmolality is associated with changes in gene expression. To identify novel genes and pathways that are affected by high osmolality we performed microarray experiments using primary cultured rat inner medullary collecting duct cells cultivated at 300, 600, or 900 mosmol/kg for six days. Compared to 300 mosmol/kg more than 2000 genes showed significant changes in expression at 600 or 900 mosmol/kg. Pathway analysis revealed that the WNT/beta-catenin pathway was also affected. Western blot analysis confirmed the down regulation of beta-catenin and of phosphorylated beta-catenin protein. Immunofluorescence analysis indicated massive changes in intracellular localization of beta-catenin. At 300 mosmol/kg beta-catenin was distributed diffusively within the cells. At higher osmolalities beta-catenin was concentrated at the cell to cell contacts and in the nucleus. Similar effects were observed for phosphorylated beta-catenin. We also observed striking changes in cell morphology. While at 300 mosmol/kg the actin filaments were diffusively distributed the cultivation at 600 mosmol/kg was associated with massive reorganisation and enrichment of the actin filaments at the cell to cell contacts. Staining of the microtubules with beta-tubulin clearly showed the primary cilia in cells cultivated at 300 mosmol/kg. Surprisingly the length of the cilia was drastically reduced in cells cultivated at 600 mosmol/kg. The analysis of the underlying physiological mechanisms and the consequences for cilia related signalling at different osmolalities could help to add new aspects to cilia function.

A Rab8 Guanine Nucleotide Exchange Factor-Effector Interaction Network Regulates Primary Ciliogenesis

Primary cilia are microtubule-based solitary membrane projections on the cell surface that play important roles in signaling and development. Recent studies have demonstrated that polarized vesicular trafficking involving the small GTPase Rab8 and its guanine nucleotide exchange factor Rabin8 is essential for primary ciliogenesis. In this study, we show that a highly conserved region of Rabin8 is pivotal for its activation as a guanine nucleotide exchange factor for Rab8. In addition, in its activated conformation, Rabin8 interacts with Sec15, a subunit of the exocyst and downstream effector of Rab8. Expression of constitutively activated Rab8 promotes the association of Sec15 with Rabin8. Using immunofluorescence microscopy, we found that Sec15 co-localized with Rab8 along the primary cilium. Inhibition of Sec15 function in cells led to defects in primary ciliogenesis. The Rabin8-Rab8-Sec15 interaction may couple the activation of Rab8 to the recruitment of the Rab8 effector and is involved in the regulation of vesicular trafficking for primary cilium formation.