Analysis of cortical cell polarity by imaging flow cytometry.

Metastasis is the main cause of cancer-related death and therapies specifically targeting metastasis are highly needed. Cortical cell polarity (CCP) is a prometastatic property of circulating tumor cells affecting their ability to exit blood vessels and form new metastases that constitute a promising point of attack to prevent metastasis. However, conventional fluorescence microscopy on single cells and manual quantification of CCP are time-consuming and unsuitable for screening regulators. In this study, we developed an imaging flow cytometry-based method for high-throughput screening of factors affecting CCP in melanoma cells. The artificial intelligence-supported analysis method we developed is highly reproducible, accurate, and orders of magnitude faster than manual quantification. Additionally, this method is flexible and can be adapted to include additional cellular parameters. In a small-scale pilot experiment using polarity-, cytoskeleton-, or membrane-affecting drugs, we demonstrate that our workflow provides a straightforward and efficient approach for screening factors affecting CCP in cells in suspension and provide insights into the specific function of these drugs in this cellular system. The method and workflow presented here will facilitate large-scale studies to reveal novel cell-intrinsic as well as systemic factors controlling CCP during metastasis.

Hypoxia and Ezrin Expression in Primary Melanoma Have High Prognostic Relevance.

Hypoxia affects tumor aggressiveness and activates pathways associated with epithelial mesenchymal transition (EMT) which are crucial for tumor progress. In this study, the correlation of hypoxia and EMT with sentinel lymph node status and tumor-specific survival was investigated in primary melanomas. CD34 for capillary count and Hypoxia inducible factor-1α (HIF-1α) as hypoxia indicators as well as Ezrin and L1-Cell Adhesion Molecule (L1CAM), both critical proteins contributing to EMT, were analyzed using immunohistochemistry in 49 melanoma patients with long follow-up (F/U, mean 110 months; range 12−263 months). We found a significant correlation between Breslow tumor thickness and Ezrin expression (p = 0.018). L1CAM expression in primary melanoma was significantly associated with HIF-1α expression (p < 0.0001) and sentinel lymph node metastasis (p = 0.011). Furthermore, low capillary count, reflecting hypoxic condition, was significantly associated with Ezrin expression (p = 0.047) and decreased tumor-specific survival (p = 0.035). In addition, patients with high Ezrin expression in their primary melanoma had a dramatic loss of life early in their F/U period (mean survival time 29 months; range 15−44 month). Our results highlight the relevance of Ezrin, L1CAM and HIF-1α as prognostic markers in melanoma patients. Additionally, we demonstrate that hypoxia in primary melanoma affects EMT and is at least partly responsible for early metastatic dissemination.

Purification and crystal structure of human ODA16: Implications for ciliary import of outer dynein arms by the intraflagellar transport machinery.

Motile cilia protrude from cell surfaces and are necessary to create movement of cells and fluids in the body. At the molecular level, cilia contain several dynein molecular motor complexes including outer dynein arms (ODAs) that are attached periodically to the ciliary axoneme, where they hydrolyse ATP to create the force required for bending and motility of the cilium. ODAs are preassembled in the cytoplasm and subsequently trafficked into the cilium by the intraflagellar transport (IFT) system. In the case of the green alga Chlamydomonas reinhardtii, the adaptor protein ODA16 binds to ODAs and directly to the IFT complex component IFT46 to facilitate the ciliary import of ODAs. Here, we purified recombinant human IFT46 and ODA16, determined the high-resolution crystal structure of the ODA16 protein, and carried out direct interaction studies of IFT46 and ODA16. The human ODA16 C-terminal 320 residues adopt the fold of an eight-bladed ß-propeller with high overall structural similarity to the Chlamydomonas ODA16. However, the small 80 residue N-terminal domain, which in Chlamydomonas ODA16 is located on top of the ß-propeller and is required to form the binding cleft for IFT46, has no visible electron density in case of the human ODA16 structure. Furthermore, size exclusion chromatography and pull-down experiments failed to detect a direct interaction between human ODA16 and IFT46. These data suggest that additional factors may be required for the ciliary import of ODAs in human cells with motile cilia.

The role of polarisation of circulating tumour cells in cancer metastasis.

Metastasis is the spread of cancer cells from a primary tumour to a distant site of the body. Metastasising tumour cells have to survive and readjust to different environments, such as heterogeneous solid tissues and liquid phase in lymph- or blood circulation, which they achieve through a high degree of plasticity that renders them adaptable to varying conditions. One defining characteristic of the metastatic process is the transition of tumour cells between different polarised phenotypes, ranging from differentiated epithelial polarity to migratory front-rear polarity. Here, we review the polarisation types adopted by tumour cells during the metastatic process and describe the recently discovered single-cell polarity in liquid phase observed in circulating tumour cells. We propose that single-cell polarity constitutes a mode of polarisation of the cell cortex that is uncoupled from the intracellular polarisation machinery, which distinguishes single-cell polarity from other types of polarity identified so far. We discuss how single-cell polarity can contribute to tumour metastasis and the therapeutic potential of this new discovery.

Crystal structure of intraflagellar transport protein 80 reveals a homo-dimer required for ciliogenesis.

Oligomeric assemblies of intraflagellar transport (IFT) particles build cilia through sequential recruitment and transport of ciliary cargo proteins within cilia. Here we present the 1.8 Å resolution crystal structure of the Chlamydomonas IFT-B protein IFT80, which reveals the architecture of two N-terminal ß-propellers followed by an α-helical extension. The N-terminal ß-propeller tethers IFT80 to the IFT-B complex via IFT38 whereas the second ß-propeller and the C-terminal α-helical extension result in IFT80 homo-dimerization. Using CRISPR/Cas to create biallelic Ift80 frameshift mutations in IMCD3 mouse cells, we demonstrate that IFT80 is absolutely required for ciliogenesis. Structural mapping and rescue experiments reveal that human disease-causing missense mutations do not cluster within IFT80 and form functional IFT particles. Unlike missense mutant forms of IFT80, deletion of the C-terminal dimerization domain prevented rescue of ciliogenesis. Taken together our results may provide a first insight into higher order IFT complex formation likely required for IFT train formation.

Single cell polarity in liquid phase facilitates tumour metastasis.

Dynamic polarisation of tumour cells is essential for metastasis. While the role of polarisation during dedifferentiation and migration is well established, polarisation of metastasising tumour cells during phases of detachment has not been investigated. Here we identify and characterise a type of polarisation maintained by single cells in liquid phase termed single-cell (sc) polarity and investigate its role during metastasis. We demonstrate that sc polarity is an inherent feature of cells from different tumour entities that is observed in circulating tumour cells in patients. Functionally, we propose that the sc pole is directly involved in early attachment, thereby affecting adhesion, transmigration and metastasis. In vivo, the metastatic capacity of cell lines correlates with the extent of sc polarisation. By manipulating sc polarity regulators and by generic depolarisation, we show that sc polarity prior to migration affects transmigration and metastasis in vitro and in vivo.

Crystal structure of tetrameric human Rabin8 GEF domain.

Rab GTPases and their effectors, activators and guanine nucleotide exchange factors (GEFs) are essential for vesicular transport. Rab8 and its GEF Rabin8 function in formation of the cilium organelle important for developmental signaling and sensory reception. Here, we show by size exclusion chromatography and analytical ultracentrifugation that Rabin8 exists in equilibrium between dimers and tetramers. The crystal structure of tetrameric Rabin8 GEF domain reveals an occluded Rab8 binding site suggesting that this oligomer is enzymatically inactive, a notion we verify experimentally using Rabin8/Rab8 GEF assays. We outline a procedure for the purification of active dimeric Rabin8 GEF-domain for in vitro activity assays.

A Dual Role of Caspase-8 in Triggering and Sensing Proliferation-Associated DNA Damage, a Key Determinant of Liver Cancer Development.

Concomitant hepatocyte apoptosis and regeneration is a hallmark of chronic liver diseases (CLDs) predisposing to hepatocellular carcinoma (HCC). Here, we mechanistically link caspase-8-dependent apoptosis to HCC development via proliferation- and replication-associated DNA damage. Proliferation-associated replication stress, DNA damage, and genetic instability are detectable in CLDs before any neoplastic changes occur. Accumulated levels of hepatocyte apoptosis determine and predict subsequent hepatocarcinogenesis. Proliferation-associated DNA damage is sensed by a complex comprising caspase-8, FADD, c-FLIP, and a kinase-dependent function of RIPK1. This platform requires a non-apoptotic function of caspase-8, but no caspase-3 or caspase-8 cleavage. It may represent a DNA damage-sensing mechanism in hepatocytes that can act via JNK and subsequent phosphorylation of the histone variant H2AX.

Canonical NF-κB signaling in hepatocytes acts as a tumor-suppressor in hepatitis B virus surface antigen-driven hepatocellular carcinoma by controlling the unfolded protein response.

UNLABELLED: Chronic hepatitis B virus (HBV) infection remains the most common risk factor for hepatocellular carcinoma (HCC). Efficient suppression of HBV viremia and necroinflammation as a result of nucleos(t)ide analogue treatment is able to reduce HCC incidence; nevertheless, hepatocarcinogenesis can occur in the absence of active hepatitis, correlating with high HBV surface antigen (HBsAg) levels. Nuclear factor κB (NF-κB) is a central player in chronic inflammation and HCC development. However, in the absence of severe chronic inflammation, the role of NF-κB signaling in HCC development remains elusive. As a model of hepatocarcinogenesis driven by accumulation of HBV envelope polypeptides, HBsAg transgenic mice, which show no HBV-specific immune response, were crossed to animals with hepatocyte-specific inhibition of canonical NF-κB signaling. We detected prolonged, severe endoplasmic reticulum stress already at 20 weeks of age in NF-κB-deficient hepatocytes of HBsAg-expressing mice. The unfolded protein response regulator binding immunoglobulin protein/78-kDa glucose-regulated protein was down-regulated, activating transcription factor 6, and eIF2α were activated with subsequent overexpression of CCAAT/enhancer binding protein homologous protein. Notably, immune cell infiltrates and liver transaminases were unchanged. However, as a result of this increased cellular stress, insufficient hepatocyte proliferation due to G1 /S-phase cell cycle arrest with overexpression of p27 and emergence of ductular reactions was detected. This culminated in increased DNA damage already at 20 weeks of age and finally led to 100% HCC incidence due to NF-κB inhibition. CONCLUSION: The role of canonical NF-κB signaling in HCC development depends on the mode of liver damage; in the case of HBsAg-driven hepatocarcinogenesis, NF-κB in hepatocytes acts as a critical tumor suppressor by augmenting the endoplasmic reticulum stress response.

Metabolic activation of intrahepatic CD8+ T cells and NKT cells causes nonalcoholic steatohepatitis and liver cancer via cross-talk with hepatocytes.

Hepatocellular carcinoma (HCC), the fastest rising cancer in the United States and increasing in Europe, often occurs with nonalcoholic steatohepatitis (NASH). Mechanisms underlying NASH and NASH-induced HCC are largely unknown. We developed a mouse model recapitulating key features of human metabolic syndrome, NASH, and HCC by long-term feeding of a choline-deficient high-fat diet. This induced activated intrahepatic CD8(+) T cells, NKT cells, and inflammatory cytokines, similar to NASH patients. CD8(+) T cells and NKT cells but not myeloid cells promote NASH and HCC through interactions with hepatocytes. NKT cells primarily cause steatosis via secreted LIGHT, while CD8(+) and NKT cells cooperatively induce liver damage. Hepatocellular LTßR and canonical NF-κB signaling facilitate NASH-to-HCC transition, demonstrating that distinct molecular mechanisms determine NASH and HCC development.

An ezrin-rich, rigid uropod-like structure directs movement of amoeboid blebbing cells.

Melanoma cells can switch between an elongated mesenchymal-type and a rounded amoeboid-type migration mode. The rounded 'amoeboid' form of cell movement is driven by actomyosin contractility resulting in membrane blebbing. Unlike elongated A375 melanoma cells, rounded A375 cells do not display any obvious morphological front-back polarisation, although polarisation is thought to be a prerequisite for cell movement. We show that blebbing A375 cells are polarised, with ezrin (a linker between the plasma membrane and actin cytoskeleton), F-actin, myosin light chain, plasma membrane, phosphatidylinositol (4,5)-bisphosphate and ß1-integrin accumulating at the cell rear in a uropod-like structure. This structure does not have the typical protruding shape of classical leukocyte uropods, but, as for those structures, it is regulated by protein kinase C. We show that the ezrin-rich uropod-like structure (ERULS) is an inherent feature of polarised A375 cells and not a consequence of cell migration, and is necessary for cell invasion. Furthermore, we demonstrate that membrane blebbing is reduced at this site, leading to a model in which the rigid ezrin-containing structure determines the direction of a moving cell through localised inhibition of membrane blebbing.

MicroRNA-200 family members differentially regulate morphological plasticity and mode of melanoma cell invasion.

BACKGROUND: A functional role of microRNAs (miRNAs or miRs) in neoplasia and metastasis is becoming clear, and the miR-200 family has received much attention for potentially regulating tumor progression. The miRNAs of this family have been shown to suppress epithelial-mesenchymal transition, and their down-regulation in some tumors promotes invasion and metastasis. Interestingly, while miR-200 is down-regulated in some cancers, it is up-regulated in others. PRINCIPAL FINDINGS: We show that levels of miR-200 are increased in melanoma cell lines compared to normal melanocytes and that miR-200 family members play a role in determining modes of tumor cell migration. Individual tumor cells can invade in either elongated, "mesenchymal-type" or rounded, "amoeboid-like" modes and these two modes of invasion are inter-convertible [1]. In melanoma cell lines, expression of miR-200 members does not suppress invasion but rather leads to a switch between modes of invasion. MicroRNA-200c results in a higher proportion of cells adopting the rounded, amoeboid-like mode of invasion, while miR-200a results in a protrusion-associated elongated mode of invasion. Functional target identification studies suggest that the morphological effects of miR-200c may be mediated by reduced expression of MARCKS, which has been linked to formation of cell protrusions. In contrast miR-200a reduces actomyosin contractility, a feature of rounded morphology. SIGNIFICANCE: Overall our findings call into question the general role of miR-200 in suppressing invasion and metastasis, and highlight novel distinguishing characteristics of individual miR-200 family members.

Regulation of Ras localization by acylation enables a mode of intracellular signal propagation.

Growth factor stimulation generates transient H-Ras activity at the plasma membrane but sustained activity at the Golgi. Two overlapping regulatory networks control compartmentalized H-Ras activity: the guanosine diphosphate-guanosine triphosphate cycle and the acylation cycle, which constitutively traffics Ras isoforms that can be palmitoylated between intracellular membrane compartments. Quantitative imaging of H-Ras activity after decoupling of these networks revealed regulation of H-Ras activity at the plasma membrane but not at the Golgi. Nevertheless, upon stimulation with epidermal growth factor, Ras activity at the Golgi displayed a pulse-like profile similar to that at the plasma membrane but also remained high after the initial stimulus. A compartmental model that included the acylation cycle and H-Ras regulation at the plasma membrane accounted for the pulse-like profile of H-Ras activity at the Golgi but implied that sustained H-Ras activity at the Golgi required H-Ras activation at an additional compartment, which we experimentally determined to be the endoplasmic reticulum. Thus, in addition to maintaining the localization of Ras, the acylation cycle underlies a previously unknown form of signal propagation similar to radio transmission in its generation of a constitutive Ras "carrier wave" that transmits Ras activity between subcellular compartments.