Filopodia and adhesion in cancer cell motility

Loss of giant obscurins from breast epithelium promotes epithelial-to-mesenchymal transition, tumorigenicity and metastasis

Obscurins, encoded by the single OBSCN gene, are giant cytoskeletal proteins with structural and regulatory roles. The OBSCN gene is highly mutated in different types of cancers. Loss of giant obscurins from breast epithelial cells confers them with a survival and growth advantage, following exposure to DNA-damaging agents. Here we demonstrate that the expression levels and subcellular distribution of giant obscurins are altered in human breast cancer biopsies compared with matched normal samples. Stable clones of non-tumorigenic MCF10A cells lacking giant obscurins fail to form adhesion junctions, undergo epithelial-to-mesenchymal transition and generate >100-μm mammospheres bearing markers of cancer-initiating cells. Obscurin-knockdown MCF10A cells display markedly increased motility as a sheet in 2-dimensional (2D) substrata and individually in confined spaces and invasion in 3D matrices. In line with these observations, actin filaments redistribute to extending filopodia where they exhibit increased dynamics. MCF10A cells that stably express the K-Ras oncogene and obscurin short hairpin RNA (shRNA), but not scramble control shRNA, exhibit increased primary tumor formation and lung colonization after subcutaneous and tail vein injections, respectively. Collectively, our findings reveal that loss of giant obscurins from breast epithelium results in disruption of the cell-cell contacts and acquisition of a mesenchymal phenotype that leads to enhanced tumorigenesis, migration and invasiveness in vitro and in vivo.

Microfabricated Systems and Assays for Studying the Cytoskeletal Organization, Micromechanics, and Motility Patterns of Cancerous Cells

Cell motions are driven by coordinated actions of the intracellular cytoskeleton - actin, microtubules (MTs) and substrate/focal adhesions (FAs). This coordination is altered in metastatic cancer cells resulting in deregulated and increased cellular motility. Microfabrication tools, including photolithography, micromolding, microcontact printing, wet stamping and microfluidic devices have emerged as a powerful set of experimental tools with which to probe and define the differences in cytoskeleton organization/dynamics and cell motility patterns in non-metastatic and metastatic cancer cells. In this review, we discuss four categories of microfabricated systems: (i) micropatterned substrates for studying of cell motility sub-processes (for example, MT targeting of FAs or cell polarization); (ii) systems for studying cell mechanical properties, (iii) systems for probing overall cell motility patterns within challenging geometric confines relevant to metastasis (for example, linear and ratchet geometries), and (iv) microfluidic devices that incorporate co-cultures of multiple cells types and chemical gradients to mimic in vivo intravasation/extravasation steps of metastasis. Together, these systems allow for creating controlled microenvironments that not only mimic complex soft tissues, but are also compatible with live cell high-resolution imaging and quantitative analysis of single cell behavior.

Control of cell migration through mRNA localization and local translation

Cell migration plays an important role in many normal and pathological functions such as development, wound healing, immune defense, and tumor metastasis. Polarized migrating cells exhibit asymmetric distribution of many cytoskeletal proteins, which is believed to be critical for establishing and maintaining cell polarity and directional cell migration. To target these proteins to the site of function, cells use a variety of mechanisms such as protein transport and messenger RNA (mRNA) localization-mediated local protein synthesis. In contrast to the former which is intensively investigated and relatively well understood, the latter has been understudied and relatively poorly understood. However, recent advances in the study of mRNA localization and local translation have demonstrated that mRNA localization and local translation are specific and effective ways for protein localization and are crucial for embryo development, neuronal function, and many other cellular processes. There are excellent reviews on mRNA localization, transport, and translation during development and other cellular processes. This review will focus on mRNA localization-mediated local protein biogenesis and its impact on somatic cell migration.

Non-muscle myosins in tumor progression, cancer cell invasion, and metastasis

The actin cytoskeleton, which regulates cell polarity, adhesion, and migration, can influence cancer progression, including initial acquisition of malignant properties by normal cells, invasion of adjacent tissues, and metastasis to distant sites. Actin-dependent molecular motors, myosins, play key roles in regulating tumor progression and metastasis. In this review, we examine how non-muscle myosins regulate neoplastic transformation and cancer cell migration and invasion. Members of the myosin superfamily can act as either enhancers or suppressors of tumor progression. This review summarizes the current state of knowledge on how mutations or epigenetic changes in myosin genes and changes in myosin expression may affect tumor progression and patient outcomes and discusses the proposed mechanisms linking myosin inactivation or upregulation to malignant phenotype, cancer cell migration, and metastasis.

Molecular dissection of the mechanism by which EWS/FLI expression compromises actin cytoskeletal integrity and cell adhesion in Ewing sarcoma

Ewing sarcoma is the second-most-common bone cancer in children. Driven by an oncogenic chromosomal translocation that results in the expression of an aberrant transcription factor, EWS/FLI, the disease is typically aggressive and micrometastatic upon presentation. Silencing of EWS/FLI in patient-derived tumor cells results in the altered expression of hundreds to thousands of genes and is accompanied by dramatic morphological changes in cytoarchitecture and adhesion. Genes encoding focal adhesion, extracellular matrix, and actin regulatory proteins are dominant targets of EWS/FLI-mediated transcriptional repression. Reexpression of genes encoding just two of these proteins, zyxin and α5 integrin, is sufficient to restore cell adhesion and actin cytoskeletal integrity comparable to what is observed when the EWS/FLI oncogene expression is compromised. Using an orthotopic xenograft model, we show that EWS/FLI-induced repression of α5 integrin and zyxin expression promotes tumor progression by supporting anchorage-independent cell growth. This selective advantage is paired with a tradeoff in which metastatic lung colonization is compromised.

Modification and biological evaluation of thiazole derivatives as novel inhibitors of metastatic cancer cell migration and invasion

Fascin has recently emerged as a potential therapeutic target, as its expression in cancer cells is closely associated with tumor progression and metastasis. Following the initial discovery of a series of thiazole derivatives that demonstrated potent antimigration and antiinvasion activities via possible inhibition of fascin function, we report here the design and synthesis of 63 new thiazole derivatives by further structural modifications in search of more potent fascin inhibitors. The 5 series of analogues with longer alkyl chain substitutions on the thiazole nitrogen exhibited greater antimigration activities than those with other structural motifs. The most potent analogue, 5p, inhibited 50% of cell migration at 24 nM. Moreover, the thiazole analogues showed strong antiangiogenesis activity, blocking new blood vessel formation in a chicken embryo membrane assay. Finally, a functional study was conducted to investigate the mechanism of action via interaction with the F-actin bundling protein fascin.

miR-206 inhibits cell migration through direct targeting of the actin-binding protein coronin 1C in triple-negative breast cancer

Patients with triple-negative breast cancer (TNBC) have an overall poor prognosis, which is primarily due to a high metastatic capacity of these tumors. Novel therapeutic approaches to target the signaling pathways that promote metastasis are desirable, in order to improve the outcome for these patients. A loss of function of a microRNA, miR-206, is related to increased metastasis potential in breast cancers but the mechanism is not known. In this study, we show that miR-206 was decreased in TNBC clinical tumor samples and cell lines whereas one of its predicted targets, actin-binding protein CORO1C, was increased. Expression of miR-206 significantly reduced proliferation and migration while repressing CORO1C mRNA and protein levels. We demonstrate that miR-206 interacts with the 3'-untranslated region (3'-UTR) of CORO1C and regulates this gene post-transcriptionally. This post-transcriptional regulation was dependent on two miR-206-binding sites within the 3'-UTR of CORO1C and was relieved by mutations of corresponding sites. Further, silencing of CORO1C reduced tumor cell migration and affected the actin skeleton and cell morphology, similar to miR-206 expression, but did not reduce proliferation. In accordance with this, overexpression of CORO1C rescued the inhibitory effect of miR-206 on cell migration. Our findings suggest that miR-206 represses tumor cell migration through direct targeting of CORO1C in TNBC cells which modulates the actin filaments. This pathway is a novel mechanism that offers a mechanistic basis through which the metastatic potential of TNBC tumors could be targeted.

Two-way regulation between cells and aligned collagen fibrils: local 3D matrix formation and accelerated neural differentiation of human decidua parietalis placental stem cells

It has been well established that an aligned matrix provides structural and signaling cues to guide cell polarization and cell fate decision. However, the modulation role of cells in matrix remodeling and the feedforward effect on stem cell differentiation have not been studied extensively. In this study, we report on the concerted changes of human decidua parietalis placental stem cells (hdpPSCs) and the highly ordered collagen fibril matrix in response to cell-matrix interaction. With high-resolution imaging, we found the hdpPSCs interacted with the matrix by deforming the cell shape, harvesting the nearby collagen fibrils, and reorganizing the fibrils around the cell body to transform a 2D matrix to a localized 3D matrix. Such a unique 3D matrix prompted high expression of β-1 integrin around the cell body that mediates and facilitates the stem cell differentiation toward neural cells. The study offers insights into the coordinated, dynamic changes at the cell-matrix interface and elucidates cell modulation of its matrix to establish structural and biochemical cues for effective cell growth and differentiation.

Gigantol, a bibenzyl from Dendrobium draconis, inhibits the migratory behavior of non-small cell lung cancer cells

Lung cancer is one of the most common causes of cancer death due to its high metastasis potential. The process of cancer migration is an early step that is required for successful metastasis. The discovery and development of natural compounds for cancer therapy have garnered increasing attention in recent years. Gigantol (1) is a bibenzyl compound derived from the Thai orchid, Dendrobium draconis. It exhibits significant cytotoxic activity against several cancer cell lines; however, until recently, the role of 1 on tumor metastasis has not been characterized. This study demonstrates that 1 suppresses the migratory behavior of non-small cell lung cancer H460 cells. Western blot analysis reveals that 1 down-regulates caveolin-1 (Cav-1), activates ATP-dependent tyrosine kinase (phosphorylated Akt at Ser 473), and cell division cycle 42 (Cdc42), thereby suppressing filopodia formation. The inhibitory effect of 1 on cell movement is also exhibited in another lung cancer cell line, H292, but not in normal human keratinocytes (HaCat). The inhibitory activity of 1 on lung cancer migration suggests that this compound may be suitable for further development for the treatment of cancer metastasis.

Elevated expression of myosin X in tumours contributes to breast cancer aggressiveness and metastasis

BACKGROUND

Myosin X (MYO10) was recently reported to promote tumour invasion by transporting integrins to filopodial tips in breast cancer. However, the role of MYO10 in tumours remains poorly defined. Here, we report that MYO10 is required in invadopodia to mediate invasive growth and extracellular matrix degradation, which depends on the binding of MYO10's pleckstrin homology domain to PtdIns(3,4,5)P3.

METHODS

The expression of MYO10 and its associations with clinicopathological and biological factors were examined in breast cancer cells and breast cancer specimens (n=120). Cell migration and invasion were investigated after the silencing of MYO10. The ability of cells to form invadopodia was studied using a fluorescein isothiocyanate-conjugated gelatin degradation assay. A mouse model was established to study tumour invasive growth and metastasis in vivo.

RESULTS

Elevated MYO10 levels were correlated with oestrogen receptor status, progesterone receptor status, poor differentiation, and lymph node metastasis. Silencing MYO10 reduced cell migration and invasion. Invadopodia were responsible for MYO10's role in promoting invasion. Furthermore, decreased invasive growth and lung metastasis were observed in the MYO10-silenced nude mouse model.

CONCLUSIONS

Our findings suggest that elevated MYO10 expression increases the aggressiveness of breast cancer; this effect is dependent on the involvement of MYO10 in invadopodial formation.

Identification of GPM6A and GPM6B as potential new human lymphoid leukemia-associated oncogenes

BACKGROUND

Previously, we found that the Graffi murine leukemia virus (MuLV) is able to induce a wide spectrum of hematologic malignancies in vivo. Using high-density oligonucleotide microarrays, we established the gene expression profiles of several of these malignancies, thereby specifically focusing on genes deregulated in the lymphoid sub-types. We observed over-expression of a variety of genes, including Arntl2, Bfsp2, Gfra2, Gpm6a, Gpm6b, Nln, Fbln1, Bmp7, Etv5 and Celsr1 and, in addition, provided evidence that Fmn2 and Parm-1 may act as novel oncogenes. In the present study, we assessed the expression patterns of eight selected human homologs of these genes in primary human B-cell malignancies, and explored the putative oncogenic potential of GPM6A and GPM6B.

METHODS

The gene expression levels of the selected human homologs were tested in human B-cell malignancies by semi-quantitative RT-PCR. The protein expression profiles of human GPM6A and GPM6B were analyzed by Western blotting. The localization and the effect of GPM6A and GPM6B on the cytoskeleton were determined using confocal and indirect immunofluorescence microscopy. To confirm the oncogenic potential of GPM6A and GPM6B, classical colony formation assays in soft agar and focus forming assays were used. The effects of these proteins on the cell cycle were assessed by flow cytometry analysis.

RESULTS

Using semi-quantitative RT-PCR, we found that most of the primary B-cell malignancies assessed showed altered expression patterns of the genes tested, including GPM6A and GPM6B. Using confocal microscopy, we found that the GPM6A protein (isoform 3) exhibits a punctate cytoplasmic localization and that the GPM6B protein (isoform 4) exhibits a peri-nuclear and punctate cytoplasmic localization. Interestingly, we found that exogenous over-expression of both proteins in NIH/3T3 cells alters the actin and microtubule networks and induces the formation of long filopodia-like protrusions. Additionally, we found that these over-expressing NIH/3T3 cells exhibit anchorage-independent growth and enhanced proliferation rates. Cellular transformation (i.e., loss of contact inhibition) was, however, only observed after exogenous over-expression of GPM6B.

CONCLUSIONS

Our results indicate that several human homologs of the genes found to be deregulated in Graffi MuLV experimental mouse models may serve as candidate biomarkers for human B-cell malignancies. In addition, we found that GPM6A and GPM6B may act as novel oncogenes in the development of these malignancies.

Capping protein is essential for cell migration in vivo and for filopodial morphology and dynamics

This study shows that capping protein (CP) is essential for mammalian cell migration in vitro and in vivo. The authors also show that CP is present in filopodia of multiple cell types and that it regulates filopodial structure and function. Thus CP function in both lamellipodia and filopodia may contribute to efficient migration.

Capping protein (CP) binds to barbed ends of growing actin filaments and inhibits elongation. CP is essential for actin-based motility in cell-free systems and in Dictyostelium. Even though CP is believed to be critical for creating the lamellipodial actin structure necessary for protrusion and migration, CP's role in mammalian cell migration has not been directly tested. Moreover, recent studies have suggested that structures besides lamellipodia, including lamella and filopodia, may have unappreciated roles in cell migration. CP has been postulated to be absent from filopodia, and thus its role in filopodial activity has remained unexplored. We report that silencing CP in both cultured mammalian B16F10 cells and in neurons of developing neocortex impaired cell migration. Moreover, we unexpectedly observed that low levels of CP were detectable in the majority of filopodia. CP depletion decreased filopodial length, altered filopodial shape, and reduced filopodial dynamics. Our results support an expansion of the potential roles that CP plays in cell motility by implicating CP in filopodia as well as in lamellipodia, both of which are important for locomotion in many types of migrating cells.

Integrin signalling and traffic during axon growth and regeneration

Adult corticospinal tract axons do not regenerate because they have low intrinsic growth ability, and are exposed to inhibitory molecules after injury. PNS axons have a better regenerative capacity, mediated in part by integrins (extracellular matrix receptors). These are subject to complex regulation by signalling and trafficking. Recent studies have found that integrin mediated axon growth relies on signalling via focal adhesion molecules, and that integrins are inactivated by inhibitory molecules in the CNS. Forced activation of integrins can overcome inhibition and increase axon regeneration, however integrins are not transported into some CNS axons. Studies of PNS integrin traffic have identified molecules that can be manipulated to increase axonal integrin expression, suggesting strategies for repairing the injured spinal cord.

NADPH oxidase complex-derived reactive oxygen species, the actin cytoskeleton, and Rho GTPases in cell migration

SIGNIFICANCE

Rho GTPases are historically known to be central regulators of actin cytoskeleton reorganization. This affects many processes including cell migration. In addition, members of the Rac subfamily are known to be involved in reactive oxygen species (ROS) production through the regulation of NADPH oxidase (Nox) activity. This review focuses on relationships between Nox-regulated ROS, Rho GTPases, and cytoskeletal reorganization, in the context of cell migration.

RECENT ADVANCES

It has become clear that ROS participate in the regulation of certain Rho GTPase family members, thus mediating cytoskeletal reorganization.

CRITICAL ISSUES

The role of the actin cytoskeleton in providing a scaffold for components of the Nox complex needs to be examined in the light of these new advances. During cell migration, Rho GTPases, ROS, and cytoskeletal organization appear to function as a complex regulatory network. However, more work is needed to fully elucidate the interactions between these factors and their potential in vivo importance.

FUTURE DIRECTIONS

Ultrastructural analysis, that is, electron microscopy, particularly immunogold labeling, will enable direct visualization of subcellular compartments. This in conjunction with the analysis of tissues lacking specific Rho GTPases, and Nox components will facilitate a detailed examination of the interactions of these structures with the actin cytoskeleton. In combination with the analysis of ROS production, including its subcellular location, these data will contribute significantly to our understanding of this intricate network under physiological conditions. Based on this, in vivo and in vitro studies can then be combined to elucidate the signaling pathways involved and their targets.

Cofilin drives cell-invasive and metastatic responses to TGF-β in prostate cancer

Cofilin (CFL) is an F-actin-severing protein required for the cytoskeleton reorganization and filopodia formation, which drives cell migration. CFL binding and severing of F-actin is controlled by Ser3 phosphorylation, but the contributions of this step to cell migration during invasion and metastasis of cancer cells are unclear. In this study, we addressed the question in prostate cancer cells, including the response to TGF-β, a critical regulator of migration. In cells expressing wild-type CFL, TGF-β treatment increased LIMK-2 activity and cofilin phosphorylation, decreasing filopodia formation. Conversely, constitutively active CFL (SerAla) promoted filipodia formation and cell migration mediated by TGF-β. Notably, in cocultures of prostate cancer epithelial cells and cancer-associated fibroblasts, active CFL promoted invasive migration in response to TGF-β in the microenvironment. Further, constitutively active CFL elevated the metastatic ability of prostate cancer cells in vivo. We found that levels of active CFL correlated with metastasis in a mouse model of prostate tumor and that in human prostate cancer, CFL expression was increased significantly in metastatic tumors. Our findings show that the actin-severing protein CFL coordinates responses to TGF-β that are needed for invasive cancer migration and metastasis.

Characterization of Leukocyte Formin FMNL1 Expression in Human Tissues

Formins are cytoskeleton regulating proteins characterized by a common FH2 structural domain. As key players in the assembly of actin filaments, formins direct dynamic cytoskeletal processes that influence cell shape, movement and adhesion. The large number of formin genes, fifteen in the human, suggests distinct tasks and expression patterns for individual family members, in addition to overlapping functions. Several formins have been associated with invasive cell properties in experimental models, linking them to cancer biology. One example is FMNL1, which is considered to be a leukocyte formin and is known to be overexpressed in lymphomas. Studies on FMNL1 and many other formins have been hampered by a lack of research tools, especially antibodies suitable for staining paraffin-embedded formalin-fixed tissues. Here we characterize, using bioinformatics tools and a validated antibody, the expression pattern of FMNL1 in human tissues and study its subcellular distribution. Our results indicate that FMNL1 expression is not restricted to hematopoietic tissues and that neoexpression of FMNL1 can be seen in epithelial cancer.

StarD13 is a tumor suppressor in breast cancer that regulates cell motility and invasion

Breast cancer is one of the most commonly diagnosed cancers in women around the world. In general, the more aggressive the tumor, the more rapidly it grows and the more likely it metastasizes. Members of the Rho subfamily of small GTP-binding proteins (GTPases) play a central role in breast cancer cell motility and metastasis. The switch between active GTP-bound and inactive GDP-bound state is regulated by guanine nucleotide exchange factors (GEFs), GTPase-activating proteins (GAPs) and guanine-nucleotide dissociation inhibitors (GDIs). We studied the role of StarD13, a recently identified Rho-GAP that specifically inhibits the function of RhoA and Cdc42. We aimed to investigate its role in breast cancer proliferation and metastasis. The levels of expression of this Rho-GAP in tumor tissues of different grades were assayed using immunohistochemistry. We observed that, while the level of StarD13 expression decreases in cancer tissues compared to normal tissues, it increases as the grade of the tumor increased. This was consistent with the fact that although StarD13 was indeed a tumor suppressor in our breast cancer cells, as seen by its effect on cell proliferation, it was needed for cancer cell motility. In fact, StarD13 knockdown resulted in an inhibition of cell motility and cells were not able to detach their tail and move forward. Our study describes, for the first time, a tumor suppressor that plays a positive role in cancer motility.

Mutant p53-associated myosin-X upregulation promotes breast cancer invasion and metastasis

Mutations of the tumor suppressor TP53 are present in many forms of human cancer and are associated with increased tumor cell invasion and metastasis. Several mechanisms have been identified for promoting dissemination of cancer cells with TP53 mutations, including increased targeting of integrins to the plasma membrane. Here, we demonstrate a role for the filopodia-inducing motor protein Myosin-X (Myo10) in mutant p53-driven cancer invasion. Analysis of gene expression profiles from 2 breast cancer data sets revealed that MYO10 was highly expressed in aggressive cancer subtypes. Myo10 was required for breast cancer cell invasion and dissemination in multiple cancer cell lines and murine models of cancer metastasis. Evaluation of a Myo10 mutant without the integrin-binding domain revealed that the ability of Myo10 to transport β₁ integrins to the filopodia tip is required for invasion. Introduction of mutant p53 promoted Myo10 expression in cancer cells and pancreatic ductal adenocarcinoma in mice, whereas suppression of endogenous mutant p53 attenuated Myo10 levels and cell invasion. In clinical breast carcinomas, Myo10 was predominantly expressed at the invasive edges and correlated with the presence of TP53 mutations and poor prognosis. These data indicate that Myo10 upregulation in mutant p53-driven cancers is necessary for invasion and that plasma-membrane protrusions, such as filopodia, may serve as specialized metastatic engines.

Loss of myoferlin redirects breast cancer cell motility towards collective migration

Cell migration plays a central role in the invasion and metastasis of tumors. As cells leave the primary tumor, they undergo an epithelial to mesenchymal transition (EMT) and migrate as single cells. Epithelial tumor cells may also migrate in a highly directional manner as a collective group in some settings. We previously discovered that myoferlin (MYOF) is overexpressed in breast cancer cells and depletion of MYOF results in a mesenchymal to epithelial transition (MET) and reduced invasion through extracellular matrix (ECM). However, the biomechanical mechanisms governing cell motility during MYOF depletion are poorly understood. We first demonstrated that lentivirus-driven shRNA-induced MYOF loss in MDA-MB-231 breast cancer cells (MDA-231(MYOF-KD)) leads to an epithelial morphology compared to the mesenchymal morphology observed in control (MDA-231(LTVC)) and wild-type cells. Knockdown of MYOF led to significant reductions in cell migration velocity and MDA-231(MYOF-KD) cells migrated directionally and collectively, while MDA-231(LTVC) cells exhibited single cell migration. Decreased migration velocity and collective migration were accompanied by significant changes in cell mechanics. MDA-231(MYOF-KD) cells exhibited a 2-fold decrease in cell stiffness, a 2-fold increase in cell-substrate adhesion and a 1.5-fold decrease in traction force generation. In vivo studies demonstrated that when immunocompromised mice were implanted with MDA-231(MYOF-KD) cells, tumors were smaller and demonstrated lower tumor burden. Moreover, MDA-231(MYOF-KD) tumors were highly circularized and did not invade locally into the adventia in contrast to MDA-231(LTVC)-injected animals. Thus MYOF loss is associated with a change in tumor formation in xenografts and leads to smaller, less invasive tumors. These data indicate that MYOF, a previously unrecognized protein in cancer, is involved in MDA-MB-231 cell migration and contributes to biomechanical alterations. Our results indicate that changes in biomechanical properties following loss of this protein may be an effective way to alter the invasive capacity of cancer cells.

Dock4 forms a complex with SH3YL1 and regulates cancer cell migration

Dock4 is a member of the Dock180 family of proteins that mediates cancer cell migration through activation of Rac. However, the regulatory mechanism of Dock4 remains unclear. In this study, we show that the C-terminal proline-rich region of Dock4 is essential for the Dock4 mediated promotion of cell migration in MDA-MB-231 breast cancer cells. We found that a phosphoinositide-binding protein SH3YL1 interacted with the C-terminal proline-rich region of Dock4. Interaction of SH3YL1 with Dock4 promoted Dock4-mediated Rac1 activation and cell migration. Mutations in the phosphoinositide-binding domain disrupted the ability of SH3YL1 to promote Dock4-mediated cell migration. In addition, depletion of SH3YL1 in MDA-MB-231 cells suppressed cell migration. Taken together, these results provide evidence for a novel and functionally important interaction between Dock4 and SH3YL1 to promote cancer cell migration by regulating Rac1 activity.

Connexins, gap junctions and tissue invasion

Formation of metastases negatively impacts the survival prognosis of cancer patients. Globally, if the various steps involved in their formation are relatively well identified, the molecular mechanisms responsible for the emergence of invasive cancer cells are still incompletely resolved. Elucidating what are the mechanisms that allow cancer cells to evade from the tumor is a crucial point since it is the first step of the metastatic potential of a solid tumor. In order to be invasive, cancer cells have to undergo transformations such as down-regulation of cell-cell adhesions, modification of cell-matrix adhesions and acquisition of proteolytic properties. These transformations are accompanied by the capacity to "activate" stromal cells, which may favor the motility of the invasive cells through the extracellular matrix. Since modulation of gap junctional intercellular communication is known to be involved in cancer, we were interested to consider whether these different transformations necessary for the acquisition of invasive phenotype are related with gap junctions and their structural proteins, the connexins. In this review, emerging roles of connexins and gap junctions in the process of tissue invasion are proposed.

Exploring the role of lipids in intercellular conduits: breakthroughs in the pipeline

It has been known for more than a century that most of the plant cells are connected to their neighbors through membranous pores perforating the cell wall, namely plasmodesmata (PDs). The recent discovery of tunneling nanotubes (TNTs), thin membrane bridges established between distant mammalian cells, suggests that intercellular communication mediated through cytoplasmic continuity could be a conserved feature of eukaryotic organisms. Although TNTs differ from PDs in their formation and architecture, both are characterized by a continuity of the plasma membrane between two cells, delimiting a nanotubular channel supported by actin-based cytoskeleton. Due to this unusual membrane organization, lipids are likely to play critical roles in the formation and stability of intercellular conduits like TNTs and PDs, but also in regulating the transfer through these structures. While it is crucial for a better understanding of those fascinating communication highways, the study of TNT lipid composition and dynamics turned out to be extremely challenging. The present review aims to give an overview of the recent findings in this context. We will also discuss some of the promising imaging approaches, which might be the key for future breakthroughs in the field and could also benefit the research on PDs.

Effect of StarD13 on colorectal cancer proliferation, motility and invasion

Colon cancer is a cancer of the epithelial cells lining the colon. It is mainly divided into different stages according to the invasiveness and metastatic ability of the tumor. Many mutations are acquired which leads to the development of this malignancy. These occur in entities that greatly affect the cell cycle, cell signaling pathways and cell motility, which all involve the action of Rho GTPases. The protein of interest in the present study was DLC2, also known as StarD13 or START-GAP2, a GTPase-activating protein (GAP) for Rho and Cdc42. Literature data indicate that this protein is considered a tumor-suppressor in hepatocellular carcinoma. Previous research in our laboratory confirmed StarD13 as a tumor suppressor in astrocytoma and in breast cancer. In the present study, we investigated the role of StarD13 in colon cancer. When overexpressed, StarD13 was found to lead to a decrease in cell proliferation in colon cancer cells. Consistently, knockdown of StarD13 led to an increase in cell proliferation. This showed that, similarly to its role in astrocytoma and breast cancer, StarD13 appears to be a tumor suppressor in colon cancer as well. We also examined the role of StarD13 in cell motility. StarD13 knockdown resulted in the inhibition of 2D cell motility. This was due to the inhibition of Rho; consequently Rac-dependent focal complexes were not formed nor detached for the cells to move forward. However, StarD13 knockdown led to an increase in 3D cell motility. Although StarD13 was indeed a tumor suppressor in our colon cancer cells, as evidenced by its effect on cell proliferation, it was required for cancer cell invasion. The present study further describes the role of StarD13 as a tumor suppressor as well as a Rho GAP.

Enhanced filopodium formation and stem-like phenotypes in a novel metastatic head and neck cancer cell model

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer in the world, and metastasis is the major cause of cancer-related mortality. Prevention or elimination of metastasis may improve the survival of cancer patients; however, the availability of systemic HNSCC cell model with which to investigate the mechanisms of metastasis is limited. In the present study, we established a set of metastatic cell lines from HNSCC cells. In combination with their low-tumorigenic and high-tumorigenic ancestor cell lines, a cell model containing cell lines with varying malignant characteristics was established. Transcriptome analysis revealed distinct signatures among the metastatic cell lines, in comparison to the ancestor cell lines. Signaling of GTPase RhoA and mammalian embryonic stem cell pluripotency were identified in the metastatic cells. Moreover, we examined the expression of genes related to epithelial-mesenchymal transition (EMT) (Snail, Slug, Twist, vimentin and fibronectin) and stemness (Oct4, Nanog and Bmi1). The capabilities of the cells for migration, invasion, spheroid formation and pulmonary colonization in nude mice were determined. Together, we demonstrated gain of Slug expression, filopodium formation and stem-like properties in metastatic HNSCC cells, rendering this model a powerful tool for the development of diagnostic biomarkers and identification of therapeutic targets for HNSCC.

Filopodia are dispensable for endothelial tip cell guidance

Actin filaments are instrumental in driving processes such as migration, cytokinesis and endocytosis and provide cells with mechanical support. During angiogenesis, actin-rich filopodia protrusions have been proposed to drive endothelial tip cell functions by translating guidance cues into directional migration and mediating new contacts during anastomosis. To investigate the structural organisation, dynamics and functional importance of F-actin in endothelial cells (ECs) during angiogenesis in vivo, we generated a transgenic zebrafish line expressing Lifeact-EGFP in ECs. Live imaging identifies dynamic and transient F-actin-based structures, such as filopodia, contractile ring and cell cortex, and more persistent F-actin-based structures, such as cell junctions. For functional analysis, we used low concentrations of Latrunculin B that preferentially inhibited F-actin polymerisation in filopodia. In the absence of filopodia, ECs continued to migrate, albeit at reduced velocity. Detailed morphological analysis reveals that ECs generate lamellipodia that are sufficient to drive EC migration when filopodia formation is inhibited. Vessel guidance continues unperturbed during intersegmental vessel development in the absence of filopodia. Additionally, hypersprouting induced by loss of Dll4 and attraction of aberrant vessels towards ectopic sources of Vegfa165 can occur in the absence of endothelial filopodia protrusion. These results reveal that the induction of tip cells and the integration of endothelial guidance cues do not require filopodia. Anastomosis, however, shows regional variations in filopodia requirement, suggesting that ECs might rely on different protrusive structures depending on the nature of the environment or of angiogenic cues.

Actin structure-dependent stepping of myosin 5a and 10 during processive movement

How myosin 10, an unconventional myosin, walks processively along actin is still controversial. Here, we used single molecule fluorescence techniques, TIRF and FIONA, to study the motility and the stepping mechanism of dimerized myosin 10 heavy-meromyosin-like fragment on both single actin filaments and two-dimensional F-actin rafts cross-linked by fascin or α-actinin. As a control, we also tracked and analyzed the stepping behavior of the well characterized processive motor myosin 5a. We have shown that myosin 10 moves processively along both single actin filaments and F-actin rafts with a step size of 31 nm. Moreover, myosin 10 moves more processively on fascin-F-actin rafts than on α-actinin-F-actin rafts, whereas myosin 5a shows no such selectivity. Finally, on fascin-F-actin rafts, myosin 10 has more frequent side steps to adjacent actin filaments than myosin 5a in the F-actin rafts. Together, these results reveal further single molecule features of myosin 10 on various actin structures, which may help to understand its cellular functions.

Strong association of fascin expression with triple negative breast cancer and basal-like phenotype in African-American women

BACKGROUND

Fascin, an actin bundling protein, plays a critical role in cell motility due to formation of actin rich protrusions called filopodia, important in cell migration, invasion and metastatic spread. Fascin overexpression has been associated with epithelial to mesenchymal transition and correlates with progression and unfavourable prognosis in breast carcinoma.

OBJECTIVE

To evaluate fascin expression by immunohistochemistry and correlate the expression pattern with clinicopathological parameters in breast cancer in African-American (AA) women, in whom triple negative breast cancer (TNBC), an aggressive subtype, is more prevalent.

METHODS

Tissue microarrays were constructed from formalin-fixed, paraffin-embedded blocks of tumour tissue from primary breast carcinomas in 202 AA women. Immunohistochemical detection of fascin was correlated with four major subtypes of breast carcinoma (luminal A, luminal B, human epidermal growth factor receptor 2 and triple negative (TN)) and other clinicopathological factors, including age, grade, tumour size, stage, regional lymph node status and survival.

RESULTS

We observed a significant association between fascin expression and TN subtype, oestrogen receptor (ER) negativity, progesterone receptor (PR) negativity, Elston-Nottingham (EN) grade 3 and decreased overall survival. There was also a significant association between expression of CK 5/6, a marker of basal-like phenotype, and fascin expression.

CONCLUSION

These results suggest that fascin is a marker for TN subtype having a basal-like phenotype and decreased overall survival. Fascin may represent a target for therapy in TNBC in AA women.

NF-κB-mediated transcriptional upregulation of TNFAIP2 by the Epstein-Barr virus oncoprotein, LMP1, promotes cell motility in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC), which is closely associated with Epstein-Barr virus (EBV), is a metastasis-prone epithelial cancer. We previously showed that tumor necrosis factor α-induced protein 2 (TNFAIP2) is highly expressed in NPC tumor tissues and is correlated with metastasis and poor survival in NPC patients. However, the underlying mechanism remains unclear. In this study, we demonstrate that the EBV oncoprotein, latent membrane protein 1 (LMP1), can transcriptionally induce TNFAIP2 expression via NF-κB. Quantitative RT-PCR and western blotting revealed that LMP1 induces TNFAIP2 expression through its C-terminal-activating region (CTAR2) domain, which is required for transduction of NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) signaling. Inhibition of NF-κB activation or depletion of p65 (a component of NF-κB) by RNA interference abolished the LMP1-induced expression of TNFAIP2, whereas ectopic expression of p65 was sufficient to induce TNFAIP2 expression. Luciferase reporter assays showed that LMP1 transcriptionally induces TNFAIP2 expression through a newly identified NF-κB-binding site within the TNFAIP2 promoter (-3,869 to -3,860 bp). Immunohistochemical analysis of NPC biopsy specimens further revealed a significant correlation between the protein levels of TNFAIP2 and activated p65 (R=0.689, P<0.001), indicating that our findings are clinically relevant. Immunofluorescence microscopy and co-immunoprecipitation assays showed that TNFAIP2 associates with actin and is involved in the formation of actin-based membrane protrusions. Furthermore, transwell migration assays demonstrated that TNFAIP2 contributes to LMP1-induced cell motility. Collectively, these findings provide novel insights into the regulation of TNFAIP2 and its role in promoting NPC tumor progression.

FiloDetect: automatic detection of filopodia from fluorescence microscopy images

Background

Filopodia are small cellular projections that help cells to move through and sense their environment. Filopodia play crucial roles in processes such as development and wound-healing. Also, increases in filopodia number or size are characteristic of many invasive cancers and are correlated with increased rates of metastasis in mouse experiments. Thus, one possible route to developing anti-metastatic therapies is to target factors that influence the filopodia system. Filopodia can be detected by eye using confocal fluorescence microscopy, and they can be manually annotated in images to quantify filopodia parameters. Although this approach is accurate, it is slow, tedious and not entirely objective. Manual detection is a significant barrier to the discovery and quantification of new factors that influence the filopodia system.

Results

Here, we present FiloDetect, an automated tool for detecting, counting and measuring the length of filopodia in fluorescence microscopy images. The method first segments the cell from the background, using a modified triangle threshold method, and then extracts the filopodia using a series of morphological operations. We verified the accuracy of FiloDetect on Rat2 and B16F1 cell images from three different labs, showing that per-cell filopodia counts and length estimates are highly correlated with the manual annotations. We then used FiloDetect to assess the role of a lipid kinase on filopodia production in breast cancer cells. Experimental results show that PI4KIII β expression leads to an increase in filopodia number and length, suggesting that PI4KIII β is involved in driving filopodia production.

Conclusion

FiloDetect provides accurate and objective quantification of filopodia in microscopy images, and will enable large scale comparative studies to assess the effects of different genetic and chemical perturbations on filopodia production in different cell types, including cancer cell lines.

Reconstruction of an integrated genome-scale co-expression network reveals key modules involved in lung adenocarcinoma

Our goal of this study was to reconstruct a “genome-scale co-expression network” and find important modules in lung adenocarcinoma so that we could identify the genes involved in lung adenocarcinoma. We integrated gene mutation, GWAS, CGH, array-CGH and SNP array data in order to identify important genes and loci in genome-scale. Afterwards, on the basis of the identified genes a co-expression network was reconstructed from the co-expression data. The reconstructed network was named “genome-scale co-expression network”. As the next step, 23 key modules were disclosed through clustering. In this study a number of genes have been identified for the first time to be implicated in lung adenocarcinoma by analyzing the modules. The genes EGFR, PIK3CA, TAF15, XIAP, VAPB, Appl1, Rab5a, ARF4, CLPTM1L, SP4, ZNF124, LPP, FOXP1, SOX18, MSX2, NFE2L2, SMARCC1, TRA2B, CBX3, PRPF6, ATP6V1C1, MYBBP1A, MACF1, GRM2, TBXA2R, PRKAR2A, PTK2, PGF and MYO10 are among the genes that belong to modules 1 and 22. All these genes, being implicated in at least one of the phenomena, namely cell survival, proliferation and metastasis, have an over-expression pattern similar to that of EGFR. In few modules, the genes such as CCNA2 (Cyclin A2), CCNB2 (Cyclin B2), CDK1, CDK5, CDC27, CDCA5, CDCA8, ASPM, BUB1, KIF15, KIF2C, NEK2, NUSAP1, PRC1, SMC4, SYCE2, TFDP1, CDC42 and ARHGEF9 are present that play a crucial role in cell cycle progression. In addition to the mentioned genes, there are some other genes (i.e. DLGAP5, BIRC5, PSMD2, Src, TTK, SENP2, PSMD2, DOK2, FUS and etc.) in the modules.

Hybrid liposomes inhibit tumor growth and lung metastasis of murine osteosarcoma cells

Antitumor effects of hybrid liposomes (HL) composed of l-α-dimyristoylphosphatidylcholine (DMPC) and polyoxyethylene(23) dodecyl ether (C₁₂(EO)₂₃) on the metastatic growth of murine osteosarcoma (LM8) cells were investigated in vitro and in vivo. Remarkable inhibitory effects of HL-23 on the growth of LM8 cells were obtained through the induction of apoptotic cell death in vitro. It was also indicated that HL-23 should dramatically suppress the invasion of LM8 cells and the formation of filopodia on the cell surface in vitro. Furthermore, significantly high therapeutic effects were observed in the homograft mouse models of LM8 cells with lung metastasis after the treatment with HL-23 in vivo. That is, the histological analysis demonstrated that the primary tumor growth of LM8 cells implanted subcutaneously into the mice was inhibited along with the induction of apoptosis. In addition, it was found that HL-23 significantly decreased the lung metastasis of LM8 cells in the mouse models through the inhibition of primary tumor invasion. These results suggest that HL-23 could be a novel agent for the chemotherapy of osteosarcoma.

Signaling networks of Rho GTPases in cell motility

The last decades have witnessed an exponential increase in our knowledge of Rho GTPase signaling network which further highlighted the cross talk between these proteins and the complexity of their signaling pathways. In this review, we summarize the upstream and downstream players from Rho GTPases that are mainly involved in actin polymerization leading to cell motility and potentially playing a role in cancer cell metastasis.

A comprehensive analysis of adiponectin QTLs using SNP association, SNP cis-effects on peripheral blood gene expression and gene expression correlation identified novel metabolic syndrome (MetS) genes with potential role in carcinogenesis and systemic inflammation

BACKGROUND

Metabolic syndrome (MetS) is an aberration associated with increased risk for cancer and inflammation. Adiponectin, an adipocyte-produced abundant protein hormone, has countering effect on the diabetogenic and atherogenic components of MetS. Plasma levels of adiponectin are negatively correlated with onset of cancer and cancer patient mortality. We previously performed microsatellite linkage analyses using adiponectin as a surrogate marker and revealed two QTLs on chr5 (5p14) and chr14 (14q13).

METHODS

Using individuals from 85 extended families that contributed to the linkage and who were measured for 42 clinical and biologic MetS phenotypes, we tested QTL-based SNP associations, peripheral white blood cell (PWBC) gene expression, and the effects of cis-acting SNPs on gene expression to discover genomic elements that could affect the pathophysiology and complications of MetS.

RESULTS

Adiponectin levels were found to be highly intercorrelated phenotypically with the majority of MetS traits. QTL-specific haplotype-tagging SNPs associated with MetS phenotypes were annotated to 14 genes whose function could influence MetS biology as well as oncogenesis or inflammation. These were mechanistically categorized into four groups: cell-cell adhesion and mobility, signal transduction, transcription and protein sorting. Four genes were highly prioritized: cadherin 18 (CDH18), myosin X (MYO10), anchor protein 6 of AMPK (AKAP6), and neuronal PAS domain protein 3 (NPAS3). PWBC expression was detectable only for the following genes with multi-organ or with multi-function properties: NPAS3, MARCH6, MYO10 and FBXL7. Strong evidence of cis-effects on the expression of MYO10 in PWBC was found with SNPs clustered near the gene's transcription start site. MYO10 expression in PWBC was marginally correlated with body composition (p = 0.065) and adipokine levels in the periphery (p = 0.064). Variants of genes AKAP6, NPAS3, MARCH6 and FBXL7 have been previously reported to be associated with insulin resistance, inflammatory markers or adiposity studies using genome-wide approaches whereas associations of CDH18 and MYO10 with MetS traits have not been reported before.

CONCLUSIONS

Adiponectin QTLs-based SNP association and mRNA expression identified genes that could mediate the association between MetS and cancer or inflammation.

Marker-free phenotyping of tumor cells by fractal analysis of reflection interference contrast microscopy images

Phenotyping of tumor cells by marker-free quantification is important for cancer diagnostics. For the first time, fractal analysis of reflection interference contrast microscopy images of single living cells was employed as a new method to distinguish between different nanoscopic membrane features of tumor cells. Since tumor progression correlates with a higher degree of chaos within the cell, it can be quantified mathematically by fractality. Our results show a high accuracy in identifying malignant cells with a failure chance of 3%, which is far better than today's applied methods.

KIF14 negatively regulates Rap1a-Radil signaling during breast cancer progression

The kinesin KIF14 associates with the PDZ domain of Radil and negatively regulates Rap1-mediated inside-out integrin activation by tethering Radil on microtubules.

The small GTPase Rap1 regulates inside-out integrin activation and thereby influences cell adhesion, migration, and polarity. Several Rap1 effectors have been described to mediate the cellular effects of Rap1 in a context-dependent manner. Radil is emerging as an important Rap effector implicated in cell spreading and migration, but the molecular mechanisms underlying its functions are unclear. We report here that the kinesin KIF14 associates with the PDZ domain of Radil and negatively regulates Rap1-mediated inside-out integrin activation by tethering Radil on microtubules. The depletion of KIF14 led to increased cell spreading, altered focal adhesion dynamics, and inhibition of cell migration and invasion. We also show that Radil is important for breast cancer cell proliferation and for metastasis in mice. Our findings provide evidence that the concurrent up-regulation of Rap1 activity and increased KIF14 levels in several cancers is needed to reach optimal levels of Rap1–Radil signaling, integrin activation, and cell–matrix adhesiveness required for tumor progression.

Halting metastasis through CXCR4 inhibition

Metastasis occurs when cancer cells leave the primary tumor site and migrate to distant parts of the body. The CXCR4-SDF-1 pathway facilitates this migration, and its expression has become the hallmark of several metastatic cancers. Targeted approaches are currently being developed to inhibit this pathway, and several candidates are now in clinical trials. Continued exploration of CXCR4 inhibitors will generate compounds that have improved activity over current candidates.

Controlling the cortical actin motor

Actin is the essential force-generating component of the microfilament system, which powers numerous motile processes in eukaryotic cells and undergoes dynamic remodeling in response to different internal and external signaling. The ability of actin to polymerize into asymmetric filaments is the inherent property behind the site-directed force-generating capacity that operates during various intracellular movements and in surface protrusions. Not surprisingly, a broad variety of signaling pathways and components are involved in controlling and coordinating the activities of the actin microfilament system in a myriad of different interactions. The characterization of these processes has stimulated cell biologists for decades and has, as a consequence, resulted in a huge body of data. The purpose here is to present a cellular perspective on recent advances in our understanding of the microfilament system with respect to actin polymerization, filament structure and specific folding requirements.

Clinicopathological significance of fascin and CD44v6 expression in endometrioid carcinoma

Background

Fascin and CD44v6 may have significant roles as biomarkers in tumour progression and metastasis. In endometrioid carcinomas, the fascin expression profile is less defined, and the significance of CD44v6 is uncertain. We aimed to investigate the expressions of both fascin and CD44v6 in endometrioid carcinomas and to evaluate their inter-relation with clinicopathological parameters.

Methods

Fascin and CD44v6 expressions were evaluated, individually and in combination, in a series of 47 endometrioid carcinomas and 10 proliferative endometrium samples. The staining extent and intensity of both markers in tumour cells were scored semiquantitatively. The relationship between immunoexpressions and clinicopathological variables was assessed.

Results

The expression rates of fascin and CD44v6 in endometrioid carcinoma were 72.34% and 46.80%, respectively. Although these expression rates were higher than those in proliferative endometrial samples, fascin expression showed a statistically significant difference from the normal group (p = 0.02), but CD44v6 did not differ (p = 0.54). Fascin expression was significantly correlated with tumour grade (p = 0.003) and neural invasion (p = 0.036) in a univariate analysis. In contrast, no significant correlation was found between CD44v6 and any of the clinicopathological parameters.

Conclusions

Our findings suggest that fascin might be an independent prognostic indicator in the different steps of extracellular matrix invasion. On the other hand, CD44v6 was not a predictive factor in endometrioid cancer.

Virtual Slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/8511594927206899.

Channel-independent influence of connexin 43 on cell migration

In this review we focus on the role of connexins, especially of Cx43, as modulators of migration - a fundamental process in embryogenesis and in physiologic functions of the adult organism. This impact of connexins is partly mediated by their function as intercellular channels but an increasing number of studies support the view that at least part of the effects are truly independent of the channel function. The channel-independent function comprises extrinsic guidance of migrating cells due to connexin mediated cell adhesion as well as intracellular processes. Cx43 has been shown to exert effects on migration by interfering with receptor signalling, cytoskeletal remodelling and tubulin dynamics. These effects are mainly dependent on the presence of the carboxyl tail of Cx43. The molecular basis of this channel-independent connexin function is still not yet fully understood but early results open an exciting view towards new functions of connexins in the cell. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.