Invadosome regulation by adhesion signaling

TGFB1I1 promotes cell proliferation and migration in urothelial carcinoma

Urothelial carcinoma (UC) is common cancer worldwide with a high prevalence in Taiwan, especially in the upper urinary tract, including the renal pelvis and ureter, also classifying as upper urinary tract urothelial carcinoma. Here, we aim to find a representative prognostic marker that strongly correlates to this type of carcinoma. Transforming growth factor beta-1-induced transcript 1 (TGFB1I1) is a cofactor of cellular TGF-β1 and interacts with various nuclear receptors. The previous study showed that TGFB1I1 promotes focal adhesion formation, contributing to the epithelial-mesenchymal transition (EMT) with actin cytoskeleton and vimentin through TGFB1I1 regulation. We aim to reveal the role of TGFB1I1 in the tumorigenesis of UC. In silico and clinicopathological data of upper urinary tract urothelial carcinoma (UTUC) and urinary bladder urothelial carcinoma (UBUC) were accessed and analyzed for IHC staining regarding tumor characteristics, including survival outcome. Finally, an in vitro study was performed to demonstrate the biological changes of UC cells. In UTUC, overexpression of TGFB1I1 was significantly correlated with advanced tumor stage, papillary configuration, and frequent mitosis. Meanwhile, overexpression of TGFB1I1 was significantly correlated with advanced tumor stage and histological grade in UBUC. Moreover, the in vitro study shows that TGFB1I1 affects cell proliferation, viability, migration and wound healing. The EMT markers also decreased upon TGFB1I1 knockdown. In this study, we identified that TGFB1I1 regulates UC cell proliferation and viability and induces the EMT to facilitate cell migration in vitro, leading to its essential role in promoting tumor aggressiveness in both UTUC and UBUC.

TRIM29 promotes bladder cancer invasion by regulating the intermediate filament network and focal adhesion

Bladder cancer is a common malignancy whose lethality is determined by invasive potential. We have previously shown that TRIM29, also known as ATDC, is transcriptionally regulated by TP63 in basal bladder cancers where it promotes invasive progression and metastasis, but the molecular events which promote invasion and metastasis downstream of TRIM29 remained poorly understood. Here we identify stimulation of bladder cancer migration as the specific role of TRIM29 during invasion. We show that TRIM29 physically interacts with K14 + intermediate filaments which in turn regulates focal adhesion stability. Further, we find that both K14 and the focal adhesion protein, ZYX are required for bladder cancer migration and invasion. Taken together, these results establish a role for TRIM29 in the regulation of cytoskeleton and focal adhesions during invasion and identify a pathway with therapeutic potential.

Interfering with the ERC1-LL5β interaction disrupts plasma membrane-Associated platforms and affects tumor cell motility

Cell migration requires a complex array of molecular events to promote protrusion at the front of motile cells. The scaffold protein LL5β interacts with the scaffold ERC1, and recruits it at plasma membrane-associated platforms that form at the front of migrating tumor cells. LL5 and ERC1 proteins support protrusion during migration as shown by the finding that depletion of either endogenous protein impairs tumor cell motility and invasion. In this study we have tested the hypothesis that interfering with the interaction between LL5β and ERC1 may be used to interfere with the function of the endogenous proteins to inhibit tumor cell migration. For this, we identified ERC1(270-370) and LL5β(381-510) as minimal fragments required for the direct interaction between the two proteins. The biochemical characterization demonstrated that the specific regions of the two proteins, including predicted intrinsically disordered regions, are implicated in a reversible, high affinity direct heterotypic interaction. NMR spectroscopy further confirmed the disordered nature of the two fragments and also support the occurrence of interaction between them. We tested if the LL5β protein fragment interferes with the formation of the complex between the two full-length proteins. Coimmunoprecipitation experiments showed that LL5β(381-510) hampers the formation of the complex in cells. Moreover, expression of either fragment is able to specifically delocalize endogenous ERC1 from the edge of migrating MDA-MB-231 tumor cells. Coimmunoprecipitation experiments show that the ERC1-binding fragment of LL5β interacts with endogenous ERC1 and interferes with the binding of endogenous ERC1 to full length LL5β. Expression of LL5β(381-510) affects tumor cell motility with a reduction in the density of invadopodia and inhibits transwell invasion. These results provide a proof of principle that interfering with heterotypic intermolecular interactions between components of plasma membrane-associated platforms forming at the front of tumor cells may represent a new approach to inhibit cell invasion.

Multiscale model of the different modes of cancer cell invasion

MOTIVATION

Mathematical models of biological processes altered in cancer are built using the knowledge of complex networks of signaling pathways, detailing the molecular regulations inside different cell types, such as tumor cells, immune and other stromal cells. If these models mainly focus on intracellular information, they often omit a description of the spatial organization among cells and their interactions, and with the tumoral microenvironment.

RESULTS

We present here a model of tumor cell invasion simulated with PhysiBoSS, a multiscale framework, which combines agent-based modeling and continuous time Markov processes applied on Boolean network models. With this model, we aim to study the different modes of cell migration and to predict means to block it by considering not only spatial information obtained from the agent-based simulation but also intracellular regulation obtained from the Boolean model.

Our multiscale model integrates the impact of gene mutations with the perturbation of the environmental conditions and allows the visualization of the results with 2D and 3D representations. The model successfully reproduces single and collective migration processes and is validated on published experiments on cell invasion. In silico experiments are suggested to search for possible targets that can block the more invasive tumoral phenotypes.

AVAILABILITY AND IMPLEMENTATION

https://github.com/sysbio-curie/Invasion_model_PhysiBoSS.

TGF-β1 signalling in Alzheimer's pathology and cytoskeletal reorganization: a specialized Tau perspective

Microtubule-associated protein, Tau has been implicated in Alzheimer's disease for its detachment from microtubules and formation of insoluble intracellular aggregates within the neurons. Recent findings have suggested the expulsion of Tau seeds in the extracellular domain and their prion-like propagation between neurons. Transforming Growth Factor-β1 (TGF-β1) is a ubiquitously occurring cytokine reported to carry out immunomodulation and neuroprotection in the brain. TGF-β-mediated regulation occurs at the level of neuronal survival and differentiation, glial activation (astrocyte and microglia), amyloid production-distribution-clearance and neurofibrillary tangle formation, all of which contributes to Alzheimer's pathophysiology. Its role in the reorganization of cytoskeletal architecture and remodelling of extracellular matrix to facilitate cellular migration has been well-documented. Microglia are the resident immune sentinels of the brain responsible for surveying the local microenvironment, migrating towards the beacon of pertinent damage and phagocytosing the cellular debris or patho-protein deposits at the site of insult. Channelizing microglia to target extracellular Tau could be a good strategy to combat the prion-like transmission and seeding problem in Alzheimer's disease. The current review focuses on reaffirming the role of TGF-β1 signalling in Alzheimer's pathology and cytoskeletal reorganization and considers utilizing the approach of TGF-β-triggered microglia-mediated targeting of extracellular patho-protein, Tau, as a possible potential strategy to combat Alzheimer's disease.

Proteomic Markers for Mechanobiological Properties of Metastatic Cancer Cells

The major cause (more than 90%) of all cancer-related deaths is metastasis, thus its prediction can critically affect the survival rate. Metastases are currently predicted by lymph-node status, tumor size, histopathology and genetic testing; however, all these are not infallible, and obtaining results may require weeks. The identification of new potential prognostic factors will be an important source of risk information for the practicing oncologist, potentially leading to enhanced patient care through the proactive optimization of treatment strategies. Recently, the new mechanobiology-related techniques, independent of genetics, based on the mechanical invasiveness of cancer cells (microfluidic, gel indentation assays, migration assays etc.), demonstrated a high success rate for the detection of tumor cell metastasis propensity. However, they are still far away from clinical implementation due to complexity. Hence, the exploration of novel markers related to the mechanobiological properties of tumor cells may have a direct impact on the prognosis of metastasis. Our concise review deepens our knowledge of the factors that regulate cancer cell mechanotype and invasion, and incites further studies to develop therapeutics that target multiple mechanisms of invasion for improved clinical benefit. It may open a new clinical dimension that will improve cancer prognosis and increase the effectiveness of tumor therapies.

Plectin promotes tumor formation by B16 mouse melanoma cells via regulation of Rous sarcoma oncogene activity

BACKGROUND

Melanoma is a malignant tumor characterized by high proliferation and aggressive metastasis. To address the molecular mechanisms of the proto-oncogene, Rous sarcoma oncogene (Src), which is highly activated and promotes cell proliferation, migration, adhesion, and metastasis in melanoma. Plectin, a cytoskeletal protein, has recently been identified as a Src-binding protein that regulates Src activity in osteoclasts. Plectin is a candidate biomarker of certain tumors because of its high expression and the target of anti-tumor reagents such as ruthenium pyridinecarbothioamide. The molecular mechanisms by which plectin affects melanoma is still unclear. In this study, we examined the role of plectin in melanoma tumor formation.

METHODS

We used CRISPR/Cas9 gene editing to knock-out plectin in B16 mouse melanoma cells. Protein levels of plectin and Src activity were examined by western blotting analysis. In vivo tumor formation was assessed by subcutaneous injection of B16 cells into nude mice and histological analysis performed after 2 weeks by Hematoxylin-Eosin (H&E) staining. Cell proliferation was evaluated by direct cell count, cell counting kit-8 assays, cyclin D1 mRNA expression and Ki-67 immunostaining. Cell aggregation and adhesion were examined by spheroid formation, dispase-based dissociation assay and cell adhesion assays.

RESULTS

In in vivo tumor formation assays, depletion of plectin resulted in low-density tumors with large intercellular spaces. In vitro experiments revealed that plectin-deficient B16 cells exhibit reduced cell proliferation and reduced cell-to-cell adhesion. Since Src activity is reduced in plectin-deficient melanomas, we examined the relationship between plectin and Src signaling. Src overexpression in plectin knockout B16 cells rescued cell proliferation and improved cell-to-cell adhesion and cell to extracellular matrix adhesion.

CONCLUSION

These results suggest that plectin plays critical roles in tumor formation by promoting cell proliferation and cell-to-cell adhesion through Src signaling activity in melanoma cells.

Megakaryocytes form linear podosomes devoid of digestive properties to remodel medullar matrix

Bone marrow megakaryocytes (MKs) undergo a maturation involving contacts with the microenvironment before extending proplatelets through sinusoids to deliver platelets in the bloodstream. We demonstrated that MKs assemble linear F-actin-enriched podosomes on collagen I fibers. Microscopy analysis evidenced an inverse correlation between the number of dot-like versus linear podosomes over time. Confocal videomicroscopy confirmed that they derived from each-other. This dynamics was dependent on myosin IIA. Importantly, MKs progenitors expressed the Tks4/5 adaptors, displayed a strong gelatinolytic ability and did not form linear podosomes. While maturing, MKs lost Tks expression together with digestive ability. However, those MKs were still able to remodel the matrix by exerting traction on collagen I fibers through a collaboration between GPVI, ß1 integrin and linear podosomes. Our data demonstrated that a change in structure and composition of podosomes accounted for the shift of function during megakaryopoiesis. These data highlight the fact that members of the invadosome family could correspond to different maturation status of the same entity, to adapt to functional responses required by differentiation stages of the cell that bears them.

The circle of life: Phases of podosome formation, turnover and reemergence

Podosomes are highly dynamic actin-rich structures in a variety of cell types, especially monocytic cells. They fulfill multiple functions such as adhesion, mechanosensing, or extracellular matrix degradation, thus allowing cells to detect and respond to a changing environment. These abilities are based on an intricate architecture that enables podosomes to sense mechanical properties of their substratum and to transduce them intracellularly in order to generate an appropriate cellular response. These processes are enabled through the tightly orchestrated interplay of more than 300 different components that are dynamically recruited during podosome formation and turnover. In this review, we discuss the different phases of the podosome life cycle and the current knowledge on regulatory factors that impact on the genesis, activity, dissolution and reemergence of podosomes. We also highlight mechanoregulatory processes that become important during these different stages, on the level of individual podosomes, and also at podosome sub- and superstructures.

Acidic microenvironment enhances MT1-MMP-mediated cancer cell motility through integrin β1/cofilin/F-actin axis

Tumor acidic microenvironment is the main feature of many solid tumors. As a part of the tumor microenvironment, it has a profound impact on the occurrence and development of tumors. However, the research on how tumor cells sense the changes of the external microenvironment and how the intracellular subcellular structures transmit the signals from extracellular to intracellular is unclear. In this study, we identify that the acidic microenvironment enhances cancer cell motility, and the expression of membrane-anchored membrane type 1-matrix metalloproteinase is also associated with cell motility, which indicates more degradation of the ECM under the acidic microenvironment. Moreover, the expression of cofilin is low in the acidic microenvironment, and the F-actin filaments are distributed more along the cells. The cytoskeletal F-actin changes are consistent with the potential of a high-invasive phenotype. Further study reveals the upstream control of the signal transductions from extracellular to intracellular, that is, the integrin β1 functions to trigger the biological responses under the acidic microenvironment. Our results demonstrate that the acidic microenvironment enhances cancer cell motility through the integrin β1/cofilin/F-actin signal axis. This study clearly shows the scheme of the signal transmissions from extracellular to intracellular and further reveals the cytoskeletal roles for the contributions of cancer cell motility under acidic microenvironment, which provides new targets for cancer intervention from the biochemical and biophysical perspectives.

Molecular Basis of Prostate Cancer and Natural Products as Potential Chemotherapeutic and Chemopreventive Agents

Prostate cancer is the second most common malignant cancer in males. It involves a complex process driven by diverse molecular pathways that closely related to the survival, apoptosis, metabolic and metastatic characteristics of aggressive cancer. Prostate cancer can be categorized into androgen dependent prostate cancer and castration-resistant prostate cancer and cure remains elusive due to the developed resistance of the disease. Natural compounds represent an extraordinary resource of structural scaffolds with high diversity that can offer promising chemical agents for making prostate cancer less devastating and curable. Herein, those natural compounds of different origins and structures with potential cytotoxicity and/or in vivo anti-tumor activities against prostate cancer are critically reviewed and summarized according to the cellular signaling pathways they interfere. Moreover, the anti-prostate cancer efficacy of many nutrients, medicinal plant extracts and Chinese medical formulations were presented, and the future prospects for the application of these compounds and extracts were discussed. Although the failure of conventional chemotherapy as well as involved serious side effects makes natural products ideal candidates for the treatment of prostate cancer, more investigations of preclinical and even clinical studies are necessary to make use of these medical substances reasonably. Therefore, the elucidation of structure-activity relationship and precise mechanism of action, identification of novel potential molecular targets, and optimization of drug combination are essential in natural medicine research and development.

The binding of different model membranes with PKCε C2 domain is not dependent on membrane curvature but affects the sequence of events during unfolding

The C2 domain of novel protein kinases C (nPKC) binds to membranes in a Ca2+-independent way contributing to the activation of these enzymes. We have studied the C2 domain of one of these nPKCs, namely PKCε, and confirmed that it establishes a strong interaction with POPA, which is clearly visible through changes in chemical shifts detected through 31P-MAS-NMR and the protection that it exerts on the domain against thermal denaturation seen through DSC and FT-IR. In this study, using two-dimensional correlation analysis (2D-COS) applied to infrared spectra, we determined the sequence of events that occur during the thermal unfolding of the domain and highlighted some differences when phosphatidic acid or cardiolipin are present. Finally, by means of FRET and DLS experiments, we wanted to determine the effect of membrane curvature on the domain/membrane interaction by using lysophosphatidylcholine to introduce positive curvature as a control and we observed that the effect of these phospholipids on the protein binding is not exerted through the change of membrane curvature.

PI(3,4)P2-mediated membrane tubulation promotes integrin trafficking and invasive cell migration

Invadopodia are integrin-mediated adhesions with abundant PI(3,4)P₂ However, the functional role of PI(3,4)P₂ in adhesion signaling remains unclear. Here, we find that the PI(3,4)P₂ biogenesis regulates the integrin endocytosis at invadopodia. PI(3,4)P₂ is locally produced by PIK3CA and SHIP2 and is concentrated at the trailing edge of the invadopodium arc. The PI(3,4)P₂-rich compartment locally forms small puncta (membrane buds) in a SNX9-dependent manner, recruits dynein activator Hook1 through AKTIP, and rearranges into micrometer-long tubular invaginations (membrane tubes). The uncurving membrane tube extends rapidly, follows the retrograde movement of dynein along microtubule tracks, and disconnects from the plasma membrane. Activated integrin-beta3 is locally internalized through the pathway of PI(3,4)P₂-mediated membrane invagination and is then actively recycled. Blockages of PI3K, SHIP2, and SNX9 suppress integrin-beta3 endocytosis, delay adhesion turnover, and impede transwell invasion of MEF-Src and MDA-MB-231 cells. Thus, the production of PI(3,4)P₂ promotes invasive cell migration by stimulating the trafficking of integrin receptor at the invadopodium.

Endothelin-1 drives invadopodia and interaction with mesothelial cells through ILK

Cancer cells use actin-based membrane protrusions, invadopodia, to degrade stroma and invade. In serous ovarian cancer (SOC), the endothelin A receptor (ETAR) drives invadopodia by a not fully explored coordinated function of β-arrestin1 (β-arr1). Here, we report that β-arr1 links the integrin-linked kinase (ILK)/βPIX complex to activate Rac3 GTPase, acting as a central node in the adhesion-based extracellular matrix (ECM) sensing and degradation. Downstream, Rac3 phosphorylates PAK1 and cofilin and promotes invadopodium-dependent ECM proteolysis and invasion. Furthermore, ETAR/ILK/Rac3 signaling supports the communication between cancer and mesothelial cells, favoring SOC cell adhesion and transmigration. In vivo, ambrisentan, an ETAR antagonist, inhibits the adhesion and spreading of tumor cells to intraperitoneal organs, and invadopodium marker expression. As prognostic factors, high EDNRA/ILK expression correlates with poor SOC clinical outcome. These findings provide a framework for the ET-1R/β-arr1 pathway as an integrator of ILK/Rac3-dependent adhesive and proteolytic signaling to invadopodia, favoring cancer/stroma interactions and metastatic behavior.

Biomechanical regulation of focal adhesion and invadopodia formation

Integrin adhesions are a structurally and functionally diverse family of transmembrane, multi-protein complexes that link the intracellular cytoskeleton to the extracellular matrix (ECM). The different members of this family, including focal adhesions (FAs), focal complexes, fibrillar adhesions, podosomes and invadopodia, contain many shared scaffolding and signaling ‘adhesome’ components, as well as distinct molecules that perform specific functions, unique to each adhesion form. In this Hypothesis, we address the pivotal roles of mechanical forces, generated by local actin polymerization or actomyosin-based contractility, in the formation, maturation and functionality of two members of the integrin adhesions family, namely FAs and invadopodia, which display distinct structures and functional properties. FAs are robust and stable ECM contacts, associated with contractile stress fibers, while invadopodia are invasive adhesions that degrade the underlying matrix and penetrate into it. We discuss here the mechanisms, whereby these two types of adhesion utilize a similar molecular machinery to drive very different – often opposing cellular activities, and hypothesize that early stages of FAs and invadopodia assembly use similar biomechanical principles, whereas maturation of the two structures, and their ‘adhesive’ and ‘invasive’ functionalities require distinct sources of biomechanical reinforcement.

Mechanical Cues Affect Migration and Invasion of Cells From Three Different Directions

Cell migration and invasion is a key driving factor for providing essential cellular functions under physiological conditions or the malignant progression of tumors following downward the metastatic cascade. Although there has been plentiful of molecules identified to support the migration and invasion of cells, the mechanical aspects have not yet been explored in a combined and systematic manner. In addition, the cellular environment has been classically and frequently assumed to be homogeneous for reasons of simplicity. However, motility assays have led to various models for migration covering only some aspects and supporting factors that in some cases also include mechanical factors. Instead of specific models, in this review, a more or less holistic model for cell motility in 3D is envisioned covering all these different aspects with a special emphasis on the mechanical cues from a biophysical perspective. After introducing the mechanical aspects of cell migration and invasion and presenting the heterogeneity of extracellular matrices, the three distinct directions of cell motility focusing on the mechanical aspects are presented. These three different directions are as follows: firstly, the commonly used invasion tests using structural and structure-based mechanical environmental signals; secondly, the mechano-invasion assay, in which cells are studied by mechanical forces to migrate and invade; and thirdly, cell mechanics, including cytoskeletal and nuclear mechanics, to influence cell migration and invasion. Since the interaction between the cell and the microenvironment is bi-directional in these assays, these should be accounted in migration and invasion approaches focusing on the mechanical aspects. Beyond this, there is also the interaction between the cytoskeleton of the cell and its other compartments, such as the cell nucleus. In specific, a three-element approach is presented for addressing the effect of mechanics on cell migration and invasion by including the effect of the mechano-phenotype of the cytoskeleton, nucleus and the cell's microenvironment into the analysis. In precise terms, the combination of these three research approaches including experimental techniques seems to be promising for revealing bi-directional impacts of mechanical alterations of the cellular microenvironment on cells and internal mechanical fluctuations or changes of cells on the surroundings. Finally, different approaches are discussed and thereby a model for the broad impact of mechanics on cell migration and invasion is evolved.

β1 integrin-mediated signaling regulates MT1-MMP phosphorylation to promote tumor cell invasion

Malignant cancer cells can invade extracellular matrix (ECM) through the formation of F-actin-rich subcellular structures termed invadopodia. ECM degradation at invadopodia is mediated by matrix metalloproteinases (MMPs), and recent findings indicate that membrane-anchored membrane type 1-matrix metalloproteinase (MT1-MMP, also known as MMP14) has a primary role in this process. Maintenance of an invasive phenotype is dependent on internalization of MT1-MMP from the plasma membrane and its recycling to sites of ECM remodeling. Internalization of MT1-MMP is dependent on its phosphorylation, and here we examine the role of β1 integrin-mediated signaling in this process. Activation of β1 integrin using the antibody P4G11 induced phosphorylation and internalization of MT1-MMP and resulted in increased cellular invasiveness and invadopodium formation in vitro We also observed phosphorylation of Src and epidermal growth factor receptor (EGFR) and an increase in their association in response to β1 integrin activation, and determined that Src and EGFR promote phosphorylation of MT1-MMP on Thr567 These results suggest that MT1-MMP phosphorylation is regulated by a β1 integrin-Src-EGFR signaling pathway that promotes recycling of MT1-MMP to sites of invadopodia formation during cancer cell invasion.This article has an associated First Person interview with the first author of the paper.

Poji: a Fiji-based tool for analysis of podosomes and associated proteins

Podosomes are actin-based adhesion and invasion structures in a variety of cell types, with podosome-forming cells displaying up to several hundreds of these structures. Podosome number, distribution and composition can be affected by experimental treatments or during regular turnover, necessitating a tool that is able to detect even subtle differences in podosomal properties. Here, we present a Fiji-based macro code termed 'Poji' ('podosome analysis by Fiji'), which serves as an easy-to-use tool to characterize a variety of cellular and podosomal parameters, including area, fluorescence intensity, relative enrichment of associated proteins and radial podosome intensity profiles. This tool should be useful to gain more detailed insight into the regulation, architecture and functions of podosomes. Moreover, we show that Poji is easily adaptable for the analysis of invadopodia and associated extracellular matrix degradation, and likely also of other micron-size punctate structures. This article describes the workflow of the Poji macro, presents several examples of its applications, and also points out limitations, as well as respective solutions, and adaptable features to streamline the analysis.This article has an associated First Person interview with the first author of the paper.

MMP-mediated modulation of ECM environment during axonal growth and NMJ development

Motor neurons, skeletal muscles, and perisynaptic Schwann cells interact with extracellular matrix (ECM) to form the tetrapartite synapse in the peripheral nervous system. Dynamic remodeling of ECM composition is essential to diversify its functions for distinct cellular processes during neuromuscular junction (NMJ) development. In this review, we give an overview of the proteolytic regulation of ECM proteins, particularly by secreted and membrane-type matrix metalloproteinases (MMPs), in axonal growth and NMJ development. It is suggested that MMP-2, MMP-9, and membrane type 1-MMP (MT1-MMP) promote axonal outgrowth and regeneration upon injury by clearing the glial scars at the lesion site. In addition, these MMPs also play roles in neuromuscular synaptogenesis, ranging from spontaneous formation of synaptic specializations to activity-dependent synaptic elimination, via proteolytic cleavage or degradation of growth factors, neurotrophic factors, and ECM molecules. For instance, secreted MMP-3 has been known to cleave agrin, the main postsynaptic differentiation inducer, further highlighting the importance of MMPs in NMJ formation and maintenance. Furthermore, the increased level of several MMPs in myasthenia gravis (MG) patient suggest the pathophysiological mechanisms of MMP-mediated proteolytic degradation in MG pathogenesis. Finally, we speculate on potential major future directions for studying the regulatory functions of MMP-mediated ECM remodeling in axonal growth and NMJ development.

The Role of Calmodulin in Tumor Cell Migration, Invasiveness, and Metastasis

Calmodulin (CaM) is the principal Ca²⁺ sensor protein in all eukaryotic cells, that upon binding to target proteins transduces signals encoded by global or subcellular-specific changes of Ca²⁺ concentration within the cell. The Ca²⁺/CaM complex as well as Ca²⁺-free CaM modulate the activity of a vast number of enzymes, channels, signaling, adaptor and structural proteins, and hence the functionality of implicated signaling pathways, which control multiple cellular functions. A basic and important cellular function controlled by CaM in various ways is cell motility. Here we discuss the role of CaM-dependent systems involved in cell migration, tumor cell invasiveness, and metastasis development. Emphasis is given to phosphorylation/dephosphorylation events catalyzed by myosin light-chain kinase, CaM-dependent kinase-II, as well as other CaM-dependent kinases, and the CaM-dependent phosphatase calcineurin. In addition, the role of the CaM-regulated small GTPases Rac1 and Cdc42 (cell division cycle protein 42) as well as CaM-binding adaptor/scaffold proteins such as Grb7 (growth factor receptor bound protein 7), IQGAP (IQ motif containing GTPase activating protein) and AKAP12 (A kinase anchoring protein 12) will be reviewed. CaM-regulated mechanisms in cancer cells responsible for their greater migratory capacity compared to non-malignant cells, invasion of adjacent normal tissues and their systemic dissemination will be discussed, including closely linked processes such as the epithelial–mesenchymal transition and the activation of metalloproteases. This review covers as well the role of CaM in establishing metastatic foci in distant organs. Finally, the use of CaM antagonists and other blocking techniques to downregulate CaM-dependent systems aimed at preventing cancer cell invasiveness and metastasis development will be outlined.

The Leptin induced Hic-5 expression and actin puncta formation by the FAK/Src-dependent pathway in MCF10A mammary epithelial cells

Introduction: Leptin is a hormone secreted by adipocytes that has been associated with the epithelial-mesenchymal transition (EMT). Additionally, leptin promotes the migration and invasion of mammary epithelial cells through the activation of FAK and Src kinases, which are part of a regulatory complex of signaling pathways that promotes the expression of proteins related to the formation of proteolytic structures involved in the invasion and progression of cancer. Recently, overexpression and activation of Hic-5 during the EMT have been shown to induce the formation of actin puncta; these structures are indicative of the formation and functionality of invadopodia, which promote the local degradation of extracellular matrix components and cancer metastasis. Objective: To evaluate the role of FAK and Src kinases in the expression of Hic-5 during the epithelial-mesenchymal transition induced by leptin in MCF10A cells. Materials and methods: We used specific inhibitors of FAK (PF-573228) and Src (PP2) to evaluate Hic-5 expression and subcellular localization by Western blot and immunofluorescence assays and to investigate the formation of actin puncta by epifluorescence in MCF10A cells stimulated with leptin. Results: Leptin induced an increase in Hic-5 expression and the formation of actin puncta. Pretreatment with inhibitors of FAK (PF-573228) and Src (PP2) promoted a decrease in Hic-5 expression and actin puncta formation in the non-tumorigenic mammary epithelial cell line MCF10A. Conclusion: In MCF10A cells, leptin-induced Hic-5 expression and perinuclear localization, as well as the formation of actin puncta through a mechanism dependent on the kinase activity of FAK and Src.

Costameres, dense plaques and podosomes: the cell matrix adhesions in cardiovascular mechanosensing

The stiffness of the cardiovascular environment changes during ageing and in disease and contributes to disease incidence and progression. For instance, increased arterial stiffness can lead to atherosclerosis, while stiffening of the heart due to fibrosis can increase the chances of heart failure. Cells can sense the stiffness of the extracellular matrix through integrin adhesions and other mechanosensitive structures and in response to this initiate mechanosignalling pathways that ultimately change the cellular behaviour. Over the past decades, interest in mechanobiology has steadily increased and with this also our understanding of the molecular basis of mechanosensing and transduction. However, much of our knowledge about the mechanisms is derived from studies investigating focal adhesions in non-muscle cells, which are distinct in several regards from the cell-matrix adhesions in cardiomyocytes (costameres) or vascular smooth muscle cells (dense plaques or podosomes). Therefore, we will look here first at the evidence for mechanical sensing in the cardiovascular system, before comparing the different cytoskeletal arrangements and adhesion sites in cardiomyocytes and vascular smooth muscle cells and what is known about mechanical sensing through the various structures.

Correlative 3D Structured Illumination Microscopy and Single-Molecule Localization Microscopy for Imaging Cancer Invasion

Super-resolution microscopy methods enable resolution of biological molecules in their cellular or tissue context at the nanoscale. Different methods have their strengths and weaknesses. Here we present a method that enables correlative confocal, structured illumination microscopy (SIM) and single-molecule localization microscopy (SMLM) imaging of structures involved in formation of invadopodia on the same sample. This enables up to four colors to be visualized in three dimensions at a resolution of between 120 and 10 nm for SIM and SMLM, respectively.

β-hCG promotes epithelial ovarian cancer metastasis through ERK/MMP2 signaling pathway

Epithelial ovarian cancer (EOC) is the most lethal gynecologic malignancy, with typically extensive intraperitoneal implantation leading to poor prognosis. Our previous study preliminarily demonstrated β-hCG can promote tumorigenesis in immortalized nontumorigenic ovarian epithelial cells. In this study, the roles and mechanisms of β-hCG in regulating EOC proliferation and metastasis were thoroughly explored. First, histologically, β-hCG was aberrantly overexpressed in human EOC metastatic tissues, and significantly correlated with FIGO stage, tumor size, differentiation, histologic grade and high grade serous ovarian carcinoma (HGSOC) (P < 0.05). However, serologically, β-hCG expression showed no significant difference between EOC and nonmalignant ovarian patients. Second, β-hCG was confirmed to have no significant effects on EOC proliferation in vitro and in vivo, while β-hCG upregulation was proven to promote migration and invasion ability in ES-2 and OVCAR-3 cells in vitro (P < 0.05), and β-hCG downregulation in SKOV3 cells had the opposite effect. Moreover, more invadopodia protrusions, mitochondria accumulations and cytoskeletal rearrangements were observed in β-hCG-overexpressing ES-2 cells, while β-hCG-depleted SKOV3 cells produced the opposite effect. Furthermore, β-hCG was confirmed to clearly facilitate intraperitoneal metastasis in nude mouse orthotopic ovarian xenograft models. Importantly, these effects of β-hCG were mediated by activation of the ERK/MMP2 signaling pathway, independently of luteinizing hormone/chorionic gonadotropin receptor (LHCGR) presence, and inhibition the pathway with the p-ERK1/2 inhibitor SCH772984 significantly impaired the tumor-promoting effects induced by β-hCG. Collectively, these data provide new insight into the roles and mechanisms of β-hCG in regulating EOC metastasis through ERK/MMP2 signaling pathway and may become a new target for therapeutic intervention.

Cellular tension encodes local Src-dependent differential β1 and β3 integrin mobility

Integrins are transmembrane receptors that have a pivotal role in mechanotransduction processes by connecting the extracellular matrix to the cytoskeleton. Although it is well established that integrin activation/inhibition cycles are due to highly dynamic interactions, whether integrin mobility depends on local tension and cytoskeletal organization remains surprisingly unclear. Using an original approach combining micropatterning on glass substrates to induce standardized local mechanical constraints within a single cell with temporal image correlation spectroscopy, we measured the mechanosensitive response of integrin mobility at the whole cell level and in adhesion sites under different mechanical constraints. Contrary to β1 integrins, high tension increases β3 integrin residence time in adhesive regions. Chimeric integrins and structure–function studies revealed that the ability of β3 integrins to specifically sense local tensional organization is mostly encoded by its cytoplasmic domain and is regulated by tuning the affinity of its NPXY domains through phosphorylation by Src family kinases.

Every step of the way: integrins in cancer progression and metastasis

Cell adhesion to the extracellular matrix is fundamental to tissue integrity and human health. Integrins are the main cellular adhesion receptors that through multifaceted roles as signalling molecules, mechanotransducers and key components of the cell migration machinery are implicated in nearly every step of cancer progression from primary tumour development to metastasis. Altered integrin expression is frequently detected in tumours, where integrins have roles in supporting oncogenic growth factor receptor (GFR) signalling and GFR-dependent cancer cell migration and invasion. In addition, integrins determine colonization of metastatic sites and facilitate anchorage-independent survival of circulating tumour cells. Investigations describing integrin engagement with a growing number of versatile cell surface molecules, including channels, receptors and secreted proteins, continue to lead to the identification of novel tumour-promoting pathways. Integrin-mediated sensing, stiffening and remodelling of the tumour stroma are key steps in cancer progression supporting invasion, acquisition of cancer stem cell characteristics and drug resistance. Given the complexity of integrins and their adaptable and sometimes antagonistic roles in cancer cells and the tumour microenvironment, therapeutic targeting of these receptors has been a challenge. However, novel approaches to target integrins and antagonism of specific integrin subunits in stringently stratified patient cohorts are emerging as potential ways forward.

Identification of a membrane-less compartment regulating invadosome function and motility

Depletion of liprin-α1, ERC1 or LL5 scaffolds inhibits extracellular matrix degradation by invasive cells. These proteins co-accumulate near invadosomes in NIH-Src cells, identifying a novel invadosome–associated compartment distinct from the core and adhesion ring of invadosomes. Depletion of either protein perturbs the organization of invadosomes without influencing the recruitment of MT1-MMP metalloprotease. Liprin-α1 is not required for de novo formation of invadosomes after their disassembly by microtubules and Src inhibitors, while its depletion inhibits invadosome motility, thus affecting matrix degradation. Fluorescence recovery after photobleaching shows that the invadosome–associated compartment is dynamic, while correlative light immunoelectron microscopy identifies bona fide membrane–free invadosome–associated regions enriched in liprin-α1, which is virtually excluded from the invadosome core. The results indicate that liprin-α1, LL5 and ERC1 define a novel dynamic membrane-less compartment that regulates matrix degradation by affecting invadosome motility.

Invading, Leading and Navigating Cells in Caenorhabditis elegans: Insights into Cell Movement in Vivo

Highly regulated cell migration events are crucial during animal tissue formation and the trafficking of cells to sites of infection and injury. Misregulation of cell movement underlies numerous human diseases, including cancer. Although originally studied primarily in two-dimensional in vitro assays, most cell migrations in vivo occur in complex three-dimensional tissue environments that are difficult to recapitulate in cell culture or ex vivo Further, it is now known that cells can mobilize a diverse repertoire of migration modes and subcellular structures to move through and around tissues. This review provides an overview of three distinct cellular movement events in Caenorhabditis elegans-cell invasion through basement membrane, leader cell migration during organ formation, and individual cell migration around tissues-which together illustrate powerful experimental models of diverse modes of movement in vivo We discuss new insights into migration that are emerging from these in vivo studies and important future directions toward understanding the remarkable and assorted ways that cells move in animals.

Rac3 regulates breast cancer invasion and metastasis by controlling adhesion and matrix degradation

The initial step of metastasis is the local invasion of tumor cells into the surrounding tissue. Invadopodia are actin-based protrusions that mediate the matrix degradation necessary for invasion and metastasis of tumor cells. We demonstrate that Rac3 GTPase is critical for integrating the adhesion of invadopodia to the extracellular matrix (ECM) with their ability to degrade the ECM in breast tumor cells. We identify two pathways at invadopodia important for integrin activation and delivery of matrix metalloproteinases: through the upstream recruiter CIB1 as well as the downstream effector GIT1. Rac3 activity, at and surrounding invadopodia, is controlled by Vav2 and βPIX. These guanine nucleotide exchange factors regulate the spatiotemporal dynamics of Rac3 activity, impacting GIT1 localization. Moreover, the GTPase-activating function of GIT1 toward the vesicular trafficking regulator Arf6 GTPase is required for matrix degradation. Importantly, Rac3 regulates the ability of tumor cells to metastasize in vivo. The Rac3-dependent mechanisms we show in this study are critical for balancing proteolytic activity and adhesive activity to achieve a maximally invasive phenotype.

Cellular distribution of invadopodia is regulated by nanometer scale surface protein patterns

Invadopodia are proteolytic structures formed by cancer cells. It is not known whether their cellular distribution can be regulated by the organization of the extracellular matrix or the organization of the golgi complex or whether they have an adhesion requirement. Here, we used electron beam lithography to fabricate fibronectin (FN) nanodots with isotropic and gradient micrometer scale spacings on K-casein and laminin backgrounds. Investigating cancer cells cultured on protein nanopatterns, we showed that (i) presence of FN nanodots on a K-casein background decreased percent of cells with neutral invadopodia polarization compared to FN control surfaces; (ii) presence of a gradient of FN nanodots on a K-casein background increased percent of cells with negative invadopodia polarization compared to FN control surfaces; (iii) polarization of the golgi complex was similar to that of invadopodia in agreement with a spatial link; (iv) local adhesion did not necessarily appear to be a prerequisite for invadopodia formation.

Roles of paxillin family members in adhesion and ECM degradation coupling at invadosomes

The exact functions of all paxillin family members in mechanosensing and adhesion at invadosomes are unclear. Petropoulos et al. show that redundant and specific activities of paxillin and Hic-5 can couple original adhesion and ECM degradation in invadosomes.

Invadosomes are acto-adhesive structures able to both bind the extracellular matrix (ECM) and digest it. Paxillin family members—paxillin, Hic-5, and leupaxin—are implicated in mechanosensing and turnover of adhesion sites, but the contribution of each paxillin family protein to invadosome activities is unclear. We use genetic approaches to show that paxillin and Hic-5 have both redundant and distinctive functions in invadosome formation. The essential function of paxillin-like activity is based on the coordinated activity of LD motifs and LIM domains, which support invadosome assembly and morphology, respectively. However, paxillin preferentially regulates invadosome assembly, whereas Hic-5 regulates the coupling between ECM degradation and acto-adhesive functions. Mass spectrometry analysis revealed new partners that are important for paxillin and Hic-5 specificities: paxillin regulates the acto-adhesive machinery through janus kinase 1 (JAK1), whereas Hic-5 controls ECM degradation via IQGAP1. Integrating the redundancy and specificities of paxillin and Hic-5 in a functional complex provides insights into the coupling between the acto-adhesive and ECM-degradative machineries in invadosomes.

Harnessing membrane trafficking to promote cancer spreading and invasion: The case of RAB2A

How cancer disseminates and metastasizes remains an outstanding open question. Emerging evidence indicates that membrane trafficking is frequently harnessed by tumors of epithelial origin to acquire a mesenchymal program of invasiveness. However, the critical molecular hubs used by cancer cells this context have only began to be elucidated. Here, we discussed the results of a recent phenotypic screening that led to the identification of the small GTPase RAB2A, not previously involved in cancer dissemination, as pivotal for the acquisition of pericellular proteolysis, cell dissemination and distant metastatic spreading of human breast cancer. At the cellular levels, RAB2A controls both canonical polarized Golgi-to-Plasma membrane trafficking of the junctional protein E-cadherin, and post-endocytic trafficking of the membrane-bound metalloprotease, MT1-MMP. This finding reveals an unexpected plasticity in the control of diverse trafficking routes exerted by RAB2A through canonical (Golgi stacking) and non-canonical (late endosome recycling) functional interactions, contributing to break established membrane trafficking dogma on the rigorous molecular distinction between polarized Golgi and post endocytic routes. Finally, they suggest that epithelial cancers may specifically select for those molecules that enable them to control multiple trafficking routes, in turn essential for the regulation of activities necessary for acquisition of mesenchymal traits.

CD11c/CD18 Dominates Adhesion of Human Monocytes, Macrophages and Dendritic Cells over CD11b/CD18

Complement receptors CR3 (CD11b/CD18) and CR4 (CD11c/CD18) belong to the family of beta2 integrins and are expressed mainly by myeloid cell types in humans. Previously, we proved that CR3 rather than CR4 plays a key role in phagocytosis. Here we analysed how CD11b and CD11c participate in cell adhesion to fibrinogen, a common ligand of CR3 and CR4, employing human monocytes, monocyte-derived macrophages (MDMs) and monocyte-derived dendritic cells (MDDCs) highly expressing CD11b as well as CD11c. We determined the exact numbers of CD11b and CD11c on these cell types by a bead-based technique, and found that the ratio of CD11b/CD11c is 1.2 for MDDCs, 1.7 for MDMs and 7.1 for monocytes, suggesting that the function of CD11c is preponderant in MDDCs and less pronounced in monocytes. Applying state-of-the-art biophysical techniques, we proved that cellular adherence to fibrinogen is dominated by CD11c. Furthermore, we found that blocking CD11b significantly enhances the attachment of MDDCs and MDMs to fibrinogen, demonstrating a competition between CD11b and CD11c for this ligand. On the basis of the cell surface receptor numbers and the measured adhesion strength we set up a model, which explains the different behavior of the three cell types.

The Cytoskeletal Adapter Protein Spinophilin Regulates Invadopodia Dynamics and Tumor Cell Invasion in Glioblastoma

Glioblastoma is a primary brain cancer that is resistant to all treatment modalities. This resistance is due, in large part, to invasive cancer cells that disperse from the main tumor site, escape surgical resection, and contribute to recurrent secondary lesions. The adhesion and signaling mechanisms that drive glioblastoma cell invasion remain enigmatic, and as a result there are no effective anti-invasive clinical therapies. Here we have characterized a novel adhesion and signaling pathway comprised of the integrin αvβ8 and its intracellular binding partner, Spinophilin (Spn), which regulates glioblastoma cell invasion in the brain microenvironment. We show for the first time that Spn binds directly to the cytoplasmic domain of β8 integrin in glioblastoma cells. Genetically targeting Spn leads to enhanced invasive cell growth in preclinical models of glioblastoma. Spn regulates glioblastoma cell invasion by modulating the formation and dissolution of invadopodia. Spn-regulated invadopodia dynamics are dependent, in part, on proper spatiotemporal activation of the Rac1 GTPase. Glioblastoma cells that lack Spn showed diminished Rac1 activities, increased numbers of invadopodia, and enhanced extracellular matrix degradation. Collectively, these data identify Spn as a critical adhesion and signaling protein that is essential for modulating glioblastoma cell invasion in the brain microenvironment.

IMPLICATIONS

Tumor cell invasion is a major clinical obstacle in glioblastoma and this study identifies a new signaling pathway regulated by Spinophilin in invasive glioblastoma. Mol Cancer Res; 14(12); 1277-87. ©2016 AACR.

Cellular and Molecular Mechanisms of MT1-MMP-Dependent Cancer Cell Invasion

Metastasis is responsible for most cancer-associated deaths. Accumulating evidence based on 3D migration models has revealed a diversity of invasive migratory schemes reflecting the plasticity of tumor cells to switch between proteolytic and nonproteolytic modes of invasion. Yet, initial stages of localized regional tumor dissemination require proteolytic remodeling of the extracellular matrix to overcome tissue barriers. Recent data indicate that surface-exposed membrane type 1-matrix metalloproteinase (MT1-MMP), belonging to a group of membrane-anchored MMPs, plays a central role in pericellular matrix degradation during basement membrane and interstitial tissue transmigration programs. In addition, a large body of work indicates that MT1-MMP is targeted to specialized actin-rich cell protrusions termed invadopodia, which are responsible for matrix degradation. This review describes the multistep assembly of actin-based invadopodia in molecular details. Mechanisms underlying MT1-MMP traffic to invadopodia through endocytosis/recycling cycles, which are key to the invasive program of carcinoma cells, are discussed.

Significance of kinase activity in the dynamic invadosome

Invadosomes are actin rich protrusive structures that facilitate invasive migration in multiple cell types. Comprised of invadopodia and podosomes, these highly dynamic structures adhere to and degrade the extracellular matrix, and are also thought to play a role in mechanosensing. Many extracellular signals have been implicated in invadosome stimulation, activating complex signalling cascades to drive the formation, activity and turnover of invadosomes. While the structural components of invadosomes have been well studied, the regulation of invadosome dynamics is still poorly understood. Protein kinases are essential to this regulation, affecting all stages of invadosome dynamics and allowing tight spatiotemporal control of their activity. Invadosome organisation and function have been linked to pathophysiological states such as cancer invasion and metastasis; therapeutic targeting of invadosome regulatory components is thus warranted. In this review, we discuss the involvement of kinase signalling in every stage of the invadosome life cycle and evaluate its significance.

Mechanotransduction pulls the strings of matrix degradation at invadosome

Degradation of the extracellular matrix is a critical step of tumor cell invasion. Both protease-dependent and -independent mechanisms have been described as alternate processes in cancer cell motility. Interestingly, some effectors of protease-dependent degradation are focalized at invadosomes and are directly coupled with contractile and adhesive machineries composed of multiple mechanosensitive proteins. This review presents recent findings in protease-dependent mechanisms elucidating the ways the force affects extracellular matrix degradation by targeting protease expression and activity at invadosome. The aim is to highlight mechanosensing and mechanotransduction processes to direct the degradative activity at invadosomes, with the focus on membrane tension, proteases and mechanosensitive ion channels.

A new front in cell invasion: The invadopodial membrane

Invadopodia are F-actin-rich membrane protrusions that breach basement membrane barriers during cell invasion. Since their discovery more than 30 years ago, invadopodia have been extensively investigated in cancer cells in vitro, where great advances in understanding their composition, formation, cytoskeletal regulation, and control of the matrix metalloproteinase MT1-MMP trafficking have been made. In contrast, few studies examining invadopodia have been conducted in vivo, leaving their physiological regulation unclear. Recent live-cell imaging and gene perturbation studies in C. elegans have revealed that invadopodia are formed with a unique invadopodial membrane, defined by its specialized lipid and associated protein composition, which is rapidly recycled through the endolysosome. Here, we provide evidence that the invadopodial membrane is conserved and discuss its possible functions in traversing basement membrane barriers. Discovery and examination of the invadopodial membrane has important implications in understanding the regulation, assembly, and function of invadopodia in both normal and disease settings.

RAB2A controls MT1-MMP endocytic and E-cadherin polarized Golgi trafficking to promote invasive breast cancer programs

The mechanisms of tumor cell dissemination and the contribution of membrane trafficking in this process are poorly understood. Through a functional siRNA screening of human RAB GTPases, we found that RAB2A, a protein essential for ER-to-Golgi transport, is critical in promoting proteolytic activity and 3D invasiveness of breast cancer (BC) cell lines. Remarkably, RAB2A is amplified and elevated in human BC and is a powerful and independent predictor of disease recurrence in BC patients. Mechanistically, RAB2A acts at two independent trafficking steps. Firstly, by interacting with VPS39, a key component of the late endosomal HOPS complex, it controls post-endocytic trafficking of membrane-bound MT1-MMP, an essential metalloprotease for matrix remodeling and invasion. Secondly, it further regulates Golgi transport of E-cadherin, ultimately controlling junctional stability, cell compaction, and tumor invasiveness. Thus, RAB2A is a novel trafficking determinant essential for regulation of a mesenchymal invasive program of BC dissemination.

Podosome dynamics and location in vascular smooth muscle cells require CLASP-dependent microtubule bending

Extracellular matrix (ECM) remodeling during physiological processes is mediated by invasive protrusions called podosomes. Positioning and dynamics of podosomes define the extent of ECM degradation. Microtubules are known to be involved in podosome regulation, but the role of microtubule (MT) network configuration in podosome dynamics and positioning is not well understood. Here, we show that the arrangement of the microtubule network defines the pattern of podosome formation and relocation in vascular smooth muscle cells (VSMCs). We show that microtubule plus-end targeting facilitates de novo formation of podosomes, in addition to podosome remodeling. Moreover, specialized bent microtubules with plus ends reversed towards the cell center promote relocation of podosomes from the cell edge to the cell center, resulting in an evenly distributed podosome pattern. Microtubule bending is induced downstream of protein kinase C (PKC) activation and requires microtubule-stabilizing proteins known as cytoplasmic linker associated proteins (CLASPs) and retrograde actin flow. Similar to microtubule depolymerization, CLASP depletion by siRNA blocks microtubule bending and eliminates centripetal relocation of podosomes. Podosome relocation also coincides with translocation of podosome-stimulating kinesin KIF1C, which is known to move preferentially along CLASP-associated microtubules. These findings indicate that CLASP-dependent microtubule network configuration is critical to the cellular location and distribution of KIF1C-dependent podosomes. © 2016 Wiley Periodicals, Inc.

Proteolytic Enzymes Clustered in Specialized Plasma-Membrane Domains Drive Endothelial Cells' Migration

In vitro cultured endothelial cells forming a continuous monolayer establish stable cell-cell contacts and acquire a “resting” phenotype; on the other hand, when growing in sparse conditions these cells acquire a migratory phenotype and invade the empty area of the culture. Culturing cells in different conditions, we compared expression and clustering of proteolytic enzymes in cells having migratory versus stationary behavior. In order to observe resting and migrating cells in the same microscopic field, a continuous cell monolayer was wounded. Increased expression of proteolytic enzymes was evident in cell membranes of migrating cells especially at sprouting sites and in shed membrane vesicles. Gelatin zymography and western blotting analyses confirmed that in migrating cells, expression of membrane-bound and of vesicle-associated proteolytic enzymes are increased. The enzymes concerned include MMP-2, MMP-9, MT1-MMP, seprase, DPP4 (DiPeptidyl Peptidase 4) and uPA. Shed membrane vesicles were shown to exert degradative activity on ECM components and produce substrates facilitating cell migration. Vesicles shed by migrating cells degraded ECM components at an increased rate; as a result their effect on cell migration was amplified. Inhibiting either Matrix Metallo Proteases (MMPs) or Serine Integral Membrane Peptidases (SIMPs) caused a decrease in the stimulatory effect of vesicles, inhibiting the spontaneous migratory activity of cells; a similar result was also obtained when a monoclonal antibody acting on DPP4 was tested. We conclude that proteolytic enzymes have a synergistic stimulatory effect on cell migration and that their clustering probably facilitates the proteolytic activation cascades needed to produce maximal degradative activity on cell substrates during the angiogenic process.

Cell adhesion and invasion mechanisms that guide developing axons

Axon extension, guidance and tissue invasion share many similarities to normal cell migration and cancer cell metastasis. Proper cell and growth cone migration requires tightly regulated adhesion complex assembly and detachment from the extracellular matrix (ECM). In addition, many cell types actively remodel the ECM using matrix metalloproteases (MMPs) to control tissue invasion and cell dispersal. Targeting and activating MMPs is a tightly regulated process, that when dysregulated, can lead to cancer cell metastasis. Interestingly, new evidence suggests that growth cones express similar cellular and molecular machinery as migrating cells to clutch retrograde actin flow on ECM proteins and target matrix degradation, which may be used to facilitate axon pathfinding through the basal lamina and across tissues.

The microenvironment controls invadosome plasticity

Invadosomes are actin-based structures involved in extracellular matrix degradation. Invadosomes is a term that includes podosomes and invadopodia, which decorate normal and tumour cells, respectively. They are mainly organised into dots or rosettes, and podosomes and invadopodia are often compared and contrasted. Various internal or external stimuli have been shown to induce their formation and/or activity. In this Commentary, we address the impact of the microenvironment and the role of matrix receptors on the formation, and dynamic and degradative activities of invadosomes. In particular, we highlight recent findings regarding the role of type I collagen fibrils in inducing the formation of a new linear organisation of invadosomes. We will also discuss invadosome plasticity more generally and emphasise its physio-pathological relevance.

The involvement of mutant Rac1 in the formation of invadopodia in cultured melanoma cells

In this article, we discuss the complex involvement of a Rho-family GTPase, Rac1, in cell migration and in invadopodia-mediated matrix degradation. We discuss the involvement of invadopodia in invasive cell migration, and their capacity to promote cancer metastasis. Considering the regulation of invadopodia formation, we describe studies that demonstrate the role of Rac1 in the metastatic process, and the suggestion that this effect is attributable to the capacity of Rac1 to promote invadopodia formation. This notion is demonstrated here by showing that knockdown of Rac1 in melanoma cells expressing a wild-type form of this GTPase, reduces invadopodia-dependent matrix degradation. Interestingly, we also show that excessive activity of Rac1, displayed by the P29S, hyperactive, "fast cycling" mutant of Rac1, which is present in 5-10% of melanoma tumors, inhibits invadopodia function. Moreover, knockdown of this hyperactive mutant enhanced matrix degradation, indicating that excessive Rac1 activity by this mutant can negatively regulate invadopodia formation and function.

Cellular protrusions--lamellipodia, filopodia, invadopodia and podosomes--and their roles in progression of orofacial tumours: current understanding

BACKGROUND

Protrusive structures formed by migrating and invading cells are termed lamellipodia, filopodia, invadopodia and podosomes. Lamellipodia and filopodia appear on the leading edges of migrating cells and function to command the direction of the migrating cells. Invadopodia and podosomes are special F-actin-rich matrix-degrading structures that arise on the ventral surface of the cell membrane. Invadopodia are found in a variety of carcinomatous cells including squamous cell carcinoma of head and neck region whereas podosomes are found in normal highly motile cells of mesenchymal and myelomonocytic lineage. Invadopodia-associated protein markers consisted of 129 proteins belonging to different functional classes including WASP, NWASP, cortactin, Src kinase, Arp 2/3 complex, MT1-MMP and F-actin. To date, our current understanding on the role(s) of these regulators of actin dynamics in tumors of the orofacial region indicates that upregulation of these proteins promotes invasion and metastasis in oral squamous cell carcinoma, is associated with poor/worst prognostic outcome in laryngeal cancers, contributes to the persistent growth and metastasis characteristics of salivary gland adenoid cystic carcinoma, is a significant predictor of increased cancer risk in oral mucosal premalignant lesions and enhances local invasiveness in jawbone ameloblastomas.

Cytoskeletal signaling in TGFβ-induced epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is a physiological process that plays an important role in embryonic development and wound healing and is appropriated during pathological conditions including fibrosis and cancer metastasis. EMT can be initiated by a variety of factors, including transforming growth factor (TGF)-β, and is characterized by loss of epithelial features including cell-cell contacts and apicobasal polarity and acquisition of a motile, mesenchymal phenotype. A key feature of EMT is reorganization of the cytoskeleton and recent studies have elucidated regulation mechanisms governing this process. This review describes changes in gene expression patterns of cytoskeletal associated proteins during TGFβ-induced EMT. It further reports TGFβ-induced intracellular signaling cascades that regulate cytoskeletal reorganization during EMT. Finally, it highlights how changes in cytoskeletal architecture during EMT can regulate gene expression, thus further promoting EMT progression.

Regulation of invadopodia by mechanical signaling

Mechanical rigidity in the tumor microenvironment is associated with a high risk of tumor formation and aggressiveness. Adhesion-based signaling driven by a rigid microenvironment is thought to facilitate invasion and migration of cancer cells away from primary tumors. Proteolytic degradation of extracellular matrix (ECM) is a key component of this process and is mediated by subcellular actin-rich structures known as invadopodia. Both ECM rigidity and cellular traction stresses promote invadopodia formation and activity, suggesting a role for these structures in mechanosensing. The presence and activity of mechanosensitive adhesive and signaling components at invadopodia further indicates the potential for these structures to utilize myosin-dependent forces to probe and remodel their ECM environments. Here, we provide a brief review of the role of adhesion-based mechanical signaling in controlling invadopodia and invasive cancer behavior.

Integrin-mediated adhesion as self-sustained waves of enzymatic activation

Integrin receptors mediate interaction between the cellular actin-cytoskeleton and extracellular matrix. Based on their activation properties, we propose a reaction-diffusion model where the kinetics of the two-state receptors is modulated by their lipidic environment. This environment serves as an activator variable, while a second variable plays the role of a scaffold protein and controls the self-sustained activation of the receptors. Due to receptor diffusion which couples dynamically the activator and the inhibitor, our model connects major classes of reaction diffusion systems for excitable media. Spot and rosette solutions, characterized by receptor clustering into localized static or dynamic structures, are organized into a phase diagram. It is shown that diffusion and kinetics of receptors determines the dynamics and the stability of these structures. We discuss this model as a precursor model for cell signaling in the context of podosomes forming actoadhesive metastructures, and we study how generic signaling defects influence their organization.