Transforming growth factor beta induces rosettes of podosomes in primary aortic endothelial cells

Vesicle transport of matrix metalloproteinases

Multicellular organisms consist of cells and extracellular matrix (ECM). ECM creates a cellular microenvironment, and cells locally degrade the ECM according to their cellular activity. A major group of enzymes that modify ECM belongs to matrix metalloproteinases (MMPs) and play major roles in various pathophysiological events. ECM degradation by MMPs does not occur in all cellular surroundings but only where it is necessary, and cells achieve this by directionally secreting these proteolytic enzymes. Recent studies have indicated that such enzyme secretion is achieved by targeted vesicle transport along the microtubules, and several kinesin superfamily proteins (KIFs) have been identified as responsible motor proteins involved in the processes. This chapter discusses recent findings of the vesicle transport of MMPs and their roles.

SRC and TKS5 mediated podosome formation in fibroblasts promotes extracellular matrix invasion and pulmonary fibrosis

The activation and accumulation of lung fibroblasts resulting in aberrant deposition of extracellular matrix components, is a pathogenic hallmark of Idiopathic Pulmonary Fibrosis, a lethal and incurable disease. In this report, increased expression of TKS5, a scaffold protein essential for the formation of podosomes, was detected in the lung tissue of Idiopathic Pulmonary Fibrosis patients and bleomycin-treated mice. Τhe profibrotic milieu is found to induce TKS5 expression and the formation of prominent podosome rosettes in lung fibroblasts, that are retained ex vivo, culminating in increased extracellular matrix invasion. Tks5+/- mice are found resistant to bleomycin-induced pulmonary fibrosis, largely attributed to diminished podosome formation in fibroblasts and decreased extracellular matrix invasion. As computationally predicted, inhibition of src kinase is shown to potently attenuate podosome formation in lung fibroblasts and extracellular matrix invasion, and bleomycin-induced pulmonary fibrosis, suggesting pharmacological targeting of podosomes as a very promising therapeutic option in pulmonary fibrosis.

Microglia degrade Tau oligomers deposit via purinergic P2Y12-associated podosome and filopodia formation and induce chemotaxis

BACKGROUND

Tau protein forms neurofibrillary tangles and becomes deposited in the brain during Alzheimer's disease (AD). Tau oligomers are the most reactive species, mediating neurotoxic and inflammatory activity. Microglia are the immune cells in the central nervous system, sense the extracellular Tau via various cell surface receptors. Purinergic P2Y12 receptor can directly interact with Tau oligomers and mediates microglial chemotaxis via actin remodeling. The disease-associated microglia are associated with impaired migration and express a reduced level of P2Y12, but elevate the level of reactive oxygen species and pro-inflammatory cytokines.

RESULTS

Here, we studied the formation and organization of various actin microstructures such as-podosome, filopodia and uropod in colocalization with actin nucleator protein Arp2 and scaffold protein TKS5 in Tau-induced microglia by fluorescence microscopy. Further, the relevance of P2Y12 signaling either by activation or blockage was studied in terms of actin structure formations and Tau deposits degradation by N9 microglia. Extracellular Tau oligomers facilitate the microglial migration via Arp2-associated podosome and filopodia formation through the involvement of P2Y12 signaling. Similarly, Tau oligomers induce the TKS5-associated podosome clustering in microglial lamella in a time-dependent manner. Moreover, the P2Y12 was evidenced to localize with F-actin-rich podosome and filopodia during Tau-deposit degradation. The blockage of P2Y12 signaling resulted in decreased microglial migration and Tau-deposit degradation.

CONCLUSIONS

The P2Y12 signaling mediate the formation of migratory actin structures like- podosome and filopodia to exhibit chemotaxis and degrade Tau deposit. These beneficial roles of P2Y12 in microglial chemotaxis, actin network remodeling and Tau clearance can be intervened as a therapeutic target in AD.

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.

Actin cytoskeleton in angiogenesis

Actin, one of the most abundant intracellular proteins in mammalian cells, is a critical regulator of cell shape and polarity, migration, cell division, and transcriptional response. Angiogenesis, or the formation of new blood vessels in the body is a well-coordinated multi-step process. Endothelial cells lining the blood vessels acquire several new properties such as front-rear polarity, invasiveness, rapid proliferation and motility during angiogenesis. This is achieved by changes in the regulation of the actin cytoskeleton. Actin remodelling underlies the switch between the quiescent and angiogenic state of the endothelium. Actin forms endothelium-specific structures that support uniquely endothelial functions. Actin regulators at endothelial cell-cell junctions maintain the integrity of the blood-tissue barrier while permitting trans-endothelial leukocyte migration. This review focuses on endothelial actin structures and less-recognised actin-mediated endothelial functions. Readers are referred to other recent reviews for the well-recognised roles of actin in endothelial motility, barrier functions and leukocyte transmigration. Actin generates forces that are transmitted to the extracellular matrix resulting in vascular matrix remodelling. In this review, we attempt to synthesize our current understanding of the roles of actin in vascular morphogenesis. We speculate on the vascular bed specific differences in endothelial actin regulation and its role in the vast heterogeneity in endothelial morphology and function across the various tissues of our body.

Endothelial Cell Metabolism in Vascular Functions

Simple Summary

Recent findings in the field of vascular biology are nourishing the idea that targeting the endothelial cell metabolism may be an alternative strategy to antiangiogenic therapy, as well as a novel therapeutic approach for cardiovascular disease. Deepening the molecular mechanisms regulating how ECs re-adapt their metabolic status in response to the changeable conditions of the tissue microenvironment may be beneficial to develop novel innovative treatments to counteract the aberrant growth of vasculature.

Abstract

The endothelium is the innermost layer of all blood and lymphatic vessels composed of a monolayer of specialized endothelial cells (ECs). It is regarded as a dynamic and multifunctional endocrine organ that takes part in essential processes, such as the control of blood fluidity, the modulation of vascular tone, the regulation of immune response and leukocyte trafficking into perivascular tissues, and angiogenesis. The inability of ECs to perform their normal biological functions, known as endothelial dysfunction, is multi-factorial; for instance, it implicates the failure of ECs to support the normal antithrombotic and anti-inflammatory status, resulting in the onset of unfavorable cardiovascular conditions such as atherosclerosis, coronary artery disease, hypertension, heart problems, and other vascular pathologies. Notably, it is emerging that the ability of ECs to adapt their metabolic status to persistent changes of the tissue microenvironment could be vital for the maintenance of vascular functions and to prevent adverse vascular events. The main purpose of the present article is to shed light on the unique metabolic plasticity of ECs as a prospective therapeutic target; this may lead to the development of novel strategies for cardiovascular diseases and cancer.

miR-155 regulates physiological angiogenesis but an miR-155-rich microenvironment disrupts the process by promoting unproductive endothelial sprouting

Angiogenesis involves cell specification orchestrated by regulatory interactions between the vascular endothelial growth factor and Notch signaling pathways. However, the role of microRNAs in these regulations remains poorly explored. Here we show that a controlled level of miR-155 is essential for proper angiogenesis. In the mouse retina angiogenesis model, antimiR-155 altered neovascularization. In vitro assays established that endogenous miR-155 is involved in podosome formation, activation of the proteolytic machinery and cell migration but not in morphogenesis. The role of miR-155 was explored using miR-155 mimics. In vivo, exposing the developing vasculature to miR-155 promoted hypersprouting, thus phenocopying defects associated with Notch deficiency. Mechanistically, miR-155 overexpression weakened Notch signaling by reducing Smad1/5 expression, leading to the formation of tip cell-like cells which did not reach full invasive capacity and became unable to undergo morphogenesis. These results identify miR-155 as a novel regulator of physiological angiogenesis and as a novel actor of pathological angiogenesis.

StarD13 negatively regulates invadopodia formation and invasion in high-grade serous (HGS) ovarian adenocarcinoma cells by inhibiting Cdc42

Metastasis remains the main challenge to overcome for treating ovarian cancers. In this study, we investigate the potential role of the Cdc42 GAP StarD13 in the modulation of cell motility, invasion in ovarian cancer cells. StarD13 depletion does not affect the 2D motility of ovarian cancer cells. More importantly, StarD13 inhibits matrix degradation, invadopodia formation and cell invasion through the inhibition of Cdc42. StarD13 does not localize to mature TKS4-labeled invadopodia that possess matrix degradation ability, while a Cdc42 FRET biosensor, detects Cdc42 activation in these invadopodia. In fact, StarD13 localization and Cdc42 activation appear mutually exclusive in invadopodial structures. Finally, for the first time we uncover a potential role of Cdc42 in the direct recruitment of TKS4 to invadopodia. This study emphasizes the specific role of StarD13 as a narrow spatial regulator of Cdc42, inhibiting invasion, suggesting the suitability of StarD13 for targeted therapy.

Baculovirus actin-rearrangement-inducing factor ARIF-1 induces the formation of dynamic invadosome clusters

The baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV), a pathogen of lepidopteran insects, has a striking dependence on the host cell actin cytoskeleton. During the delayed-early stage of infection, AcMNPV was shown to induce the accumulation of actin at the cortex of infected cells. However, the dynamics and molecular mechanism of cortical actin assembly remained unknown. Here, we show that AcMNPV induces dynamic cortical clusters of dot-like actin structures that mediate degradation of the underlying extracellular matrix and therefore function similarly to clusters of invadosomes in mammalian cells. Furthermore, we find that the AcMNPV protein actin-rearrangement-inducing factor-1 (ARIF-1), which was previously shown to be necessary and sufficient for cortical actin assembly and efficient viral infection in insect hosts, is both necessary and sufficient for invadosome formation. We mapped the sequences within the C-terminal cytoplasmic region of ARIF-1 that are required for invadosome formation and identified individual tyrosine and proline residues that are required for organizing these structures. Additionally, we found that ARIF-1 and the invadosome-associated proteins cortactin and the Arp2/3 complex localize to invadosomes and Arp2/3 complex is required for their formation. These ARIF-1-induced invadosomes may be important for the function of ARIF-1 in systemic virus spread.

Focal adhesion dynamics in cellular function and disease

Acting as a bridge between the cytoskeleton of the cell and the extra cellular matrix (ECM), the cell-ECM adhesions with integrins at their core, play a major role in cell signalling to direct mechanotransduction, cell migration, cell cycle progression, proliferation, differentiation, growth and repair. Biochemically, these adhesions are composed of diverse, yet an organised group of structural proteins, receptors, adaptors, various enzymes including protein kinases, phosphatases, GTPases, proteases, etc. as well as scaffolding molecules. The major integrin adhesion complexes (IACs) characterised are focal adhesions (FAs), invadosomes (podosomes and invadopodia), hemidesmosomes (HDs) and reticular adhesions (RAs). The varied composition and regulation of the IACs and their signalling, apart from being an integral part of normal cell survival, has been shown to be of paramount importance in various developmental and pathological processes. This review per-illustrates the recent advancements in the research of IACs, their crucial roles in normal as well as diseased states. We have also touched on few of the various methods that have been developed over the years to visualise IACs, measure the forces they exert and study their signalling and molecular composition. Having such pertinent roles in the context of various pathologies, these IACs need to be understood and studied to develop therapeutical targets. We have given an update to the studies done in recent years and described various techniques which have been applied to study these structures, thereby, providing context in furthering research with respect to IAC targeted therapeutics.

VEGF-Induced Endothelial Podosomes via ROCK2-Dependent Thrombomodulin Expression Initiate Sprouting Angiogenesis

[Figure: see text].

Tissue remodeling by invadosomes

One of the strategies used by cells to degrade and remodel the extracellular matrix (ECM) is based on invadosomes, actin-based force-producing cell–ECM contacts that function in adhesion and migration and are characterized by their capacity to mediate pericellular proteolysis of ECM components. Invadosomes found in normal cells are called podosomes, whereas invadosomes of invading cancer cells are named invadopodia. Despite their broad involvement in cell migration and in protease-dependent ECM remodeling and their detection in living organisms and in fresh tumor tissue specimens, the specific composition and dynamic behavior of podosomes and invadopodia and their functional relevance in vivo remain poorly understood. Here, we discuss recent findings that underline commonalities and peculiarities of podosome and invadopodia in terms of organization and function and propose an updated definition of these cellular protrusions, which are increasingly relevant in patho-physiological tissue remodeling.

Angiogenesis: A Cellular Response to Traumatic Injury

ABSTRACT

The development of new vasculature plays a significant role in a number of chronic disease states, including neoplasm growth, peripheral arterial disease, and coronary artery disease, among many others. Traumatic injury and hemorrhage, however, is an immediate, often dramatic pathophysiologic insult that can also necessitate neovascularization to promote healing. Traditional understanding of angiogenesis involved resident endothelial cells branching outward from localized niches in the periphery. Additionally, there are a small number of circulating endothelial progenitor cells that participate directly in the process of neovessel formation. The bone marrow stores a relatively small number of so-called pro-angiogenic hematopoietic progenitor cells-that is, progenitor cells of a hematopoietic potential that differentiate into key structural cells and stimulate or otherwise support local cell growth/differentiation at the site of angiogenesis. Following injury, a number of cytokines and intercellular processes are activated or modulated to promote development of new vasculature. These processes initiate and maintain a robust response to vascular insult, allowing new vessels to canalize and anastomose and provide timely oxygen delivering to healing tissue. Ultimately as we better understand the key players in the process of angiogenesis we can look to develop novel techniques to promote healing following injury.

Podosomes in endothelial cell--microenvironment interactions

PURPOSE OF REVIEW

The discovery of podosomes in endothelial cells during the process of angiogenesis in vivo opens a new era in vascular biology. Podosomes are actin-based microdomains located at the plasma membrane that have been extensively described but in vitro and in other cells. This review focuses on podosomes in endothelial cells and aims to rise hypotheses about when and how these structures mediate cell--microenvironment interactions.

RECENT FINDINGS

A wealth of new information regarding podosome organization and functioning has been collected in simple 2D models. Characterization of their modular architecture has unravelled their mechanics. However, context matters and podosome characteristics and functioning are shaped by the microenvironment. Although matrix degradation was seen as the typical function of podosomes, mechanosensing now appears equally prominent and involved in setting of the proteolytic machinery. Endothelial podosomes breach the basement membrane, and are thus, involved in vascular remodelling.

SUMMARY

In endothelial cells, podosomes are involved in breaking up the basement membrane, giving the cells the opportunity to invade adjacent tissues and to engage in new cell--cell interactions. Such functions are particularly relevant to vascular biology and the exploration of podosomes in in vivo settings should bring clues to many unanswered questions.

Advances in Understanding TKS4 and TKS5: Molecular Scaffolds Regulating Cellular Processes from Podosome and Invadopodium Formation to Differentiation and Tissue Homeostasis

Scaffold proteins are typically thought of as multi-domain "bridging molecules." They serve as crucial regulators of key signaling events by simultaneously binding multiple participants involved in specific signaling pathways. In the case of epidermal growth factor (EGF)-epidermal growth factor receptor (EGFR) binding, the activated EGFR contacts cytosolic SRC tyrosine-kinase, which then becomes activated. This process leads to the phosphorylation of SRC-substrates, including the tyrosine kinase substrates (TKS) scaffold proteins. The TKS proteins serve as a platform for the recruitment of key players in EGFR signal transduction, promoting cell spreading and migration. The TKS4 and the TKS5 scaffold proteins are tyrosine kinase substrates with four or five SH3 domains, respectively. Their structural features allow them to recruit and bind a variety of signaling proteins and to anchor them to the cytoplasmic surface of the cell membrane. Until recently, TKS4 and TKS5 had been recognized for their involvement in cellular motility, reactive oxygen species-dependent processes, and embryonic development, among others. However, a number of novel functions have been discovered for these molecules in recent years. In this review, we attempt to cover the diverse nature of the TKS molecules by discussing their structure, regulation by SRC kinase, relevant signaling pathways, and interaction partners, as well as their involvement in cellular processes, including migration, invasion, differentiation, and adipose tissue and bone homeostasis. We also describe related pathologies and the established mouse models.

Intersection of TKS5 and FGD1/CDC42 signaling cascades directs the formation of invadopodia

Tumor cells exposed to a physiological matrix of type I collagen fibers form elongated collagenolytic invadopodia, which differ from dotty-like invadopodia forming on the gelatin substratum model. The related scaffold proteins, TKS5 and TKS4, are key components of the mechanism of invadopodia assembly. The molecular events through which TKS proteins direct collagenolytic invadopodia formation are poorly defined. Using coimmunoprecipitation experiments, identification of bound proteins by mass spectrometry, and in vitro pull-down experiments, we found an interaction between TKS5 and FGD1, a guanine nucleotide exchange factor for the Rho-GTPase CDC42, which is known for its role in the assembly of invadopodial actin core structure. A novel cell polarity network is uncovered comprising TKS5, FGD1, and CDC42, directing invadopodia formation and the polarization of MT1-MMP recycling compartments, required for invadopodia activity and invasion in a 3D collagen matrix. Additionally, our data unveil distinct signaling pathways involved in collagenolytic invadopodia formation downstream of TKS4 or TKS5 in breast cancer cells.

Septin2 mediates podosome maturation and endothelial cell invasion associated with angiogenesis

Podosomes are compartmentalized actin-rich adhesions, defined by their ability to locally secrete proteases and remodel extracellular matrix. Matrix remodeling by endothelial podosomes facilitates invasion and thereby vessel formation. However, the mechanisms underlying endothelial podosome formation and function remain unclear. Here, we demonstrate that Septin2, Septin6, and Septin7 are required for maturation of nascent endothelial podosomes into matrix-degrading organelles. We show that podosome development occurs through initial mobilization of the scaffolding protein Tks5 and F-actin accumulation, followed by later recruitment of Septin2. Septin2 localizes around the perimeter of podosomes in close proximity to the basolateral plasma membrane, and phosphoinositide-binding residues of Septin2 are required for podosome function. Combined, our results suggest that the septin cytoskeleton forms a diffusive barrier around nascent podosomes to promote their maturation. Finally, we show that Septin2-mediated regulation of podosomes is critical for endothelial cell invasion associated with angiogenesis. Therefore, targeting of Septin2-mediated podosome formation is a potentially attractive anti-angiogenesis strategy.

Integration of biochemical and topographic cues for the formation and spatial distribution of invadosomes in nasopharyngeal epithelial cells

Invadosomes are invasive protrusions generated by cells which can secrete matrix metalloproteinases for focal digestion of extracellular matrix. They also aid invasive cancer cells in their transmigration through vascular endothelium. However, how the physical and chemical cues in a three-dimensional (3D) system signal the spatial localization of invadosomes remains largely unknown. Here we study the topographic guidance of invadosome formation in invasive nasopharyngeal cells under the stimulation of an inflammatory cytokine, TGF-β1, using engineered gratings with different width and depth. We first report that TGF-β1 can act as an external signal to upregulate the formation of invadosomes with a random distribution on a plane 2D surface. When the cells were seeded on parallel 3D gratings of 5 µm width and 1 µm depth, most of the invadosomes aligned to the edges of the gratings, indicating a topographic cue to the control of invadosome localization. While the number of invadosomes per cell were not upregulated when the cells were seeded on 3D topography, guidance of invadosomes localization to edges is correlated with cell migration directionality on 1 µm deep gratings. Invadosomes preferentially form at edges when the cells move at a lower speed and are guided along narrow gratings. The invadosomes forming at 3D edges also have a longer half-life than those forming on a plane surface. These data suggest that there are integrated biochemical and 3D geometric cues underlying the spatial regulation of invasive structures so as to elicit efficient invasion or metastasis of cells. STATEMENT OF SIGNIFICANCE: Nasopharyngeal cells were integrated with the biological cues and matrix topography to govern the activity and spatial distribution of invadosomes. The biochemical induction of invadosome formation by TGF-β1 in nasopharyngeal cells was observed. When the cells were seeded on parallel 3D gratings, most of the invadosomes aligned to the edges of the gratings due to topographical induced invadosome localization. While the number of invadosomes per cell were not upregulated, guidance of invadosomes localization to edges is correlated with cell migration directionality on 1 µm deep gratings. Invadosomes preferentially form at edges with a higher stability when the cells are guided along narrow gratings. The integrated biochemical and 3D geometric cues could elicit efficient invasion or metastasis of cells.

A Critical Update of the Assessment and Acute Management of Patients with Severe Burns

Significance: Burns are debilitating, life threatening, and difficult to assess and manage. Recent advances in assessment and management have occurred since a comprehensive review of the care of patients with severe burns was last published, which may influence research and clinical practice. Recent Advances: Recent advances have occurred in the understanding of burn pathophysiology, which has led to the identification of potential biomarkers of burn severity, such as protein C. There is new evidence about the potential superiority of natural colloids over crystalloids during fluid resuscitation, and new evidence about components of initial and perioperative management, including an improved understanding of pain following burns. Critical Issues: The limitations of the clinical examination highlight the need for imaging and biomarkers to assist in estimations of burn severity. Fluid resuscitation reduces mortality, although there is conjecture over the ideal method. The subsequent perioperative period is associated with significant morbidity and the evidence for preventing and treating pain, infection, and fluid overload while maximizing wound healing potential is described. Future Directions: Promising developments are ongoing in imaging technology, histopathology, biomarkers, and wound healing adjuncts such as hyperbaric oxygen therapy, topical negative pressure therapy, stem cell treatments, and skin substitutes. The greatest benefit from further research on management of patients with burns would most likely be derived from the elucidation of optimal fluid resuscitation protocols, pain management protocols, and surgical techniques from randomized controlled trials.

Nck adapter proteins promote podosome biogenesis facilitating extracellular matrix degradation and cancer invasion

Background

Podosomes are membrane‐bound adhesive structures formed by actin remodeling. They are capable of extracellular matrix (ECM) degradation, which is a prerequisite for cancer cell invasion and metastasis. The signaling mechanism of podosome formation is still unknown in cancer. We previously reported that Nck adaptors regulate directional cell migration and endothelial lumen formation by actin remodeling, while deficiency of Nck reduces cancer metastasis. This study evaluated the role of Nck adaptors in podosome biogenesis and cancer invasion.

Methods

This study was conducted in vitro using both healthy cells (Human Umbilical Vein Endothelial Cell, 3T3 fibroblasts) and cancer cells (prostate cancer cell line; PC3, breast cancer cell line; MDA‐MB‐231). Confocal and TIRF imaging of cells expressing Green Fluorescence Protein (GFP)  mutant under altered levels of Nck or downstream of kinase 1 (Dok1) was used to evaluate the podosome formation and fluorescent gelatin matrix degradation. Levels of Nck in human breast carcinoma tissue sections were detected by immune histochemistry using Nck polyclonal antibody. Biochemical interaction of Nck/Dok1 was detected in podosome forming cells using immune precipitation and far‐western blotting.

Results

This study demonstrates that ectopic expression of Nck1 and Nck2 can induce the endothelial podosome formation in vitro. Nck silencing by short‐hairpin RNA blocked podosome biogenesis and ECM degradation in cSrc‐Y530F transformed endothelial cells in this study. Immunohistochemical analysis revealed the Nck overexpression in human breast carcinoma tissue sections. Immunoprecipitation and far‐western blotting revealed the biochemical interaction of Nck/p62Dok in podosome forming cells.

Conclusions

Nck adaptors in interaction with Dok1 induce podosome biogenesis and ECM degradation facilitating cancer cell invasion, and therefore a bona fide target of cancer therapy.

Podosome formation impairs endothelial barrier function by sequestering zonula occludens proteins

Podosomes and tight junctions (TJs) are subcellular compartments that both exist in endothelial cells and localize at cell surfaces. In contrast to the well-characterized role of TJs in maintaining cerebrovascular integrity, the specific function of endothelial podosomes remains unknown. Intriguingly, we discovered cross-talk between podosomes and TJs in human brain endothelial cells. Tight junction scaffold proteins ZO-1 and ZO-2 localize at podosomes in response to phorbol-12-myristate-13-acetate treatment. We found that both ZO proteins are essential for podosome formation and function. Rather than being derived from new protein synthesis, podosomal ZO-1 and ZO-2 are relocated from a pre-existing pool found at the peripheral plasma membrane with enhanced physical interaction with cortactin, a known protein marker for podosomes. Sequestration of ZO proteins in podosomes weakens tight junction complex formation, leading to increased endothelial cell permeability. This effect can be further attenuated by podosome inhibitor PP2. Altogether, our data revealed a novel cellular function of podosomes, specifically, their ability to negatively regulate tight junction and endothelial barrier integrity, which have been linked to a variety of cerebrovascular diseases.

Enhanced endothelial motility and multicellular sprouting is mediated by the scaffold protein TKS4

Endothelial cell motility has fundamental role in vasculogenesis and angiogenesis during developmental or pathological processes. Tks4 is a scaffold protein known to organize the cytoskeleton of lamellipodia and podosomes, and thus modulating cell motility and invasion. In particular, Tks4 is required for the localization and activity of membrane type 1-matrix metalloproteinase, a key factor for extracellular matrix (ECM) cleavage during cell migration. While its role in transformed cells is well established, little is known about the function of Tks4 under physiological conditions. In this study we examined the impact of Tks4 gene silencing on the functional activity of primary human umbilical vein endothelial cells (HUVEC) and used time-lapse videomicrosopy and quantitative image analysis to characterize cell motility phenotypes in culture. We demonstrate that the absence of Tks4 in endothelial cells leads to impaired ECM cleavage and decreased motility within a 3-dimensional ECM environment. Furthermore, absence of Tks4 also decreases the ability of HUVEC cells to form multicellular sprouts, a key requirement for angiogenesis. To establish the involvement of Tks4 in vascular development in vivo, we show that loss of Tks4 leads sparser vasculature in the fetal chorion in the Tks4-deficient ‘nee’ mouse strain.

Nrf2 Sequesters Keap1 Preventing Podosome Disassembly: A Quintessential Duet Moonlights in Endothelium

AIMS

Nrf2 (nuclear factor erythroid 2-like 2) is a transcription factor known to modulate blood vessel formation. Various experimental settings, however, attribute to Nrf2 either stimulatory or repressive influence on angiogenesis. Our findings unveil the mechanism of Nrf2-dependent vessel formation, which reaches beyond transactivation of gene expression and reconciles previous discrepancies.

RESULTS

We provide evidence that growth differentiation factor 15 (GDF-15)- and stromal cell-derived factor 1 (SDF-1)-induced angiogenesis strongly depends on the presence of Nrf2 protein but does not rely on its transcriptional activity. Instead, Nrf2 serves as a protein restraining Keap1 (Kelch-like ECH-associated protein 1), its known transcriptional repressor. Angiogenic response is abrogated in Nrf2-deficient endothelial cells but not in cells expressing dominant negative form or Keap1-binding fragment of Nrf2. Deficiency of Nrf2 protein available for Keap1 leads to the overabundance of RhoGAP1 (Rho GTPase-activating protein 1), the protein regulating cell division cycle 42 (Cdc42) activity. This impairs podosome assembly and disrupts actin rearrangements, thereby preventing angiogenesis. Effects of Nrf2 deficiency can be rescued by concomitant knockdown of RhoGAP1 or Keap1. Importantly, in the established murine model of Nrf2 deficiency, the N-terminal fragment of Nrf2 containing Keap1 binding domain is preserved. Thus, this model can be used to characterize Nrf2 as a transcription factor, but not as a Keap1-sequestering protein. Innovation and Conclusion: To date, the significance of Nrf2 in cell function has been ascribed solely to the regulation of transcription. We demonstrate that Nrf2 serves as a protein tethering Keap1 to allow podosome assembly and angiogenesis. Moreover, we emphasize that the new Nrf2 function of a Keap1 scavenger implies revisiting the interpretation of some of the previous data on the Nrf2-Keap1 system.

Keratinocyte growth factor (KGF) induces podosome formation via integrin-Erk1/2 signaling in human immortalized oral epithelial cells

Recent study established the role of integrins in keratinocyte growth factor (KGF)-induced oral epithelial adhesion and rete peg elongation. However, how extracellular matrix (ECM) remodeling cooperates with the increased epithelial adhesion during rete peg elongation has yet to be determined. Podosomes are cell-matrix contact structures that combine several abilities, including adhesion and matrix degradation. In the present study, we identified podosome formation at the ventral side of human immortalized oral epithelial cells (HIOECs) upon KGF treatment. Moreover, podosomal components including integrin α6，β4，α3，β1 and MMP14 colocalized with the F-actin-cortactin complex and matrix degradation assays demonstrated the ability of the F-actin-cortactin complex to degrade matrix. Inhibition both of integrin subunits β4 and β1 with specific blocking antibodies and inhibition of Erk1/2 abrogated the KGF-induced podosome formation. Notably, knockdown of integrin subunits β4 and β1 with specific small interfering RNA (siRNA) downregulated the phosphorylation levels of Erk1/2. In contrast, inhibition of both Erk1/2 could upregulate the expression of integrin subunits β4 and β1. These results demonstrate that KGF induces podosome formation via integrin-Erk1/2 signaling in HIOECs, suggesting a novel mechanism by which integrins enhance oral epithelial adhesion and rete peg elongation.

Integrins: Moonlighting Proteins in Invadosome Formation

Invadopodia are actin-rich protrusions developed by transformed cells in 2D/3D environments that are implicated in extracellular matrix (ECM) remodeling and degradation. These structures have an undoubted association with cancer invasion and metastasis because invadopodium formation in vivo is a key step for intra/extravasation of tumor cells. Invadopodia are closely related to other actin-rich structures known as podosomes, which are typical structures of normal cells necessary for different physiological processes during development and organogenesis. Invadopodia and podosomes are included in the general term 'invadosomes,' as they both appear as actin puncta on plasma membranes next to extracellular matrix metalloproteinases, although organization, regulation, and function are slightly different. Integrins are transmembrane proteins implicated in cell-cell and cell-matrix interactions and other important processes such as molecular signaling, mechano-transduction, and cell functions, e.g., adhesion, migration, or invasion. It is noteworthy that integrin expression is altered in many tumors, and other pathologies such as cardiovascular or immune dysfunctions. Over the last few years, growing evidence has suggested a role of integrins in the formation of invadopodia. However, their implication in invadopodia formation and adhesion to the ECM is still not well known. This review focuses on the role of integrins in invadopodium formation and provides a general overview of the involvement of these proteins in the mechanisms of metastasis, taking into account classic research through to the latest and most advanced work in the field.

Hic-5 regulates Src-induced invadopodia rosette formation and organization

Fibroblasts transformed by the proto-oncogene Src form individual invadopodia that can spontaneously self-organize into large matrix-degrading superstructures called rosettes. However, the mechanisms by which the invadopodia can spatiotemporally reorganize their architecture is not well understood. Here, we show that Hic-5, a close relative of the scaffold protein paxillin, is essential for the formation and organization of rosettes in active Src-transfected NIH3T3 fibroblasts and cancer-associated fibroblasts. Live cell imaging, combined with domain-mapping analysis of Hic-5, identified critical motifs as well as phosphorylation sites that are required for the formation and dynamics of rosettes. Using pharmacological inhibition and mutant expression, we show that FAK kinase activity, along with its proximity to and potential interaction with the LD2,3 motifs of Hic-5, is necessary for rosette formation. Invadopodia dynamics and their coalescence into rosettes were also dependent on Rac1, formin, and myosin II activity. Superresolution microscopy revealed the presence of formin FHOD1 and INF2-mediated unbranched radial F-actin fibers emanating from invadopodia and rosettes, which may facilitate rosette formation. Collectively, our data highlight a novel role for Hic-5 in orchestrating the organization of invadopodia into higher-order rosettes, which may promote the localized matrix degradation necessary for tumor cell invasion.

[Variations on the theme of podosomes, context matters]

Podosomes are actin-based microdomains connecting the cell with its extracellular matrix. Contractile actin-myosin cables assemble them into a network that constitutes a versatile cellular superstructure. Discovered and extensively described in in vitro conditions, podosomes now appear as major actors of specific physiological processes. They share common characteristics but their morphology and their effect on cell functioning can only be apprehended in specific cellular contexts. We focus here on three cellular processes involving podosomes and discuss their properties in context.

Cell Migration in Microfluidic Devices: Invadosomes Formation in Confined Environments

The last 20 years have seen the blooming of microfluidics technologies applied to biological sciences. Microfluidics provides effective tools for biological analysis, allowing the experimentalists to extend their playground to single cells and single molecules, with high throughput and resolution which were inconceivable few decades ago. In particular, microfluidic devices are profoundly changing the conventional way of studying the cell motility and cell migratory dynamics. In this chapter we will furnish a comprehensive view of the advancements made in the research domain of confinement-induced cell migration, thanks to the use of microfluidic devices. The chapter is subdivided in three parts. Each section will be addressing one of the fundamental questions that the microfluidic technology is contributing to unravel: (i) where cell migration takes place, (ii) why cells migrate and, (iii) how the cells migrate. The first introductory part is devoted to a thumbnail, and partially historical, description of microfluidics and its impact in biological sciences. Stress will be put on two aspects of the devices fabrication process, which are crucial for biological applications: materials used and coating methods. The second paragraph concerns the cell migration induced by environmental cues: chemical, leading to chemotaxis, mechanical, at the basis of mechanotaxis, and electrical, which induces electrotaxis. Each of them will be addressed separately, highlighting the fundamental role of microfluidics in providing the well-controlled experimental conditions where cell migration can be induced, investigated and ultimately understood. The third part of the chapter is entirely dedicated to how the cells move in confined environments. Invadosomes (the joint name for podosomes and invadopodia) are cell protrusion that contribute actively to cell migration or invasion. The formation of invadosomes under confinement is a research topic that only recently has caught the attention of the scientific community: microfluidic design is helping shaping the future direction of this emerging field of research.

Variations on the theme of podosomes: A matter of context

Extensive in vitro studies have described podosomes as actin-based structures at the plasma membrane, connecting the cell with its extracellular matrix and endowed with multiple capabilities. Contractile actin-myosin cables assemble them into a network that constitutes a multifaceted cellular superstructure taking different forms - with common characteristics - but manifesting different properties depending on the context of study. Their morphology and their role in cell functioning and behavior are therefore now apprehended in in vivo or in vitro situations relevant to physiological processes. We focus here on three of them, namely: macrophage migration, antigen presentation by dendritic cells and endothelial cell sprouting during angiogenesis to highlight the characteristics of podosomes and their functioning shaped by the microenvironment.

Biogenesis of podosome rosettes through fission

Podosomes are dynamic actin-based membrane protrusions that are important for extracellular matrix degradation and invasive cell motility. Individual podosomes are often found to organize into large rosette-like structures in some types of cells, such as osteoclasts, endothelial cells, Src-transformed fibroblasts, and certain highly invasive cancer cells. In this study, we show that new podosome rosettes arise through one of two mechanisms; de novo assembly or fission of a pre-existing podosome rosette in Src-transformed fibroblasts. Fission is a more efficient way than de novo assembly to generate new podosome rosettes in these cells. Podosome rosettes undergoing fission possess higher motility and a stronger matrix-degrading capability. Podosome rosette fission may be the result of polarized myosin II-mediated contractility of these structures, which is coordinately regulated by myosin light chain kinase and Rho-associated kinase II. Collectively, this study unveils a previously unknown mechanism-fission for the biogenesis of podosome rosettes.

Oval Cells Contribute to Fibrogenesis of Marginal Liver Grafts under Stepwise Regulation of Aldose Reductase and Notch Signaling

Background and Aims: Expanded donor criteria poses increased risk for late phase complications such as fibrosis that lead to graft dysfunction in liver transplantation. There remains a need to elucidate the precise mechanisms of post-transplant liver damage in order to improve the long-term outcomes of marginal liver grafts. In this study, we aimed to examine the role of oval cells in fibrogenic development of marginal liver grafts and explore the underlying mechanisms.

Methods: Using an orthotopic rat liver transplantation model and human post-transplant liver biopsy tissues, the dynamics of oval cells in marginal liver grafts was evaluated by the platform integrating immuno-labeling techniques and ultrastructure examination. Underlying mechanisms were further explored in oval cells and an Aldose reductase (AR) knockout mouse model simulating marginal graft injury.

Results: We demonstrated that activation of aldose reductase initiated oval cell proliferation in small-for-size fatty grafts during ductular reaction at the early phase after transplantation. These proliferative oval cells subsequently showed prevailing biliary differentiation and exhibited features of mesenchymal transition including dynamically co-expressing epithelial and mesenchymal markers, developing microstructures for extra-cellular matrix degradation (podosomes) or cell migration (filopodia and blebs), and acquiring the capacity in collagen production. Mechanistic studies further indicated that transition of oval cell-derived biliary cells toward mesenchymal phenotype ensued fibrogenesis in marginal grafts under the regulation of notch signaling pathway.

Conclusions: Oval cell activation and their subsequent lineage commitment contribute to post-transplant fibrogenesis of small-for-size fatty liver grafts. Interventions targeting oval cell dynamics may serve as potential strategies to refine current clinical management.

Optogenetic interrogation of integrin αVβ3 function in endothelial cells

The integrin αVβ3 is reported to promote angiogenesis in some model systems but not in others. Here, we used optogenetics to study the effects of αVβ3 interaction with the intracellular adapter kindlin-2 (Fermt2) on endothelial cell functions potentially relevant to angiogenesis. Because interaction of kindlin-2 with αVβ3 requires the C-terminal three residues of the β3 cytoplasmic tail (Arg-Gly-Thr; RGT), optogenetic probes LOVpep and ePDZ1 were fused to β3ΔRGT-GFP and mCherry-kindlin-2, respectively, and expressed in β3 integrin-null microvascular endothelial cells. Exposure of the cells to 450 nm (blue) light caused rapid and specific interaction of kindlin-2 with αVβ3 as assessed by immunofluorescence and total internal reflection fluorescence (TIRF) microscopy, and it led to increased endothelial cell migration, podosome formation and angiogenic sprouting. Analyses of kindlin-2 mutants indicated that interaction of kindlin-2 with other kindlin-2 binding partners, including c-Src, actin, integrin-linked kinase and phosphoinositides, were also likely necessary for these endothelial cell responses. Thus, kindlin-2 promotes αVβ3-dependent angiogenic functions of endothelial cells through its simultaneous interactions with β3 integrin and several other binding partners. Optogenetic approaches should find further use in clarifying spatiotemporal aspects of vascular cell biology.

Invadosomes are coming: new insights into function and disease relevance

Invadopodia and podosomes are discrete, actin-based molecular protrusions that form in cancer cells and normal cells, respectively, in response to diverse signaling pathways and extracellular matrix cues. Although they participate in a host of different cellular processes, they share a common functional theme of controlling pericellular proteolytic activity, which sets them apart from other structures that function in migration and adhesion, including focal adhesions, lamellipodia, and filopodia. In this review, we highlight research that explores the function of these complex structures, including roles for podosomes in embryonic and postnatal development, in angiogenesis and remodeling of the vasculature, in maturation of the postsynaptic membrane, in antigen sampling and recognition, and in cell-cell fusion mechanisms, as well as the involvement of invadopodia at multiple steps of the metastatic cascade, and how all of this may apply in the treatment of human disease states. Finally, we explore recent research that implicates a novel role for exosomes and microvesicles in invadopodia-dependent and invadopodia-independent mechanisms of invasion, respectively.

Proteases Revisited: Roles and Therapeutic Implications in Fibrosis

Proteases target many substrates, triggering changes in distinct biological processes correlated with cell migration, EMT/EndMT and fibrosis. Extracellular protease activity, demonstrated by secreted and membrane-bound protease forms, leads to ECM degradation, activation of other proteases (i.e., proteolysis of nonactive zymogens), decomposition of cell-cell junctions, release of sequestered growth factors (TGF-β and VEGF), activation of signal proteins and receptors, degradation of inflammatory inhibitors or inflammation-related proteins, and changes in cell mechanosensing and motility. Intracellular proteases, mainly caspases and cathepsins, modulate lysosome activity and signal transduction pathways. Herein, we discuss the current knowledge on the multidimensional impact of proteases on the development of fibrosis.

Matrix Metalloproteinases -14, -9 and -2 are Localized to the Podosome and Involved in Podosome Development in the A7r5 Smooth Muscle Cell

Aim

The purpose of the study was to localize matrix metalloproteinase (MMP)-14, -9, and -2 in the A7r5 smooth muscle cell and to understand the interaction between these MMPs and the cytoskeleton. This interaction was observed under non-stimulating and phorbol 12, 13-dibutyrate (PDBu)-stimulating conditions.

Methods

Confocal microscopy was utilized to define the localizations of MMPs and tissue inhibitor of matrix metalloproteinases (TIMPs) in the A7r5 cell and to determine interaction between MMPs and the cytoskeleton. Under PDBu-stimulating conditions, the presence of MMP active forms and activity by gel zymography was evaluated in the A7r5 cell. Actin and microtubule-polymerization inhibitors were used to evaluate MMP interaction with the cytoskeleton and the cytoskeleton was observed on matrix and within a Type I collagen gel.

Results

MMP-14, -9, and -2 were localized to the podosome in the A7r5 smooth muscle cell and interactions were seen with these MMPs and the actin cytoskeleton. PDBu-stimulation induced increases in the protein abundance of the active forms of the MMPs and MMP-2 activity was increased. MMPs also interact with a-actin and not β-tubulin in the A7r5 cell. Galardin, also known as GM-6001, was shown to inhibit podosome formation and prevented MMP localization to the podosome. This broad spectrum MMP inhibitor also prevented collagen gel contraction and prevented cell adhesion and spreading of A7r5 cells within this collagen matrix.

Conclusion

MMPs are important in the formation and function of podosomes in the A7r5 smooth muscle cell. MMPs interact with a-actin and not β-tubulin in the A7r5 cell. Podosomes play an important role in cell migration and understanding the function of podosomes can lead to insights into cancer metastasis and cardiovascular disease.

HMEC-1 adopt the mixed amoeboid-mesenchymal migration type during EndMT

The contribution of endothelial cells to scar and fibrotic tissue formation is undisputedly connected to their ability to undergo the endothelial-to-mesenchymal transition (EndMT) towards fibroblast phenotype-resembling cells. The migration model of fibroblasts and fibroblast-resembling cells is still not fully understood. It may be either a Rho/ROCK-independent, an integrin- and MMP-correlated ECM degradation-dependent, a mesenchymal model or Rho/ROCK-dependent, integrin adhesion- and MMP activity-independent, an amoeboid model. Here, we hypothesized that microvascular endothelial cells (HMEC-1) undergoing EndMT adopt an intermediate state of drifting migration model between the mesenchymal and amoeboid protrusive types in the early stages of fibrosis. We characterized the response of HMEC-1 to TGF-β2, a well-known mediator of EndMT within the microvasculature. We observed that TGF-β2 induces up to an intermediate mesenchymal phenotype in HMEC-1. In parallel, MMP-2 is upregulated and is responsible for most proteolytic activity. Interestingly, the migration of HMEC-1 undergoing EndMT is dependent on both ECM degradation and invadosome formation associated with MMP-2 proteolytic activity and Rho/ROCK cytoskeleton contraction. In conclusion, the transition from mesenchymal towards amoeboid movement highlights a molecular plasticity mechanism in endothelial cell migration in skin fibrosis.

Macrophages and RhoA Pathway in Transplanted Organs

RhoA is a small GTPase that, via its downstream effectors, regulates a variety of cell functions such as cytokinesis, cell migration, vesicular trafficking, and phagocytosis. As such the RhoA pathway is also pivotal for proper functioning of immune cells including macrophages. By controlling actin cytoskeleton organization, RhoA pathway modulates macrophage's polarity and basic functions: phagocytosis, migration, and extracellular matrix degradation. Numerous studies indicate that macrophages are very important effectors contributing to acute and chronic rejection of transplanted organs. In this review we discuss the role of RhoA pathway in governance of macrophage's functions in terms of transplanted organs.

Podosome assembly is controlled by the GTPase ARF1 and its nucleotide exchange factor ARNO

Podosomes represent a class of integrin-mediated cell-matrix adhesions formed by migrating and matrix-degrading cells. We demonstrate that in macrophage-like THP1 cells and fibroblasts stimulated to produce podosomes, down-regulation of the G-protein ARF1 or the ARF1 guanine nucleotide exchange factor, ARNO, by small, interfering RNA or pharmacological inhibitors led to striking podosome elimination. Concomitantly, treatments inducing podosome formation increased the level of guanosine triphosphate (GTP)-bound ARF1. ARNO was found to colocalize with the adhesive rings of podosomes, whereas ARF1 was localized to vesicular structures transiently contacting podosome rings. Inhibition of ARF1 led to an increase in RhoA-GTP levels and triggered assembly of myosin-IIA filaments in THP1 cells, whereas the suppression of myosin-IIA rescued podosome formation regardless of ARF1 inhibition. Finally, expression of constitutively active ARF1 in fibroblasts induced formation of putative podosome precursors: actin-rich puncta coinciding with matrix degradation sites and containing proteins of the podosome core but not of the adhesive ring. Thus, ARNO-ARF1 regulates formation of podosomes by inhibition of RhoA/myosin-II and promotion of actin core assembly.

Metalloproteinase MT1-MMP islets act as memory devices for podosome reemergence

The authors find that matrix metalloproteinase MT1-MMP is enriched at the plasma membrane of macrophage podosomes, where it persists beyond podosome lifetime and, through binding to the subcortical actin cytoskeleton, forms subcellular signposts that facilitate podosome reformation.

Podosomes are dynamic cell adhesions that are also sites of extracellular matrix degradation, through recruitment of matrix-lytic enzymes, particularly of matrix metalloproteinases. Using total internal reflection fluorescence microscopy, we show that the membrane-bound metalloproteinase MT1-MMP is enriched not only at podosomes but also at distinct “islets” embedded in the plasma membrane of primary human macrophages. MT1-MMP islets become apparent upon podosome dissolution and persist beyond podosome lifetime. Importantly, the majority of MT1-MMP islets are reused as sites of podosome reemergence. siRNA-mediated knockdown and recomplementation analyses show that islet formation is based on the cytoplasmic tail of MT1-MMP and its ability to bind the subcortical actin cytoskeleton. Collectively, our data reveal a previously unrecognized phase in the podosome life cycle and identify a structural function of MT1-MMP that is independent of its proteolytic activity. MT1-MMP islets thus act as cellular memory devices that enable efficient and localized reformation of podosomes, ensuring coordinated matrix degradation and invasion.

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.

VEGF-A stimulates podosome-mediated collagen-IV proteolysis in microvascular endothelial cells

Podosomes are dynamic cell-matrix contact structures that combine several key abilities, including adhesion, matrix degradation and mechanosensing. These actin-based cytoskeletal structures have been mostly studied in monocytic cells, but much less is known about those formed in other lineages. In this study, we characterise podosomes in capillary-derived microvascular endothelial cells. We identify two types of podosomes: constitutive podosomes that form in the absence of specific stimulation and induced podosomes that arise in response to the angiogenic factor VEGF-A. Constitutive and VEGF-A-induced podosomes share similar components but exhibit marked differences in terms of gelatinolytic activity. We also show that the extracellular matrix proteins laminin and collagen-IV are key determinants of the VEGF-A response, but neither collagen-I nor fibronectin are conducive for podosome induction. Moreover, only collagen-IV elicits the formation of proteolytically active podosomes through a mechanism involving increased Src phosphorylation, p190RhoGAP-B (also known as ARHGAP5) relocalisation and MT1-MMP (also known as MMP14) cell surface exposure at podosome sites. We hypothesise that by promoting podosome formation, VEGF-A enables endothelial cells to overcome the basement membrane barrier to allow sprouting outwards from the existing vasculature.

Force Matters: Biomechanical Regulation of Cell Invasion and Migration in Disease

Atherosclerosis, cancer, and various chronic fibrotic conditions are characterized by an increase in the migratory behavior of resident cells and the enhanced invasion of assorted exogenous cells across a stiffened extracellular matrix (ECM). This stiffened scaffold aberrantly engages cellular mechanosignaling networks in cells, which promotes the assembly of invadosomes and lamellae for cell invasion and migration. Accordingly, deciphering the conserved molecular mechanisms whereby matrix stiffness fosters invadosome and lamella formation could identify therapeutic targets to treat fibrotic conditions, and reducing ECM stiffness could ameliorate disease progression.

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.

Podosomes and invadopodia: tools to breach vascular basement membrane

The vascular basement membrane (BM) is a thin and dense cross-linked extracellular matrix layer that covers and protects blood vessels. Understanding how cells cross the physical barrier of the vascular BM will provide greater insight into the potentially critical role of vascular BM breaching in cancer extravasation, leukocyte trafficking and angiogenic sprouting. In the last year, new evidence has mechanistically linked the breaching of vascular BM with the formation of specific cellular micro-domains known as podosomes and invadopodia. These structures are specialized cell-matrix contacts with an inherent ability to degrade the extracellular matrix. Specifically, the formation of podosomes or invadopodia was shown as an important step in vascular sprouting and tumor cell extravasation, respectively. Here, we review and comment on these recent findings and explore the functions of podosomes and invadopodia within the context of pathological processes such as tumor dissemination and tumor angiogenesis.