Adhesion rings surround invadopodia and promote maturation

DCLK1-Mediated Regulation of Invadopodia Dynamics and Matrix Metalloproteinase Trafficking Drives Invasive Progression in Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a major health concern due to its high mortality from poor treatment responses and locoregional tumor invasion into life sustaining structures in the head and neck. A deeper comprehension of HNSCC invasion mechanisms holds the potential to inform targeted therapies that may enhance patient survival. We previously reported that doublecortin like kinase 1 (DCLK1) regulates invasion of HNSCC cells. Here, we tested the hypothesis that DCLK1 regulates proteins within invadopodia to facilitate HNSCC invasion. Invadopodia are specialized subcellular protrusions secreting matrix metalloproteinases that degrade the extracellular matrix (ECM). Through a comprehensive proteome analysis comparing DCLK1 control and shDCLK1 conditions, our findings reveal that DCLK1 plays a pivotal role in regulating proteins that orchestrate cytoskeletal and ECM remodeling, contributing to cell invasion. Further, we demonstrate in TCGA datasets that DCLK1 levels correlate with increasing histological grade and lymph node metastasis. We identified higher expression of DCLK1 in the leading edge of HNSCC tissue. Knockdown of DCLK1 in HNSCC reduced the number of invadopodia, cell adhesion and colony formation. Using super resolution microscopy, we demonstrate localization of DCLK1 in invadopodia and colocalization with mature invadopodia markers TKS4, TKS5, cortactin and MT1-MMP. We carried out phosphoproteomics and validated using immunofluorescence and proximity ligation assays, the interaction between DCLK1 and motor protein KIF16B. Pharmacological inhibition or knockdown of DCLK1 reduced interaction with KIF16B, secretion of MMPs, and cell invasion. This research unveils a novel function of DCLK1 within invadopodia to regulate the trafficking of matrix degrading cargo. The work highlights the impact of targeting DCLK1 to inhibit locoregional invasion, a life-threatening attribute of HNSCC.

Role of Microenvironmental Components in Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell cancer (HNSCC) is one of the ten most common malignant neoplasms, characterized by an aggressive course, high recurrence rate, poor response to treatment, and low survival rate. This creates the need for a deeper understanding of the mechanisms of the pathogenesis of this cancer. The tumor microenvironment (TME) of HNSCC consists of stromal and immune cells, blood and lymphatic vessels, and extracellular matrix. It is known that HNSCC is characterized by complex relationships between cancer cells and TME components. TME components and their dynamic interactions with cancer cells enhance tumor adaptation to the environment, which provides the highly aggressive potential of HNSCC and resistance to antitumor therapy. Basic research aimed at studying the role of TME components in HNSCC carcinogenesis may serve as a key to the discovery of both new biomarkers-predictors of prognosis and targets for new antitumor drugs. This review article focuses on the role and interaction with cancer of TME components such as newly formed vessels, cancer-associated fibroblasts, and extracellular matrix.

Mechanisms and roles of podosomes and invadopodia

Cell invasion into the surrounding extracellular matrix or across tissue boundaries and endothelial barriers occurs in both physiological and pathological scenarios such as immune surveillance or cancer metastasis. Podosomes and invadopodia, collectively called 'invadosomes', are actin-based structures that drive the proteolytic invasion of cells, by forming highly regulated platforms for the localized release of lytic enzymes that degrade the matrix. Recent advances in high-resolution microscopy techniques, in vivo imaging and high-throughput analyses have led to considerable progress in understanding mechanisms of invadosomes, revealing the intricate inner architecture of these structures, as well as their growing repertoire of functions that extends well beyond matrix degradation. In this Review, we discuss the known functions, architecture and regulatory mechanisms of podosomes and invadopodia. In particular, we describe the molecular mechanisms of localized actin turnover and microtubule-based cargo delivery, with a special focus on matrix-lytic enzymes that enable proteolytic invasion. Finally, we point out topics that should become important in the invadosome field in the future.

ARHGAP17 regulates the spatiotemporal activity of Cdc42 at invadopodia

Invadopodia formation is regulated by Rho GTPases. However, the molecular mechanisms that control Rho GTPase signaling at invadopodia remain poorly understood. Here, we have identified ARHGAP17, a Cdc42-specific RhoGAP, as a key regulator of invadopodia in breast cancer cells and characterized a novel ARHGAP17-mediated signaling pathway that controls the spatiotemporal activity of Cdc42 during invadopodia turnover. Our results show that during invadopodia assembly, ARHGAP17 localizes to the invadopodia ring and restricts the activity of Cdc42 to the invadopodia core, where it promotes invadopodia growth. Invadopodia disassembly starts when ARHGAP17 translocates from the invadopodia ring to the core, in a process that is mediated by its interaction with the Cdc42 effector CIP4. Once at the core, ARHGAP17 inactivates Cdc42 to promote invadopodia disassembly. Our results in invadopodia provide new insights into the coordinated transition between the activation and inactivation of Rho GTPases.

New Perspectives on the Role of Integrin-Linked Kinase (ILK) Signaling in Cancer Metastasis

Simple Summary

Today, the vast majority of deaths from cancer are due to cancer metastasis. Metastasis requires that cancer cells escape from the initial tumor, travel through blood vessels, and form new tumors in distant host tissues. Integrin-linked kinase (ILK) is overexpressed by many types of cancer cells and provides both structural and signaling functions that are important for successful metastasis. Here, we discuss recent findings that show how ILK is involved in promoting physical changes important for cell motility and invasion, and how ILK relays signals to other machinery components during metastasis, including interactions with components of the immune system and communication between cancer cells and normal cells, to affect the process of metastasis. We also discuss the contribution of ILK to therapeutic resistance and examine efforts to target ILK for the treatment of metastatic disease.

Abstract

Cancer metastasis is a major barrier to the long-term survival of cancer patients. In cancer cells, integrin engagement downstream of cell-extracellular matrix (ECM) interactions results in the recruitment of cytoskeletal and signaling molecules to form multi-protein complexes to promote processes critical for metastasis. One of the major functional components of these complexes is Integrin Linked Kinase (ILK). Here, we discuss recent advances in our understanding of the importance of ILK as a signaling effector in processes linked to tumor progression and metastasis. New mechanistic insights as to the role of ILK in cellular plasticity, epithelial mesenchymal transition (EMT), migration, and invasion, including the impact of ILK on the formation of invadopodia, filopodia-like protrusions (FLPs), and Neutrophil Extracellular Trap (NET)-induced motility are highlighted. Recent findings detailing the contribution of ILK to therapeutic resistance and the importance of ILK as a potentially therapeutically tractable vulnerability in both solid tumors and hematologic malignancies are discussed. Indeed, pharmacologic inhibition of ILK activity using specific small molecule inhibitors is effective in curtailing the contribution of ILK to these processes, potentially offering a novel therapeutic avenue for inhibiting critical steps in the metastatic cascade leading to reduced drug resistance and increased therapeutic efficacy.

Indoxyl sulfate- and P-cresol-induced monocyte adhesion and migration is mediated by integrin-linked kinase-dependent podosome formation

Cardiovascular disease is an important cause of death in patients with chronic kidney disease (CKD). Protein-bound uremic toxins, such as p-cresyl and indoxyl sulfate (IS), are poorly removed during hemodialysis, leading to vascular endothelial dysfunction and leukocyte extravasation. These processes can be related to dynamic adhesion structures called podosomes. Several studies have indicated the role of integrin-linked kinase (ILK) in the accumulation of integrin-associated proteins in podosomes. Here, we investigated the involvement of ILK and podosome formation in the adhesion and extravasation of monocytes under p-cresol (pc) and IS exposure. Incubation of THP-1 human monocyte cells with these toxins upregulated ILK kinase activity. Together, both toxins increased cell adhesion, podosome formation, extracellular matrix degradation, and migration of THP-1 cells, whereas ILK depletion with specific small interfering RNAs suppressed these processes. Interestingly, F-actin colocalized with cortactin in podosome cores, while ILK was colocalized in podosome rings under toxin stimulation. Podosome Wiskott-Aldrich syndrome protein (WASP)-interacting protein (WIP) and AKT protein depletion demonstrated that monocyte adhesion depends on podosome formation and that the ILK/AKT signaling pathway is involved in these processes. Ex vivo experiments showed that both toxins induced adhesion and podosome formation in leukocytes from wild-type mice, whereas these effects were not observed in leukocytes of conditional ILK-knockdown animals. In summary, under pc and IS stimulation, monocytes increase podosome formation and transmigratory capacity through an ILK/AKT signaling pathway-dependent mechanism, which could lead to vascular injury. Therefore, ILK could be a potential therapeutic target for the treatment of vascular damage associated with CKD.

An enzyme involved in organizing structural proteins into protrusions of the cell membrane helps facilitate the movement of white blood cells that occurs in chronic kidney disease and can lead to cardiovascular damage. Laura Calleros from the University of Alcalá, Madrid, Spain, and colleagues showed how toxic metabolites that build up in the bloodstream as kidneys fail induce the activity of an enzyme called integrin-linked kinase (ILK). This enzyme in turn spurs white blood cells to form protrusions called podosomes that make the cells more mobile, enabling them to move out of blood vessels and into surrounding tissues where they can cause inflammation -mediated injury. ILK inactivation reversed these effects. Therapies that target the enzyme could therefore help limit the cardiovascular complications of chronic kidney disease.

Epithelial Mesenchymal Transition (EMT) and Associated Invasive Adhesions in Solid and Haematological Tumours

In solid tumours, cancer cells that undergo epithelial mesenchymal transition (EMT) express characteristic gene expression signatures that promote invasive migration as well as the development of stemness, immunosuppression and drug/radiotherapy resistance, contributing to the formation of currently untreatable metastatic tumours. The cancer traits associated with EMT can be controlled by the signalling nodes at characteristic adhesion sites (focal contacts, invadopodia and microtentacles) where the regulation of cell migration, cell cycle progression and pro-survival signalling converge. In haematological tumours, ample evidence accumulated during the last decade indicates that the development of an EMT-like phenotype is indicative of poor disease prognosis. However, this EMT phenotype has not been directly linked to the assembly of specific forms of adhesions. In the current review we discuss the role of EMT in haematological malignancies and examine its possible link with the progression towards more invasive and aggressive forms of these tumours. We also review the known types of adhesions formed by haematological malignancies and speculate on their possible connection with the EMT phenotype. We postulate that understanding the architecture and regulation of EMT-related adhesions will lead to the discovery of new therapeutic interventions to overcome disease progression and resistance to therapies.

PIP3 abundance overcomes PI3K signaling selectivity in invadopodia

PI3Kβ is required for invadopodia-mediated matrix degradation by breast cancer cells. Invadopodia maturation requires GPCR activation of PI3Kβ and its coupling to SHIP2 to produce PI(3,4)P2 . We now test whether selectivity for PI3Kβ is preserved under conditions of mutational increases in PI3K activity. In breast cancer cells where PI3Kβ is inhibited, short-chain diC8-PIP3  rescues gelatin degradation in a SHIP2-dependent manner; rescue by diC8-PI(3,4)P2  is SHIP2-independent. Surprisingly, the expression of either activated PI3Kβ or PI3Kα mutants rescued the effects of PI3Kβ inhibition. In both cases, gelatin degradation was SHIP2-dependent. These data confirm the requirement for PIP3 conversion to PI(3,4)P2 for invadopodia function and suggest that selectivity for distinct PI3K isotypes may be obviated by mutational activation of the PI3K pathway.

Matrix Metalloproteinases Shape the Tumor Microenvironment in Cancer Progression

Cancer progression with uncontrolled tumor growth, local invasion, and metastasis depends largely on the proteolytic activity of numerous matrix metalloproteinases (MMPs), which affect tissue integrity, immune cell recruitment, and tissue turnover by degrading extracellular matrix (ECM) components and by releasing matrikines, cell surface-bound cytokines, growth factors, or their receptors. Among the MMPs, MMP-14 is the driving force behind extracellular matrix and tissue destruction during cancer invasion and metastasis. MMP-14 also influences both intercellular as well as cell-matrix communication by regulating the activity of many plasma membrane-anchored and extracellular proteins. Cancer cells and other cells of the tumor stroma, embedded in a common extracellular matrix, interact with their matrix by means of various adhesive structures, of which particularly invadopodia are capable to remodel the matrix through spatially and temporally finely tuned proteolysis. As a deeper understanding of the underlying functional mechanisms is beneficial for the development of new prognostic and predictive markers and for targeted therapies, this review examined the current knowledge of the interplay of the various MMPs in the cancer context on the protein, subcellular, and cellular level with a focus on MMP14.

Liprins in oncogenic signaling and cancer cell adhesion

Liprins are a multifunctional family of scaffold proteins, identified by their involvement in several important neuronal functions related to signaling and organization of synaptic structures. More recently, the knowledge on the liprin family has expanded from neuronal functions to processes relevant to cancer progression, including cell adhesion, cell motility, cancer cell invasion, and signaling. These proteins consist of regions, which by prediction are intrinsically disordered, and may be involved in the assembly of supramolecular structures relevant for their functions. This review summarizes the current understanding of the functions of liprins in different cellular processes, with special emphasis on liprins in tumor progression. The available data indicate that liprins may be potential biomarkers for cancer progression and may have therapeutic importance.

Ubiquitous membrane-bound DNase activity in podosomes and invadopodia

Podosomes and invadopodia, collectively termed invadosomes, are adhesive and degradative membrane structures formed in many types of cells and are well known for recruiting various proteases. However, another major class of degradative enzymes, deoxyribonuclease (DNase), remains unconfirmed and not studied in invadosomes. Here, using surface-immobilized nuclease sensor (SNS), we demonstrated that invadosomes recruit DNase to their core regions, which degrade extracellular double-stranded DNA. We further identified the DNase as GPI-anchored membrane-bound DNase X. DNase recruitment is ubiquitous and consistent in invadosomes of all tested cell types. DNase activity exhibits within a minute after actin nucleation, functioning concomitantly with protease in podosomes but preceding it in invadopodia. We further showed that macrophages form DNase-active podosome rosettes surrounding bacteria or micropatterned antigen islets, and the podosomes directly degrade bacterial DNA on a surface, exhibiting an apparent immunological function. Overall, this work reports DNase in invadosomes for the first time, suggesting a richer arsenal of degradative enzymes in invadosomes than known before.

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.

The multiple roles of actin-binding proteins at invadopodia

Invadopodia are actin-rich membrane protrusions that facilitate cancer cell dissemination by focusing on proteolytic activity and clearing paths for migration through physical barriers, such as basement membranes, dense extracellular matrices, and endothelial cell junctions. Invadopodium formation and activity require spatially and temporally regulated changes in actin filament organization and dynamics. About three decades of research have led to a remarkable understanding of how these changes are orchestrated by sequential recruitment and coordinated activity of different sets of actin-binding proteins. In this chapter, we provide an update on the roles of the actin cytoskeleton during the main stages of invadopodium development with a particular focus on actin polymerization machineries and production of pushing forces driving extracellular matrix remodeling.

Protrudin-mediated ER-endosome contact sites promote MT1-MMP exocytosis and cell invasion

Cancer cells break tissue barriers by use of small actin-rich membrane protrusions called invadopodia. Complete invadopodia maturation depends on protrusion outgrowth and the targeted delivery of the matrix metalloproteinase MT1-MMP via endosomal transport by mechanisms that are not known. Here, we show that the ER protein Protrudin orchestrates invadopodia maturation and function. Protrudin formed contact sites with MT1-MMP-positive endosomes that contained the RAB7-binding Kinesin-1 adaptor FYCO1, and depletion of RAB7, FYCO1, or Protrudin inhibited MT1-MMP-dependent extracellular matrix degradation and cancer cell invasion by preventing anterograde translocation and exocytosis of MT1-MMP. Moreover, when endosome translocation or exocytosis was inhibited by depletion of Protrudin or Synaptotagmin VII, respectively, invadopodia were unable to expand and elongate. Conversely, when Protrudin was overexpressed, noncancerous cells developed prominent invadopodia-like protrusions and showed increased matrix degradation and invasion. Thus, Protrudin-mediated ER-endosome contact sites promote cell invasion by facilitating translocation of MT1-MMP-laden endosomes to the plasma membrane, enabling both invadopodia outgrowth and MT1-MMP exocytosis.

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.

Integrin-Linked Kinase Links Integrin Activation to Invadopodia Function and Invasion via the p(T567)-Ezrin/NHERF1/NHE1 Pathway

Tumor cell invasion depends largely on degradation of the extracellular matrix (ECM) by protease-rich structures called invadopodia, whose formation and activity requires the convergence of signaling pathways engaged in cell adhesion, actin assembly, membrane regulation and ECM proteolysis. It is known that β1-integrin stimulates invadopodia function through an invadopodial p(T567)-ezrin/NHERF1/NHE1 signal complex that regulates NHE1-driven invadopodia proteolytic activity and invasion. However, the link between β1-integrin and this signaling complex is unknown. In this study, in metastatic breast (MDA-MB-231) and prostate (PC-3) cancer cells, we report that integrin-linked kinase (ILK) integrates β1-integrin with this signaling complex to regulate invadopodia activity and invasion. Proximity ligation assay experiments demonstrate that, in invadopodia, ILK associates with β1-integrin, NHE1 and the scaffold proteins p(T567)-ezrin and NHERF1. Activation of β1-integrin increased both invasion and invadopodia activity, which were specifically blocked by inhibition of either NHE1 or ILK. We conclude that ILK integrates β1-integrin with the ECM proteolytic/invasion signal module to induce NHE1-driven invadopodial ECM proteolysis and cell invasion.

Tumor microenvironment and immune-related therapies of head and neck squamous cell carcinoma

Head and neck squamous cell carcinomas (HNSCCs) are a type of common malignant tumor, mainly manifesting as oropharyngeal, oral cavity, laryngopharyngeal, hypopharyngeal, and laryngeal cancers. These highly aggressive malignant tumors reportedly affect more than 830,000 patients worldwide every year. Currently, the main treatments for HNSCC include surgery, radiotherapy, chemotherapy, and immunotherapy, as well as combination therapy. However, the overall 5-year survival rate of HNSCC has remained 50%, and it has not significantly improved in the past 10 years. Previous studies have shown that the tumor microenvironment (TME) plays a crucial role in the recurrence, metastasis, and drug resistance of patients with HNSCC. In this review, we summarize the role of anti-tumor and pro-tumor immune cells, as well as extracellular components in the TME of HNSCC. We also discuss classical HNSCC immunotherapy and highlight examples of clinical trials using CTLA-4 inhibitors and programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1)-related combination therapies. We also outline some molecules in the TME known to regulate immunosuppressive cells. Furthermore, the role and underlying mechanism of radiation therapy on the TME, immune cells, and immune response are discussed.

Cross-talk between the calcium channel TRPV4 and reactive oxygen species interlocks adhesive and degradative functions of invadosomes

Invadosomes support cell invasion by coupling both acto-adhesive and extracellular matrix degradative functions, which are apparently antagonistic. β1-integrin dynamics regulate this coupling, but the actual sensing mechanism and effectors involved have not yet been elucidated. Using genetic and reverse genetic approaches combined with biochemical and imaging techniques, we now show that the calcium channel TRPV4 colocalizes with β1-integrins at the invadosome periphery and regulates its activation and the coupling of acto-adhesive and degradative functions. TRPV4-mediated regulation of podosome function depends on its ability to sense reactive oxygen species (ROS) in invadosomes' microenvironment and involves activation of the ROS/calcium-sensitive kinase Ask1 and binding of the motor MYO1C. Furthermore, disease-associated TRPV4 gain-of-function mutations that modulate ECM degradation are also implicated in the ROS response, which provides new perspectives in our understanding of the pathophysiology of TRPV4 channelopathies.

A Fluorescent Gelatin Degradation Assay to Study Melanoma Breakdown of Extracellular Matrix

In order to protrude within a dense tissue, tumor cells have to develop the ability to digest the extracellular matrix (ECM). Melanoma cells, similarly to other types of tumor cells, form invadopodia, membranous invaginations rich in filamentous actin and several other proteins including matrix metalloproteinases (MMPs). MMPs degrade ECM structural proteins such as collagens, fibronectin, or laminin. Here we describe an assay that allows the detection of gelatinase activity exhibited by tumor cells under 2D conditions and methods to present obtained data in both a quantitative and a qualitative manner.

Hold on or Cut? Integrin- and MMP-Mediated Cell-Matrix Interactions in the Tumor Microenvironment

The tumor microenvironment (TME) has become the focus of interest in cancer research and treatment. It includes the extracellular matrix (ECM) and ECM-modifying enzymes that are secreted by cancer and neighboring cells. The ECM serves both to anchor the tumor cells embedded in it and as a means of communication between the various cellular and non-cellular components of the TME. The cells of the TME modify their surrounding cancer-characteristic ECM. This in turn provides feedback to them via cellular receptors, thereby regulating, together with cytokines and exosomes, differentiation processes as well as tumor progression and spread. Matrix remodeling is accomplished by altering the repertoire of ECM components and by biophysical changes in stiffness and tension caused by ECM-crosslinking and ECM-degrading enzymes, in particular matrix metalloproteinases (MMPs). These can degrade ECM barriers or, by partial proteolysis, release soluble ECM fragments called matrikines, which influence cells inside and outside the TME. This review examines the changes in the ECM of the TME and the interaction between cells and the ECM, with a particular focus on MMPs.

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.

Tumor Cellular and Microenvironmental Cues Controlling Invadopodia Formation

During the metastatic progression, invading cells might achieve degradation and subsequent invasion into the extracellular matrix (ECM) and the underlying vasculature using invadopodia, F-actin-based and force-supporting protrusive membrane structures, operating focalized proteolysis. Their formation is a dynamic process requiring the combined and synergistic activity of ECM-modifying proteins with cellular receptors, and the interplay with factors from the tumor microenvironment (TME). Significant advances have been made in understanding how invadopodia are assembled and how they progress in degradative protrusions, as well as their disassembly, and the cooperation between cellular signals and ECM conditions governing invadopodia formation and activity, holding promise to translation into the identification of molecular targets for therapeutic interventions. These findings have revealed the existence of biochemical and mechanical interactions not only between the actin cores of invadopodia and specific intracellular structures, including the cell nucleus, the microtubular network, and vesicular trafficking players, but also with elements of the TME, such as stromal cells, ECM components, mechanical forces, and metabolic conditions. These interactions reflect the complexity and intricate regulation of invadopodia and suggest that many aspects of their formation and function remain to be determined. In this review, we will provide a brief description of invadopodia and tackle the most recent findings on their regulation by cellular signaling as well as by inputs from the TME. The identification and interplay between these inputs will offer a deeper mechanistic understanding of cell invasion during the metastatic process and will help the development of more effective therapeutic strategies.

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.

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.

Increased Stiffness Inhibits Invadopodia Formation and Cell Migration in 3D

Cancer cells typically invade through basement membranes (BMs) at key points during metastasis, including primary tumor invasion, intravasation, and extravasation. Cells extend invadopodia protrusions to create channels in the nanoporous BM through which they can invade, either via proteolytic degradation or mechanical force. Increased matrix stiffness can promote cancer progression, and two-dimensional (2D) culture studies indicate that increased stiffness promotes invadopodia degradation activity. However, invadopodia can function mechanically, independent of their degradative activity, and cells do not form fully matured invadopodia or migrate in the direction of the invadopodia in 2D environments. Here, we elucidated the impact of matrix stiffness on the mechanical mode of invadopodia activity of cancer cells cultured in three-dimensional BM-like matrices. Invadopodia formation and cell migration assays were performed for invasive breast cancer cells cultured in mechanically plastic, nanoporous, and minimally degradable interpenetrating networks of reconstituted BM matrix and alginate, which presented a range of elastic moduli from 0.4 to 9.3 kPa. Across this entire range of stiffness, we find that cells form mature invadopodia that often precede migration in the direction of the protrusion. However, at higher stiffness, cells form shorter and more transient invadopodia and are less likely to extend invadopodia overall, contrasting with results from 2D studies. Subsequently, cell migration is diminished in stiff environments. Thus, although previous studies indicate that increased stiffness may promote malignant phenotypes and the degradative activity of invadopodia, our findings show that increased stiffness physically restricts invadopodia extension and cell migration in three-dimensional, BM-like environments.

Invadopodia: clearing the way for cancer cell invasion

The invasive nature of many cancer cells involves the formation of F-actin-based, lipid-raft-enriched membrane protrusions known as invadopodia or, more broadly, invadosomes. Invadopodia are specialized adhesive structures arising from ventral cell surface within cell-extracellular matrix (ECM) contacts and concentrate high proteolytic activities that allow cells to overcome the dense scaffold of local microenvironment, comprising a natural barrier to cell spreading. This degradative activity distinguishes invadopodia from other adhesive structures like focal adhesions, lamellipodia or filopodia, and is believed to drive cancer progression.

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.

The SHCA adapter protein cooperates with lipoma-preferred partner in the regulation of adhesion dynamics and invadopodia formation

SHC adaptor protein (SHCA) and lipoma-preferred partner (LPP) mediate transforming growth factor β (TGFβ)-induced breast cancer cell migration and invasion. Reduced expression of either protein diminishes breast cancer lung metastasis, but the reason for this effect is unclear. Here, using total internal reflection fluorescence (TIRF) microscopy, we found that TGFβ enhanced the assembly and disassembly rates of paxillin-containing adhesions in an SHCA-dependent manner through the phosphorylation of the specific SHCA tyrosine residues Tyr-239, Tyr-240, and Tyr-313. Using a BioID proximity labeling approach, we show that SHCA exists in a complex with a variety of actin cytoskeletal proteins, including paxillin and LPP. Consistent with a functional interaction between SHCA and LPP, TGFβ-induced LPP localization to cellular adhesions depended on SHCA. Once localized to the adhesions, LPP was required for TGFβ-induced increases in cell migration and adhesion dynamics. Mutations that impaired LPP localization to adhesions (mLIM1) or impeded interactions with the actin cytoskeleton via α-actinin (ΔABD) abrogated migratory responses to TGFβ. Live-cell TIRF microscopy revealed that SHCA clustering at the cell membrane preceded LPP recruitment. We therefore hypothesize that, in the presence of TGFβ, SHCA promotes the formation of small, dynamic adhesions by acting as a nucleator of focal complex formation. Finally, we defined a previously unknown function for SHCA in the formation of invadopodia, a process that also required LPP. Our results reveal that SHCA controls the formation and function of adhesions and invadopodia, two key cellular structures required for breast cancer metastasis.

Evaluation of lumican effects on morphology of invading breast cancer cells, expression of integrins and downstream signaling

The small leucine-rich proteoglycan lumican regulates estrogen receptors (ERs)-associated functional properties of breast cancer cells, expression of matrix macromolecules, and epithelial-to-mesenchymal transition. However, it is not known whether the ER-dependent lumican effects on breast cancer cells are related to the expression of integrins and their intracellular signaling pathways. Here, we analyzed the effects of lumican in three breast cancer cell lines: the highly metastatic ERβ-positive MDA-MB-231, cells with the respective ERβ-suppressed (shERβMDA-MB-231), and lowly invasive ERα-positive MCF-7/c breast cancer cells. Scanning electron microscopy, confocal microscopy, real-time PCR, western blot, and cell adhesion assays were performed. Lumican effects on breast cancer cell morphology were also investigated in 3-dimensional collagen cultures. Lumican treatment induced cell-cell contacts and cell grouping and inhibited microvesicles and microvilli formation. The expression of the cell surface adhesion receptor CD44, its isoform and variants, hyaluronan (HA), and HA synthases was also investigated. Lumican inhibited the expression of CD44 and HA synthases, and its effect on cell adhesion revealed a major role of α1, α2, α3, αVβ3, and αVβ5 integrins in MDA-MB-231 cells, but not in MCF-7/c cells. Lumican upregulated the expression of α2 and β1 integrin subunits both in MDA-MB-231 and in shERβMDA-MB-231 as compared to MCF-7/c cells. Downstream signaling pathways for integrins, such as FAK, ERK 1/2 MAPK 42/44, and Akt, were found to be downregulated by lumican. Our data shed light to the molecular mechanisms responsible for the anticancer activity of lumican in invasive breast cancer.

Direct measurement of vertical forces shows correlation between mechanical activity and proteolytic ability of invadopodia

Mechanobiology plays a prominent role in cancer invasion and metastasis. The ability of a cancer to degrade extracellular matrix (ECM) is likely connected to its invasiveness. Many cancer cells form invadopodia-micrometer-sized cellular protrusions that promote invasion through matrix degradation (proteolysis). Although it has been hypothesized that invadopodia exert mechanical force that is implicated in cancer invasion, direct measurements remain elusive. Here, we use a recently developed interferometric force imaging technique that provides piconewton resolution to quantify invadopodial forces in cells of head and neck squamous carcinoma and to monitor their temporal dynamics. We compare the force exerted by individual protrusions to their ability to degrade ECM and investigate the mechanical effects of inhibiting invadopodia through overexpression of microRNA-375. By connecting the biophysical and biochemical characteristics of invadopodia, our study provides a new perspective on cancer invasion that, in the future, may help to identify biomechanical targets for cancer therapy.

Integrin-associated molecules and signalling cross talking in osteoclast cytoskeleton regulation

In the ageing skeleton, the balance of bone reconstruction could commonly be broken by the increasing of bone resorption and decreasing of bone formation. Consequently, the bone resorption gradually occupies a dominant status. During this imbalance process, osteoclast is unique cell linage act the bone resorptive biological activity, which is a highly differentiated ultimate cell derived from monocyte/macrophage. The erosive function of osteoclasts is that they have to adhere the bone matrix and migrate along it, in which adhesive cytoskeleton recombination of osteoclast is essential. In that, the podosome is a membrane binding microdomain organelle, based on dynamic actin, which forms a cytoskeleton superstructure connected with the plasma membrane. Otherwise, as the main adhesive protein, integrin regulates the formation of podosome and cytoskeleton, which collaborates with the various molecules including: c-Cbl, p130^Cas , c-Src and Pyk2, through several signalling cascades cross talking, including: M-CSF and RANKL. In our current study, we discuss the role of integrin and associated molecules in osteoclastogenesis cytoskeletal, especially podosomes, regulation and relevant signalling cascades cross talking.

IKKε phosphorylates kindlin-2 to induce invadopodia formation and promote colorectal cancer metastasis

Invadopodia formation is a key driver of cancer metastasis. The noncanonical IkB-related kinase IKKε has been implicated in cancer metastasis, but its roles in invadopodia formation and colorectal cancer (CRC) metastasis are unclear. Methods: Immunofluorescence, gelatin-degradation assay, wound healing assay and transwell invasion assay were used to determine the influence of IKKε over-expression, knockdown and pharmacological inhibition on invadopodia formation and the migratory and invasive capacity of CRC cells in vitro. Effects of IKKε knockdown or pharmacological inhibition on CRC metastasis were examined in mice. Immunohistochemistry staining was used to detect expression levels of IKKε in CRC patient tissues, and its association with prognosis in CRC patients was also analyzed. Immunoprecipitation, western blotting and in vitro kinase assay were constructed to investigate the molecular mechanisms. Results: IKKε co-localizes with F-actin and the invadopodia marker Tks5 at the gelatin-degrading sites of CRC cells. Genetic over-expression/knockdown or pharmacological inhibition of IKKε altered invadopodia formation and the migratory and invasive capacity of CRC cells in vitro. In vivo, knockdown or pharmacological inhibition of IKKε significantly suppressed metastasis of CRC cells in mice. IKKε knockdown also inhibited invadopodia formation in vivo. Clinical investigation of tumor specimens from 191 patients with CRC revealed that high IKKε expression correlates with metastasis and poor prognosis of CRC. Mechanistically, IKKε directly binds to and phosphorylates kindlin-2 at serine 159; this effect mediates the IKKε-induced invadopodia formation and promotion of CRC metastasis. Conclusions: We identify IKKε as a novel regulator of invadopodia formation and a unique mechanism by which IKKε promotes the metastasis of CRC. Our study suggests that IKKε is a potential target to suppress CRC metastasis.

Probing the mechanical landscape – new insights into podosome architecture and mechanics

Podosomes are dynamic adhesion structures formed constitutively by macrophages, dendritic cells and osteoclasts and transiently in a wide variety of cells, such as endothelial cells and megakaryocytes. They mediate numerous functions, including cell–matrix adhesion, extracellular matrix degradation, mechanosensing and cell migration. Podosomes present as micron-sized F-actin cores surrounded by an adhesive ring of integrins and integrin–actin linkers, such as talin and vinculin. In this Review, we highlight recent research that has considerably advanced our understanding of the complex architecture–function relationship of podosomes by demonstrating that the podosome ring actually consists of discontinuous nano-clusters and that the actin network in between podosomes comprises two subsets of unbranched actin filaments, lateral and dorsal podosome-connecting filaments. These lateral and dorsal podosome-connecting filaments connect the core and ring of individual podosomes and adjacent podosomes, respectively. We also highlight recent insights into the podosome cap as a novel regulatory module of actomyosin-based contractility. We propose that these newly identified features are instrumental for the ability of podosomes to generate protrusion forces and to mechanically probe their environment. Furthermore, these new results point to an increasing complexity of podosome architecture and have led to our current view of podosomes as autonomous force generators that drive cell migration.

PI3Kβ links integrin activation and PI(3,4)P2 production during invadopodial maturation

The invasion of tumor cells from the primary tumor is mediated by invadopodia, actin-rich protrusive organelles that secrete matrix metalloproteases and degrade the extracellular matrix. This coupling between protrusive activity and matrix degradation facilitates tumor invasion. We previously reported that the PI3Kβ isoform of PI 3-kinase, which is regulated by both receptor tyrosine kinases and G protein-coupled receptors, is required for invasion and gelatin degradation in breast cancer cells. We have now defined the mechanism by which PI3Kβ regulates invadopodia. We find that PI3Kβ is specifically activated downstream from integrins, and is required for integrin-stimulated spreading and haptotaxis as well as integrin-stimulated invadopodia formation. Surprisingly, these integrin-stimulated and PI3Kβ-dependent responses require the production of PI(3,4)P2 by the phosphoinositide 5'-phosphatase SHIP2. Thus, integrin activation of PI3Kβ is coupled to the SHIP2-dependent production of PI(3,4)P2, which regulates the recruitment of PH domain-containing scaffolds such as lamellipodin to invadopodia. These findings provide novel mechanistic insight into the role of PI3Kβ in the regulation of invadopodia in breast cancer cells.

Regulation of extracellular matrix degradation and metastatic spread by IQGAP1 through endothelin-1 receptor signalling in ovarian cancer

The invasive phenotype of serous ovarian cancer (SOC) cells is linked to the formation of actin-based protrusions, invadopodia, operating extracellular matrix (ECM) degradation and metastatic spread. Growth factor receptors might cause engagement of integrin-related proteins, like the polarity protein IQ-domain GTPase-activating protein 1 (IQGAP1), to F-actin core needed for invadopodia functions. Here, we investigated whether IQGAP1 forms a signalosome with endothelin-1 (ET-1)/β-arrestin1 (β-arr1) network, as signal-integrating module for adhesion components, cytoskeletal remodelling and ECM degradation. In SOC cells, ET-1 receptor (ET-1R) activation, besides altering IQGAP1 expression and localization, coordinates the binding of IQGAP1 with β-arr1, representing a "hotspot" for ET-1R-induced invasive signalling. We demonstrated that the molecular interaction of IQGAP1 with β-arr1 affects relocalization of focal adhesion components, as vinculin, and cytoskeleton dynamics, through the regulation of invadopodia-related pathways. In particular, ET-1R deactivates Rac1 thereby promoting RhoA/C activation for the correct functions of invasive structures. Silencing of either IQGAP1 or β-arr1, or blocking ET-1R activation with a dual antagonist macitentan, prevents matrix metalloproteinase (MMP) activity, invadopodial function, transendothelial migration and cell invasion. In vivo, targeting ET-1R/β-arr1 signalling controls the process of SOC metastasis, associated with reduced levels of IQGAP1, as well as other invadopodia effectors, such as vinculin, phospho-cortactin and membrane type 1-MMP. High expression of ETAR/β-arr1/IQGAP1 positively correlates with poor prognosis, validating the clinical implication of this signature in early prognosis of SOC. These data establish the ET-1R-driven β-arr1/IQGAP1 interaction as a prerequisite for the dynamic integration of pathways in fostering invadopodia and metastatic process in human SOC.

Invadopodia formation: An important step in matrix stiffness-regulated tumor invasion and metastasis

Highly motile and invasive abilities are symbolic features of metastatic tumor cells. Being a critical molecular event for maintaining the highly migratory and invasive capabilities of tumor cells, invadopodia formation undoubtedly determines the progression of tumor invasion and metastasis. Growing numbers of studies suggest that increased matrix stiffness, as a notable property of physical mechanics in solid tumors, participates in the regulation of tumor invasion and metastasis via different molecular mechanisms. However, to date the relevant mechanisms of matrix stiffness-induced invadopodia formation and activity in tumor cells remain largely unclear. This paper is to make a review on the structure and function of invadopodia, the stages and inductive factors of invadopodia formation, the regulatory mechanisms of matrix stiffness-induced invadopodia formation and so on, with an aim to reveal the important roles of invadopodia in matrix stiffness-regulated tumor invasion and metastasis.

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.

The extracellular matrix in tumor progression and metastasis

The extracellular matrix (ECM) constitutes the scaffold of tissues and organs. It is a complex network of extracellular proteins, proteoglycans and glycoproteins, which form supramolecular aggregates, such as fibrils and sheet-like networks. In addition to its biochemical composition, including the covalent intermolecular cross-linkages, the ECM is also characterized by its biophysical parameters, such as topography, molecular density, stiffness/rigidity and tension. Taking these biochemical and biophysical parameters into consideration, the ECM is very versatile and undergoes constant remodeling. This review focusses on this remodeling of the ECM under the influence of a primary solid tumor mass. Within this tumor stroma, not only the cancer cells but also the resident fibroblasts, which differentiate into cancer-associated fibroblasts (CAFs), modify the ECM. Growth factors and chemokines, which are tethered to and released from the ECM, as well as metabolic changes of the cells within the tumor bulk, add to the tumor-supporting tumor microenvironment. Metastasizing cancer cells from a primary tumor mass infiltrate into the ECM, which variably may facilitate cancer cell migration or act as barrier, which has to be proteolytically breached by the infiltrating tumor cell. The biochemical and biophysical properties therefore determine the rates and routes of metastatic dissemination. Moreover, primed by soluble factors of the primary tumor, the ECM of distant organs may be remodeled in a way to facilitate the engraftment of metastasizing cancer cells. Such premetastatic niches are responsible for the organotropic preference of certain cancer entities to colonize at certain sites in distant organs and to establish a metastasis. Translational application of our knowledge about the cancer-primed ECM is sparse with respect to therapeutic approaches, whereas tumor-induced ECM alterations such as increased tissue stiffness and desmoplasia, as well as breaching the basement membrane are hallmark of malignancy and diagnostically and histologically harnessed.

MMP Secretion Rate and Inter-invadopodia Spacing Collectively Govern Cancer Invasiveness

Invadopodia are micron-sized invasive structures that mediate extracellular matrix (ECM) degradation through a combination of membrane-bound and soluble matrix metalloproteinases (MMPs). However, how such localized degradation is converted into pores big enough for cancer cells to invade, and the relative contributions of membrane-bound versus soluble MMPs to this process remain unclear. In this article, we address these questions by combining experiments and simulations. We show that in MDA-MB-231 cells, an increase in ECM density enhances invadopodia-mediated ECM degradation and decreases inter-invadopodia spacing. ECM degradation is mostly mediated by soluble MMPs, which are activated by membrane-bound MT1-MMP. We present a computational model of invadopodia-mediated ECM degradation, which recapitulates the above observations and identifies MMP secretion rate as an important regulator of invadopodia stability. Simulations with multiple invadopodia suggest that inter-invadopodia spacing and MMP secretion rate collectively dictate the size of the degraded zones. Taken together, our results suggest that for creating pores conducive for cancer invasion, cells must tune inter-invadopodia spacing and MMP secretion rate in an ECM density-dependent manner, thereby striking a balance between invadopodia penetration and ECM degradation.

Claudin-7 modulates cell-matrix adhesion that controls cell migration, invasion and attachment of human HCC827 lung cancer cells

Claudins are a family of tight junction proteins, and serve important roles in epithelial barrier, selective ion transports and cancer metastasis. Although the exact role of claudin-7 in human lung cancer has not been completely elucidated, recent clinical studies have demonstrated that claudin-7 is associated with the survival of patients with lung cancer. Our previous studies have demonstrated that claudin-7 forms a protein complex with integrin β1 in human lung cancer cells. The knockdown (KD) of claudin-7 by short hairpin RNA (shRNA) reduced integrin β1 expression and increased the cell proliferative rate, whereas claudin-7 re-expression in the KD cells decreased the cell proliferation. It is unknown as to whether claudin-7 and integrin β1 regulate cell proliferation and invasion synergistically or independently. In the present study, it was observed that ectopic expression of integrin β1 in claudin-7 KD lung cancer cells did not reduce the cell proliferation. However, integrin β1-transfected cells migrated more effectively in wound healing and cell invasion assays and were more adhesive in a cell attachment assay when compared with those of claudin-7 KD cells. This indicates that claudin-7 controls cell proliferation, while cell attachment and motility were regulated partially through integrin β1. Additionally, claudin-7 overexpression in claudin-7 KD cells resulted in an improved ability to attach to the surface of cell culture plates and a higher expression of focal adhesion proteins when compared with claudin-7 non-KD control cells, which supports the role of claudin-7 in cell adhesion and motility. Taken together, these data suggest that claudin-7 regulates cell motility through integrin β1, providing additional insight into the roles of claudins in carcinogenesis and cancer cell metastasis.

Cortactin Phosphorylation by Casein Kinase 2 Regulates Actin-Related Protein 2/3 Complex Activity, Invadopodia Function, and Tumor Cell Invasion

Malregulation of the actin cytoskeleton enhances tumor cell motility and invasion. The actin-binding protein cortactin facilitates branched actin network formation through activation of the actin-related protein (Arp) 2/3 complex. Increased cortactin expression due to gene amplification is observed in head and neck squamous cell carcinoma (HNSCC) and other cancers, corresponding with elevated tumor progression and poor patient outcome. Arp2/3 complex activation is responsible for driving increased migration and extracellular matrix (ECM) degradation by governing invadopodia formation and activity. Although cortactin-mediated activation of Arp2/3 complex and invadopodia regulation has been well established, signaling pathways responsible for governing cortactin binding to Arp2/3 are unknown and potentially present a new avenue for anti-invasive therapeutic targeting. Here we identify casein kinase (CK) 2α phosphorylation of cortactin as a negative regulator of Arp2/3 binding. CK2α directly phosphorylates cortactin at a conserved threonine (T24) adjacent to the canonical Arp2/3 binding motif. Phosphorylation of cortactin T24 by CK2α impairs the ability of cortactin to bind Arp2/3 and activate actin nucleation. Decreased invadopodia activity is observed in HNSCC cells with expression of CK2α phosphorylation-null cortactin mutants, shRNA-mediated CK2α knockdown, and with the CK2α inhibitor Silmitasertib. Silmitasertib inhibits HNSCC collective invasion in tumor spheroids and orthotopic tongue tumors in mice. Collectively these data suggest that CK2α-mediated cortactin phosphorylation at T24 is critical in regulating cortactin binding to Arp2/3 complex and pro-invasive activity, identifying a potential targetable mechanism for impairing HNSCC invasion. IMPLICATIONS: This study identifies a new signaling pathway that contributes to enhancing cancer cell invasion.Visual Overview: http://mcr.aacrjournals.org/content/molcanres/17/4/987/F1.large.jpg.

TKS5-positive invadopodia-like structures in human tumor surgical specimens

Invadopodia, cancer cell protrusions with proteolytic activity, are functionally associated with active remodeling of the extracellular matrix. Here, we show that the invadopodia-related protein TKS5 is expressed in human pancreatic adenocarcinoma lines, and demonstrate that pancreatic cancer cells depend on TKS5 for invadopodia formation and function. Immunofluorescence staining of human pancreatic cancer cells reveals that TKS5 is a marker of mature and immature invadopodia. We also analyze the co-staining patterns of TKS5 and the commonly used invadopodia marker Cortactin, and find only partial co-localization of these two proteins at invadopodia, with a large fraction of TKS5-positive invadopodia lacking detectable levels of Cortactin. Whereas compelling evidence exist on the role of invadopodia as mediators of invasive migration in cultured cells and in animal models of cancer, these structures have never been detected inside human tumors. Here, using antibodies against TKS5 and Cortactin, we describe for the first time structures strongly resembling invadopodia in various paraffin-embedded human tumor surgical specimens from pancreas and other organs. Our results strongly suggest that invadopodia are present inside human tumors, and warrants further investigation on their regulation and occurrence in surgical specimens, and on the value of TKS5 antibodies as pathological research and diagnostic tools.

Expression of human papillomavirus oncoproteins E6 and E7 inhibits invadopodia activity but promotes cell migration in HPV-positive head and neck squamous cell carcinoma cells

Background

The rapid increase in the incidence of head and neck squamous cell carcinoma (HNSCC) is caused by high‐risk human papillomavirus (HPV) infections. The HPV oncogenes E6 and E7 promote carcinogenesis by disrupting signaling pathways that control survival and proliferation. Although these cancers are often diagnosed with metastases, the mechanisms that regulate their dissemination are unknown.

Aims

The aim of this study was to determine whether the HPV‐16 E6 and E7 oncogenes affected the invasive and migratory properties of HNSCC cells which promote their spread and metastasis.

Methods and results

Invasiveness was determined using invadopodia assays which allow for quantitation of extracellular matrix (ECM) degradation by invadopodia which are proteolytic membrane protrusions that facilitate invasion. Using cell lines and genetic manipulations, we found that HPV inhibited invadopodia activity in aggressive cell lines which was mediated by the E6 and E7 oncogenes. Given these findings, we also tested whether HPV caused differences in the migratory ability of HNSCC cells using Transwell assays. In contrast to our invadopodia results, we found no correlation between HPV status and cell migration; however, blocking the expression of the E6 and E7 oncoproteins in a HPV‐positive (HPV⁺) HNSCC cell line resulted in decreased migration.

Conclusions

Our data suggest that the E6 and E7 oncoproteins are negative regulators of invadopodia activity but may promote migration in HPV⁺ HNSCC cells. Despite the need for ECM proteolysis to penetrate most tissues, the unique structure of the head and neck tissues in which these cancers arise may facilitate the spread of migratory cancer cells without significant proteolytic ability.

Cdk5-mediated phosphorylation regulates phosphatidylinositol 4-phosphate 5-kinase type I γ 90 activity and cell invasion

Phosphatidylinositol 4-phosphate 5-kinase type I γ (PIPKIγ90) regulates cell migration, invasion, and metastasis. However, it is unknown how cellular signals regulate those processes. Here, we show that cyclin-dependent kinase 5 (Cdk5), a protein kinase that regulates cell migration and invasion, phosphorylates PIPKIγ90 at S453, and that Cdk5-mediated PIPKIγ90 phosphorylation is essential for cell invasion. Moreover, Cdk5-mediated phosphorylation down-regulates the activity of PIPKIγ90 and the secretion of fibronectin, an extracellular matrix protein that regulates cell migration and invasion. Furthermore, inhibition of PIPKIγ activity with the chemical inhibitor UNC3230 suppresses fibronectin secretion in a dose-dependent manner, whereas depletion of Cdk5 enhances fibronectin secretion. With total internal reflection fluorescence microscopy, we found that secreted fibronectin appears as round dots, which colocalize with Tks5 and CD9 but not with Zyxin. These data suggest that Cdk5-mediated PIPKIγ90 phosphorylation regulates cell invasion by controlling PIPKIγ90 activity and fibronectin secretion.-Li, L., Kołodziej, T., Jafari, N., Chen, J., Zhu, H., Rajfur, Z., Huang, C. Cdk5-mediated phosphorylation regulates phosphatidylinositol 4-phosphate 5-kinase type I γ 90 activity and cell invasion.

Actin assembly mechanisms at a glance

The actin cytoskeleton and associated motor proteins provide the driving forces for establishing the astonishing morphological diversity and dynamics of mammalian cells. Aside from functions in protruding and contracting cell membranes for motility, differentiation or cell division, the actin cytoskeleton provides forces to shape and move intracellular membranes of organelles and vesicles. To establish the many different actin assembly functions required in time and space, actin nucleators are targeted to specific subcellular compartments, thereby restricting the generation of specific actin filament structures to those sites. Recent research has revealed that targeting and activation of actin filament nucleators, elongators and myosin motors are tightly coordinated by conserved protein complexes to orchestrate force generation. In this Cell Science at a Glance article and the accompanying poster, we summarize and discuss the current knowledge on the corresponding protein complexes and their modes of action in actin nucleation, elongation and force generation.

Laminin-111 peptide C16 regulates invadopodia activity of malignant cells through β1 integrin, Src and ERK 1/2

Laminin peptides influence tumor behavior. In this study, we addressed whether laminin peptide C16 (KAFDITYVRLKF, γ1 chain) would increase invadopodia activity of cells from squamous cell carcinoma (CAL27) and fibrosarcoma (HT1080). We found that C16 stimulates invadopodia activity over time in both cell lines. Rhodamine-conjugated C16 decorates the edge of cells, suggesting a possible binding to membrane receptors. Flow cytometry showed that C16 increases activated β1 integrin, and β1 integrin miRNA-mediated depletion diminishes C16-induced invadopodia activity in both cell lines. C16 stimulates Src and ERK 1/2 phosphorylation, and ERK 1/2 inhibition decreases peptide-induced invadopodia activity. C16 also increases cortactin phosphorylation in both cells lines. Based on our findings, we propose that C16 regulates invadopodia activity over time of squamous carcinoma and fibrosarcoma cells, probably through β1 integrin, Src and ERK 1/2 signaling pathways.

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.