Transient mechanical strain promotes the maturation of invadopodia and enhances cancer cell invasion in vitro

Cancer cell invasion is influenced by various biomechanical forces found within the microenvironment. We have previously found that invasion is enhanced in fibrosarcoma cells when transient mechanical stimulation is applied within an in vitro mechano-invasion assay. This enhancement of invasion is dependent on cofilin (CFL1), a known regulator of invadopodia maturation. Invadopodia are actin-rich structures present in invasive cancer cells that are enzymatically active and degrade the surrounding extracellular matrix to facilitate invasion. In this study, we examine changes in gene expression in response to tugging on matrix fibers. Interestingly, we find that integrin β3 expression is downregulated and leads to an increase in cofilin activity, as evidenced by a reduction in its Ser3 phosphorylation levels. As a result, invadopodia lengthen and have increased enzymatic activity, indicating that transient mechanical stimulation promotes the maturation of invadopodia leading to increased levels of cell invasion. Our results are unique in defining an invasive mechanism specific to the invasive process of cancer cells that is triggered by tugging forces in the microenvironment, as opposed to rigidity, compression or stretch forces.

A RhoG-mediated signaling pathway that modulates invadopodia dynamics in breast cancer cells

One of the hallmarks of cancer is the ability of tumor cells to invade surrounding tissues and metastasize. During metastasis, cancer cells degrade the extracellular matrix, which acts as a physical barrier, by developing specialized actin-rich membrane protrusion structures called invadopodia. The formation of invadopodia is regulated by Rho GTPases, a family of proteins that regulates the actin cytoskeleton. Here, we describe a novel role for RhoG in the regulation of invadopodia disassembly in human breast cancer cells. Our results show that RhoG and Rac1 have independent and opposite roles in the regulation of invadopodia dynamics. We also show that SGEF (also known as ARHGEF26) is the exchange factor responsible for the activation of RhoG during invadopodia disassembly. When the expression of either RhoG or SGEF is silenced, invadopodia are more stable and have a longer lifetime than in control cells. Our findings also demonstrate that RhoG and SGEF modulate the phosphorylation of paxillin, which plays a key role during invadopodia disassembly. In summary, we have identified a novel signaling pathway involving SGEF, RhoG and paxillin phosphorylation, which functions in the regulation of invadopodia disassembly in breast cancer cells.

EP4 receptor promotes invadopodia and invasion in human breast cancer

The production of Prostaglandin E₂ (PGE₂) is elevated in human breast cancer cells. The abnormal expression of COX-2, which is involved in the synthesis of PGE₂, was recently reported as a critical determinant for invasiveness of human breast cancer cells. Autocrine and paracrine PGE₂-mediated stimulation of the PGE₂ receptor EP4 transduces multiple signaling pathways leading to diverse patho-physiological effects, including tumor cell invasion and metastasis. It is known that PGE₂-induced EP4 activation can transactivate the intracellular signaling pathway of the epidermal growth factor receptor (EGFR). In malignant cancer cells, EGFR pathway activation promotes invadopodia protrusions, which further leads to degradation of the surrounding extracellular matrix (ECM). Despite the known influence of EP4 on the EGFR signaling pathway, the effect of EP4 stimulation on invadopodia formation in human breast cancer was never tested directly. Here we demonstrate the involvement of EP4 in invasion and its effect on invadopodia in breast cancer MDA-MB-231 cells using 2D invadopodia and 3D invasion in vitro assays as well as intravital microscopy. The results show that stimulation with the selective EP4 agonist CAY10598 or PGE₂ promotes invadopodia-mediated degradation of the ECM, as well as the invasion of breast cancer cells in in vitro models. The effect on matrix degradation can be abrogated via direct inhibition of EP4 signaling as well as via inhibition of EGFR tyrosine kinase, indicating that EP4-mediated effects on invadopodia-driven degradation are EGFR dependent. Finally, using xenograft mouse models, we show that short-term systemic treatment with CAY10598 results in a >9-fold increase in the number of invadopodia. These findings highlight the importance of further investigation on the role of EP4-EGFR crosstalk in invadopodia formation.

Blockage of glycolysis by targeting PFKFB3 suppresses tumor growth and metastasis in head and neck squamous cell carcinoma

BACKGROUND

Many cancers including head and neck squamous cell carcinoma (HNSCC) are characterized by a metabolic rewiring with increased glucose uptake and lactate production, termed as aerobic glycolysis. Targeting aerobic glycolysis presents a promising strategy for cancer therapy. This study investigates the therapeutic potential of glycolysis blockage by targeting phosphofructokinase-2/fructose-2, 6-bisphosphatase 3 (PFKFB3) in HNSCC.

METHODS

1-(4-pyridinyl)-3-(2-quinolinyl)-2-propen-1-one (PFK15) was used as a selective antagonist of PFKFB3. Glycolytic flux was determined by measuring glucose uptake, lactate production and ATP yield. PFKFB3 expression was examined using HNSCC tissue arrays. Cell proliferation, apoptosis and motility were analysed. HNSCC xenograft mouse model and metastasis mouse model were established to examine the therapeutic efficacy of PFK15 in vivo.

RESULTS

HNSCC showed an increased PFKFB3 expression compared with adjacent mucosal tissues (P < 0.01). Targeting PFKFB3 via PFK15 significantly reduced the glucose uptake, lactate production and ATP generation in HNSCC cell lines. PFK15 suppressed cell proliferation, halted cell cycle progression and induced cell apoptosis. The invadopodia of HNSCC cells was markedly reduced after PFK15 treatment, thereby impairing cell motility and extracellular matrix degradation ability. The in vivo data from the xenograft mice models proved that PFK15 administration suppressed the tumor growth. And the results from the metastatic mice models showed administration of PFK15 alleviated the lung metastasis of HNSCC and extended the life expectancy of mice.

CONCLUSIONS

The pharmacological inhibition of PFKFB3 via PFK15 suppressed tumor growth and alleviated metastasis in HNSCC, offering a promising strategy for cancer therapy.

Expression of N-WASP is regulated by HiF1α through the hypoxia response element in the N-WASP promoter

Cancer cell migration and invasion involves temporal and spatial regulation of actin cytoskeleton reorganization, which is regulated by the WASP family of proteins such as N-WASP (Neural- Wiskott Aldrich Syndrome Protein). We have previously shown that expression of N-WASP was increased under hypoxic conditions. In order to characterize the regulation of N-WASP expression, we constructed an N-WASP promoter driven GFP reporter construct, N-WASP^pro-GFP. Transfection of N-WASP^pro-GFP construct and plasmid expressing HiF1α (Hypoxia Inducible factor 1α) enhanced the expression of GFP suggesting that increased expression of N-WASP under hypoxic conditions is mediated by HiF1α. Sequence analysis of the N-WASP promoter revealed the presence of two hypoxia response elements (HREs) characterized by the consensus sequence 5′-GCGTG-3′ at -132 bp(HRE1) and at -662 bp(HRE2) relative to transcription start site (TSS). Site-directed mutagenesis of HRE1(-132) but not HRE2(-662) abolished the HiF1α induced activation of N-WASP promoter. Similarly ChIP assay demonstrated that HiF1α bound to HRE1(-132) but not HRE2(-662) under hypoxic condition. MDA-MB-231 cells but not MDA-MB-231^KD cells treated with hypoxia mimicking agent, DMOG showed enhanced gelatin degradation. Similarly MDA-MB-231^KD(N-WASP^pro-N-WASP^R) cells expressing N-WASP^R under the transcriptional regulation of WT N-WASP^pro but not MDA-MB-231^KD(N-WASP^proHRE1-N-WASP^R) cells expressing N-WASP^R under the transcriptional regulation of N-WASP^proHRE1 showed enhanced gelatin degradation when treated with DMOG. Thus indicating the importance of N-WASP in hypoxia induced invadopodia formation. Thus, our data demonstrates that hypoxia-induced activation of N-WASP expression is mediated by interaction of HiF1α with the HRE1(-132) and explains the role of N-WASP in hypoxia induced invadopodia formation.

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Expression of N-WASP expression is enhanced under hypoxia conditions.

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N-WASP is essential for hypoxia induced invasion.

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HiF1α binds to hypoxia response element (HRE) in N-WASP promoter.

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HRE1 is essential for hypoxia induced invadopodia activity

The role and regulation of Rab40b-Tks5 complex during invadopodia formation and cancer cell invasion

Invadopodia formation and extracellular matrix degradation are key events during cancer cell invasion, yet little is known about mechanisms mediating these processes. Here, we report that Rab40b plays a key role in mediating invadopodia function during breast cancer cell invasion. We also identify Tks5 (also known as SH3PXD2A), a known Src kinase substrate, as a new Rab40b effector protein and show that Tks5 functions as a tether that mediates Rab40b-dependent targeting of transport vesicles containing MMP2 and MMP9 to the extending invadopodia. Importantly, we also demonstrate that Rab40b and Tks5 levels are regulated by known tumor suppressor microRNA miR-204. This is the first study that identifies a new Rab40b–Tks5- and miR-204-dependent invadopodia transport pathway that regulates MMP2 and MMP9 secretion, and extracellular matrix remodeling during cancer progression.

Highlighted Article: Rab40b plays a key role in mediating invadopodia function during breast cancer cell invasion by binding to Tks5 and functioning as a tether mediating MMP2 and MMP9 targeting to the extending invadopodia.

Comprehensive proteome profiling of glioblastoma-derived extracellular vesicles identifies markers for more aggressive disease

Extracellular vesicles (EVs) play key roles in glioblastoma (GBM) biology and represent novel sources of biomarkers that are detectable in the peripheral circulation. Despite this notionally non-invasive approach to assess GBM tumours in situ, a comprehensive GBM EV protein signature has not been described. Here, EVs secreted by six GBM cell lines were isolated and analysed by quantitative high-resolution mass spectrometry. Overall, 844 proteins were identified in the GBM EV proteome, of which 145 proteins were common to EVs secreted by all cell lines examined; included in the curated EV compendium (Vesiclepedia_559; http://microvesicles.org). Levels of 14 EV proteins significantly correlated with cell invasion (invadopodia production; r² > 0.5, p < 0.05), including several proteins that interact with molecules responsible for regulating invadopodia formation. Invadopodia, actin-rich membrane protrusions with proteolytic activity, are associated with more aggressive disease and are sites of EV release. Gene levels corresponding to invasion-related EV proteins showed that five genes (annexin A1, actin-related protein 3, integrin-β1, insulin-like growth factor 2 receptor and programmed cell death 6-interacting protein) were significantly higher in GBM tumours compared to normal brain in silico, with common functions relating to actin polymerisation and endosomal sorting. We also show that Cavitron Ultrasonic Surgical Aspirator (CUSA) washings are a novel source of brain tumour-derived EVs, demonstrated by particle tracking analysis, TEM and proteome profiling. Quantitative proteomics corroborated the high levels of proposed invasion-related proteins in EVs enriched from a GBM compared to low-grade astrocytoma tumour. Large-scale clinical follow-up of putative biomarkers, particularly the proposed survival marker annexin A1, is warranted.

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.

Macrophages promote matrix protrusive and invasive function of breast cancer cells via MIP-1β dependent upregulation of MYO3A gene in breast cancer cells

The potential of a tumor cell to metastasize profoundly depends on its microenvironment, or "niche" interactions with local components. Tumor-associated-macrophages (TAMs) are the most abundant subpopulation of tumor stroma and represent a key component of tumor microenvironment. The dynamic interaction of cancer cells with neighboring TAMs actively drive cancer progression and metastatic transformation through intercellular signaling networks that need better elucidation. Thus, current study was planned for discerning paracrine communication networks operational between TAMs, and breast cancer cells with special reference to cancer cell invasion and dissemination to distant sites. Here, we report role of MIP-1β in enhancing invasive potential of metastatic breast cancer MDA-MB-231 and MDA-MB-468 cells. In addition, the poorly metastatic MCF-7 cells were also rendered invasive by MIP-1β. The MIP-1β-driven cancer cell invasion was dependent on upregulated expression levels of MYO3A gene, which encodes an unconventional myosin super-family protein harboring a kinase domain. Ex ovo study employing Chick-embryo-model and in vivo Syngenic 4T1/BALB/c mice-model further corroborated aforementioned in vitro findings, thereby substantiating their physiological relevance. Concordantly, human breast cancer specimen exhibited significant association between mRNA expression levels of MIP-1β and MYO3A. Both, MIP-1β and MYO3A exhibited positive correlation with MMP9, an established molecular determinant of cancer cell invasion. Higher expression of these genes correlated with poor survival of breast cancer patients. Collectively, these results point toward so far undisclosed MIP-1β/MYO3A axis being operational during metastasis, wherein macrophage-derived MIP-1β potentiated cancer cell invasion and metastasis via up regulation of MYO3A gene within cancer cells. Our study exposes opportunities for devising potential anti-metastatic strategies for efficient clinical management of breast cancer.

A new front in cell invasion: The invadopodial membrane

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

Sorting nexin 9 negatively regulates invadopodia formation and function in cancer cells

The ability of cancer cells to degrade the extracellular matrix and invade interstitial tissues contributes to their metastatic potential. We recently showed that overexpression of sorting nexin 9 (SNX9) leads to increased cell invasion and metastasis in animal models, which correlates with increased SNX9 protein expression in metastases from human mammary cancers. Here, we report that SNX9 expression is reduced relative to neighboring normal tissues in primary breast tumors, and progressively reduced in more aggressive stages of non-small-cell lung cancers. We show that SNX9 is localized at invadopodia where it directly binds the invadopodia marker TKS5 and negatively regulates invadopodia formation and function. SNX9 depletion increases invadopodia number and the local recruitment of MT1-MMP by decreasing its internalization. Together, these effects result in increased localized matrix degradation. We further identify SNX9 as a Src kinase substrate and show that this phosphorylation is important for SNX9 activity in regulating cell invasion, but is dispensable for its function in regulating invadopodia. The diversified changes associated with SNX9 expression in cancer highlight its importance as a central regulator of cancer cell behavior.

Signatures of breast cancer metastasis at a glance

Gene expression profiling has yielded expression signatures from which prognostic tests can be derived to facilitate clinical decision making in breast cancer patients. Some of these signatures are based on profiling of whole tumor tissue (tissue signatures), which includes all tumor and stromal cells. Prognostic markers have also been derived from the profiling of metastasizing tumor cells, including circulating tumor cells (CTCs) and migratory-disseminating tumor cells within the primary tumor. The metastasis signatures based on CTCs and migratory-disseminating tumor cells have greater potential for unraveling cell biology insights and mechanistic underpinnings of tumor cell dissemination and metastasis. Of clinical interest is the promise that stratification of patients into high or low metastatic risk, as well as assessing the need for cytotoxic therapy, might be improved if prognostics derived from these two types of signatures are used in a combined way. The aim of this Cell Science at a Glance article and accompanying poster is to navigate through both types of signatures and their derived prognostics, as well as to highlight biological insights and clinical applications that could be derived from them, especially when they are used in combination.

The microenvironment controls invadosome plasticity

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

The CD44s splice isoform is a central mediator for invadopodia activity

The ability for tumor cells to spread and metastasize to distant organs requires proteolytic degradation of extracellular matrix (ECM). This activity is mediated by invadopodia, actin-rich membrane protrusions that are enriched for proteases. However, the mechanisms underlying invadopodia activity are not fully understood. Here, we report that a specific CD44 splice isoform, CD44s, is an integral component in invadopodia. We show that CD44s, but not another splice isoform CD44v, is localized in invadopodia. Small hairpin (sh)RNA-mediated depletion of CD44s abolishes invadopodia activity, prevents matrix degradation and decreases tumor cell invasiveness. Our results suggest that CD44s promotes cortactin phosphorylation and recruits MT1-MMP (also known as MMP14) to sites of matrix degradation, which are important activities for invadopodia function. Importantly, we show that depletion of CD44s inhibits breast cancer cell metastasis to the lung in animals. These findings suggest a crucial mechanism underlying the role of the CD44s splice isoform in breast cancer metastasis.

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

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

Matrix rigidity differentially regulates invadopodia activity through ROCK1 and ROCK2

ROCK activity increases due to ECM rigidity in the tumor microenvironment and promotes a malignant phenotype via actomyosin contractility. Invasive migration is facilitated by actin-rich adhesive protrusions known as invadopodia that degrade the ECM. Invadopodia activity is dependent on matrix rigidity and contractile forces suggesting that mechanical factors may regulate these subcellular structures through ROCK-dependent actomyosin contractility. However, emerging evidence indicates that the ROCK1 and ROCK2 isoforms perform different functions in cells suggesting that alternative mechanisms may potentially regulate rigidity-dependent invadopodia activity. In this study, we found that matrix rigidity drives ROCK signaling in cancer cells but that ROCK1 and ROCK2 differentially regulate invadopodia activity through separate signaling pathways via contractile (NM II) and non-contractile (LIMK) mechanisms. These data suggest that the mechanical rigidity of the tumor microenvironment may drive ROCK signaling through distinct pathways to enhance the invasive migration required for cancer progression and metastasis.

Actin Filament Structures in Migrating Cells

Cell migration is necessary for several developmental processes in multicellular organisms. Furthermore, many physiological processes such as wound healing and immunological events in adult animals are dependent on cell migration. Consequently, defects in cell migration are linked to various diseases including immunological disorders as well as cancer progression and metastasis formation. Cell migration is driven by specific protrusive and contractile actin filament structures, but the types and relative contributions of these actin filament arrays vary depending on the cell type and the environment of the cell. In this chapter, we introduce the most important actin filament structures that contribute to mesenchymal and amoeboid cell migration modes and discuss the mechanisms by which the assembly and turnover of these structures are controlled by various actin-binding proteins.

Analysis of Invadopodia Formation in Breast Cancer Cells

Metastasis is the major cause of breast cancer deaths. To spread from the primary tumor sites to distant tissues, solid tumor cells need to degrade the surrounding extracellular matrix (ECM). The protrusive membrane structures named invadopodia have been shown to play a critical role in the degradation of the ECM and invasion of invasive cancer cells. In this chapter, we describe a detailed protocol to examine invadopodia in human breast cancer cells.

KISS1R signaling promotes invadopodia formation in human breast cancer cell via β-arrestin2/ERK

Kisspeptins (KPs), peptide products of the KISS1 gene are endogenous ligands for the kisspeptin receptor (KISS1R), a G protein-coupled receptor. In numerous cancers, KISS1R signaling plays anti-metastatic roles. However, we have previously shown that in breast cancer cells lacking the estrogen receptor (ERα), kisspeptin-10 stimulates cell migration and invasion by cross-talking with the epidermal growth factor receptor (EGFR), via a β-arrestin-2-dependent mechanism. To further define the mechanisms by which KISS1R stimulates invasion, we determined the effect of down-regulating KISS1R expression in triple negative breast cancer cells. We found that depletion of KISS1R reduced their mesenchymal phenotype and invasiveness. We show for the first time that KISS1R signaling induces invadopodia formation and activation of key invadopodia proteins, cortactin, cofilin and membrane type I matrix metalloproteases (MT1-MMP). Moreover, KISS1R stimulated invadopodia formation occurs via a new pathway involving a β-arrestin2 and ERK1/2-dependent mechanism, independent of Src. Taken together, our findings suggest that targeting the KISS1R signaling axis might be a promising strategy to inhibit invasiveness and metastasis.

Lysophosphatidic acid activates the RhoA and NF-κB through Akt/IκBα signaling and promotes prostate cancer invasion and progression by enhancing functional invadopodia formation

We have demonstrated previously that increased RhoA and nuclear factor (NF)-κB activities are associated with increased PC-3 prostate cancer cell invasion and that lysophosphatidic acid (LPA) significantly increases cancer invasion through RhoA and NF-κB activation. In this study, we identified the intermediate signaling molecules and specialized cell structures which are activated by LPA, resulting in enhanced cellular invasion. LPA-induced Akt and IκBα signaling pathways were necessary for RhoA and NF-κB activation, and these LPA effects were abolished by RhoA inhibition. Mice injected with PC-3 cells expressing dominant-negative RhoA N19 developed significantly less tumor growth compared with those injected with control (pcDNA 3.1). In addition, LPA treatment increased functional invadopodia formation. Activation of RhoA and NF-κB through the Akt and IκBα signaling pathway was required for LPA-stimulated gelatin degradation activity. LPA administration increased tumor growth and osteolytic lesions in a mouse xenograft model. These results indicate that LPA promotes PC-3 cell invasion by increasing functional invadopodia formation via upregulating RhoA and NF-κB signaling which contributes to prostate cancer progression. Therefore, the LPA and RhoA-NF-κB signaling axis may represent key molecular targets to inhibit prostate cancer invasion and progression.

Active invadopodia of mesenchymally migrating cancer cells contain both β and γ cytoplasmic actin isoforms

Invadopodia are actin-rich protrusions formed by mesenchymally migrating cancer cells. They are mainly composed of actin, actin-associated proteins, integrins and proteins of signaling machineries. These protrusions display focalized proteolytic activity towards the extracellular matrix. It is well known that polymerized (F-)actin is present in these structures, but the nature of the actin isoform has not been studied before. We here show that both cytoplasmic actin isoforms, β- and γ-actin, are present in the invadopodia of MDA-MB-231 breast cancer cells cultured on a 2D-surface, where they colocalize with the invadopodial marker cortactin. Invadopodial structures formed by the cells in a 3D-collagen matrix also contain β- and γ-actin. We demonstrate this using isoform-specific antibodies and expression of fluorescently-tagged actin isoforms. Additionally, using simultaneous expression of differentially tagged β- and γ-actin in cells, we show that the actin isoforms are present together in a single invadopodium. Cells with an increased level of β- or γ-actin, display a similar increase in the number and size of invadopodia in comparison to control cells. Moreover, increasing the level of either actin isoforms also increases invasion velocity.

Regulation of invadopodia by mechanical signaling

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

Augmentation of invadopodia formation in temozolomide-resistant or adopted glioma is regulated by c-Jun terminal kinase-paxillin axis

Temozolomide (TMZ) is one of the few effective anticancer agents against gliomas. However, acquisition of TMZ resistance or adaptation by gliomas is currently a crucial problem, especially increased invasiveness which is critical for the determination of clinical prognosis. This study investigated the molecular regulatory mechanisms of TMZ resistance in gliomas involved in invasiveness, particularly invadopodia formation, a molecular complex formed at the invasive front to cause extracellular matrix degradation during cellular local invasion. The TMZ-resistant clone of the U343 MG human glioma cell line (U343-R cells) was established. U343-R cells demonstrated higher invadopodia formation compared with U343 cells without TMZ resistance (U343-Con cells). Immunoblot analysis of DNA damage-related mitogen-activated protein kinase signals found increased phosphorylation of c-Jun terminal kinase (JNK) and higher activation of its downstream signaling in U343-R cells compared with U343-Con cells. Treatment of U343-R cells with specific inhibitors of JNK or siRNA targeting JNK suppressed up-regulation of invadopodia formation. In addition, paxillin, one of the known JNK effectors which is phosphorylated and affects cell migration, was phosphorylated at serine 178 in JNK activity-dependent manner. Expression of paxillin with mutation of the serine 178 phosphorylation site in U343-R cells blocked invadopodia formation. The present findings suggest that increased formation of invadopodia in U343-R cells is mediated by hyperactivation of JNK-paxillin signaling, and both JNK and paxillin might become targets of novel therapies against TMZ-resistant gliomas.

Significance of caveolin-1 and matrix metalloproteinase 14 gene expression in canine mammary tumours

Canine mammary tumours (CMTs) are the most common neoplasms affecting female dogs. There is an urgent need for molecular biomarkers that can detect early stages of the disease in order to improve accuracy of CMT diagnosis. The aim of this study was to examine whether caveolin-1 (Cav-1) and matrix metalloproteinase 14 (MMP14) are associated with CMT histological malignancy and invasion. Sixty-five benign and malignant CMT samples and six normal canine mammary glands were analysed using quantitative reverse transcription-polymerase chain reaction. Cav-1 and MMP14 genes were highly expressed in CMT tissues compared to normal tissues. Cav-1 especially was overexpressed in malignant and invasive CMT tissues. When a CMT cell line was cultured on fluorescent gelatin-coated coverslips, localisation of Cav-1 was observed at invadopodia-mediated degradation sites of the gelatin matrix. These findings suggest that Cav-1 may be involved in CMT invasion and that the markers may be useful for estimating CMT malignancy.

Spatial regulation of tumor cell protrusions by RhoC

Systemic metastasis is the dissemination of cancer cells from the primary tumor to distant organs and is the primary cause of death in cancer patients. How do cancer cells leave the primary tumor mass? The ability of the tumor cells to form different types of actin-rich protrusions including invasive protrusions (invadopodia) and locomotory protrusions (lamellipodia [2D] or pseudopodia [3D]), facilitate the invasion and dissemination of the tumor cells. Rho-family of p21 small GTPases plays a direct role in regulating the actin dynamics in these intracellular compartments. Recent studies have shown that the signaling molecules including RhoC/p190RhoGEF/p190RhoGAP acts as a “molecular compass” in order to direct the spatial and temporal dynamics of the formation of these invasive and locomotory protrusions leading to efficient invasion.