N-WASP-mediated invadopodium formation is involved in intravasation and lung metastasis of mammary tumors

Nck deficiency is associated with delayed breast carcinoma progression and reduced metastasis

Nck promotes breast carcinoma progression and metastasis by directing the polarized interaction of carcinoma cells with collagen fibrils, decreasing actin turnover, and enhancing the localization and activity of MMP14 at the cell surface through modulation of the spatiotemporal activation of Cdc42 and RhoA.

Although it is known that noncatalytic region of tyrosine kinase (Nck) regulates cell adhesion and migration by bridging tyrosine phosphorylation with cytoskeletal remodeling, the role of Nck in tumorigenesis and metastasis has remained undetermined. Here we report that Nck is required for the growth and vascularization of primary tumors and lung metastases in a breast cancer xenograft model as well as extravasation following injection of carcinoma cells into the tail vein. We provide evidence that Nck directs the polarization of cell–matrix interactions for efficient migration in three-dimensional microenvironments. We show that Nck advances breast carcinoma cell invasion by regulating actin dynamics at invadopodia and enhancing focalized extracellular matrix proteolysis by directing the delivery and accumulation of MMP14 at the cell surface. We find that Nck-dependent cytoskeletal changes are mechanistically linked to enhanced RhoA but restricted spatiotemporal activation of Cdc42. Using a combination of protein silencing and forced expression of wild-type/constitutively active variants, we provide evidence that Nck is an upstream regulator of RhoA-dependent, MMP14-mediated breast carcinoma cell invasion. By identifying Nck as an important driver of breast carcinoma progression and metastasis, these results lay the groundwork for future studies assessing the therapeutic potential of targeting Nck in aggressive cancers.

VCA nanobodies target N-WASp to reduce invadopodium formation and functioning

Invasive cancer cells develop small actin-based protrusions called invadopodia, which perform a primordial role in metastasis and extracellular matrix remodelling. Neural Wiskott-Aldrich syndrome protein (N-WASp) is a scaffold protein which can directly bind to actin monomers and Arp2/3 and is a crucial player in the formation of an invadopodium precursor. Expression modulation has pointed to an important role for N-WASp in invadopodium formation but the role of its C-terminal VCA domain in this process remains unknown. In this study, we generated alpaca nanobodies against the N-WASp VCA domain and investigated if these nanobodies affect invadopodium formation. By using this approach, we were able to study functions of a selected functional/structural N-WASp protein domain in living cells, without requiring overexpression, dominant negative mutants or siRNAs which target the gene, and hence the entire protein. When expressed as intrabodies, the VCA nanobodies significantly reduced invadopodium formation in both MDA-MB-231 breast cancer and HNSCC61 head and neck squamous cancer cells. Furthermore, expression of distinct VCA Nbs (VCA Nb7 and VCA Nb14) in PC-3 prostate cancer cells resulted in reduced overall matrix degradation without affecting MMP9 secretion/activation or MT1-MMP localisation at invadopodial membranes. From these results, we conclude that we have generated nanobodies targeting N-WASp which reduce invadopodium formation and functioning, most likely via regulation of N-WASp—Arp2/3 complex interaction, indicating that this region of N-WASp plays an important role in these processes.

Conditional knock out of N-WASP in keratinocytes causes skin barrier defects and atopic dermatitis-like inflammation

Neural-Wiskott Aldrich Syndrome Protein (N-WASP) is expressed ubiquitously and regulates actin cytoskeleton remodeling. In order to characterize the role of N-WASP in epidermal homeostasis and cutaneous biology, we generated conditional N-WASP knockout mouse using CK14-cre (cytokeratin 14) to ablate expression of N-WASP in keratinocytes. N-WASP^K14KO (N-WASP^fl/fl; CK14-Cre) mice were born following Mendelian genetics suggesting that N-WASP expression in keratinocytes is not essential during embryogenesis. N-WASP^K14KO mice exhibited stunted growth, alopecia, dry and wrinkled skin. The dry skin in N-WASP^K14KO mice is probably due to increased transepidermal water loss (TEWL) caused by barrier function defects as revealed by dye penetration assay. N-WASP^K14KO mice developed spontaneous inflammation in the neck and face 10 weeks after birth. Histological staining revealed thickening of the epidermis, abnormal cornified layer and extensive infiltration of immune cells (mast cells, eosinophils and T-lymphocytes) in N-WASP^K14KO mice skin compared to control mice. N-WASP^K14KO mice had higher serum levels of IL-1α, TNF-α, IL-6 and IL-17 compared to control mice. Thus our results suggest that conditional N-WASP knockout in keratinocytes leads to compromised skin barrier, higher infiltration of immune cells and hyperproliferation of keratinocytes due to increased production of cytokines highlighting the importance of N-WASP in maintaining the skin homeostasis.

Actinin-1 and actinin-4 play essential but distinct roles in invadopodia formation by carcinoma cells

Invadopodia are ventral membrane protrusions formed by cancer cells that degrade the extracellular matrix (ECM) during tumor invasion and metastasis. Formation of invadopodia is initiated by the assembly of actin filaments (F-actin) that results from the coordinated activation of several actin regulatory proteins. Actinin-1 and actinin-4 are actin bundling proteins expressed in non-muscle cells and actinin-4 is preferentially associated with malignant phenotypes of carcinoma cells. In this study, we investigated the role of actinin-1 and -4 in invadopodia formation. Expression of both actinin-1 and -4 tended to be higher in invasive and metastatic breast carcinoma cell lines than in non-invasive ones. Immunofluorescence analysis revealed that actinin-1 and -4 colocalized at core actin structures of invadopodia. Time-lapse imaging showed that appearance of both actinins at invadopodia is concomitant with the assembly of F-actin. Knockdown of either actinin-1 or actinin-4 suppressed the formation of invadopodia and degradation of the ECM by carcinoma cells. Interestingly, overexpression of actinin-4, but not actinin-1, significantly promoted the formation of invadopodia and this activity required the actin binding domains and the unique N-terminal motif that exists only in actinin-4. These results demonstrate that both actinin-1 and actinin-4 participate in the assembly of F-actin at invadopodia. Additionally, actinin-4 may have a selective advantage in accelerating invadopodia-mediated invasion of carcinoma cells.

Altered signaling associated with chronic arsenic exposure in human skin keratinocytes

Modulation of signaling pathways upon chronic arsenic exposure remains poorly studied. Here, we carried out SILAC-based quantitative phosphoproteomics analysis to dissect the signaling induced upon chronic arsenic exposure in human skin keratinocyte cell line, HaCaT. We identified 4171 unique phosphosites derived from 2000 proteins. We observed differential phosphorylation of 406 phosphosites (twofold) corresponding to 305 proteins. Several pathways involved in cytoskeleton maintenance and organization were found to be significantly enriched (p<0.05). Our data revealed altered phosphorylation of proteins associated with adherens junction remodeling and actin polymerization. Kinases such as protein kinase C iota type (PRKCI), mitogen-activated protein kinase kinase kinase 1 (MAP3K1), tyrosine-protein kinase BAZ1B (BAZ1B) and STE20 like kinase (SLK) were found to be hyperphosphorylated. Our study provides novel insights into signaling perturbations associated with chronic arsenic exposure in human skin keratinocytes. All MS/MS data have been deposited to the ProteomeXchange with identifier PXD004868.

Procedures and applications of long-term intravital microscopy

Intravital microscopy (IVM) is increasingly used in biomedical research to study dynamic processes at cellular and subcellular resolution in their natural environment. Long-term IVM especially can be applied to visualize migration and proliferation over days to months within the same animal without recurrent surgeries. Skin can be repetitively imaged without surgery. To intermittently visualize cells in other organs, such as liver, mammary gland and brain, different imaging windows including the abdominal imaging window (AIW), dermal imaging window (DIW) and cranial imaging window (CIW) have been developed. In this review, we describe the procedure of window implantation and pros and cons of each technique as well as methods to retrace a position of interest over time. In addition, different fluorescent biosensors to facilitate the tracking of cells for different purposes, such as monitoring cell migration and proliferation, are discussed. Finally, we consider new techniques and possibilities of how long-term IVM can be even further improved in the future.

Invadosomes are coming: new insights into function and disease relevance

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

Intratumoral Cancer Cell Intravasation Can Occur Independent of Invasion into the Adjacent Stroma

Intravasation, active entry of cancer cells into the circulation, is often considered to be a relatively late event in tumor development occurring after stromal invasion. Here, we provide evidence that intravasation can be initiated early during tumor development and proceed in parallel to or independent of tumor invasion into surrounding stroma. By applying direct and unbiased intravasation-scoring methods to two histologically distinct human cancer types in live-animal models, we demonstrate that intravasation takes place almost exclusively within the tumor core, involves intratumoral vasculature, and does not involve vasculotropic cancer cells invading tumor-adjacent stroma and migrating along tumor-converging blood vessels. Highlighting an additional role for EGFR in cancer, we find that EGFR is required for the development of an intravasation-sustaining intratumoral vasculature. Intratumoral localization of intravasation supports the notion that overt metastases in cancer patients could be initiated much earlier during cancer progression than appreciated within conventional clinical tumor staging systems.

Reverse transendothelial cell migration in inflammation: to help or to hinder?

The endothelium provides a strong barrier separating circulating blood from tissue. It also provides a significant challenge for immune cells in the bloodstream to access potential sites of infection. To mount an effective immune response, leukocytes traverse the endothelial layer in a process known as transendothelial migration. Decades of work have allowed dissection of the mechanisms through which immune cells gain access into peripheral tissues, and subsequently to inflammatory foci. However, an often under-appreciated or potentially ignored question is whether transmigrated leukocytes can leave these inflammatory sites, and perhaps even return across the endothelium and re-enter circulation. Although evidence has existed to support "reverse" transendothelial migration for a number of years, it is only recently that mechanisms associated with this process have been described. Here we review the evidence that supports both reverse transendothelial migration and reverse interstitial migration within tissues, with particular emphasis on some of the more recent studies that finally hint at potential mechanisms. Additionally, we postulate the biological significance of retrograde migration, and whether it serves as an additional mechanism to limit pathology, or provides a basis for the dissemination of systemic inflammation.

LPP is a Src substrate required for invadopodia formation and efficient breast cancer lung metastasis

We have previously shown that lipoma preferred partner (LPP) mediates TGFβ-induced breast cancer cell migration and invasion. Herein, we demonstrate that diminished LPP expression reduces circulating tumour cell numbers, impairs cancer cell extravasation and diminishes lung metastasis. LPP localizes to invadopodia, along with Tks5/actin, at sites of matrix degradation and at the tips of extravasating breast cancer cells as revealed by intravital imaging of the chick chorioallantoic membrane (CAM). Invadopodia formation, breast cancer cell extravasation and metastasis require an intact LPP LIM domain and the ability of LPP to interact with α-actinin. Finally, we show that Src-mediated LPP phosphorylation at specific tyrosine residues (Y245/301/302) is critical for invadopodia formation, breast cancer cell invasion and metastasis. Together, these data define a previously unknown function for LPP in the formation of invadopodia and reveal a requirement for LPP in mediating the metastatic ability of breast cancer cells.

Tumor Cell Invadopodia: Invasive Protrusions that Orchestrate Metastasis

Invadopodia are a subset of invadosomes that are implicated in the integration of signals from the tumor microenvironment to support tumor cell invasion and dissemination. Recent progress has begun to define how tumor cells regulate the plasticity necessary for invadopodia to assemble and function efficiently in the different microenvironments encountered during dissemination in vivo. Exquisite mapping by many laboratories of the pathways involved in integrating diverse invadopodium initiation signals, from growth factors, to extracellular matrix (ECM) and cell-cell contact in the tumor microenvironment, has led to insight into the molecular basis of this plasticity. Here, we integrate this new information to discuss how the invadopodium is an important conductor that orchestrates tumor cell dissemination during metastasis.

Neural Wiskott-Aldrich syndrome protein (nWASP) is implicated in human lung cancer invasion

Abstract

Lung cancer is one of the most commonly diagnosed cancers with survival much lower in patients diagnosed with distal metastases. It is therefore imperative to identify pathways involved in lung cancer invasion and metastasis and to consider the therapeutic potential of agents that can interfere with these molecular pathways. This study examines nWASP expression in human lung cancer tissues and explores the effect of nWASP inhibition and knockdown on lung cancer cell behaviour.

Methods

QPCR has been used to measure nWASP transcript expression in human lung cancer tissues. The effect of wiskostatin, an nWASP inhibitor, on A-549 and SK-MES-1 lung carcinoma cell growth, adhesion, migration and invasion was also examined using several in vitro functional assays, including ECIS, and immunofluorescence staining. The effect of nWASP knockdown using siRNA on particular behaviours of lung cancer cells was also examined.

Results

Patients with high levels of nWASP expression in tumour tissues have significantly lower survival rates. nWASP transcript levels were found to correlate with lymph node involvement (p = 0.042). nWASP inhibition and knockdown was shown to significantly impair lung cancer cell growth. nWASP inhibition also affected other cell behaviours, in SK-MES-1 invasion and A-549 cell motility, adhesion and migration. Paxillin and FAK activity are reduced in lung cancer cell lines following wiskostatin and nWASP knockdown as shown by immunofluorescence and western blot.

Conclusions

These findings highlight nWASP as an important potential therapeutic target in lung cancer invasion and demonstrate that inhibiting nWASP activity using the inhibitor wiskostatin can significantly alter cell behaviour in vitro.

Differential role for PAK1 and PAK4 during the invadopodia lifecycle

PAK1 and PAK4 are members of the p-21 activated kinase family of serine/threonine kinases. PAK1 has previously been implicated in both the formation and disassembly of invasive cell protrusions, termed invadopodia. We recently reported a novel role for PAK4 during invadopodia maturation and confirmed a specific role for PAK1 in invadopodia formation; findings we will review here. Moreover, we found that PAK4 induction of maturation is delivered via interaction with the RhoA regulator PDZ-RhoGEF. We can now reveal that loss of PAK4 expression leads to changes in invadopodia dynamics. Ultimately we propose that PAK4 but not PAK1 is a key mediator of RhoA activity and provide further evidence that modulation of PAK4 expression levels leads to changes in RhoA activity.

Inhibitory cortactin nanobodies delineate the role of NTA- and SH3-domain-specific functions during invadopodium formation and cancer cell invasion

Cancer cells exploit different strategies to escape from the primary tumor, gain access to the circulation, disseminate throughout the body, and form metastases, the leading cause of death by cancer. Invadopodia, proteolytically active plasma membrane extensions, are essential in this escape mechanism. Cortactin is involved in every phase of invadopodia formation, and its overexpression is associated with increased invadopodia formation, extracellular matrix degradation, and cancer cell invasion. To analyze endogenous cortactin domain function in these processes, we characterized the effects of nanobodies that are specific for the N-terminal acidic domain of cortactin and expected to target small epitopes within this domain. These nanobodies inhibit cortactin-mediated actin-related protein (Arp)2/3 activation, and, after their intracellular expression in cancer cells, decrease invadopodia formation, extracellular matrix degradation, and cancer cell invasion. In addition, one of the nanobodies affects Arp2/3 interaction and invadopodium stability, and a nanobody targeting the Src homology 3 domain of cortactin enabled comparison of 2 functional regions in invadopodium formation or stability. Given their common and distinct effects, we validate cortactin nanobodies as an instrument to selectively block and study distinct domains within a protein with unprecedented precision, aiding rational future generation of protein domain-selective therapeutic compounds.-Bertier, L., Boucherie, C., Zwaenepoel, O., Vanloo, B., Van Troys, M., Van Audenhove, I., Gettemans, J. Inhibitory cortactin nanobodies delineate the role of NTA- and SH3-domain-specific functions during invadopodium formation and cancer cell invasion.

N-WASP promotes invasion and migration of cervical cancer cells through regulating p38 MAPKs signaling pathway

Neural Wiskott-Aldrich syndrome protein (N-WASP) is an important member of the WASP family involved in the actin cytoskeleton reorganization. Recent evidence suggests that N-WASP may play important roles in tumor progression and metastasis. However, the contribution of N-WASP to cervical cancer is still unknown. The present study focused on elucidating the role of N-WASP in the malignant behavior of cervical cancer cells. We found that N-WASP overexpressed in cervical cancer tissues compared with paired paracancerous tissues and normal tissues, and similar results were observed in several cervical cancer cell lines. Furthermore, we demonstrated that overexpression of N-WASP facilitated migration and invasion of cervical cancer cells, while downregulation of N-WASP resulted in decreased cell migration and invasion. In addition, the data showed that N-WASP might promote invasion and migration of cervical cancer cells via regulating the activity of p38 MAPKs pathway. Altogether, the study suggested that N-WASP might serve as an oncogene in cervical cancer, and provided novel insights into the mechanism that how N-WASP promoted invasion and migration of cervical 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.

Tumor Associated Macrophages as Therapeutic Targets for Breast Cancer

Tumor-associated macrophages (TAMs) are the most abundant inflammatory infiltrates in the tumor stroma. TAMs promote tumor growth by suppressing immunocompetent cells, including neovascularization and supporting cancer stem cells. In the chapter, we discuss recent efforts in reprogramming or inhibiting tumor-protecting properties of TAMs, and developing potential strategies to increase the efficacy of breast cancer treatment.

A metastasis biomarker (MetaSite Breast™ Score) is associated with distant recurrence in hormone receptor-positive, HER2-negative early-stage breast cancer

Metastasis is the primary cause of death in early-stage breast cancer. We evaluated the association between a metastasis biomarker, which we call "Tumor Microenviroment of Metastasis" (TMEM), and risk of recurrence. TMEM are microanatomic structures where invasive tumor cells are in direct contact with endothelial cells and macrophages, and which serve as intravasation sites for tumor cells into the circulation. We evaluated primary tumors from 600 patients with Stage I-III breast cancer treated with adjuvant chemotherapy in trial E2197 (NCT00003519), plus endocrine therapy for hormone receptor (HR)+ disease. TMEM were identified and enumerated using an analytically validated, fully automated digital pathology/image analysis method (MetaSite Breast™), hereafter referred to as MetaSite Score (MS). The objectives were to determine the association between MS and distant relapse free interval (DRFI) and relapse free interval (RFI). MS was not associated with tumor size or nodal status, and correlated poorly with Oncotype DX Recurrence Score (r = 0.29) in 297 patients with HR+/HER2- disease. Proportional hazards models revealed a significant positive association between continuous MS and DRFI (p = 0.001) and RFI (p = 0.00006) in HR+/HER2- disease in years 0-5, and by MS tertiles for DRFI (p = 0.04) and RFI (p = 0.01), but not after year 5 or in triple negative or HER2+ disease. Multivariate models in HR+/HER- disease including continuous MS, clinical covariates, and categorical Recurrence Score (<18, 18-30, > 30) showed MS is an independent predictor for 5-year RFI (p = 0.05). MetaSite Score provides prognostic information for early recurrence complementary to clinicopathologic features and Recurrence Score.

CCL2/EGF positive feedback loop between cancer cells and macrophages promotes cell migration and invasion in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) represents the most frequent malignancy in the head and neck region, and the survival rate has not been improved significantly over the past three decades. It has been reported the infiltrated macrophages contribute to the malignant progression of HNSCC. However, the crosstalk between macrophages and cancer cells remains poorly understood. In the present study, we explored interactions between monocytes/macrophages and HNSCC cells by establishing the direct co-culture system, and found that the crosstalk promoted the migration and invasion of cancer cells by enhancing the invadopodia formation through a CCL2/EGF positive feedback loop. Our results demonstrated HNSCC cells educated monocytes into M2-like macrophages by releasing C-C motif chemokine ligand 2 (CCL2, or MCP-1). And the M2-like macrophages secreted epithelial growth factor (EGF), which increased the motility of HNSCC cells by enhancing the invadopodia formation. These subcellular pseudopodia degraded extracellular matrix (ECM), facilitating tumor local invasion and distant metastasis. Moreover, EGF up-regulated CCL2 expression in HNSCC cells, which recruited monocytes and turned them into M2-like macrophages, thus forming a positive feedback paracrine loop. Finally, we reported that curcumin, a powerful natural drug, suppressed the production of EGF and CCL2 in macrophages and cancer cells, respectively, blocking the feedback loop and suppressing the migration and invasion of HNSCC cells. These results shed light on the possibilities and approaches based on targeting the crosstalk between cancer cells and monocytes/macrophages in HNSCC for potential cancer therapy.

Platelet derived growth factor receptor alpha mediates nodal metastases in papillary thyroid cancer by driving the epithelial-mesenchymal transition

Recently platelet derived growth factor receptor-alpha (PDGFRα) was recognized as a potential target to treat aggressive papillary thyroid cancer given its strong association with lymph node metastases. However, it is unclear how PDGFRα potentiates metastases and if it works through the canonical MAPK pathway traditionally linked to PTC oncogenesis. We explored the phenotypic changes driven by PDGFRα activation in human papillary thyroid cancer (PTC) cells and the downstream signalling cascades through which they are effected. We demonstrate that PDGFRα drives an impressive phenotypic change in PTC cell lines as documented by significant cytoskeletal rearrangement, increased migratory potential, and the formation of invadopodia. Cells lacking PDGFRα formed compact and dense spheroids, whereas cells expressing active PDGFRα exhibited invadopodia in three-dimensional culture. To achieve this, active PDGFRα provoked downstream activation of the MAPK/Erk, PI3K/Akt and STAT3 pathways. We further confirmed the role of PDGFRα as a transformative agent promoting the epithelial to mesenchymal transition of PTC cells, through the augmentation of Snail and Slug expression. Crenolanib, a small molecule inhibitor of PDGFRα, suppressed the levels of Snail and Slug and almost completely reversed all the phenotypic changes. We demonstrate that PDGFRα activation is an essential component that drives aggressiveness in PTC cells, and that the signaling pathways are complex, involving not only the MAPK/Erk but also the PI3K/Akt and STAT3 pathways. This argues for upstream targeting of the PDGFRα given the redundancy of oncogenic pathways in PTC, especially in patients whose tumors over-express this tyrosine kinase receptor.

Myogenic differentiation depends on the interplay of Grb2 and N-WASP

Myogenesis requires a well-coordinated withdrawal from cell cycle, morphological changes and cell fusion mediated by actin cytoskeleton. Grb2 is an adaptor protein whose central SH2 domain binds to phosphorylated tyrosine residues of activated receptors and activates intracellular signaling pathway, while its N-terminal and C-terminal SH3 domains bind to proline rich proteins such as N-WASP (Neural-Wiskott Aldrich Syndrome Protein). We found that the expression of Grb2 was increased at the beginning of differentiation and remained constant during differentiation in C2C12 myoblasts. Knocking down endogenous Grb2 expression caused a significant increase in the fusion index and expression of MyHC, a terminal differentiation marker when compared with the control. Over expression of Grb2 in C2C12 (C2C12^Grb2-Myc) reduced myotube formation and expression of MyHC. Similarly over expression of Grb2^P49L-Myc (N-terminal SH3 domain mutant) or Grb2^R86K-Myc (SH2 domain mutant) inhibited myogenic differentiation of C2C12 cells. However, the expression of Grb2^P206L-Myc (C-terminal SH3 domain mutant) did not inhibit myotube formation and expression of MyHC. This suggests that the C-terminal SH3 domain of Grb2 is critical for the inhibition of myogenic differentiation. The C2C12^Grb2-Myc cells have reduced phalloidin staining at late stages of differentiation. Expression of N-WASP in C2C12^Grb2-Myc cells rescued the myogenic defect and increased phalloidin staining (increased F-actin) in these cells. Thus our results suggest that Grb2 is a negative regulator of myogenesis and reduces myogenic differentiation by inhibiting actin polymerization/remodeling through its C-terminal SH3 domain.

Conditional knockout of N-WASP in mouse fibroblast caused keratinocyte hyper proliferation and enhanced wound closure

Neural-Wiskott Aldrich Syndrome Protein (N-WASP) is expressed ubiquitously, regulates actin polymerization and is essential during mouse development. We have previously shown that N-WASP is critical for cell-ECM adhesion in fibroblasts. To characterize the role of N-WASP in fibroblast for skin development, we generated a conditional knockout mouse model in which fibroblast N-WASP was ablated using the Cre recombinase driven by Fibroblast Specific Protein promoter (Fsp-Cre). N-WASP^FKO (N-WASP^fl/fl; Fsp-cre) were born following Mendelian genetics, survived without any visible abnormalities for more than 1 year and were sexually reproductive, suggesting that expression of N-WASP in fibroblast is not critical for survival under laboratory conditions. Histological sections of N-WASP^FKO mice skin (13 weeks old) showed thicker epidermis with higher percentage of cells staining for proliferation marker (PCNA), suggesting that N-WASP deficient fibroblasts promote keratinocyte proliferation. N-WASP^FKO mice skin had elevated collagen content, elevated expression of FGF7 (keratinocyte growth factor) and TGFβ signaling proteins. Wound healing was faster in N-WASP^FKO mice compared to control mice and N-WASP deficient fibroblasts were found to have enhanced collagen gel contraction properties. These results suggest that N-WASP deficiency in fibroblasts improves wound healing by growth factor-mediated enhancement of keratinocyte proliferation and increased wound contraction in mice.

Macrophage-dependent tumor cell transendothelial migration is mediated by Notch1/MenaINV-initiated invadopodium formation

The process of intravasation involving transendothelial migration is a key step in metastatic spread. How the triple cell complex composed of a macrophage, Mena over-expressing tumor cell and endothelial cell, called the tumor microenvironment of metastasis (TMEM), facilitates tumor cell transendothelial migration is not completely understood. Previous work has shown that the physical contact between a macrophage and tumor cell results in the formation of invadopodia, actin-rich matrix degrading protrusions, important for tumor cell invasion and transendothelial migration and tumor cell dissemination. Herein, we show that the macrophage-induced invadopodium is formed through a Notch1/Mena^INV signaling pathway in the tumor cell upon macrophage contact. This heterotypic tumor cell – macrophage interaction results in the upregulation of Mena^INV through the activation of MENA transcription. Notch1 and Mena^INV expression are required for tumor cell transendothelial migration, a necessary step during intravasation. Inhibition of the Notch signaling pathway blocked macrophage-induced invadopodium formation in vitro and the dissemination of tumor cells from the primary tumor in vivo. Our findings indicate a novel role for Notch1 signaling in the regulation of Mena^INV expression and transendothelial migration and provide mechanistic information essential to the use of therapeutic inhibitors of metastasis.

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

MenaINV dysregulates cortactin phosphorylation to promote invadopodium maturation

Invadopodia, actin-based protrusions of invasive carcinoma cells that focally activate extracellular matrix-degrading proteases, are essential for the migration and intravasation of tumor cells during dissemination from the primary tumor. We have previously shown that cortactin phosphorylation at tyrosine residues, in particular tyrosine 421, promotes actin polymerization at newly-forming invadopodia, promoting their maturation to matrix-degrading structures. However, the mechanism by which cells regulate the cortactin tyrosine phosphorylation-dephosphorylation cycle at invadopodia is unknown. Mena, an actin barbed-end capping protein antagonist, is expressed as various splice-isoforms. The Mena^INV isoform is upregulated in migratory and invasive sub-populations of breast carcinoma cells, and is involved in tumor cell intravasation. Here we show that forced Mena^INV expression increases invadopodium maturation to a far greater extent than equivalent expression of other Mena isoforms. Mena^INV is recruited to invadopodium precursors just after their initial assembly at the plasma membrane, and promotes the phosphorylation of cortactin tyrosine 421 at invadopodia. In addition, we show that cortactin phosphorylation at tyrosine 421 is suppressed by the phosphatase PTP1B, and that PTP1B localization to the invadopodium is reduced by Mena^INV expression. We conclude that Mena^INV promotes invadopodium maturation by inhibiting normal dephosphorylation of cortactin at tyrosine 421 by the phosphatase PTP1B.

Safflower Yellow Prevents Pulmonary Metastasis of Breast Cancer by Inhibiting Tumor Cell Invadopodia

Carthamus tinctorius L. is a traditional Chinese medicine that activates blood circulation and dissipates blood stasis, and has been extensively used as antitumor treatment in a clinical setting in single or in compound preparation form. However, empirical evidence and a better understanding of the possible mechanisms involved are still required. Here, we investigated the role of safflower yellow (SY), the active ingredient of C. tinctorius, in the pulmonary metastasis of breast cancer, and the underlying mechanism of action. EGF-meditated time- and dose-dependent cell response profiles were applied to screen for the activity of SY in vitro, while orthotopic lung metastasis and intravenous injection were used to evaluate the antimetastatic role of SY in vivo. SY could dose-dependently inhibit EGF-mediated time- and dose-dependent cell response profiles by inhibiting cytoskeletal rearrangement. We also found that SY significantly inhibited the migration of breast cancer cells in vitro and pulmonary metastasis of breast cancer cells in vivo. Consistent with these phenotypes, formation of invadopodia and the expression of MMP-9 and p-Src proteins were decreased after EGF stimulation in MBA-MD-231 cells treat with SY, as well as in lung metastatic foci. Additionally, circulating tumor cells retained in lung capillaries were also reduced. These results suggest that the antimetastatic effect of SY is due to its inhibition of invadopodia formation, which occurs mainly through Src-dependent cytoskeleton rearrangement. We suggest that SY should be considered as a potential novel therapeutic agent for the treatment of breast cancer.

PAK4 suppresses PDZ-RhoGEF activity to drive invadopodia maturation in melanoma cells

Cancer cells are thought to use actin rich invadopodia to facilitate matrix degradation. Formation and maturation of invadopodia requires the co-ordained activity of Rho-GTPases, however the molecular mechanisms that underlie the invadopodia lifecycle are not fully elucidated. Previous work has suggested a formation and disassembly role for Rho family effector p-21 activated kinase 1 (PAK1) however, related family member PAK4 has not been explored. Systematic analysis of isoform specific depletion using in vitro and in vivo invasion assays revealed there are differential invadopodia-associated functions. We consolidated a role for PAK1 in the invadopodia formation phase and identified PAK4 as a novel invadopodia protein that is required for successful maturation. Furthermore, we find that PAK4 (but not PAK1) mediates invadopodia maturation likely via inhibition of PDZ-RhoGEF. Our work points to an essential role for both PAKs during melanoma invasion but provides a significant advance in our understanding of differential PAK function.

Endothelin-1 receptor drives invadopodia: Exploiting how β-arrestin-1 guides the way

Metastatization is a complex multistep process requiring fine-tuned regulated cytoskeleton re-modeling, mediated by the cross-talk of actin with interacting partners, such as the Rho GTPases. Our expanding knowledge of invadopodia, small invasive membrane protrusions composed of a core of F-actin, actin regulators and actin-binding proteins, and hotspots for secretion of extracellular matrix (ECM) proteinases, contributes to clarify critical steps of the metastatic program. Growth factor receptors and their intermediate signaling molecules, along with matrix adhesion and rigidity, pH and hypoxia, act as drivers of cytoskeleton changes and invadopodia formation. We recently pro-posed a novel route map by which cancer cells regulates invadopodia dynamics supporting metastasis as response to the endothelin A receptor (ET_AR), among the highly druggable G-protein coupled receptors in cancer. The metastatic behavior exhibited by ovarian cancer cells overe-xpressing ET_AR is now explained by the interplay with β-arrestin1 (β-arr1), a scaffold protein acting as signal-integrating module of RhoC and cofilin signaling for specific invadopodia formation, accomplished by its interaction with a Rho guanine nucleotide exchange factor (GEF), PDZ-RhoGEF, in a G-protein independent manner. Here, we summarize this novel activation of the RhoC pathway from ET_AR/β-arr1 signaling that may be exploited therapeutically and discuss new perspectives for future directions of investigations.

NPM-ALK phosphorylates WASp Y102 and contributes to oncogenesis of anaplastic large cell lymphoma

Mechanisms by which NPM-ALK signaling regulates cell migration, invasion and contributes to the oncogenesis of anaplastic large cell lymphoma (ALCL) are not completely understood. In an attempt to identify novel actin signaling pathways regulated by NPM-ALK, a comprehensive phosphoproteome analysis of ALCL cell lines was performed in the presence or absence of NPM-ALK activity. Numerous phosphoproteins involved in actin dynamics including Wiskott-Aldrich syndrome protein (WASp) were regulated by NPM-ALK. Network analysis revealed that WASp is a central component of the NPM-ALK-dependent actin signaling pathway. Here we show that NPM-ALK phosphorylates WASp at its known activation site (Y290) as well as at a novel residue (Y102). Phosphorylation of WASp at Y102 negatively regulates its interaction with Wiskott-Aldrich interacting protein and decreases its protein stability. Phosphorylation of WASp at Y102 enhances anchorage-independent growth and tumor growth in an in vivo xenograft model and enhances invasive properties of ALCL. We show that knock-down of WASp or expression of Y102F mutant of WASp decreases colony formation and in vivo tumor growth. Our results show that WASp is a novel substrate of ALK and has a critical role in regulating invasiveness and oncogenesis of ALCL.

The ZEB1/miR-200c feedback loop regulates invasion via actin interacting proteins MYLK and TKS5

Epithelial to mesenchymal transition (EMT) is a developmental process which is aberrantly activated during cancer invasion and metastasis. Elevated expression of EMT-inducers like ZEB1 enables tumor cells to detach from the primary tumor and invade into the surrounding tissue. The main antagonist of ZEB1 in controlling EMT is the microRNA-200 family that is reciprocally linked to ZEB1 in a double negative feedback loop. Here, we further elucidate how the ZEB1/miR-200 feedback loop controls invasion of tumor cells. The process of EMT is attended by major changes in the actin cytoskeleton. Via in silico screening of genes encoding for actin interacting proteins, we identified two novel targets of miR-200c - TKS5 and MYLK (MLCK). Co-expression of both genes with ZEB1 was observed in several cancer cell lines as well as in breast cancer patients and correlated with low miR-200c levels. Depletion of TKS5 or MYLK in breast cancer cells reduced their invasive potential and their ability to form invadopodia. Whereas TKS5 is known to be a major component, we could identify MYLK as a novel player in invadopodia formation. In summary, TKS5 and MYLK represent two mediators of invasive behavior of cancer cells that are regulated by the ZEB1/miR-200 feedback loop.

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

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

miR-206 Inhibits Stemness and Metastasis of Breast Cancer by Targeting MKL1/IL11 Pathway

Purpose: Effective targeting of cancer stem cells is necessary and important for eradicating cancer and reducing metastasis-related mortality. Understanding of cancer stemness-related signaling pathways at the molecular level will help control cancer and stop metastasis in the clinic.Experimental Design: By analyzing miRNA profiles and functions in cancer development, we aimed to identify regulators of breast tumor stemness and metastasis in human xenograft models in vivo and examined their effects on self-renewal and invasion of breast cancer cells in vitro To discover the direct targets and essential signaling pathways responsible for miRNA functions in breast cancer progression, we performed microarray analysis and target gene prediction in combination with functional studies on candidate genes (overexpression rescues and pheno-copying knockdowns).Results: In this study, we report that hsa-miR-206 suppresses breast tumor stemness and metastasis by inhibiting both self-renewal and invasion. We identified that among the candidate targets, twinfilin (TWF1) rescues the miR-206 phenotype in invasion by enhancing the actin cytoskeleton dynamics and the activity of the mesenchymal lineage transcription factors, megakaryoblastic leukemia (translocation) 1 (MKL1), and serum response factor (SRF). MKL1 and SRF were further demonstrated to promote the expression of IL11, which is essential for miR-206's function in inhibiting both invasion and stemness of breast cancer.Conclusions: The identification of the miR-206/TWF1/MKL1-SRF/IL11 signaling pathway sheds lights on the understanding of breast cancer initiation and progression, unveils new therapeutic targets, and facilitates innovative drug development to control cancer and block metastasis. Clin Cancer Res; 23(4); 1091-103. ©2016 AACR.

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.

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.

Direct visualization of the phenotype of hypoxic tumor cells at single cell resolution in vivo using a new hypoxia probe

Tumor hypoxia is linked to tumor progression, metastasis, and therapy resistance. However, the underlying mechanisms behind this linkage are not fully understood. Here we present a novel fluorescent mCherry hypoxia-responsive marker that can be used in real time imaging to specifically and sensitively identify hypoxic cells in vivo at single cell resolution. Tumors derived from triple negative tumor cells expressing the hypoxia marker reveal that the hypoxic tumor cells congregate near flowing blood vessels. Using multiphoton microscopy, hypoxic MDA-MB-231 cells were directly visualized and showed a more persistent slow migration phenotype as compared to normoxic cells in the same field in vivo. Hypoxic tumor cells are enriched in the cell population that migrates toward human epithelial growth factor gradients in vivo, and has increased collagen degradation and intravasation activity, characteristics of dissemination and metastasis competent tumor cells. The hypoxia probe introduced in this study provides a specific reporter of hypoxic cell phenotypes in vivo which reveals new insights into the mechanisms by which hypoxia is linked to metastasis.

Tumor cell intravasation

The process of entering the bloodstream, intravasation, is a necessary step in the development of distant metastases. The focus of this review is on the pathways and molecules that have been identified as being important based on current in vitro and in vivo assays for intravasation. Properties of the vasculature which are important for intravasation include microvessel density and also diameter of the vasculature, with increased intravasation correlating with increased vessel diameter in some tumors. TGFB signaling can enhance intravasation at least in part through induction of EMT, and we discuss other TGFB target genes that are important for intravasation. In addition to TGFB signaling, a number of studies have demonstrated that activation of EGF receptor family members stimulates intravasation, with downstream signaling through PI3K, N-WASP, RhoA, and WASP to induce invadopodia. With respect to proteases, there is strong evidence for contributions by uPA/uPAR, while the roles of MMPs in intravasation may be more tumor specific. Other cells including macrophages, fibroblasts, neutrophils, and platelets can also play a role in enhancing tumor cell intravasation. The technology is now available to interrogate the expression patterns of circulating tumor cells, which will provide an important reality check for the model systems being used. With a better understanding of the mechanisms underlying intravasation, the goal is to provide new opportunities for improving prognosis as well as potentially developing new treatments.

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

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

The microenvironment controls invadosome plasticity

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

WIP and WICH/WIRE co-ordinately control invadopodium formation and maturation in human breast cancer cell invasion

Cancer cells form actin-rich degradative protrusions (invasive pseudopods and invadopodia), which allows their efficient dispersal during metastasis. Using biochemical and advanced imaging approaches, we demonstrate that the N-WASP-interactors WIP and WICH/WIRE play non-redundant roles in cancer cell invasion. WIP interacts with N-WASP and cortactin and is essential for invadopodium assembly, whereas WICH/WIRE regulates N-WASP activation to control invadopodium maturation and degradative activity. Our data also show that Nck interaction with WIP and WICH/WIRE modulates invadopodium maturation; changes in WIP and WICH/WIRE levels induce differential distribution of Nck. We show that WIP can replace WICH/WIRE functions and that elevated WIP levels correlate with high invasiveness. These findings identify a role for WICH/WIRE in invasiveness and highlight WIP as a hub for signaling molecule recruitment during invadopodium generation and cancer progression, as well as a potential diagnostic biomarker and an optimal target for therapeutic approaches.

Lamellipodin promotes invasive 3D cancer cell migration via regulated interactions with Ena/VASP and SCAR/WAVE

Cancer invasion is a hallmark of metastasis. The mesenchymal mode of cancer cell invasion is mediated by elongated membrane protrusions driven by the assembly of branched F-actin networks. How deregulation of actin regulators promotes cancer cell invasion is still enigmatic. We report that increased expression and membrane localization of the actin regulator Lamellipodin correlate with reduced metastasis-free survival and poor prognosis in breast cancer patients. In agreement, we find that Lamellipodin depletion reduced lung metastasis in an orthotopic mouse breast cancer model. Invasive 3D cancer cell migration as well as invadopodia formation and matrix degradation was impaired upon Lamellipodin depletion. Mechanistically, we show that Lamellipodin promotes invasive 3D cancer cell migration via both actin-elongating Ena/VASP proteins and the Scar/WAVE complex, which stimulates actin branching. In contrast, Lamellipodin interaction with Scar/WAVE but not with Ena/VASP is required for random 2D cell migration. We identified a phosphorylation-dependent mechanism that regulates selective recruitment of these effectors to Lamellipodin: Abl-mediated Lamellipodin phosphorylation promotes its association with both Scar/WAVE and Ena/VASP, whereas Src-dependent phosphorylation enhances binding to Scar/WAVE but not to Ena/VASP. Through these selective, regulated interactions Lamellipodin mediates directional sensing of epidermal growth factor (EGF) gradients and invasive 3D migration of breast cancer cells. Our findings imply that increased Lamellipodin levels enhance Ena/VASP and Scar/WAVE activities at the plasma membrane to promote 3D invasion and metastasis.

SNX9 promotes metastasis by enhancing cancer cell invasion via differential regulation of RhoGTPases

Despite current advances in cancer research, metastasis remains the leading factor in cancer-related deaths. Here, we identify sorting nexin 9 (SNX9) as a new regulator of breast cancer metastasis. We detected an increase in SNX9 expression in human breast cancer metastases compared with primary tumors and demonstrated that SNX9 expression in MDA-MB-231 breast cancer cells is necessary to maintain their ability to metastasize in a chick embryo model. Reciprocally, SNX9 knockdown impairs the process. In vitro studies using several cancer cell lines derived from a variety of human tumors revealed a role for SNX9 in cell invasion and identified mechanisms responsible for this novel function. We showed that SNX9 controls the activation of RhoA and Cdc42 GTPases and also regulates cell motility via the modulation of well-known molecules involved in metastasis, namely RhoA-ROCK and N-WASP. In addition, we have discovered that SNX9 is required for RhoGTPase-dependent, clathrin-independent endocytosis, and in this capacity, can functionally substitute to the bona fide Rho GAP, GRAF1 (GTPase Regulator Associated with Focal Adhesion Kinase). Together, our data establish novel roles for SNX9 as a multifunctional protein scaffold that regulates, and potentially coordinates, several cellular processes that together can enhance cancer cell metastasis.

Podosomes and invadopodia: tools to breach vascular basement membrane

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

CIP4 promotes metastasis in triple-negative breast cancer and is associated with poor patient prognosis

Signaling via epidermal growth factor receptor (EGFR) and Src kinase pathways promote triple-negative breast cancer (TNBC) cell invasion and tumor metastasis. Here, we address the role of Cdc42-interacting protein-4 (CIP4) in TNBC metastasis in vivo, and profile CIP4 expression in human breast cancer patients. In human TNBC cells, CIP4 knock-down (KD) led to less sustained activation of Erk kinase and impaired cell motility compared to control cells. This correlated with significant defects in 3D invasion of surrounding extracellular matrix by CIP4 KD TNBC cells when grown as spheroid colonies. In mammary orthotopic xenograft assays using both human TNBC cells (MDA-MB-231, HCC 1806) and rat MTLn3 cells, CIP4 silencing had no overt effect on tumor growth, but significantly reduced the incidence of lung metastases in each tumor model. In human invasive breast cancers, high CIP4 levels was significantly associated with high tumor stage, TNBC and HER2 subtypes, and risk of progression to metastatic disease. Together, these results implicate CIP4 in promoting metastasis in TNBCs.

A Sensitized Screen for Genes Promoting Invadopodia Function In Vivo: CDC-42 and Rab GDI-1 Direct Distinct Aspects of Invadopodia Formation

Invadopodia are specialized membrane protrusions composed of F-actin, actin regulators, signaling proteins, and a dynamically trafficked invadopodial membrane that drive cell invasion through basement membrane (BM) barriers in development and cancer. Due to the challenges of studying invasion in vivo, mechanisms controlling invadopodia formation in their native environments remain poorly understood. We performed a sensitized genome-wide RNAi screen and identified 13 potential regulators of invadopodia during anchor cell (AC) invasion into the vulval epithelium in C. elegans. Confirming the specificity of this screen, we identified the Rho GTPase cdc-42, which mediates invadopodia formation in many cancer cell lines. Using live-cell imaging, we show that CDC-42 localizes to the AC-BM interface and is activated by an unidentified vulval signal(s) that induces invasion. CDC-42 is required for the invasive membrane localization of WSP-1 (N-WASP), a CDC-42 effector that promotes polymerization of F-actin. Loss of CDC-42 or WSP-1 resulted in fewer invadopodia and delayed BM breaching. We also characterized a novel invadopodia regulator, gdi-1 (Rab GDP dissociation inhibitor), which mediates membrane trafficking. We show that GDI-1 functions in the AC to promote invadopodia formation. In the absence of GDI-1, the specialized invadopodial membrane was no longer trafficked normally to the invasive membrane, and instead was distributed to plasma membrane throughout the cell. Surprisingly, the pro-invasive signal(s) from the vulval cells also controls GDI-1 activity and invadopodial membrane trafficking. These studies represent the first in vivo screen for genes regulating invadopodia and demonstrate that invadopodia formation requires the integration of distinct cellular processes that are coordinated by an extracellular cue.

During animal development specialized cells acquire the ability move and invade into other tissues to form complex organs and structures. Understanding this cellular behavior is important medically, as cancer cells can hijack the developmental program of invasion to metastasize throughout the body. One of the most formidable barriers invasive cells face is basement membrane–-a thin, dense, sheet-like assembly of proteins and carbohydrates that surrounds most tissues. Cells deploy small, protrusive, membrane associated structures called invadopodia (invasive feet) to breach basement membranes. How invadopodia are formed and controlled during invasion has been challenging to understand, as it is difficult to examine these dynamic structures in live animals. Using the nematode worm Caenorhabditis elegans, we have conducted the first large-scale screen to isolate genes that control invadopodia in live animals. Our screen isolated 13 genes and we confirmed two are key invadopodia regulators: the Rho GTPase CDC-42 that promotes F-actin polymerization at invadopodia to generate the force to breach basement membranes, and the Rab GDI-1 that promotes membrane addition at invadopodia that may allow invadopodia to extend through basement membranes. This work provides new insights into invadopodia construction and identifies potential novel targets for anti-metastasis therapies.

Blood-brain Barrier Remodeling during Brain Metastasis Formation

Our understanding of the process of metastatic progression has improved markedly over the past decades, yet metastasis remains the most enigmatic component of cancer pathogenesis. This lack of knowledge has serious health-related implications, since metastasis is responsible for 90% of all cancer-related mortalities. The brain is considered a sanctuary site for metastatic tumor growth, where the blood-brain barrier (BBB) and other components of the brain microenvironment, provide protection to the tumor cells from immune surveillance, chemotherapeutics and other potentially harmful substances. The interactions between tumor cells and the brain microenvironment, principally brain vascular endothelium, are the critical determinants in their progression toward metastasis, dormancy, or clearance. This review discusses current knowledge of the biology of metastatic progression, with a particular focus on the tumor cell migration and colonization in the brain.

Invadopodia proteins, cortactin, N-WASP and WIP differentially promote local invasiveness in ameloblastoma

BACKGROUND

Cell migration and invasion through interstitial tissues are dependent upon several specialized characteristics of the migratory cell notably generation of proteolytic membranous protrusions or invadopodia. Ameloblastoma is a benign odontogenic epithelial neoplasm with a locally infiltrative behaviour. Cortactin and MMT1-MMP are two invadopodia proteins implicated in its local invasiveness. Other invadopodia regulators, namely N-WASP, WIP and Src kinase remain unclarified. This study addresses their roles in ameloblastoma.

MATERIALS AND METHOD

Eighty-seven paraffin-embedded ameloblastoma cases (20 unicystic, 47 solid/multicystic, 3 desmoplastic and 17 recurrent) were subjected to immunohistochemistry for expression of cortactin, N-WASP, WIP, Src kinase and F-actin, and findings correlated with clinicopathological parameters.

RESULTS

Invadopodia proteins (except Src kinase) and F-actin were widely detected in ameloblastoma (cortactin: n = 73/87, 83.9%; N-WASP: n = 59/87; 67.8%; WIP: n = 77/87; 88.5%; and F-actin: n = 87/87, 100%). Protein localization was mainly cytoplasmic and/or membranous, and occasionally nuclear for F-actin. Cortactin, which functions as an actin-scaffolding protein, demonstrated significantly higher expression levels within ameloblastoma tumoral epithelium than in stroma (P < 0.05). N-WASP, which coordinates actin polymerization and invadopodia-mediated extracellular matrix degradation, was overexpressed in the solid/multicystic subtype (P < 0.05). WIP, an upstream regulator of N-WASP, and F-actin were significantly upregulated along the tumour invasive front compared to tumour centres (P < 0.05). Except for males with cortactin overexpression, other clinical parameters (age, ethnicity and anatomical site) showed no significant correlations.

CONCLUSIONS

Present results suggest that local invasiveness of ameloblastoma is dependent upon the migratory potential of its tumour cells as defined by their distribution of cortactin, N-WASP and WIP in correlation with F-actin cytoskeletal dynamics.

Minireview: Mouse Models of Rho GTPase Function in Mammary Gland Development, Tumorigenesis, and Metastasis

Ras homolog (Rho) family small GTPases are critical regulators of actin cytoskeletal organization, cell motility, proliferation, and survival. Surprisingly, the large majority of the studies underlying our knowledge of Rho protein function have been carried out in cultured cells, and it is only recently that researchers have begun to assess Rho GTPase regulation and function in vivo. The purpose of this review is to evaluate our current knowledge of Rho GTPase function in mouse mammary gland development, tumorigenesis and metastasis. Although our knowledge is still incomplete, these studies are already uncovering important themes as to the physiological roles of Rho GTPase signaling in normal mammary gland development and function. Essential contributions of Rho proteins to breast cancer initiation, tumor progression, and metastatic dissemination have also been identified.

microRNA miR-142-3p Inhibits Breast Cancer Cell Invasiveness by Synchronous Targeting of WASL, Integrin Alpha V, and Additional Cytoskeletal Elements

MicroRNAs (miRNAs, micro ribonucleic acids) are pivotal post-transcriptional regulators of gene expression. These endogenous small non-coding RNAs play significant roles in tumorigenesis and tumor progression. miR-142-3p expression is dysregulated in several breast cancer subtypes. We aimed at investigating the role of miR-142-3p in breast cancer cell invasiveness. Supported by transcriptomic Affymetrix array analysis and confirmatory investigations at the mRNA and protein level, we demonstrate that overexpression of miR-142-3p in MDA-MB-231, MDA-MB-468 and MCF-7 breast cancer cells leads to downregulation of WASL (Wiskott-Aldrich syndrome-like, protein: N-WASP), Integrin-αV, RAC1, and CFL2, molecules implicated in cytoskeletal regulation and cell motility. ROCK2, IL6ST, KLF4, PGRMC2 and ADCY9 were identified as additional targets in a subset of cell lines. Decreased Matrigel invasiveness was associated with the miR-142-3p-induced expression changes. Confocal immunofluorescence microscopy, nanoscale atomic force microscopy and digital holographic microscopy revealed a change in cell morphology as well as a reduced cell volume and size. A more cortical actin distribution and a loss of membrane protrusions were observed in cells overexpressing miR-142-3p. Luciferase activation assays confirmed direct miR-142-3p-dependent regulation of the 3’-untranslated region of ITGAV and WASL. siRNA-mediated depletion of ITGAV and WASL resulted in a significant reduction of cellular invasiveness, highlighting the contribution of these factors to the miRNA-dependent invasion phenotype. While knockdown of WASL significantly reduced the number of membrane protrusions compared to controls, knockdown of ITGAV resulted in a decreased cell volume, indicating differential contributions of these factors to the miR-142-3p-induced phenotype. Our data identify WASL, ITGAV and several additional cytoskeleton-associated molecules as novel invasion-promoting targets of miR-142-3p in breast cancer.

Active contractility at E-cadherin junctions and its implications for cell extrusion in cancer

Cellular contractility regulates tissue cohesion and morphogenesis. In epithelia, E-cadherin adhesion couples the contractile cortices of neighboring cells together to produce tension at junctions that can be transmitted across the epithelium in a planar fashion. We have recently demonstrated that contractility is also patterned in the apical-lateral axis within epithelial junctions. Our findings highlight the role that cytoskeletal regulation plays in controlling the levels of intra-junctional tension. Of note, dysregulation of this apicolateral pattern of tension can drive oncogenic cell extrusion. In this article, we provide a detailed description of the actomyosin cytoskeleton organization during oncogenic extrusion and discuss the implications of cell extrusion in cancer.